Influence of GGBFS and silica fume on characteristics of alkali-activated Metakaolin-based concrete

Alkali-activated or geopolymer composites have been introduced as a promising green alternative to ordinary Portland cement concretes and mortars. Metakaolin (MK) is a common source material produced from the calcination of kaolin, which has been widely employed for geopolymer synthesis. The present study involves testing thirteen alkali-activated concrete mixes divided into two groups to investigate their fresh and mechanical properties. The two groups attempted to study the effect of partial replacement of MK by ground granulated blast furnace slag (GGBFS) and silica fume (SF) (ranging from 5% to 30% by MK weight). The effect of the water-to-solids ratio for MK-GGBFS and MK-SF concretes was also studied. The investigated fresh and mechanical properties were slump, density, compressive strength, compressive strength rate of development, splitting tensile strength, water absorption, abrasion resistance, and ultrasonic pulse velocity. The partial replacement of MK by GGBFS of up to 10% caused about 10% reduction in the compressive strength of geopolymer but enhanced early strength development. The conclusions derived from the study are supported by XRD analysis and SEM images. Models are proposed for estimating the mechanical properties of geopolymer concrete as a function of either the molar ratios and the aggregate content or compressive strength.