Partial replacement of metakaolin with thermally treated rice husk ash in metakaolin-based geopolymer

The influences of rice husk ash (RHA) on the reaction kinetics, mechanical property, and microstructure of metakaolin-based geopolymer (MG) were investigated. Geopolymer pastes containing different contents of RHA were prepared by sodium silicate activation. Analysis results show that both metakaolin and rice husk ash are involved in the geopolymerization, contributing to the development of mechanical properties and formation of compact microstructure. The longer reaction duration of setting time in the group incorporated RHA was ascribed to the procedure of SiO2 dissolution. The geopolymers added with RHA have a compact pore structure, which show a relatively high compressive strength. The replacement of metakaolin by RHA did not cut the total quantity of gel phase formation, but changed the form of partial gels existence and an optimal mixed point was reached at the 20% replacement level. The abundant in gel along with the pore channel and secondary filling effects make a significant contribution to the development for refinement of pore and improvement of strength. This study can be used as an indicator for the application of RHA in geopolymer, which is of great value in urging RHA towards realization in recycling. (C) 2019 Elsevier Ltd. All rights reserved.