Strength Development of Metakaolin-Based Alkali-Activated Cement

Alkali-activated materials, sometimes called geopolymers, can be used as alternative cementitious materials to conventional Portland cement. Currently, there is a significant interest in these materials due to their low CO₂ footprint. The typical applications of alkali-activated materials are within civil engineering; however, potential applications as well cementing material within the oil and gas industry are also receiving emerging interest. This paper presents a systematic study of the compressive strength development from 1 to 28 days for metakaolin-based alkali-activated cement. The results show that the compressive strength is highly dependent upon the initial Si/Al ratio in the mix design, as well as the concentration of the activator solution. Furthermore, due to the relatively low initial reactivity of the metakaolin material used, different types of co-binders were included in the slurry composition to improve early strength development. The two different co-binders tested were another, more reactive metakaolin material and Blast Furnace Slag (GGBFS). It was found that both these co-binders performed as intended, by ensuring early strength development via precipitation of K-A-S-H and C-A-S-H gels, respectively, and also by enabling subsequent strength development due to improved dissolution of the low-reactive metakaolin.