Comparative study on the effects of rice husk ash and silica fume on the freezing resistance of metakaolin-based geopolymer

In this work, the influences of the rice husk ash (RHA) and silica fume (SF) on the freezing resistance were investigated comparatively. Freezing resistance of metakaolin-based geopolymer was studied using rapid freeze–thaw cycles experiment and the reaction kinetics was investigated via setting times and isothermal conduction calorimetry (ICC). The obtained results indicated that the pore structures were improved with the incorporation of RHA or SF at the appropriate replacement level. In addition, combined with thermogravimetric analysis (TGA) and mercury intrusion porosimetry (MIP) analyses, it can be found that RHA has potential filling effect besides performing as active supplement agent, while SF can be more manifested as an active supplementary material. This was also the primary reason for the different refinement degrees in porosity of geopolymer pastes added with different supplementary cementitious materials, which was of great importance to the freezing resistance. Both RHA and SF can work as active materials to improve the mechanical properties and freezing resistance of metakaolin-based geopolymer for a wider application field.