Improving Drying Shrinkage Performance of Metakaolin-Based Geopolymers by Adding Cement

Geopolymers, as sustainable alternatives to conventional cement, face application limitations due to pronounced drying shrinkage. This study systematically investigates the effects of cement incorporation (0–40%) on the drying shrinkage mitigation and performance evolution of metakaolin-based geopolymers (MKBGs) through multi-scale characterization of mechanical properties, reaction kinetics, and pore structure refinement. Key findings reveal that 10% cement addition optimally reduces drying shrinkage through pore structure densification and elastic modulus enhancement. The cement–geopolymer hybrid system exhibited a distinctive dual-reaction mechanism: cement hydration produced C-S-H gels that refined the pore structure while simultaneously competing with and delaying the geopolymerization kinetics, as demonstrated by the extended duration of the reaction exotherm. However, cement contents exceeding 20% induce detrimental self-desiccation shrinkage, resulting in net shrinkage amplification. Microstructural analysis confirms that the optimal 10% cement dosage achieves synergistic phase evolution, with N-A-S-H and C-S-H gels co-operatively improving mechanical strength and dimensional stability. This work provides quantitative guidelines for designing shrinkage-resistant geopolymer composites through controlled cement hybridization.