Drying shrinkage inhibition effect and mechanism of polyol shrinkagex reducing admixture on the metakaolin-based geopolymer

Geopolymers, environmentally friendly materials, face application limitations due to their high drying shrinkage and propensity for cracking. The shrinkage reducing admixture (SRA) has shown promise in mitigating drying shrinkage in cement-based materials, yet its impact and mechanism in geopolymers remain uncertain. This study examines the influence of the small molecule polyol SRA-2-methyl-2,4-pentanediol on metakaolin-based geopolymer (MKG) properties and its multiscale structural development, aiming to understand the drying shrinkage behavior. The findings reveal that SRA significantly curbs the drying shrinkage of MKG while also reducing its mechanical properties. Analyses of macroscopic and microscopic properties indicate that while SRA does not alter the hydration products of MKG, it can impede the hydration process, particularly in the early stages. Specifically, SRA inhibits the formation of N-A-S-H gel, thereby reducing shrinkage caused by late-stage polycondensation. Furthermore, the alkaline environment in MKG aids SRA in lowering pore solution surface tension and increasing its contact angle, reducing drying shrinkage forces. Additionally, SRA modifies MKG's microstructure, decreasing pore volume, particularly in the 10-50 nm range, further mitigating shrinkage due to surface tension.