Characterization and fractal analysis of drying shrinkage of metakaolin-based geopolymers under gradually-decreasing humidity

This study investigated the drying shrinkage of metakaolin (MK)-based geopolymers paste under a relative humidity gradient (decreasing step-by-step) with different activator modules, activator concentrations, and liquid-solid ratios. These results were then compared with those of a cement paste with the same strength grade. The mechanisms of various factors affecting the drying shrinkage of MK-based geopolymer were elucidated using MIP and TAM Air techniques. Subsequently, fractal analysis was conducted using the pore structure data obtained through MIP to investigate the correlation between fractal dimension and drying shrinkage. The results showed that the drying shrinkage of MK-based geopolymers was greater than that of a cement paste at the same strength grade. MK-based geopolymers exhibited earlier shrinkage than the cement paste during the reduction in humidity. Moreover, the drying shrinkage of MK-based geopolymers increased with a decrease in activator modulus, and an increase in activator concentration and liquid-solid ratio. In the present study, the fractal dimension of the microcapillary exhibited an excellent relationship with the drying shrinkage at various relative humidities. This indicates that the fractal dimension can be used to evaluate the drying shrinkage performance of MK-based geopolymers.