Effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete

The effect of silica fume on the fresh and hardened properties of fly ash-based self-compacting geopolymer concrete(SCGC) was investigated in this paper.The work focused on the concrete mixes with a fixed water-to-geopolymer solid(W/Gs) ratio of 0.33 by mass and a constant total binder content of 400 kg/m3.The mass fractions of silica fume that replaced fly ash in this research were 0wt%,5wt%,10wt%,and 15wt%.The workability-related fresh properties of SCGC were assessed through slump flow,V-funnel,and L-box test methods.Hardened concrete tests were limited to compressive,splitting tensile and flexural strengths,all of which were measured at the age of 1,7,and 28 d after 48-h oven curing.The results indicate that the addition of silica fume as a partial replacement of fly ash results in the loss of workability;nevertheless,the mechanical properties of hardened SCGC are significantly improved by incorporating silica fume,especially up to 10wt%.Applying this percentage of silica fume results in 4.3% reduction in the slump flow;however,it increases the compressive strength by 6.9%,tensile strength by 12.8% and flexural strength by 11.5%.