EXPERIMENTAL AND ANALYTICAL STRENGTH

Transcription

1 EXPERIMENTAL AND ANALYTICAL STRENGTH BEHAVIOR OF SELF COMPACTING CONCRETE Dr. R. Vijay Kumar Associate Professor, Department of Civil Engineering, B V Raju Institute of Technology, Narsapur, Telangana, India. Abstract Conventional concrete tends to present a problem with regard to adequate consolidation in thin sections or areas of congested reinforcement, which leads to a large volume of entrapped air voids and compromises the strength and durability of the concrete. We can eliminate the problem by using self-compacting concrete (SCC), since it was designed to unite under its own mass. Normal concrete was designed as IS method and self-compacting concrete was designed by a simple mix design proposed by Nan Su. SCC was developed in 1988 s by Prof. Hagime Okaura in Japan. SCC was one of the latest concrete in across the world. This paper deals with the comparison of strength of normal concrete and selfcompacting concrete. An experimental and analytical study on mechanical properties, such as compressive strength, flexural strength and split tensile strength of selfcompacting concrete (SCC) and the corresponding properties of normal compacting concrete (NC) were studied at 7 and 28 days age of the concretes. Key Words: Self Compacting concrete, Portland Cement, Fly ash. Introduction The application of concrete in the realms of infrastructure, habitation, and transportation has greatly promoted the development of civilization, economic progress, and stability and of quality of life. Nowadays with the occurrence of high performance concrete (HPC); the durability and strength of concrete have been improved largely. No matter what type of building structure it is, the concrete used should be sturdy and well compacted. The main reasons for compacting any type of concrete are: To ensure attaining maximum density by removal of any entrapped air. To ensure that the concrete used is in full contact with both the steel reinforcement and the form work. Ensuring the above points not only provide additional strength to the structure but also good finish and appearance to the final product. The compacting of any conventional concrete is done through external force using mechanical device. self- compacting concrete doesn't require compacting using external force from mechanical equipment such as an immersion vibrator; instead SCC is designed in such as way that it gets compacted using its own weight and characteristics. Once applied, the self-compacting property enables the concrete to fully reinforce around the steel structures and completely fill the space within the framework. The self-compacting of concrete is achieved without losing any kind of strength, stability, or change in properties. Literature Review Okamuraet.al, [1] proposed a mix design method for SCC based on paste and mortar studies for super plasticizer compatibility followed by trail mixes. However, it is emphasized that the need to test the final product for passing ability, filling ability, and flow and segregation resistance is more relevant. Vengala et.a1, [2] found that use of fine fly ash for obtaining Self Compacting Concrete resulted in an increase of the 28 day Compressive Concrete by about 38%. 39

2 Self Compacting Concrete was achieved when volume of paste was between 0.43 and 0.45.Subramanian and Chattopadhyay et.al, [3] described the results of trails carried out to arrive at an approximate mix proportioning of Self Compacting Concrete. Self Compatibility was achieved for Water to Powder ratio ranging from 0.9 to 1.1 when Coarse Aggregate and Sand content were restricted to 46 % and 40% of the mortar volume respectively. Hooton et.al, [4] investigated on influence of silica fume replacement of cement on physical properties and resistance to sulphate attack, freezing and thawing, and alkali-silica reactivity. He reported that the maximum 28-day compressive strength was obtained at 15% silica fume replacement level at a w/b ratio of 0.35 with variable dosages of HRWRA. Yogendran et.al [5] investigated on silica fume in High-strength concrete at a constant water-binder ratio (w/b) of 0.34 and replacement percentages of 0 to 25, with varying dosages of HRWRA. The maximum 28-day compressive strength was obtained at 15% replacement level. Lewis [6] presented a broad overview on the production of micro silica, effects of standardization of micro silica concrete-both in the fresh and hardened state. Research Methodology An experimental and numerical study on mechanical properties, such as compressive strength, flexural strength and split tensile strength of self-compacting concrete (SCC) and the corresponding properties of normal compacting concrete (NC) were studied. Materials Cement Ordinary Portland Cement of 53 Grade available in local market is used in the investigation. The cement used has been tested for various properties as per IS: and found to be conforming to various specifications as per IS: Fine aggregates The locally available sand is used as fine aggregate. It should be free from clay, silt, organic impurities, etc., the sand is tested for various properties such as specific gravity, bulk density, etc., in accordance with IS: The grading or particle size distribution of fine aggregate shows that, it is close to grading or particle size distribution of fine aggregate shows that, it is close to grading zone II of IS: Coarse aggregates Machine crushed angular granite metal of 20 mm size from the local source is used as coarse aggregate. It should free from impurities such as dust, clay particles, organic matter etc., the fine and coarse aggregate are tested.the grading or particle size distribution of coarse aggregate shown close for single sized aggregate of nominal size 20 mm as per IS: Super Plasticizer High range water reducing admixture called as super plasticizers are used for improving the flow or workability for decreased water-cement ratio without sacrifice for compressive strength. These admixtures when they disperse in cement agglomerates significantly decrease a viscosity of the paste by forming a thin film around the cement particles. In the present work waterreducing admixture Glenium B233 conforming to ASTM C494 Types F, EN934-2 T3.1/3.2, IS 9103: 1999 is used. GLENIUM B233 is an admixture of a new generation based on modified polycarboxylic ether. The product has been primarily developed for applications in high performance concrete where the highest durability and performance is required. Micro silica Micro silica is an artificial pozzolanic admixture obtained from reduction of high purity quartz with coal in an electric furnace in the manufacture of silicon or ferrosilicon alloy. Elkom Micro silica was used in this work. Micro silica is the most reactive of several supplementary cementing materials for modifying the cement matrix to provide improved binders. In general,all SCM s have a pozzolanic action-a secondary hydration reaction or pozzolanicity,with the weaker calcium hydroxide that is produced during the normal hydration of the cement. At low water/cement ratios and when used with advanced super plasticisers, Micro silica demonstrates multiple effectiveness. The fine particle size and high content of amorphous silica(by standard grater than 85%) makes the 40

3 micro silica highly reactive with any alkalis in Determination of cement solution with in first few few days and weeks of C = F c/0.110 the hydration process. Given 0.11 Mpa = 20PSI This provides a homogeneous, fine grained,... C = 50/0.110 = kg/m 3 almost ceramic matrix linked with the very low Determination of micro silica content: water cement ratio governs the characteristic Assume 2% of micro silica in cement cube strength of 100Mpa concrete. Wms =0.02x529.54=10.59 kg/m 3 Results in a more homogenous finegrained cement structure. Fine spherical nature of Micro silica provides micro packing density and eliminates micro voids. Produces stronger C-S-H matrix. Marked changes in transition zone (between cement and aggregate),indicating non-micro cracked dense matrix as a result of removal of bleed water. Eliminates weak zone enabling a truly composite material in which the aggregate can be utilized as a working component and not just filler. Water Water used for mixing and curing shall be clean and free from injurious amounts of oils, acid, alkalis, salts, organic materials or other substances they may be deleterious to concrete portable water is used for mixing as well as curing of concrete as prescribed in IS: SELF COMPACTING CONCRETE Mix Design:by Nansu Method Mix Design of SCC for M 50: Characteristic = 50 Mpa Maximum size of aggregates = 20mm Specific gravity of coarse aggregates, Gg = 2.74 Specific gravity of fine aggregates, Gs = 2.67 Bulk density of loose C.A = kg/m 3 Bulk density of loose F.A = kg/ m 3 Specific gravity of cement, Gc = 3.15 Volume of fine/course aggregate ratio(s/a) = 0.55 Determination of Coarse aggregate: Assume P.F = 1.15 Amount of coarse aggregate, Wg = 1.15 x x(1-0.55) Wg = kg/ m 3 Determination Fine aggregate: Amount of fine aggregate, Ws = P.F x Wsl (s/a) = 1.15 x x 0.55 = kg/m 3 Determination of water: For water to binder ratio for Mpa is = W/B = W = (W/B)x(C+Wms) = 0.34X( ) =183.64kg/ m 3 Determination of SP dosage: SP dosage = 1.3 % of ( ) = 7.02 kg/ m 3 CONVENTIONAL CONCRETE Mix Design DESIGN PARAMETERS (FOR M50) (a) Maximum size of aggregate:20 mm (b) Degree of workability:0.90 Comp., factor (c) Degree of quality control :Good (d) Type of Exposure :Mild (e) Compressive of cement :53 N/mm 2 at 28 days (f) Selection of W/C ratio :0.40 for M50 Mix design can be defined as the process of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength and durability as economical as possible. Concrete Mix Design for M50 grade of concrete was done according to IS: and the final proportion achieved are given in table 5.4 A) Target strength for mix proportioning: f ck= f ck +ks From Table 1 standard deviation, s = 5 N/mm² Therefore target strength = x5 = N/mm² B) Selection of w/ c ratio: From Table 5 of IS 456:2000, maximum water cement ratio = 0.4 (Mild exposure) Based on experience adopt water cement ratio as 0.40; 0.4 < 0.55, hence ok 41

4 C) Selection of water content: From Table 2, maximum water content = 186 litres (for 25 mm 50 mm) slump range and for 20 mm aggregates D) Calculation of cement content: Water cement ratio = 0.40 Cement content = 186/0.4 =465kg/m3>320 kg/m3(given) From Table 5 of IS 456, minimum cement content for mild exposure condition = 300 kg/m3, Hence OK E) Mix calculations: The mix calculations per unit volume of concrete shall be as follows a) Volume of concrete = 1 m3 b) Volume of cement = mass of cement/specific gravity of cement x 1/1000 = [465/3.15] x [1/1000] = m³ c) Volume of water = [186/1] x [1/1000] = m3 d) Volume of all in aggregates (e)= a (b + c) = 1 ( ) = m3 e) Volume and weight of coarse aggregates Volume of coarse aggregate = = 0.64 m3 Weight = Volume of all in aggregates x volume of coarse aggregate x specific gravity of CA x 1000 = 0.666x0.64 x2.74 x 1000 = 1170 kg f) Volume and weight of fine aggregates Volume = x 0.36 = m³ Weight = Volume of all in aggregates x Volume of FA x specific gravity of FA x 1000 = 0.24 x 2.67 x 1000 = 641 kg I) Mix proportions : Cement = 465 kg/m³ Water = 186 kg/m³ Fine aggregate = 641 kg/m³ Coarse aggregates = 1170 kg/m³ Water cement ratio = 0.40 Results And Discussions Table:1 Acceptance criteria for SCC: S. Method Unit Typical Range of No Values Minimum Maxim 1. Slump Flow Test 2. T50cm slump Flow um Mm sec V-Funnel Test 4. V-Funnel at T5 Minutes sec 6 12 sec L-Box Test h 2/h The mix is finalised by satisfying the above conditions given in table 1 as per as per EFNARC guide lines. Table :2 Workability of Conventional Concrete: Grade of Slump test C.F Concrete (mm) M The mix was finalised by satisfying the workability conditions given in Table 2. Table:3 Mix Proportions of Self Compacting Concrete: Cement Micro Fine Coarse S.P silica aggregate aggregate The mix proportions of Self Compacting Concrete was designed by a simple mix design proposed by Nan Su was is given in Table3 and mix proportion of conventional concrete is given in Table 4. In Self compacting Concrete cement content is increased by1.14% and Fine aggregates content is increased 1.4% and Coarse aggregate is reduced up to 0.6%. Table:4 Mix Proportions of Conventional Concrete: Cement Fine Coarse Water (Kg) Aggregate (kg) Aggregate (kg) lit Table:5 Comparison of strength properties. s (in days) Compressio n Flexural Split Tensile SCC (N/m m 2 ) Conventional Concrete(N/m m 2 )

5 The comparison of strength results are shown in Table 5. The Compression strength of Self Compacting concrete is 1.03% higher than Conventional concrete. The Flexural of Self Compacting concrete is 1.92% is higher than conventional concrete. The Split Tensile of Self Compacting concrete is 1.08% is higher than conventional concrete. Self compacting concrete having slightly higher strength than conventional concrete because of SCC passing and filling ability is high. Conclusion We conclude that the quality of self compacting concrete is higher than conventional concrete. References [1] Okumura.H, Ozawa. K. Ouchi. M. (2000), Self Compacting Concrete, Structural concrete, No.1. [2] Jagadish Vengala Sudarsan, M.S., and Ranganath, R.V.(2003), Experimental study for obtaining selfcompacting concrete, Indian Concrete Journal, August, pp [3]Subramanian.S and Chattopadhyay (2002), Experiments for Mix Proportioning of Self Compacting Concrete, Indian Concrete Journal, January, Vol., PP [4] Hooten RD. Influence of silica fume replacement of cement on physical properties and resistance to Sulphate attack, Freezing and Thawing, and alkali-silica reactivity, ACI Material Journal, No. 2, 90(1993) [5] Yogendran V, Langan BW, Haque MN, Ward MA. Silica fume in High- strength concrete, ACI Material Journal, No. 2, 84(1987) [6] Lewis RC. Ensuring long term durability with high performance micro silica concrete, The Indian Concrete Journal, October 2001, pp