ABSTRACT

Concrete proves itself as a global construction material with its higher compressive strength, extreme durability and better stiffness. The concrete in structural elements like slabs, columns and beam-slab joints etc specially the areas of congested reinforcement needs high degree of compaction efforts during poring. Improper compaction/vibration affects the durability and strength of concrete structures.
However, in modern methods, concrete can be produced without compaction/vibration and that concrete is known as self-compacting concrete (SCC). This study is focused on to produce high strength SCC by adding supplementary cementations materials (SCMs) and steel fibers. The SCMs are used as partial replacement of cement to reduce the cement content thus addressing the issues of economy and environment. Since the high strength concretes are susceptible to the cracks, due to its brittle nature particularly under tension and bending. Thus the fibers are used to improve the strength both under tension bending. Two SCMs silica fume (SF) and fly ash (FA) were adopted during this study. The replacement level of cement with SF was 5 to 20% and that of FA was maintained as 5 to 30% with 5% increment by weight of cement in both the cases. Steel fibers were used as fiber reinforcement as volumetric fraction of total volume of concrete being from 0.1% to 0.2% with an increment of 0.05%. The study was carried in two phases. During first phase binary and ternary blended SCCs were produced by adding SF and FA with different dosage. Since the flow of concrete is a major parameter to produce SCC Which is normally maintained by adding SP and viscosity modifying agent (V MA) in certain cases. Followed by preliminary studies and EFNARC guidelines, the w/b was fixed at 0.34, binder content at 500 kg/m3 and superplasticzer (SP) dosage was adjusted as per the requirement. A total 35 mixes were prepared and their properties were investigated in fresh and hardened state. The flow properties of SCCs were investigated with different tests as compared to the normal concrete. Slump flow time and diameter, V-funnel time, J-ring height, L-box and V-iünnel time at 5 min tests were performed to investigate the flow properties in fresh state while the compressive, spilt tensile and flexural strength tests were performed in hardened state. The results showed both the fresh and hardened properties of SCCs depends on the binary and ternary use SCMs. Further, all the fresh properties values of all the mixes remained within the specified range of EFNARC. Similarly the strength properties increased with the addition of SCMs. But the increase is more pronounced when both the cementations materials are added combine. The mix M20 observed the maximum compressive strength of 63.39 MPa. The increment in compressive strength is about 18% of their respective controlled mix (CM). Splitting tensile and flexural strength of concrete showed the identical trend as of compressive strength. During phase-II, the effect of the steel fibers was investigated. Two mixes M20 (IO%SF 15%FA) M14 (5%SF 15%FA) were selected in the basis of the results of phase-I for the purpose. It was found that the fibers slightly reduces the flow ability of SCC, however the values are within the range specified by EFNARC. The compressive and tensile strength decreased marginally about 2.57%. As expected the flexural strength increases by 18%. on the basis of the results the mix with 5% SF, 15% FA and 0.15% steel fibers was optimized yields compressive, spilt tensile and flexural strength 61.12MPa, 5.04MPa and 7.15MPa respectively, which are approximately 14%, 102%, 40% greater than the ordinary SCC without cementations materials and steel fibers.
Keywords: Self-compacting concrete, high strength SCC, workability of SCC,
Steel fiber reinforced SCC, cementations materials, fiber reinforced SCC, fly ash.
Silica fume, steel fibers fresh properties of SCC, hardened properties of SCC.