Estimation of ground granulated blast furnace slag and rice husk ash cementing efficiency in low and medium grade self-compacting concretes

Abstract

Ternary blended Self Compacting Concrete (SCC) made with rice husk ash (RHA) and GGBFS (ground granulated blast furnace slag) has developed as a substitute to normal concrete. It has advantages such as less cement usage, energy usage, cost and for other ecological and socio-economic benefits. The current work quantifies the 3, 7 and 28-days cementitious efficiency for various percentages of RHA and GGBFS combination in SCC. The usage of GGBFS in M20 and M40 SCC reduces workability but increases compressive and tensile strength when compared with OPC based SCC. The optimum GGBFS is found to be 30% for low and medium strength levels of SCC. For M20 and M40, 30% GGBFS reduces workability slightly but still within desired limits. So after various trial mixes it was found that 27% GGBFS by weight of OPC and 3% RHA by weight of GGBFS quantity can be admixed to OPC SCC to achieve similar strength and workability and also better rate of strength regain in early days of hardening. In M20 and M40 grades of SCC, 3% RHA by weight of GGBFS quantity is replaced. Due to addition of GGBFS to SCC will enhance the later age compressive strength but early age compressive strength decreases while the desired workability is controlled using SP appropriately. This is true for all grades of GGBFS based SCC. In M20 GGBFS based SCC, the strength gain at 3 days is nearly 9% but the compressive strength at 28 days increased by 31%. In M40, GGBFS based SCC, the strength gain at 3 days is nearly 14% but the compressive strength at 28 days increased by 21%. RHA is added as replacement of cement to improve the early age strength of SCC. RHA addition to concrete as cement replacement may help to improve strength marginally but impacts the workability drastically so SP should be used controllably to attain the desired workability. In M20 GGBFS+RHA based SCC, the compressive strength enhancement at 3 days is 21% and the compressive strength at 28 days increased by 46%. In M40, GGBFS+RHA based SCC, the compressive strength enhancement at 3 days is 20% and at 28 days increased by 34%. Similarly tensile strength in all grades of GGBFS and RHA admixed SCC increases by around 15 to 34% in M20 grade and 9 to 36% in M40 grade SCC mix. So it can be concluded that RHA and GGBS combination principally yields early strength which is not possible in SCC mixes primary made with fly ash.