CHAPTER 1INTRODUCTION

1.1 GENERAL

Interest in the production of very high-strength concrete has been increasing over the past several years, particularly in the precast and pre-stressed concrete industries, builders of high rise concrete structures also could benefit from higher strength concrete by large reduction in dead load. Although the very high strength concrete to be used for most cast in place construction could not be applicable. Reasoning behind, it requires special care of each aspect of strength development and preventative measures. Reactive Powder Concretes (RPCs) are ultra-high strength cementitious materials composed of very fine powders with a maximum particle size of approximately 800m. In addition to the absence of the traditional coarse aggregates used to produce normal and high strength concrete, RPCs are characterized by very high silica fume content and very low water-cement (w/c) ratios. The low w/c ratios are achieved through

1.2 OBJECTIVES AND SCOPE OF THE WORK

1.2.1 Objectives

The present study focuses on developing RPC of compressive strength up to 150 MPa, to determine the effect of silica fume and content on compressive strength, to determine the effect of high temperature curing on the compressive strength and to determine the effect of addition of quartz powder on the compressive strength of RPC.1.2.2 Scope

The effects of three silica fume replacement levels (15,20and25%) are included in this study. Combined effect of 15% silica fume and 20% quartz powder is also studied. The strength studies are limited to a maximum age of 28 days. W/B ratio varied from 0.16-0.24. Super plasticizer varied from 1% -4%. Samples are cured at normal temperature and elevated temperature(90degree centigrade)

CHAPTER 2LITERATURE REVIEW

2.1 GENERAL

Reactive powder concrete (RPC) is the generic name for a class of cementitious composite materials developed by the technical division of Bouygues, S.A. France in the nearly 1990s and the worlds first RPC structure, the Sherbrooke Bridge in Canada, was constructed in July 1997. It is characterized by extremely good physical properties, particularly strength and ductility. Reactive powder concrete (RPC) is a developing composite material that will allow the concrete industry to optimize material use, generate economic benefits, and build structures that are strong, durable, and sensitive to environment. Since Reactive Powder Concrete (RPC) first appeared on the world research stage in 1994, it has received considerable attention. The original development of RPC came from the Scientific Division of Bouyges, France. Since then further development of the material has continued throughout the world (for example Australia, Canada, Japan, Korea and the United States of America) at a frenetic pace. Superior mechanical properties and durability characteristics promise that the material will have a wide and significant impact on the concrete industry. To date, the greater part of research into RPC has focused on what the material is and its properties, micromechanical analysis, potential applications and preliminary work into the structural behaviour. However in India investigations in RPC, using locally sources and materials, developing composition, mechanical properties and durability parameter are still in their infancy. This information is required to assist with the increased use of RPC in practice and to further develop analytical techniques and design standards.The addition of supplementary material, elimination of coarse aggregates, very low water/binder ratio, additional fine steel fibers, heat curing and application of pressure before and during setting were the basic concepts on which it was developed (Richard et al. 1995). Compressive strength of RPC ranges from 200 to 800 MPa, flexural strength between 30-50 MPa and Youngs modulus up to 50-60 GPa. There is a growing use of RPC owing to the outstanding mechanical properties and durability. RPC structural elements can resist chemical attack, impact loading from vehicles and vessels, and sudden kinetic loading due to earthquakes. Ultra high performance is the most important characteristic of RPC (Gilliland et al. 2007). RPC is composed of more compact and arranged hydrates. The microstructure is optimized by precise gradation of all particles in the mix to yield maximum density. It uses extensively the pozzolonic properties of highly refined silica fume and optimization of the Portland cement chemistry to produce highest strength hydrates (Cheyrezy et al. 1995; Reda et al. 1999). RPC will be suitable for pre-stressed application and for structures acquiring light and thin components such as roofs of stadiums, long span bridges, space structures, high pressure pipes, blast resistance structures and the isolation and containment of nuclear wastes (Gowripalan et al. 2003; Bonneau et al. 1996; Hassan et al. 2005). In India the work on RPC has started from last few years. SERC, Chennai, worked towards the development of the UHSPC with and without steel fibers and the effect of various heat curing regimes adopted on the strength properties of the mixtures (Harish et al.2008). Dili A.S. and Manu Santhanam (2004) have studied mix design, mechanical properties and durability aspects of RPC. The utility of RPC in actual construction is minimal or nil in India, it is because of non-availability of sufficient experimental data regarding production and performance of RPC. So the basic objective of the current investigation is to experience the production of RPC. The key issues of the study are: to develop RPC of compressive strength up to 150 MPa, to determine the effect of silica fume content on compressive strength, to determine the effect of high temperature curing on the compressive strength and to determine the effect of addition of quartz powder on the compressive strength of RPC. As the standard code is not available to design RPC, here an attempt is made to design RPC mix with locally available materials referring literature. The RPC cube specimens were cast and cured for both normal and high temperature curing. The cured specimens were tested to evaluate the compressive strength.

CHAPTER 3EXPERIMENTAL PROGRAM3.1 GENERALReactive Powder Concrete (RPC) is catching more attention now days because of its high mechanical and durability characteristics. RPC mainly comprises of cement, silica fume, silica sand, quartz powder and steel fibers. RPC has been able to produce with compressive strength ranging from 200 MPa to 800 MPa with flexural strength up to 50 MPa. Although suitable guidelines are not available to produce RPC in India, the present study focuses on developing RPC of compressive strength up to 150 MPa. Along with the development of RPC, various factors affecting the strength of RPC are studied. The 100100100 mm size RPC cube specimens were cast by varying the constituent materials and cured at both normal and high temperature before testing for their strength. The compressive strength of 142 MPa was achieved with the mix considered. It is observed from the study that w/b ratio, silica fume content, quartz powder, high temperature curing significantly affects the compressive strength of RPC. It was observed that addition of quartz powder and high temperature curing increases the compressive strength up to 10 percent when compared with specimens tested after normal room temperature curing. The material can be effectively utilized in the production of precast elements/PSC structures.3.2 MATERIAL PROPERTIES3.2.1 CementOrdinary Portland Cement (OPC) conforming to IS 12269 (53 Grade) was used for the present experimental work. Laboratory tests were conducted on cement to determine standard consistency, specific gravity, density and fineness. The results are presented in Table 3.1. Table 3.1 Properties of CementGrade53 grade

ManufacturerUltra tech

Specific gravity3.15

Fineness (m2/kg) 294

Standard consistency (%)31.25

Initial setting time (min)160

Final setting time (min)255

3.2.2 Silica FumeSilica fume was supplied by ELKEM Materials. From the laboratory tests, the specific gravity was obtained as 2.12 and density as 576kg/m3. Properties of silica fume are given the Table3.2 and the chemical composition of silica fume was tested at Central Power Research Institute (CPRI), Bangalore and the result is presented in the Table 3.3.

Table 3.2 Properties of Silica FumeSpecific Gravity2.2

Bulk Density576 (kg/m3)

Size15 m

Specific surface20,000(m2/kg)

Table 3.3 Chemical composition of Silica FumeOxide CompositionPercentage

CaO2.94

SiO284.28

Al2O31.54

Fe2O33.37

SO32.34

MgO2.09

P2O50.60

TiO20.04

Na2O1.23

K2O1.47

3.2.3 Super plasticizerCeroplast in the form of sulphonated naphthalene polymers which complies with IS: 9103-1999 was used as super plasticizer (chemical admixture) to improve the workability of concrete. It is supplied as a brown liquid instantly dispersible in water. The properties of super plasticizer obtained from manufacturer are shown in Table 3.3.Table 3.4 Properties of CeroplastSpecific Gravity1.20

Chloride contentNil

Air entrainmentApproximately 1% additional air is entrained

3.2.4 AggregateLocally available manufactured M-sand was used as aggregate. Laboratory tests were conducted on M sand to determine the different physical properties as per IS 383-1970. The properties of fine aggregate are shown in Table 3.5. The sieve analysis details of fine aggregate are presented in Table 3.6. Fine aggregate used conforms to IS 383:1970 specifications (Zone II). The grading curve of fine aggregate is shown in Fig 3.1Table 3.5 Properties of Fine AggregateSl.No.ParticularsValues

1.Specific gravity2.65

2.Fineness modulus2.49

Table 3.6 Sieve Analysis Details of Fine AggregateSieve size(mm)Mass retained(g)% mass retained(g)Cumulative % mass retained% passingIS Rangeforzone II

4.7500010090 100

2.36444.44.495.675 100

1.1826426.430.869.255 90

0.619519.550.349.735 59

0.321821.872.127.98 30

0.1519119.191.28.80 10

Fig. 3.1 Grading Curve of Fine Aggregate

3.2.5 Quartz powder

Quartz Powder, from SREE KUMARESHA enterprises, Tamilnadu (particle size ranging from 10 m to 45 m) is used. The specific gravity of quartz powder is 2.6.

3.2.6 WaterPresence of organic or inorganic impurities in water will affect the strength of concrete. Generally, water suitable for drinking is considered fit for making concrete. Hence clean drinking water available in the college water supply system was used for making concrete and for curing the specimens.

3.3 MIX PROPORTION AND METHODOLOGY

To study the influence of the constituent materials, 14 different proportions were considered by varying water-binder ratio, silica fume and quartz powder content. Cement of quantity 900 kg/m3 was kept constant for all the mixes. The water-binder ratio of the mixes varied from 0.16 to 0.24. Silica fume was added by 15 to 25 percent by weight of cement. 20 percent of quartz powder by weight cement was also added for few mixes. Super plasticizer dosage varied from 1 to 4 percent for all the mixes. Detailed mix proportioning is mentioned in Table 3.7. Table 3.7 Proportioning of RPC mixes

Mixing Procedure

The high speed mortar mixer is used to mix the ingredients of RPC. The mixing sequence is as follows: Dry mixing the powders (including cement, silica fume, quartz powder and M- sand) for about 3 minutes. Addition of sixty percentage volume of water and mix for about 3 minutes. Addition of the remaining water and super plasticizer, and mixed for about 10 minutes.

Sample Preparation and CuringFor each batch of concrete, 100 x 100 x 100 mm cubes were cast to evaluate compressive strength (IS: 10086-1999). The specimens were cured at both normal temperatures for 28 days and at 90 C for48 hours, remaining 26 days at normal temperature.

Fig.3.2 Dry mix of RPC Fig.3.3 Paste after proper mixing Fig.3.4 Mixer used for casting

3.4 TEST CONDUCTED

3.4.1. Cube Compressive Strength

Strength of concrete is an important property, which is mostly valued in concrete design and quality control. The strength of concrete gives a direct indication of its capacity to resist loads in structural applications. Also, the strength tests are relatively easy to conduct. Many other properties of concrete that are measured by more complicated tests can be deduced from the strength data by developing correlations. As per IS: 516 - 1959, the compression test can be carried out on specimens cubical or cylindrical in shape. In the present study, compression tests were carried out on 100mm x 100mm x 100mm cube specimens immediately on removal from the water. Specimens were placed in the machine so that load is applied on to the face adjacent to the cast surface. The specimen was loaded at the rate of 14 N/mm2 per minute in a compression testing machine of capacity 2000kN. The test was conducted to determine the 28 day strength of RPC.The maximum load applied to the specimen was noted and compressive strength is calculated by dividing the maximum load by the cross sectional area of the specimen. Fig. 3.5 shows the experimental set up for compressive strength tests.

Fig.3.5 Cube Compressive Strength Test

CHAPTER 4RESULTS AND DISCUSSIONS

4.1 GENERAL

Arriving at optimal composition with locally available materials is important to achieve the best overall performance of RPC. Hence, the effects of several parameters on compressive strength were investigated which include water-to-binder ratio, super plasticizer dosage, different percentage of silica fume, with and without quartz powder and curing regime. During the study it was observed that the mixes appeared to be very sensitive to any variation of the chemical composition of the binders or particle size distribution of the fillers. As there are no standard guidelines for the mix design of RPC, literature was referred to design the mixes. The silica fume content was varied from 15 to 25 percent by weight of cement to find the optimum percentage of silica fume in the production of RPC. To study the influence of addition of quartz powder to RPC, the RPC mixes were also designed with addition of quartz powder by 20 percent by weight of cement.

4.2. PROPERTIES

4.2.1. Density of RPC Specimens

The density of all the specimens recorded varied between 23.3 24.7 kN/m3.

4.2.2. Effect of Water-to-Binder Ratio on Compressive Strength of RPCThe strength of concrete is very much dependent upon the hydration reaction in which water play as critical role, particularly the amount of water used. The effect of w/b ratio on compressive strength under various curing ages is shown in Fig. 4.1. The result demonstrates that an optimal w/b ratio that gives the highest compressive strength of RPC in the present study is 0.2. The reduction in strength at lower w/b ratio may be due to the lack of adequate amount of mixing water in RPC to ensure adequate compaction and proper hydration to occur.

Fig 4.1.Effect of w/b ratio on compressive strength

Beyond this optimal w/b ratio of 0.2, it was found that compressive strength decreases with increasing w/b ratios. This may be because of more water which is susceptible to entraining air bubbles due to the folding action of the mixing process. As a result, more voids are left in the matrix which increase the porosity and thus considerably reduce the compressive strength. The compressive strengths of all mix proportions 28 days are tabulated in Table 4.1.

Table 4.1 Compressive strength of RPCSample no.Normal Curing at 27degreeAccelerated Curing at 90 degree for 48 hours

Compressive strength at 28Days(N/mm2)Compressive strength at 28Days(N/mm2)

TM-1113120

TM-2121133

TM-3127136

TM-4109120

TM-5107116

TM-685-

TM-780-

TM-878-

TM-975-

TM-1070-

TM-1163-

TM-12108135

TM-13120142

TM-14112125

3.3 Effect of Silica Fume Percentage on Compressive Strength of RPC

The effect of varying percentage of silica fume on the compressive strength of RPC mix is demonstrated in Fig.4.2. It is observed that the compressive strength tends to decrease as the silica fume dosage increases. The highest compressive strength was observed for addition of15% silica fume. The compressive strength is seen to fluctuate in the range of 15 % to 25% of silica fume regardless of water/binder ratio. As silica fume content increases, mix requires more super plasticizer to disperse in fresh concrete.

Fig.4.2 Effect of addition of silica fume3.3 Effect of Addition of Quartz Powder

From the literature it is learnt that, hydrated cement alone cannot help to elevate the strength of RPC, but other finer materials also contribute marginally. Quartz powder improves the filler effect in RPC mix. As shown in Fig.4.3. The addition of quartz powder produces the better result under accelerated curing condition than that of normal curing condition. The results show that the addition of quartz powder increases the compressive strength by 20% under the accelerated curing condition. This is possible due to increased proportion of hard, fine fillers that enhance the packing density and pore filling action. Fig.4.3 The effect of Quartz powder on compressive strength of RPC3.5 Influence of Curing Regime

An adequate supply of moisture is necessary to ensure that hydration is sufficient to reduce the porosity to a level such that the desired strength can be attained. The effect of curing regime on compressive strength under various curing ages is shown in Fig.4.4. Two curing methods were exercised, one with normal water curing at 27C, and other at 90C hot water curing for 48 hours. The compressive strength increased by 10% when cured in hot water as compared to normal curing. This indicates that curing temperature has a significant effect on the early strength development of RPC. The increased strength is due to the rapid hydration of cement at higher curing temperatures of 90C compared to that of 27C.Moreover, the pozzolonic reactions are also accelerated by the higher curing temperatures.

Fig.4.4 Effect of curing regime

CHAPTER 5CONCLUSIONS

5.1 GENERAL

The key issues of the study are: to develop RPC of compressive strength up to 150 MPa, to determine the effect of silica fume content on compressive strength, to determine the effect of high temperature curing on the compressive strength and to determine the effect of addition of quartz powder on the compressive strength of RPC.

5.2. CONCLUSIONS

The conclusions from the present investigation are based on the limited observations made during the study period and are presented below.

During the production process, it was found that an extended mixing time up to 15-20 Min. is required to obtain a consistent and homogeneous mix. The maximum compressive strength of RPC obtained in the present study is 142 MPa at w/b ratio of 0.2 with accelerated curing. In the production of RPC the optimum percentage addition of silica fume is found to be 15% (by weight of cement) with available super plasticizer. The addition of quartz powder increases the compressive strength of RPC up to 20% The high temperature curing is essential for RPC to achieve higher strength. It increases the compressive strength up to 10% when compared with normal curing.

REFERENCES

1. Abouzar Sadrekarimi (2004), Development of a Light Weight Reactive Powder Concrete. Journal of Advanced Concrete Technology Vol. 2, no. 3, pp. 409- 417.2. Dili A S., Manu Santhanam (2004),Investigation on reactive Powder Concrete: developing Ultra high- strength technology, The Indian Concrete Journal, Vol. 78, No. 4, pp. 33- 38. 3. Gilliland Scott K. Reactive Powder Concrete (RPC), A New Material for Pre-stressed. Concrete Bridge Girders, Building an International Community of structural 4. Harish K V et al.(2008),Role of ingredients and of curing regime in ultra high strength powder concretes, Journal of Structural Engineering, Vol. 34, No. 6, pp. 421-428.5. Richard P., Cheyrezy M (1995), Composition of Reactive Powder Concretes, Cement and Concrete Research, Vol. 25, No. 7, pp. 1501-1511.6. Shetty M.S. (2005), Concrete Technology - Theory and Practice, S. Chand & Company P. Ltd., New Delhi.

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