Mitigating the autogenous shrinkage of alkali-activated slag by metakaolin

This study investigates the effectiveness of metakaolin (MK) in mitigating the autogenous shrinkage of alkali activated slag (AAS). It is found that the autogenous shrinkage of AAS paste can be reduced by 40% and 50% when replacing 10% and 20% slag with MK, respectively. By providing additional Si and Al, and decreasing the pH of the pore solution, the incorporation of MK retards the formation of aluminium-modified calcium silicate hydrate (CASH) gels, the main reaction products in the studied pastes. The chemical shrinkage and pore refinement are consequently mitigated, resulting in a substantial reduction in the pore pressure. Meanwhile, the elastic modulus of AAS paste is only slightly influenced after MK addition. As a result, the autogenous shrinkage of AAS is significantly mitigated by incorporating MK. In addition, the introduction of MK would extend the setting time, slightly decrease the compressive strength, but greatly increase the flexural strength of AAS.