Ground granulated blast furnace slag and fly ash concrete

Utilization of ground granulated blast furnace slag (GGBFS) and fly ash (FA) to resolve the problem of increasing discharged and total accumulated industrial waste has attracted public concern. This article presents the research results on the effect of the replacement of up to 60 wt.% cement with GGBFS and FA, separately and in combination. It shows that mineral admixtures improve the workability of concrete mixture and reduce the required water-reducing admixture to reach a defined slump, prolonging the setting time of fresh concrete. The compressive strength of concrete with GGBFS at an early age decreases while increasing at 60 days and 90 days with the GGBFS content from 20 wt.% to 40 wt.%. The compressive strength of concrete with FA well develops at a later age, but it decreases at all ages as the FA replacement ratio increases. Cement replacement with a combined mineral admixture of 20 wt.% GGBFS and 20 wt.% FA does not significantly change the compressive strength at 28 days and later. Based on test results, the efficiency factor of mineral admixtures was calculated to use for selecting the proportion of concrete.