Relation between drying shrinkage behavior and the microstructure of metakaolin-based geopolymer

The drying shrinkage of geopolymers poses significant limitations on their potential as constructive materials. In this study, the drying shrinkage of metakaolin-based geopolymer (MKG) with different initial water/solid ratios and pore structures was investigated experimentally. According to mini-bar shrinkage experiments, the drying shrinkage-water loss relation of MKG showed two-stage behavior. The initial water/solid ratio influences the critical water loss and span of the pausing period of the shrinkage curves but not the general trend. Combined with the microstructure characterization and physical estimation, the underlying dependency of the shrinkage on the pore structure of the binder was elucidated. Capillary pressure, surface energy change, and gel densification dominate the drying shrinkage of MKG at different water loss stages. The findings indicate that besides porosity control, finer tuning of the pore size distribution is needed to control the drying shrinkage of MKG.