A Seminar Report

On

ldquo HIGH PERFORMANCE CONCRETE rdquo

In partial fulfilment of requirements for the Master of Technology In Structural engineering SUBMITTED BY

RAKESH KUMAR

ROLL NO 211037

Under the Guidance of Dr H K SHARMA

DEPARTMENT OF CIVIL ENGINEERING

N I T

KURUKSHETRA HARYANA

ABSTRACT A new class of concrete that exhibits greatly improved strength and durability properties has recently been developed The Ultra-High Performance Concrete (UHPC) tested in this research is a steel fiber reinforced concrete consisting of an optimized gradation of fine powders and a very low watercement ratio The research discussed herein provides a thorough characterization of the UHPC material properties examined at the Federal Highway Administrationrsquos Turner-Fairbank Highway Research CenterStrength testing has produced results significantly greater than those established for conventional concretes Compressive strengths range from 18 ksi for ambient air cured UHPC to 28 ksi for steam cured UHPC Tensile strength tests have been completed using both direct tests such as the mortar briquette and an indirect test namely the split cylinder Tensile strengths range from 09 to 17 ksi depending on the curing procedure and the test method employed

Durability testing has also demonstrated the enhanced

characteristics of UHPC Rapid chloride penetration results have

scaling results indicate that UHPC exhibits a high resistance to this

form of environmental attack ranged from extremely low to very low and the freeze-thaw

IntroductionHigh performance concrete (HPC) has been defined as concrete that possesses high workability high strength and high durability ACI (American Concrete Institute) has defined HPC as a concrete in which certain characteristics are developed for a particular application and environment Under the ACI definition durability is optional and this has led to a number of HPC structures which should theoretically have had very long services lives exhibiting durability associated distress early in their lives ACI also defines a high-strength concrete as concrete that has a specified compressive strength for design of 6000 psi (41 MPa) or greater

High Performance Concrete (HPC) is a concrete made with appropriate materials combined according to a selected mix design properly mixed transported placed consolidated and cured so that the resulting concrete will give excellent performance in the structure in which it is placed in the environment to which it is exposed and with the loads to which it will be subject for its design life Mix proportions for high-performance concrete (HPC) are influenced by many factors including specified performance properties locally available materials local experience personal preferences and cost With todayrsquos technology there are many products available for use in concrete to enhance its properties

The primary application for HPC have been structures requiring long service lives such as oil drilling platform long span bridges and parking structures HPC still requires good construction practice and good curing to deliver high performance

Characteristics of High-Performance Concretes

1COMPRESSIVE STRENGTH Compression testing of cylinders was the primary means used to determine the compressive strength of the UHPC This test method was also used as the control parameter to ensure consistency between batches The standard size cylinder had a diameter of 3 in and a pre-end preparation length of 6 in All the cylinders discussed in this paper had their ends prepared with an end grinder and their final lengths were approximately 195 times their diameter The cylinders were all tested according to ASTM C39 except that the load rate was changed to 150 psisec Preliminary testing has indicated that this increase in rate does not affect the strength or the modulus of the UHPC significantly enough to influence the test results The rate change was necessary to ensure that test specimens would reach the level of load required for failure in a reasonable timeframe

2 TENSILE STRENGTH

Concrete tensile strength is a property that is often disregarded due to the inherently brittle nature of the material and its low overall tensile capacity UHPC exhibits significantly improved tensile strength both before and after cracking In structural applications this tension capacity permits higher precracking tensile loads elevates post cracking section stiffnesses and provides a greater ability to withstand environmental attacks which utilize cracks to provide rapid ingress to interior concrete regions In order to use the tensile strength of UHPC it must first be quantified Many test methods have been developed to directly or

indirectly measure the tensile strength of concrete A number of these methods have been used in this research program as each test provides different information on this material behavior characteristic

3 SHRINKAGE

A limited shrinkage study has been completed on the early age shrinkage behavior of UHPC This work was completed in conjunction with the alkali-silica reaction (ASR) study that is discussed later Here 1 in by 1 in UHPC bars with 11 in length were cast and cured The shrinkage testing was completed according to ASTM C157 The initial reading was acquired immediately after stripping of the molds The final reading was taken after the curing procedure had been completed or at 28 days for the Ambient Air cured specimens Table 5 provides the results of these tests The Steam and Delayed Steam cured specimens exhibited similar shrinkage while the Tempered Steam specimens shrank approximately half as much The Ambient Air cured specimens exhibited the most shrinkage

Table 5 Shrinkage of UHPC Mortar Bars Curing Method

Bars Tested

Measurement Time(Days After Casting)

Shrinkage ()

Initial Final Average Standard Deviation

Steam 6 11 41 0047 0002 Ambient Air 6 11 281 0062 0004 Tempered Steam

6 12 41 0025 0001

Delayed Steam

6 11 180 0050 0002

4 DURABILITY OF UHPC

The durability of UHPC in terms of its resistance to internal and external environmental attack was also studied These investigations included chloride ion penetration abrasion ASR freeze-thaw and scaling testing RAPID CHLORIDE ION PENETRABILITY Rapid chloride ion penetrability tests were completed on UHPC specimens according to ASTM C1202 The electrical current was recorded at 1 minute intervals over the 6 hour timeframe resulting in the total coulombs passed value shown in Table 6 Two or three specimens were completed for each condition and specimens were tested at both 28 and 56 days The results show that the rapid chloride ion permeability is minimal regardless of the curing regime applied Also it is of note that the penetrability decreased significantly between 28 and 56 days for specimens from the Ambient Air curing regime

5 ABRASION RESISTANCE

Abrasion resistance can be an important parameter for any concrete that is exposed to contact with other materials The abrasion resistance of UHPC was measured through testing according to ASTM C944 in which a rotating abrading wheel bears on and wears away the concrete surface for a period of two minutes One modification to the standard test method was made in this program The reported test results are the product of 10 total minutes of abrasion representing five two-minute cycles completed on each specimen The abrasion testing was performed on three specimens from each of the four curing regimes However as abrasion resistance is highly dependent on the surface condition of the concrete each specimen was tested on three different surfaces First all specimens were tested on the surface formed by casting UHPC against the steel mold in which they were produced Following

these tests the cast (and now abraded) surface was sandblasted until it displayed a uniform texture The testing was then repeated for this sandblasted surface Finally the testing was again repeated for all the specimens subsequent to having the test surface ground plane using a cylinder end grinder

Abrasion resistance is directly related to the strength ofconcrete This makes high strength HPC ideal for abrasiveenvironments The abrasion resistance of HPC incorporatingsilica fume is especially high This makes silicafumeconcrete particularly useful for spillways andstilling basins and concrete pavements or concrete pavementoverlays subjected to heavy or abrasive trafficHolland and others (1986) describe how severe abrasion-erosion had occurred in the stilling basin of a damrepairs using fiber-reinforced concrete had not proven to bedurable The new HPC mix used to repair the structure thesecond time contained 386 kgm3 (650 lbyd3) of cement70 kgm3 (118 lbyd3) of silica fume admixtures and had awater to cementing materials ratio of 028 and a 90-daycompressive strength exceeding 103 MPa (15000 psi)Berra Ferrara and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resistanceThe best results were obtained with a mix using slagcement steel fibers and silica fume Mortar strengthsranged from 75 MPa to 100 MPa (11000 psi to 14500 psi)In addition to better erosion resistance less dryingshrinkage high freeze-thaw resistance and good bond tothe substrate were achievedIn Norway steel studs are allowed in tires this causessevere abrasion wear on pavement surfaces with resurfacingrequired within one to two years Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14500 psi to 17000 psi) concretehad the same abrasion resistance as granite (Helland

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

ABSTRACT A new class of concrete that exhibits greatly improved strength and durability properties has recently been developed The Ultra-High Performance Concrete (UHPC) tested in this research is a steel fiber reinforced concrete consisting of an optimized gradation of fine powders and a very low watercement ratio The research discussed herein provides a thorough characterization of the UHPC material properties examined at the Federal Highway Administrationrsquos Turner-Fairbank Highway Research CenterStrength testing has produced results significantly greater than those established for conventional concretes Compressive strengths range from 18 ksi for ambient air cured UHPC to 28 ksi for steam cured UHPC Tensile strength tests have been completed using both direct tests such as the mortar briquette and an indirect test namely the split cylinder Tensile strengths range from 09 to 17 ksi depending on the curing procedure and the test method employed

Durability testing has also demonstrated the enhanced

characteristics of UHPC Rapid chloride penetration results have

scaling results indicate that UHPC exhibits a high resistance to this

form of environmental attack ranged from extremely low to very low and the freeze-thaw

IntroductionHigh performance concrete (HPC) has been defined as concrete that possesses high workability high strength and high durability ACI (American Concrete Institute) has defined HPC as a concrete in which certain characteristics are developed for a particular application and environment Under the ACI definition durability is optional and this has led to a number of HPC structures which should theoretically have had very long services lives exhibiting durability associated distress early in their lives ACI also defines a high-strength concrete as concrete that has a specified compressive strength for design of 6000 psi (41 MPa) or greater

High Performance Concrete (HPC) is a concrete made with appropriate materials combined according to a selected mix design properly mixed transported placed consolidated and cured so that the resulting concrete will give excellent performance in the structure in which it is placed in the environment to which it is exposed and with the loads to which it will be subject for its design life Mix proportions for high-performance concrete (HPC) are influenced by many factors including specified performance properties locally available materials local experience personal preferences and cost With todayrsquos technology there are many products available for use in concrete to enhance its properties

The primary application for HPC have been structures requiring long service lives such as oil drilling platform long span bridges and parking structures HPC still requires good construction practice and good curing to deliver high performance

Characteristics of High-Performance Concretes

1COMPRESSIVE STRENGTH Compression testing of cylinders was the primary means used to determine the compressive strength of the UHPC This test method was also used as the control parameter to ensure consistency between batches The standard size cylinder had a diameter of 3 in and a pre-end preparation length of 6 in All the cylinders discussed in this paper had their ends prepared with an end grinder and their final lengths were approximately 195 times their diameter The cylinders were all tested according to ASTM C39 except that the load rate was changed to 150 psisec Preliminary testing has indicated that this increase in rate does not affect the strength or the modulus of the UHPC significantly enough to influence the test results The rate change was necessary to ensure that test specimens would reach the level of load required for failure in a reasonable timeframe

2 TENSILE STRENGTH

Concrete tensile strength is a property that is often disregarded due to the inherently brittle nature of the material and its low overall tensile capacity UHPC exhibits significantly improved tensile strength both before and after cracking In structural applications this tension capacity permits higher precracking tensile loads elevates post cracking section stiffnesses and provides a greater ability to withstand environmental attacks which utilize cracks to provide rapid ingress to interior concrete regions In order to use the tensile strength of UHPC it must first be quantified Many test methods have been developed to directly or

indirectly measure the tensile strength of concrete A number of these methods have been used in this research program as each test provides different information on this material behavior characteristic

3 SHRINKAGE

A limited shrinkage study has been completed on the early age shrinkage behavior of UHPC This work was completed in conjunction with the alkali-silica reaction (ASR) study that is discussed later Here 1 in by 1 in UHPC bars with 11 in length were cast and cured The shrinkage testing was completed according to ASTM C157 The initial reading was acquired immediately after stripping of the molds The final reading was taken after the curing procedure had been completed or at 28 days for the Ambient Air cured specimens Table 5 provides the results of these tests The Steam and Delayed Steam cured specimens exhibited similar shrinkage while the Tempered Steam specimens shrank approximately half as much The Ambient Air cured specimens exhibited the most shrinkage

Table 5 Shrinkage of UHPC Mortar Bars Curing Method

Bars Tested

Measurement Time(Days After Casting)

Shrinkage ()

Initial Final Average Standard Deviation

Steam 6 11 41 0047 0002 Ambient Air 6 11 281 0062 0004 Tempered Steam

6 12 41 0025 0001

Delayed Steam

6 11 180 0050 0002

4 DURABILITY OF UHPC

The durability of UHPC in terms of its resistance to internal and external environmental attack was also studied These investigations included chloride ion penetration abrasion ASR freeze-thaw and scaling testing RAPID CHLORIDE ION PENETRABILITY Rapid chloride ion penetrability tests were completed on UHPC specimens according to ASTM C1202 The electrical current was recorded at 1 minute intervals over the 6 hour timeframe resulting in the total coulombs passed value shown in Table 6 Two or three specimens were completed for each condition and specimens were tested at both 28 and 56 days The results show that the rapid chloride ion permeability is minimal regardless of the curing regime applied Also it is of note that the penetrability decreased significantly between 28 and 56 days for specimens from the Ambient Air curing regime

5 ABRASION RESISTANCE

Abrasion resistance can be an important parameter for any concrete that is exposed to contact with other materials The abrasion resistance of UHPC was measured through testing according to ASTM C944 in which a rotating abrading wheel bears on and wears away the concrete surface for a period of two minutes One modification to the standard test method was made in this program The reported test results are the product of 10 total minutes of abrasion representing five two-minute cycles completed on each specimen The abrasion testing was performed on three specimens from each of the four curing regimes However as abrasion resistance is highly dependent on the surface condition of the concrete each specimen was tested on three different surfaces First all specimens were tested on the surface formed by casting UHPC against the steel mold in which they were produced Following

these tests the cast (and now abraded) surface was sandblasted until it displayed a uniform texture The testing was then repeated for this sandblasted surface Finally the testing was again repeated for all the specimens subsequent to having the test surface ground plane using a cylinder end grinder

Abrasion resistance is directly related to the strength ofconcrete This makes high strength HPC ideal for abrasiveenvironments The abrasion resistance of HPC incorporatingsilica fume is especially high This makes silicafumeconcrete particularly useful for spillways andstilling basins and concrete pavements or concrete pavementoverlays subjected to heavy or abrasive trafficHolland and others (1986) describe how severe abrasion-erosion had occurred in the stilling basin of a damrepairs using fiber-reinforced concrete had not proven to bedurable The new HPC mix used to repair the structure thesecond time contained 386 kgm3 (650 lbyd3) of cement70 kgm3 (118 lbyd3) of silica fume admixtures and had awater to cementing materials ratio of 028 and a 90-daycompressive strength exceeding 103 MPa (15000 psi)Berra Ferrara and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resistanceThe best results were obtained with a mix using slagcement steel fibers and silica fume Mortar strengthsranged from 75 MPa to 100 MPa (11000 psi to 14500 psi)In addition to better erosion resistance less dryingshrinkage high freeze-thaw resistance and good bond tothe substrate were achievedIn Norway steel studs are allowed in tires this causessevere abrasion wear on pavement surfaces with resurfacingrequired within one to two years Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14500 psi to 17000 psi) concretehad the same abrasion resistance as granite (Helland

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

IntroductionHigh performance concrete (HPC) has been defined as concrete that possesses high workability high strength and high durability ACI (American Concrete Institute) has defined HPC as a concrete in which certain characteristics are developed for a particular application and environment Under the ACI definition durability is optional and this has led to a number of HPC structures which should theoretically have had very long services lives exhibiting durability associated distress early in their lives ACI also defines a high-strength concrete as concrete that has a specified compressive strength for design of 6000 psi (41 MPa) or greater

High Performance Concrete (HPC) is a concrete made with appropriate materials combined according to a selected mix design properly mixed transported placed consolidated and cured so that the resulting concrete will give excellent performance in the structure in which it is placed in the environment to which it is exposed and with the loads to which it will be subject for its design life Mix proportions for high-performance concrete (HPC) are influenced by many factors including specified performance properties locally available materials local experience personal preferences and cost With todayrsquos technology there are many products available for use in concrete to enhance its properties

The primary application for HPC have been structures requiring long service lives such as oil drilling platform long span bridges and parking structures HPC still requires good construction practice and good curing to deliver high performance

Characteristics of High-Performance Concretes

1COMPRESSIVE STRENGTH Compression testing of cylinders was the primary means used to determine the compressive strength of the UHPC This test method was also used as the control parameter to ensure consistency between batches The standard size cylinder had a diameter of 3 in and a pre-end preparation length of 6 in All the cylinders discussed in this paper had their ends prepared with an end grinder and their final lengths were approximately 195 times their diameter The cylinders were all tested according to ASTM C39 except that the load rate was changed to 150 psisec Preliminary testing has indicated that this increase in rate does not affect the strength or the modulus of the UHPC significantly enough to influence the test results The rate change was necessary to ensure that test specimens would reach the level of load required for failure in a reasonable timeframe

2 TENSILE STRENGTH

Concrete tensile strength is a property that is often disregarded due to the inherently brittle nature of the material and its low overall tensile capacity UHPC exhibits significantly improved tensile strength both before and after cracking In structural applications this tension capacity permits higher precracking tensile loads elevates post cracking section stiffnesses and provides a greater ability to withstand environmental attacks which utilize cracks to provide rapid ingress to interior concrete regions In order to use the tensile strength of UHPC it must first be quantified Many test methods have been developed to directly or

indirectly measure the tensile strength of concrete A number of these methods have been used in this research program as each test provides different information on this material behavior characteristic

3 SHRINKAGE

A limited shrinkage study has been completed on the early age shrinkage behavior of UHPC This work was completed in conjunction with the alkali-silica reaction (ASR) study that is discussed later Here 1 in by 1 in UHPC bars with 11 in length were cast and cured The shrinkage testing was completed according to ASTM C157 The initial reading was acquired immediately after stripping of the molds The final reading was taken after the curing procedure had been completed or at 28 days for the Ambient Air cured specimens Table 5 provides the results of these tests The Steam and Delayed Steam cured specimens exhibited similar shrinkage while the Tempered Steam specimens shrank approximately half as much The Ambient Air cured specimens exhibited the most shrinkage

Table 5 Shrinkage of UHPC Mortar Bars Curing Method

Bars Tested

Measurement Time(Days After Casting)

Shrinkage ()

Initial Final Average Standard Deviation

Steam 6 11 41 0047 0002 Ambient Air 6 11 281 0062 0004 Tempered Steam

6 12 41 0025 0001

Delayed Steam

6 11 180 0050 0002

4 DURABILITY OF UHPC

The durability of UHPC in terms of its resistance to internal and external environmental attack was also studied These investigations included chloride ion penetration abrasion ASR freeze-thaw and scaling testing RAPID CHLORIDE ION PENETRABILITY Rapid chloride ion penetrability tests were completed on UHPC specimens according to ASTM C1202 The electrical current was recorded at 1 minute intervals over the 6 hour timeframe resulting in the total coulombs passed value shown in Table 6 Two or three specimens were completed for each condition and specimens were tested at both 28 and 56 days The results show that the rapid chloride ion permeability is minimal regardless of the curing regime applied Also it is of note that the penetrability decreased significantly between 28 and 56 days for specimens from the Ambient Air curing regime

5 ABRASION RESISTANCE

Abrasion resistance can be an important parameter for any concrete that is exposed to contact with other materials The abrasion resistance of UHPC was measured through testing according to ASTM C944 in which a rotating abrading wheel bears on and wears away the concrete surface for a period of two minutes One modification to the standard test method was made in this program The reported test results are the product of 10 total minutes of abrasion representing five two-minute cycles completed on each specimen The abrasion testing was performed on three specimens from each of the four curing regimes However as abrasion resistance is highly dependent on the surface condition of the concrete each specimen was tested on three different surfaces First all specimens were tested on the surface formed by casting UHPC against the steel mold in which they were produced Following

these tests the cast (and now abraded) surface was sandblasted until it displayed a uniform texture The testing was then repeated for this sandblasted surface Finally the testing was again repeated for all the specimens subsequent to having the test surface ground plane using a cylinder end grinder

Abrasion resistance is directly related to the strength ofconcrete This makes high strength HPC ideal for abrasiveenvironments The abrasion resistance of HPC incorporatingsilica fume is especially high This makes silicafumeconcrete particularly useful for spillways andstilling basins and concrete pavements or concrete pavementoverlays subjected to heavy or abrasive trafficHolland and others (1986) describe how severe abrasion-erosion had occurred in the stilling basin of a damrepairs using fiber-reinforced concrete had not proven to bedurable The new HPC mix used to repair the structure thesecond time contained 386 kgm3 (650 lbyd3) of cement70 kgm3 (118 lbyd3) of silica fume admixtures and had awater to cementing materials ratio of 028 and a 90-daycompressive strength exceeding 103 MPa (15000 psi)Berra Ferrara and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resistanceThe best results were obtained with a mix using slagcement steel fibers and silica fume Mortar strengthsranged from 75 MPa to 100 MPa (11000 psi to 14500 psi)In addition to better erosion resistance less dryingshrinkage high freeze-thaw resistance and good bond tothe substrate were achievedIn Norway steel studs are allowed in tires this causessevere abrasion wear on pavement surfaces with resurfacingrequired within one to two years Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14500 psi to 17000 psi) concretehad the same abrasion resistance as granite (Helland

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

Characteristics of High-Performance Concretes

1COMPRESSIVE STRENGTH Compression testing of cylinders was the primary means used to determine the compressive strength of the UHPC This test method was also used as the control parameter to ensure consistency between batches The standard size cylinder had a diameter of 3 in and a pre-end preparation length of 6 in All the cylinders discussed in this paper had their ends prepared with an end grinder and their final lengths were approximately 195 times their diameter The cylinders were all tested according to ASTM C39 except that the load rate was changed to 150 psisec Preliminary testing has indicated that this increase in rate does not affect the strength or the modulus of the UHPC significantly enough to influence the test results The rate change was necessary to ensure that test specimens would reach the level of load required for failure in a reasonable timeframe

2 TENSILE STRENGTH

Concrete tensile strength is a property that is often disregarded due to the inherently brittle nature of the material and its low overall tensile capacity UHPC exhibits significantly improved tensile strength both before and after cracking In structural applications this tension capacity permits higher precracking tensile loads elevates post cracking section stiffnesses and provides a greater ability to withstand environmental attacks which utilize cracks to provide rapid ingress to interior concrete regions In order to use the tensile strength of UHPC it must first be quantified Many test methods have been developed to directly or

indirectly measure the tensile strength of concrete A number of these methods have been used in this research program as each test provides different information on this material behavior characteristic

3 SHRINKAGE

A limited shrinkage study has been completed on the early age shrinkage behavior of UHPC This work was completed in conjunction with the alkali-silica reaction (ASR) study that is discussed later Here 1 in by 1 in UHPC bars with 11 in length were cast and cured The shrinkage testing was completed according to ASTM C157 The initial reading was acquired immediately after stripping of the molds The final reading was taken after the curing procedure had been completed or at 28 days for the Ambient Air cured specimens Table 5 provides the results of these tests The Steam and Delayed Steam cured specimens exhibited similar shrinkage while the Tempered Steam specimens shrank approximately half as much The Ambient Air cured specimens exhibited the most shrinkage

Table 5 Shrinkage of UHPC Mortar Bars Curing Method

Bars Tested

Measurement Time(Days After Casting)

Shrinkage ()

Initial Final Average Standard Deviation

Steam 6 11 41 0047 0002 Ambient Air 6 11 281 0062 0004 Tempered Steam

6 12 41 0025 0001

Delayed Steam

6 11 180 0050 0002

4 DURABILITY OF UHPC

The durability of UHPC in terms of its resistance to internal and external environmental attack was also studied These investigations included chloride ion penetration abrasion ASR freeze-thaw and scaling testing RAPID CHLORIDE ION PENETRABILITY Rapid chloride ion penetrability tests were completed on UHPC specimens according to ASTM C1202 The electrical current was recorded at 1 minute intervals over the 6 hour timeframe resulting in the total coulombs passed value shown in Table 6 Two or three specimens were completed for each condition and specimens were tested at both 28 and 56 days The results show that the rapid chloride ion permeability is minimal regardless of the curing regime applied Also it is of note that the penetrability decreased significantly between 28 and 56 days for specimens from the Ambient Air curing regime

5 ABRASION RESISTANCE

Abrasion resistance can be an important parameter for any concrete that is exposed to contact with other materials The abrasion resistance of UHPC was measured through testing according to ASTM C944 in which a rotating abrading wheel bears on and wears away the concrete surface for a period of two minutes One modification to the standard test method was made in this program The reported test results are the product of 10 total minutes of abrasion representing five two-minute cycles completed on each specimen The abrasion testing was performed on three specimens from each of the four curing regimes However as abrasion resistance is highly dependent on the surface condition of the concrete each specimen was tested on three different surfaces First all specimens were tested on the surface formed by casting UHPC against the steel mold in which they were produced Following

these tests the cast (and now abraded) surface was sandblasted until it displayed a uniform texture The testing was then repeated for this sandblasted surface Finally the testing was again repeated for all the specimens subsequent to having the test surface ground plane using a cylinder end grinder

Abrasion resistance is directly related to the strength ofconcrete This makes high strength HPC ideal for abrasiveenvironments The abrasion resistance of HPC incorporatingsilica fume is especially high This makes silicafumeconcrete particularly useful for spillways andstilling basins and concrete pavements or concrete pavementoverlays subjected to heavy or abrasive trafficHolland and others (1986) describe how severe abrasion-erosion had occurred in the stilling basin of a damrepairs using fiber-reinforced concrete had not proven to bedurable The new HPC mix used to repair the structure thesecond time contained 386 kgm3 (650 lbyd3) of cement70 kgm3 (118 lbyd3) of silica fume admixtures and had awater to cementing materials ratio of 028 and a 90-daycompressive strength exceeding 103 MPa (15000 psi)Berra Ferrara and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resistanceThe best results were obtained with a mix using slagcement steel fibers and silica fume Mortar strengthsranged from 75 MPa to 100 MPa (11000 psi to 14500 psi)In addition to better erosion resistance less dryingshrinkage high freeze-thaw resistance and good bond tothe substrate were achievedIn Norway steel studs are allowed in tires this causessevere abrasion wear on pavement surfaces with resurfacingrequired within one to two years Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14500 psi to 17000 psi) concretehad the same abrasion resistance as granite (Helland

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

indirectly measure the tensile strength of concrete A number of these methods have been used in this research program as each test provides different information on this material behavior characteristic

3 SHRINKAGE

A limited shrinkage study has been completed on the early age shrinkage behavior of UHPC This work was completed in conjunction with the alkali-silica reaction (ASR) study that is discussed later Here 1 in by 1 in UHPC bars with 11 in length were cast and cured The shrinkage testing was completed according to ASTM C157 The initial reading was acquired immediately after stripping of the molds The final reading was taken after the curing procedure had been completed or at 28 days for the Ambient Air cured specimens Table 5 provides the results of these tests The Steam and Delayed Steam cured specimens exhibited similar shrinkage while the Tempered Steam specimens shrank approximately half as much The Ambient Air cured specimens exhibited the most shrinkage

Table 5 Shrinkage of UHPC Mortar Bars Curing Method

Bars Tested

Measurement Time(Days After Casting)

Shrinkage ()

Initial Final Average Standard Deviation

Steam 6 11 41 0047 0002 Ambient Air 6 11 281 0062 0004 Tempered Steam

6 12 41 0025 0001

Delayed Steam

6 11 180 0050 0002

4 DURABILITY OF UHPC

The durability of UHPC in terms of its resistance to internal and external environmental attack was also studied These investigations included chloride ion penetration abrasion ASR freeze-thaw and scaling testing RAPID CHLORIDE ION PENETRABILITY Rapid chloride ion penetrability tests were completed on UHPC specimens according to ASTM C1202 The electrical current was recorded at 1 minute intervals over the 6 hour timeframe resulting in the total coulombs passed value shown in Table 6 Two or three specimens were completed for each condition and specimens were tested at both 28 and 56 days The results show that the rapid chloride ion permeability is minimal regardless of the curing regime applied Also it is of note that the penetrability decreased significantly between 28 and 56 days for specimens from the Ambient Air curing regime

5 ABRASION RESISTANCE

Abrasion resistance can be an important parameter for any concrete that is exposed to contact with other materials The abrasion resistance of UHPC was measured through testing according to ASTM C944 in which a rotating abrading wheel bears on and wears away the concrete surface for a period of two minutes One modification to the standard test method was made in this program The reported test results are the product of 10 total minutes of abrasion representing five two-minute cycles completed on each specimen The abrasion testing was performed on three specimens from each of the four curing regimes However as abrasion resistance is highly dependent on the surface condition of the concrete each specimen was tested on three different surfaces First all specimens were tested on the surface formed by casting UHPC against the steel mold in which they were produced Following

these tests the cast (and now abraded) surface was sandblasted until it displayed a uniform texture The testing was then repeated for this sandblasted surface Finally the testing was again repeated for all the specimens subsequent to having the test surface ground plane using a cylinder end grinder

Abrasion resistance is directly related to the strength ofconcrete This makes high strength HPC ideal for abrasiveenvironments The abrasion resistance of HPC incorporatingsilica fume is especially high This makes silicafumeconcrete particularly useful for spillways andstilling basins and concrete pavements or concrete pavementoverlays subjected to heavy or abrasive trafficHolland and others (1986) describe how severe abrasion-erosion had occurred in the stilling basin of a damrepairs using fiber-reinforced concrete had not proven to bedurable The new HPC mix used to repair the structure thesecond time contained 386 kgm3 (650 lbyd3) of cement70 kgm3 (118 lbyd3) of silica fume admixtures and had awater to cementing materials ratio of 028 and a 90-daycompressive strength exceeding 103 MPa (15000 psi)Berra Ferrara and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resistanceThe best results were obtained with a mix using slagcement steel fibers and silica fume Mortar strengthsranged from 75 MPa to 100 MPa (11000 psi to 14500 psi)In addition to better erosion resistance less dryingshrinkage high freeze-thaw resistance and good bond tothe substrate were achievedIn Norway steel studs are allowed in tires this causessevere abrasion wear on pavement surfaces with resurfacingrequired within one to two years Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14500 psi to 17000 psi) concretehad the same abrasion resistance as granite (Helland

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

4 DURABILITY OF UHPC

The durability of UHPC in terms of its resistance to internal and external environmental attack was also studied These investigations included chloride ion penetration abrasion ASR freeze-thaw and scaling testing RAPID CHLORIDE ION PENETRABILITY Rapid chloride ion penetrability tests were completed on UHPC specimens according to ASTM C1202 The electrical current was recorded at 1 minute intervals over the 6 hour timeframe resulting in the total coulombs passed value shown in Table 6 Two or three specimens were completed for each condition and specimens were tested at both 28 and 56 days The results show that the rapid chloride ion permeability is minimal regardless of the curing regime applied Also it is of note that the penetrability decreased significantly between 28 and 56 days for specimens from the Ambient Air curing regime

5 ABRASION RESISTANCE

Abrasion resistance can be an important parameter for any concrete that is exposed to contact with other materials The abrasion resistance of UHPC was measured through testing according to ASTM C944 in which a rotating abrading wheel bears on and wears away the concrete surface for a period of two minutes One modification to the standard test method was made in this program The reported test results are the product of 10 total minutes of abrasion representing five two-minute cycles completed on each specimen The abrasion testing was performed on three specimens from each of the four curing regimes However as abrasion resistance is highly dependent on the surface condition of the concrete each specimen was tested on three different surfaces First all specimens were tested on the surface formed by casting UHPC against the steel mold in which they were produced Following

these tests the cast (and now abraded) surface was sandblasted until it displayed a uniform texture The testing was then repeated for this sandblasted surface Finally the testing was again repeated for all the specimens subsequent to having the test surface ground plane using a cylinder end grinder

Abrasion resistance is directly related to the strength ofconcrete This makes high strength HPC ideal for abrasiveenvironments The abrasion resistance of HPC incorporatingsilica fume is especially high This makes silicafumeconcrete particularly useful for spillways andstilling basins and concrete pavements or concrete pavementoverlays subjected to heavy or abrasive trafficHolland and others (1986) describe how severe abrasion-erosion had occurred in the stilling basin of a damrepairs using fiber-reinforced concrete had not proven to bedurable The new HPC mix used to repair the structure thesecond time contained 386 kgm3 (650 lbyd3) of cement70 kgm3 (118 lbyd3) of silica fume admixtures and had awater to cementing materials ratio of 028 and a 90-daycompressive strength exceeding 103 MPa (15000 psi)Berra Ferrara and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resistanceThe best results were obtained with a mix using slagcement steel fibers and silica fume Mortar strengthsranged from 75 MPa to 100 MPa (11000 psi to 14500 psi)In addition to better erosion resistance less dryingshrinkage high freeze-thaw resistance and good bond tothe substrate were achievedIn Norway steel studs are allowed in tires this causessevere abrasion wear on pavement surfaces with resurfacingrequired within one to two years Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14500 psi to 17000 psi) concretehad the same abrasion resistance as granite (Helland

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

these tests the cast (and now abraded) surface was sandblasted until it displayed a uniform texture The testing was then repeated for this sandblasted surface Finally the testing was again repeated for all the specimens subsequent to having the test surface ground plane using a cylinder end grinder

Abrasion resistance is directly related to the strength ofconcrete This makes high strength HPC ideal for abrasiveenvironments The abrasion resistance of HPC incorporatingsilica fume is especially high This makes silicafumeconcrete particularly useful for spillways andstilling basins and concrete pavements or concrete pavementoverlays subjected to heavy or abrasive trafficHolland and others (1986) describe how severe abrasion-erosion had occurred in the stilling basin of a damrepairs using fiber-reinforced concrete had not proven to bedurable The new HPC mix used to repair the structure thesecond time contained 386 kgm3 (650 lbyd3) of cement70 kgm3 (118 lbyd3) of silica fume admixtures and had awater to cementing materials ratio of 028 and a 90-daycompressive strength exceeding 103 MPa (15000 psi)Berra Ferrara and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resistanceThe best results were obtained with a mix using slagcement steel fibers and silica fume Mortar strengthsranged from 75 MPa to 100 MPa (11000 psi to 14500 psi)In addition to better erosion resistance less dryingshrinkage high freeze-thaw resistance and good bond tothe substrate were achievedIn Norway steel studs are allowed in tires this causessevere abrasion wear on pavement surfaces with resurfacingrequired within one to two years Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14500 psi to 17000 psi) concretehad the same abrasion resistance as granite (Helland

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

1990) Abrasion-resistant highway mixes usually containbetween 320 and 450 kgm3 (539 and 758 lbyd3) ofcement plus silica fume or fly ash They have water tocementing materials ratios of 022 to 036 and compressivestrengths in the range of 85 to 130 MPa (12000 to 19000psi) Applications have included new pavements andoverlays to existing pavements

6 FREEZE-THAW RESISTANCE

The freeze-thaw resistance of UHPC was tested according to ASTM C666 This specification calls for repeated cycling of specimens between the temperatures of 0 and 40ordm Fahrenheit Periodically the cycling is stopped and the dynamic modulus of elasticity of the specimens is measured The test is based on the premise that the repeated freezing and thawing will cause microscopic degradation of the concrete resulting in a decreased dynamic modulus of elasticity Prisms measuring 3 in by 4 in by 16 in were used as specimens in this series of tests Prior to initiation of the testing all specimens were at least 28 days old Figure 10 provides the results from 300 cycles of freeze-thaw testing The results show that the Steam Tempered Steam and Delayed Steam cured specimens all retained dynamic modulus characteristics close to their original characteristics The Ambient Air cured prisms displayed a continuous increase in dynamic modulus throughout the testing As every cycle contains a period of time when the prisms are standing in water it is likely that this water recharge continued the curing process during the months of freeze-thaw testing

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

7 SCALING RESISTANCE

Scaling resistance was measured in accordance with ASTM C672 This specification calls for ponding a calcium chloride solution on the concrete surface then freezing the specimen for 18 hours followed by 6 hours of thawing Two UHPC specimens from each curing regime were tested with the solution ponded on surfaces created by forming against a steel mold For the UHPC specimens discussed here 50 cycles were completed After 50 cycles the texture of the test surfaces was visually altered however no scaling was measured or observed Corrosion staining was evident near the exposed ends of some fibers

8 PermeabilityThe durability and service life of concrete exposed to weather is related to the permeability of the cover concrete protecting the reinforcement HPC typically has very low permeability to air water and chloride ions Low permeability is often specified through the use of a coulomb value such as a maximum of 1000 coulombsTest results obtained on specimens from a concrete column specified to be 70 MPa (10000 psi) at 91 days and which had not been subjected to any wet curing were as follows Water permeability of vacuum-saturated specimensAge at test 7 yearsApplied water pressure 069 MPaPermeability 76 x 10-13 cmsRapid chloride permeability (ASTM C 1202)Age at test years CoulombsThe dense pore structure of high-performance concrete which makes it so impermeable gives it characteristics that make it eminently suitable for uses where a high quality concrete would not normally be considered Latex-modified HPC is able to achieve these same low levels of permeability at normal strength levels withoutthe use of supplementary cementing materialsA large amount of concrete is used in farm structures It typically is of low quality and often porous and with a rough surface either when

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

placed or after attack by farmyard wastes Gagne Chagnon and Parizeau (1994) provided a case history of the successful application of high performance concrete for agricultural purposes In one case a farmer raising pigs on a large scale was losing about 1 kg per pig through diarrhea This problem was resolved by reconstructing the pig pens with high performance concrete Cited as beneficial properties in this application werebull Surface smoothness that is compatible with the sensitive skin of a pigletbull Non-slip surfacebull Good thermal conductivity resulting in uniform distribution of heatbull Impermeable surface to resist the growth of bacteria and virusesbull Easy to place

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

Self-Consolidating Concrete

DefinitionSCC which stands for Self-Consolidating Concrete or Self-Compacting Concrete has many other names It is also called High-Workability Concrete Self-Leveling Concrete1 or Flowing Concrete2 All the above terms are used to describe a highly workable concrete that needs little to no vibration during placement3 It is in want of a standard definition but may be nominally considered a concrete mix of exceptional deformability during casting which still meets resistance to segregation and bleeding4 Inadequate vibration of normally consolidated concrete in heavily congested areas has led to surface defects and inadequate bond with the rebar5 Because of its low viscosity during pouring self-consolidating concrete can fill heavily reinforced areas under its own weight without applying vibration SCC is also used to create ldquosuper-flatrdquo floors (1mm over a length of 4m) without post-pour leveling6 The highly flowable nature of SCC is due to very careful mix proportioning usually replacing much of the coarse aggregate with fines and cement and adding chemical admixtures It depends on the sensitive balance between creating more deformability while ensuring good stability as well as maintaining low risk of blockage

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

Viscosity Modifying AdmixturesViscosity Modifiers are used to stabilize the rheology of SCC They essentially thicken the mix to prevent segregation34 This viscosity buildup comes from the association and entanglement of polymer chains of the VMA at a low shear rate which further inhibits flow and increases viscosity At the same time added VMA causes a shear-thinning behavior decreasing viscosity when there is an increase in shear rate35There are various types of VMAs most of which are composed of either polymer or cellulose-based materials which ldquograb and holdrdquo water The most important aspect is that they do not change any properties of the mix besides viscosity36 One of the most well-known VMAs is welan gum which is a natural type of water soluble polysaccharide When used in large quantities it has proven very effective in stabilizing the rheology of SCCs37 Several commercial VMAs are also on the market and their chemical compositions are propriety secrets Currently these commercial brands and welan gum are known to be very expensive increasing cost of the mix by at least 20Consequently there is a great deal of ongoing research in the materials sciences often with financial support from industry to develop cheaper VMAs with equally reliable high performanceOne study coming out of Ryerson University in Canada tested four newly engineered polysaccharide-based VMAs Performance of four mixes with each of these new VMAs was compared to two types of control mixes one with welan gum and a one with a commercial VMA from a Canadian producer Results showed that performance of the newly developed admixtures matched or even beat the control mixes in properties of slump flow segregation bleeding flow time setting time and compressive strength An important characteristic to note is the increase in setting time caused by addition of VMAs This occurs ldquobecause the VMA polymer chains become absorbed ontocement grains and interfere with the precipitation of various minerals into solutions that influence the rate of hydration and setting

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

STRUCTURAL PROPERTIES

The basic ingredients used in SCC mixes are practically the same as those used in the conventional HPC vibrated concrete except they are mixed in different proportions and the addition of special admixtures to meet the project specifications for SCC The hardened properties are expected to be similar to those obtainable with HPC concrete Laboratory and field tests have demonstrated that the SCC hardened properties are indeed similar to those of HPC Table 3 shows some of the structural properties of SCC Items SCC

Air content () 45-60

Items Water-binder ratio () 25 to 40

Compressive strength (age 28 days) (MPa) 40 to 80

Compressive strength (age 91 days) (MPa) 55 to 100

Splitting tensile strength (age28 days) (MPa) 24 to 48

Elastic modulus (GPa) 30 to 36Shrinkage strain (x 10-6) 600 to 800

Compressive StrengthSCC compressive strengths are comparable to those of conventional vibrated concrete made with similar mix proportions and watercement ratio There is no difficulty in producing SCC with compressive strengths up to 60MPa

Tensile StrengthTensile strengths are based on the indirect splitting test on cylinders For SCC the tensile strengths and the ratios of tensile

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

and compressive strengths are in the same order of magnitude as the conventional vibrated concrete

Bond StrengthPull-out tests have been performed to determine the strength of the bond between concrete and reinforcement of different diameters In general the SCC bond strengths expressed in terms of the compressive strengths are higher than those of conventional concrete

Modulus of ElasticitySCC and conventional concrete bear a similar relationship between modulus of elasticity and compressive strength expressed in the form E(fc)05 where E = modulus of elasticity fc =compressive strength This is similar to the one recommended by ACI for conventional normal weight concrete

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

Benefits of SCCThe technologically advanced components of SCC work together to create a mix that produces numerous benefits It offers many advantages for contractors ready-mix producers and precast concrete fabricatorsFor Contractors1048707 Reduced vibration effort and noise during placing1048707 Ability to fill complex forms with limited accessibility1048707 More uniform distribution in areas of closely bunched reinforcement1048707 Rapid pumping of concrete1048707 Uniform and compact surface1048707 Less surface voids and need for rubbing and patching1048707 Improved aesthetics of flatwork for less effort

Reduced labor and construction time

For Ready-Mix Producers43441048707 Better perception from customers by offering a technically advancedhigher value concrete mixture1048707 Offers a product that saves customers time and money1048707 Faster truck turnaround1048707 More efficient use of mixing equipment and delivery1048707 Easily expands variety of products offered without adding moreequipment (eg tilt-up flatwork walls etc)1048707 Improved aesthetics of final productFor Cast-in Place Fabricators1048707 All the above plus1048707 Controlled environment allows easier quality control1048707 Easier to achieve qualities of an optimally designed mix1048707 Can better guarantee properties due to tight quality control1048707 Faster slump loss means concrete is ready for steam-curing quicker

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

In order for these parties to reap the benefits of SCC they need an increased understanding of SCCrsquos complex nature Declines in skilled labor and quality control in the construction industry will make this a more challenging task for users At the same time developers still need to provide set procedures and ways for users to quantify the qualities of mix characteristics

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

StandardsAs mentioned before there are as yet no standard definitions or specifications for SCC The term workability includes flowability mouldability cohesiveness and compactibility of fresh concrete Flowability is related to consistency Cohesiveness is a measure of compactibility and finishability usually measured by ease of dowelling and visual judgement of resistance to segregationGiventhat workability is so broadly defined by numerous other factors measuring the properties of High-Workability Concrete has gone in all directionsSome believe SCC should not be defined as a new product New products require all new testing and approval from ACI and ASTM Since it is still a developing technology many appreciate the flexibility to develop mixes according to project requirements currently the industry practice Until test methods to quantifiably characterize the concrete mix are standardized the following are several industry measurement standards used for the time being

FlowabilityThis characteristic is often termed ldquoslump flowrdquo as opposed to ldquoslumprdquo because the initial low viscosity of the SCC causes the concrete in a standard slump test to spread out and flatten so much the height difference becomes too little to accurately correlate with the flowability of the mix not to mention the difficulty in measuring the height of the slumped sample Therefore slump flow is measured as the horizontal distance of spreading Usually this dimension is 20-30 inches47

In the slump flow test a standard slump cone is used and SCC is typically poured in without consolidation effortsThe flow diameter (Fd) is the mean diameter measured in two perpendicular directions Some researchers recommend a slump flow value between 500 to 700 mm At less than 500 mm the mix may have trouble flowing in a confined space Slumpflow exceeding 700 mm could lead to segregation of the mix49

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

the L-box test measures the ability of SCC to flow in a confined space It tests to see if the concrete can flow through an L-shaped box with several grilles of rebar designed to inhibit flow Another way to measure deformability through restricted areas is the V-funnel test After concrete is filled into the funnel the bottom outlet is opened and the time until flowing stops is measured To be termed an SCC it is generally required that this flow time be less than 6 The T50 test measures rate of flow in terms of the time required for SCC to reach 19-34 inches (or 50 cm) in diameter in the slump flow test53 Bui et al states that the flow time of SCC should be no larger than 12 seconds

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

Stability

Stability is the characteristic of SCC to resist segregation It is often quantified with the Visual Stability Index which ranges from 0 to 3 in increments of 05Another more exact segregation test is to pour 2 liters fresh concrete over a 5 mm mesh and measure the mass of mortar passing though the screen in 5 min The segregation index (SI) of a stable concrete should be less than 5

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

ApplicationSCC technology originated in Japan in the early 1980s59 arising out of durability concerns due to poor compaction on the job site60 Use of SCC quickly became widespread in Japan especially since the government implemented a plan to use SCC for 50 of all concrete jobs by 2003 It then spread to Europe in the 1990rsquos after invention of polycarboxylate superplasticizers In the UK The Concrete Society has issued official measures to expand the use of SCC as a means of replacing vibratory compaction In the US and Canada SCC technology is available mostly in the form of proprietary concrete mixes from ready-mix producer subsidiaries of cement manufacturers such as Lafarge and Lehigh It is also available as specialized admixtures combining superplasticizer and viscosity modifiers Given how important maintaining mix quality of SCC is for its successful performance using SCC demands increased attention and skill In particularsuperplasticizer dramatically increases the sensitivity of the mix to water This allows little room for error in mix proportioning which can become problematic in-field when weather and timing can not always be controlled by the contractor In light of this most applications of SCC in the US have been limited to precast construction due to tighter quality control ensured in-plantcompared to in-field63 However the industry has shown eagerness to expand its use Whereas in 2000 only about 10 of the precast industry had tried SCC by 2003 the number jumped to almost 90 of which 40 used it on a regular basis Some notable projects have utilized SCC in Canada One is the Toronto International Airport where concrete had to be pumped upwards from the ground to form 101-foot tall columns Another project in Vancouver BC used SCC so little patching would be required for highly visible outrigger columns In Asia SCC was used for a monolithic foundation mat inSingapore where the concrete needed to reach massive dimensions in a short amount of time In the US a high-strength SCC was imperative for constructing tightly reinforced elements poured in below-freezing weather for the 68-story Trump Tower in New York City65 SCC has also shown

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

successful application for residential projects such as homes for Habitat for Humanity inthe Houston area

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology

Conclusion

In conclusion self-consolidating concrete is an exciting technology that has found many successful applications Although the concept has been around for a few decades new products are still emerging and better mix proportioning strategies are still in development The new generation of polycarboxylate-based superplasticizers has taken SCC a giant step forward Meanwhile multiple viscosity modifying admixtures are available while researchers continue to seek better and cheaper recipes While there is no set definition for SCC yet for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC The absence of an established industrial standard for SCC allows more creativity intailoring a mix to specific job requirements At the same time the lack of standards means devising a successful mix depends on the expertise of the producer and contractor Therefore it is clear that educating manufacturers and contractors is the crucial first step in expanding the use of SCCrsquos extremelypromising technology