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SELF COMPACTING CONCRETE

'''DURABILITY STUDIES ON SELF COMPACTING CONCRETE WITH HIGH VOLUME FLY ASH''' By Raghavendra Chincholikar Ragu23@gmail.com The increasing demand in infrastructure for day to day life need improved construction practice and performance, combined with the health and safety benefits. Self-compacting concrete, which is capable of consolidating under its own weight and occupying all the space in the forms without segregation and without any external compacting efforts, is a very attractive solution for both precast concrete and civil engineering construction. Self-compacting concrete could also be considered as an eco-friendly material as it enables the use of waste products like fly ash, Blast furnace slag (GGBS), silica fume etc. from thermal power plants, steel and silicon industries respectively. High volume fly ash concrete is a composite system with unique mechanical and durability characteristics that allow the use of large volumes of fly ash for concrete applications. With blend of adopting both the technologies High volume self-compacting concrete can be of a superior choice for future generation. In the present study, the performance of SSC higher percentage of replacement of cement with fly ash by 60% and GGBS by 20% is investigated. The use of silica fume as a modifier for fresh mix properties is also attempted. The concrete mix is designed for 55 MPa with replacements of cement by 60% fly ash, 60% fly ash + 20% slag and 60% fly Ash+20% Slag+5% Silica fume. Various parameters like cube compressive strength, change in length, weight change and flexural strength were studied with respect to partial replacements considered. For sulphate attack study, the effect of conventional curing for 3, 7 & 14 days and also raw material variation i.e. the combination of fly ash, slag and or silica fume are investigated. The sulphate medium for exposure of concrete specimens was kept at a constant concentration of 8000 ppm. Simple immersion, electrically accelerated tests are conducted to measure the resistance to chloride penetration and permeability of concrete mixes. With the observation made on the SCC mixes, it is noticed that the design self-compacting concrete incorporating High-volumes (60%) of Class F fly ash with water to powder ratio of 0.28 strengths of the order of 55 MPa can be easily done. Drop in compressive strength is very less i.e. 1.95%, 2.34% and 4.49% at the age of 28, 56 and 90 days respectively, for cubes cured in sulphate solution with respect to water curing. Cement replacement up to 85% has developed strength of 58 MPa at an age of 90 days. The charge measured on high-volume fly ash SCC usually ranges from 530 to 656 coulombs at 56 days and from 310 to 400 coulombs at 91 days. The addition of small amounts of silica fume to the high-volume fly ash concrete can increase its resistance to the chloride-ion penetration and make it extremely high. CONCLUSIONS • It is possible to design self-compacting concrete incorporating high-volumes (60%) of Class F fly ash with water to powder ratio of 0.28 to get target strength of 55 MPa. • Drop in compressive strength is very less i.e 1.95%, 2.34% and 4.49% at the age of 28, 56 and 90 days respectively, for cubes cured in sulphate solution with respect to water curing. • Cement replacement up to 85% has developed strength of 58.75 MPa at an age of 90 days. • The charge measured on high-volume fly ash SCC usually ranges from 530 to 656 coulombs at 56 days and from 310 to 400 coulombs at 91 days. • The addition of small amounts of silica fume to the high-volume fly ash concrete can increase its resistance to the chloride-ion penetration and make it extremely high. • High volume fly ash self-compacting concrete may be characterized by 56 days strength.