Self-compacting concrete: modern concrete and admixture technology

R Beissel, Sika AG, Switzerland H Lim, Sika Pte. Ltd. , Singapore

26th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 27 - 28 August 2001,

Singapore

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26th Conference on Our World in Concrete & Structures: 27 - 28 August 2001, Singapore

Self-compacting concrete: modern concrete and admixture technology

R Beissel, Sika AG, Switzerland H Lim, Sika Pte. Ltd. , Singapore

Abstract

Self-Compacting Concrete (SCC) is a modern concrete technology that allows significant advantages compared to conventional concrete. Extreme workability, self-compaction without vibration combined with high concrete quality allows new and interesting applications for the competitive users and creative specifiers of concrete. The advantages of SCC are important for the applicators (contractors) and concrete producers (Ready mixed concrete, Precast concrete) as well as for the final users of the structure.

Knowledge about its properties, design and production is essential for the successful use of SCC. Creativity is also necessary, because the use of this technology is just starting to spread and new, interesting applications for SCC are found every day.

This paper will give some information about the advantages of SCC, typical applications, influence on the cost, technical properties, test methods and creating a typical mix design. Another focus is a selection of case studies which shows a variety of projects where SCC has been used successfully. As can be seen, advantageous applications for SCC are very diverse, the reasons for using SCC can be very different.

Keywords: Self-Compacting Concrete, Concrete admixtures,

Background: The need for very fluid concrete has been existing for a long time. In earlier times this always had to be done with a high increase of the water content. The results were poor stability of the concrete because of insufficient cohesion. Segregation and bleeding caused very low concrete quality. Other very negative effects were the reduced strength and durability as well as the increased porosity of the concrete which are a result of the high water content. First research into the new technology which we now know as Self-Compacting Concrete started in Japan in the early 1990s. Since then many researches studies on fundamental characteristics have been carried out. (Selection of literature: 1-9) Modern developments like • Increased technical requirements • Growing pressure to rationalise working processes • Increased focus on ecological considerations lead, among others, to a global spread of the SCC technology.

Description: => SCC is characterised as an extremely soft and fluid concrete that does not need additional

compaction, like vibrating, because of its outstanding self-compacting properties. => SCC remains homogeneous and cohesive without segregation, separation or bleeding. => The requirements of SCC result in a mix deSign which has a much higher proportion of fines

than conventional concrete

26th Conference on Our World in Concrete & Structures: 27 - 28 August 2001, Singapore

Self-compacting concrete: modern concrete and admixture technology

R Beissel, Sika AG, Switzerland H Lim, Sika Pte. Ltd., Singapore

Abstract

Self-Compacting Concrete (SCC) is a modern concrete technology that allows significant advantages compared to conventional concrete. Extreme workability, self-compaction without vibration combined with high concrete quality allows new and interesting applications for the competitive users and creative specifiers of concrete. The advantages of SCC are important for the applicators (contractors) and concrete producers (Ready mixed concrete, Precast concrete) as well as for the final users of the structure.

Knowledge about its properties, design and production is essential for the successful use of SCC. Creativity is also necessary, because the use of this technology is just starting to spread and new, interesting applications for SCC are found every day.

This paper will give some information about the advantages of SCC, typical applications, influence on the cost, technical properties, test methods and creating a typical mix design. Another focus is a selection of case studies which shows a variety of projects where SCC has been used successfully. As can be seen, advantageous applications for SCC are very diverse, the reasons for using SCC can be very different.

Keywords: Self-Compacting Concrete, Concrete admixtures,

Background: The need for very fluid concrete has been existing for a long time. In earlier times this always had to be done with a high increase of the water content. The results were poor stability of the concrete because of insufficient cohesion. Segregation and bleeding caused very low concrete quality. Other very negative effects were the reduced strength and durability as well as the increased porosity of the concrete which are a result of the high water content. First research into the new technology which we now know as Self-Compacting Concrete started in Japan in the early 1990s. Since then many researches studies on fundamental characteristics have been carried out. (Selection of literature: 1-9) Modern developments like • Increased technical requirements • Growing pressure to rationalise working processes • Increased focus on ecological considerations lead, among others, to a global spread of the SCC technology.

Description: => SCC is characterised as an extremely soft and fluid concrete that does not need additional

compaction, like vibrating, because of its outstanding self-compacting properties. => SCC remains homogeneous and cohesive without segregation, separation or bleeding. => The requirements of SCC result in a mix design which has a much higher proportion of fines

than conventional concrete

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Fresh concrete properties: The free slump flow of the fresh concrete is between ca. 65 to 75 cm, i.e. much higher than the flow of conventional concrete. The workability time and the air content can be chosen as required.

Properties of hardened concrete: High quality concrete can be produced with SCC as well as concrete with normal requirements to final properties.

=> High strength concrete => Concrete with low permeability => Concrete with high durability, carbonation and chemical resistance => Homogeneous concrete surface and matrix

Concrete admixtures One of the main tasks when producing SCC is to have an outstandingly fluid concrete and keep its water content low at the same time. The very good workability must not allow disintegration or separation of the fresh concrete We also have a significantly increased fines content in the mix that increases the specific surface that has to be lubricated.

These facts require special concrete admixtures that • give an extremely strong plasticising effect • allow very high water reduction • help to keep the concrete stable and homogeneous Today new developments of admixtures based on the polycarboxylate technology allow the fulfilment of these requirements with some specially designed products based on a much-improved chemistry.

Milestones of concrete admixture developments Lignosulphonates: In use since ca. 1930 Water reduction up to 10% Naphthalene and Melamine based products: In use since ca. 1970 Water reduction up to 20% Polycarboxylate technology In use since 1990s Water reduction up to 40%

Mode of action: Ionic repulsion

Mode of action: Ionic repulsion

Mode of action: Steric hindrance and ionic repulsion

Advanced polycarboxylates that are used as concrete admixtures are also called "comb polymers" because of the special three-dimensional shape of their molecules. The so called "back bone" part will attach to a cement particle by ionic attraction while long "tails" extend in the opposite direction and thus result in spatial hindrance of particles joining too closely together.

Advantages of Self Compacting Concrete: The special properties of SCC result in new possibilities for concrete producers, concrete applicators and project owners. Since most projects are quite different from each other the decision criteria for choosing the concreting technique are also different.

Advantages of SCC for Contractors - No vibration work. - Higher speed of concrete placing. - Less finishing work needed, especially for slabs. - Equipment ( e.g. cranes, pumps etc. ) are needed for a shorter period of time - Less manpower needed. - Placing problems caused by heavy and dense reinforcement are reduced. - More homogeneous concrete surfaces result in reduced cost (No honey combing, washout by -bleeding etc). - Very suitable for repair jobs, be they small or large scale. - Drastic reduction of noise emission improves environment for employees and neighbours. - "White finger syndrome", a serious illness of the blood circulation which is caused by vibrations, can be prevented.

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Advantages of SCC for Ready mix Concrete Producers - Unique chance for differentiation against competition. - Additional turnover possible. - Faster turnaround of trucks. - Easier pumping.

Advantages of SCC for the Precast Concrete Industry - Higher speed of concreting, higher capacity. - Thinner elements can be produce because of excellent workability. - see allows more economic production processes. - Dramatic noise reduction results in significant improvement of working conditions. - Denser reinforcement can be filled easily.

Advantages of SCC for Specifiers and their Clients =- Faster progress of project possible. - New architectural possibilities, detailed concrete surfaces. - Less noise can extend working hours in densely populated areas. - Very smooth floor slabs can make tiling possible without installing a screed. - Durability of the structure can be improved because of reduced damages and more homogeneous concrete cover - Vibration and compacting is no longer a design criteria, Le. elements and structures can be produced more economically, e.g. thinner dimensions

Testing of SCC: Because of the outstanding flowability of see, the conventional methods for testing the workability can not be used. eommonly used today and very convenient for testing on site are the slump flow test and the "L­shaped box".

Slump flow test: This test can easily be carried out even on the job site. A normal slump cone is used and filled up to the top with the see to be tested. The concrete is not

compacted. When full, the cone is lifted with normal speed to allow the concrete to flow on a clean, smooth and horizontal surface out of metal or laminated wood. 50 cm diameter should be reached after 3-6 seconds, the final diameter should be between 65 and 75 cm. Once the concrete has stopped flowing, it has to be checked to determine any separation effects. No

bleeding should occur and the larger aggregates have to be distributed evenly. In some countries the slump cone is used upside down, because this way the cone is easier to fill.

L-shaped box In addition to the flowability and the homogeneity of the concrete the L-shaped box also allows indications of the blockage behaviour. The vertical part of the L is filled to the top, Then a gate is opened which allows the concrete to flow into the horizontal part. The time taken for the concrete to flow 40cm is measured and should be between 3-5 seconds.

Again the homogeneity of the concrete is checked after it stops flowing.

Mix design for Self Compacting Concrete General guidelines: see needs significantly higher fines content < 0.125 mm than conventional concrete. Grain size chosen is usually between 12 and 20mm, but larger aggregates can also be used. Round as well as crushed aggregates can be used wle ration has to be kept within the required limits, since the water content significantly influences the quality of the hardened concrete.

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The high specific surface of SCC mixes requires very powerful admixtures to achieve the necessary workability in combination with cohesion and homogeneity.

Cement! binder Basically most standard cements can be used to produce SCC. The cement! binder content is normally higher for SCC than for conventional concrete. The necessary amount is chosen according to the required fines content and the designed concrete quality. The maximum aggregate size also influences the total amount of cement! binder. More is needed if smaller aggregates are used. In most cases it is economical to use a mineral additive like Fly ash, Slag, Limestone powder, Silica fume etc. to increase the fines content. Example for typical cement! binder and filler content of SCC:

Maximum aggregate Cement! binder + filler size 4mm 500-650 Kg/m3 Smm 450-500 Kg/m3

16 mm 400-450 Kg/m3 32mm 375-425 Kg/m3

Fines content: Fines content depends mainly on maximum size of aggregates and the use of the concrete The fines content includes cement! binder, filler and fines from sand.

Maximum aggregate Fines content < 0.125 size mm 4mm ~ 650 Kg/m3 Smm ~550 Kg/m3 16 mm ~500 Kg/m3 32 mm ~475 Kg/m3

Water content: The rules for conventional concrete also apply for SCC: The lower the water/ cement ratio or the water content, the higher the quality of the hardened concrete regarding its:- Strength, porosity, permeability for chemicals, gases and water, durability

Mix design for Self Compacting Concrete

General Because of possible variations of properties of different concrete components, trials have to be done prior to concrete production for every batching plant or when concrete components are changed. But: Experiences of SCC producers show that after gaining the first experiences with the production of SCC, this soon becomes a standard procedure.

Examples for mix design of SCC with compressive strength of ca. 40 N/mm2

Aggregates: 0-16mm: ca. 1750 kg/m3 dry aggregates total (0-4 mm: ca. 50%; 4-S mm: ca. 15%; S-16 mm: ca. 35% )

Cement! binder: 350 kg/m3 CEM I 42.5, plus 75 kg Fly ash or 350 kg/m3 CEM 142.5 plus 75 kg stone powder or 425 kg/m3 CEM IIIA-L 32.5 or 425 kg/m3 slag cement CEM II or CEM III

Admixture: 1.2-1.5% Sika ViscoCrete 1 (-2) of total binder content (5-7 kg/m3)

Water: W/B ca 0.42-0.46

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Example for Grading curve of SCC with 16 mm aggregate.

Placing of Self-Compacting concrete Basically the placing procedure is the same for SCC as for conventional concrete, but faster and with less manpower. Conventional formwork can be used in most cases. Sometimes the requirements for the formwork are even reduced, because additional stresses caused by vibration do not appear. If the final concrete surface has to fulfil very high aesthetic requirements, it will be helpful to place the SCC under pressure, i.e. pump it into the formwork via a filling socket from the bottom. The mixing time for the production of SCC might have to be increased slightly.

Self Compacting Concrete, influence on project cost Cost increasing factors: - More demanding mix design (admixtures, fines) - Slightly extended mixing time Cost reduction factors: - Higher speed of placing - Reduced machine/ equipment cost - Possible higher concrete quality and durability - Homogeneous surfaces - Reduced manpower - Reduced finishing/ repair work - More flexibility for design, e.g. thinner elements if possible - Noise reduction (extended working hours?) - Health effects ( of interest for national economy)

Note: The importance of above factors varies greatly from project to project. In one project it might not be possible to reduce the size of the elements, in another it might reduce the cost by 20%. Example: Office building in Sweden Office buildings with 3000 m3 of concrete Final calculation:

Cost in € Conventional Self concrete Compacting

concrete Concrete cost 270.000 293.000 Labour cost 50.000 15.000 Equipment cost 10.000 2.000 Total cost for concreting work 330.000 310.000

By uSing Self-Compacting Concrete, the cost for the concreting work could be reduced by ca. 6%

Case studies with Self Compacting Concrete

Macao tower, China The total height of this tower will be 338 m. For the top 10m of the lower supporting legs SCC was used. Main reason was the heavily congested reinforcement. It was also impossible to use vibrators because of difficult access. For the construction of the top supporting legs ( Height 220 m ) another 500 m3 of sec were used for the same reasons.

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successful application in Macao

Concrete floors in France

Mix design:

OPC 450 Kg/m3 Fly ash 100 Kg/m3 20 mm 485 Kg/m3 10 mm 320 Kg/m3 River sand 815 Kg/m3 Water 175 Kg/m3 ViscoCrete 10-6 4.5-5 Kg/m3 Results: Slump flow: 650 mm for 3 hours ( inverted slump cone) 50mm flow after 4 seconds Concrete grade 55 MPa

It is becoming more common now in France to use SCC for concrete floors, also with smaller projects. Some Ready mix producers focus on this segment and are very successful with it. Main advantages of

SCC for this application are: Faster placing and less finishing work Reduced manpower Tiles can be placed directly on the concrete ( cost saving of ca. 15% )

Housing slabs USA

Typical mix design: CEM 142.5 Mineral filler 0-14mm agg. ViscoCrete 3010 Water Results: Slump flow: Concrete grade

330 Kg/m3 150 Kg/m3 1680 Kg/m3 ( dry ) 1% bwoc 190 Kg/m3

70mm 30 Mpa

Slabs for residential housing using SCC have been poured in Charleston, South Carolina, USA. Man hours could be reduced by 75% using SCC compared to conventional slump concrete. Mix design: Cement type II: 420 Kg/m3 19mm aggregate: 872 Sand: 831 W/C ratio: 0.41 ViscoCrete 5: 1 % bwoc. SCC allowed significant reduction of labour

SCC for the repair of the Rempenbridge, Switzerland This 70 years old bridge had to be closed for traffic because it was heavily affected by corrosion. The structure consisted of five girders and a concrete slab. The conventional process of repair would have been quite costly and time consuming.

SCC solution: With the SCC technology it was possible to use an economic repair method. The space between the longitudinal beams was installed with reinforcements, including pre-stressed steel cables. After this, the cavity was closed at the bottom and filled with SCC from underneath by pumping the concrete through a filling socket. Two openings in the top of each section allowed the air to escape and to control the filling operation.

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The results of this project were very satisfying and economical. The working conditions for the applicators were much improved, the time to carry out the project was significantly reduced. Conventional concrete could not have been used for this application.

Since this method adds considerable weight to the bridge, the capacity of the foundations has to be analysed.

Mix design: CEM II 435 Kg/m3 Sand 0-4mm 53% Sand 4-8mm 15% Crushed stone 8-16mm Silica fume Water Sika ViscoCrete Results:

180 I

32% 15 Kg/m3

1.4% bwoc

Slump flow 28day strength

69 cm 45-50 Mpa

Formwork pressure of 12 m high wall filled with SCC. In preparation for a huge exhibition hall in France, large scale tests were made to analyse the formwork pressure for a 12 m high wall cast with SCC in one process. Two different ways of filling were used: Filling from the top and pumping into the bottom of the formwork. Mix design: CEM II 42.5: 280 Kg/m3 Limestone filler: 170 Kg/m3 Sand: 740 Kg/m3 Gravel 0-16 915 Kg/m3 Sika ViscoCrete 4.0 Kg/m3 Water 200 I Result The actual formwork pressure with SCC was approx. 30% less than the calculated hydrostatic pressure. Both filling methods showed similar results. Surface quality was better when filled from the bottom.

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Pipe screen for railway tunnel in Zuerich, Switzerland. Prior to the construction of a railway tunnel in the centre of Zurich, supporting measures had to be taken to secure the buildings on top of the tunnel because the ground cover was extremely thin. It was decided to build a pipe screen around the top of the future tunnel to give additional support once the excavation of the tunnel is on the way. 10 pipes were driven into the soil for 150m via pipe jacking. The diameter of each pipe was 1.5m. The pipes were then heavily reinforced and filled with Self-Compacting Concrete. This way it was possible to fill the 150m long pipes in 3 segments only. With conventional concrete, ca.

10 segments would have been necessary. By using SCC the construction time for the pipes could be reduced from 207 working days for conventional concrete to 93 working days. This was a time saving of almost half a year. Altogether 2000m3 of SCC were used in this project.

Concrete details Pipe Screen: Aggregates 0-16mm Binder: 380 Kg/m3 SEM IIA-L 32.5

50 Kg/m3 Fly ash Sika ViscoCrete 2 1.7 % 28 days strength: 46.0 Mpa

References:

Khayat, K.H., Guizani, Z., "Use of Viscosity modifying Admixture to enhance stability of fluid concrete"" ACI Materials journal (94)4 (1997)332-340 Khayat, K.H., "Use of viscosity modifying admixture to reduce top-bar effect of anchored bars cast with fluid concrete", ACI Materials Journal ( 95) 2 (1998) 158-167 Miura, N., Takeda, N., Chikamatsu, R., Sogo, S.,"Application of super workable concrete to reinforced concrete structure with difficult construction conditions", Proceeding, ACI SP 140, (1993) 163-186 Nagataki, S., Fujiwara, H., "Self Compacting Properties of highly flowable Concrete", Proceedings of second international symposium on advances in concrete technology, SP 154-16 ( 1995) 301-314 Ozawa, K., Maekawa, K.,Okahoma, H., "High Performance concrete with High Filling capacity", University of Tokyo, Rilem Symposium, Admixtures for concrete, Barcelona ( 1990 ) Ozawa, K., Maekawa, K., Okahoma, H., " Development of high performance concrete", Journal of faculty of Engineering, University of Tokyo (XL 1)3 ( 1992) Schlumpf, J., Oppikofer, R., "Self Compacting Concrete", Tunnel-magazine, Germany 4/1999 Yurugi. M., Sakata, N., Iwai, M., Sakai, G.,"Mix proportion for highly workable concrete" Conference concrete 2000, edited by. R.K. Dhir, M.R. Jones, (1) (1993) 579-590 Various authors ( 67 contributions), "Self Compacting Concrete", First international RILEM symposium on SCC, Stockholm, 9/1999