Understanding efflorescence behavior and compressive strength evolution of metakaolin-based geopolymer under a pore structure perspective

Efflorescence is a concerning issue in geopolymer formulations. By accelerating efflorescence, the efflorescence behavior and compressive strength evolution were analyzed for metakaolin (MK)-based geopolymers cured at various temperatures and times. Mercury Intrusion Porosimetry (MIP) was the primary characterization method utilized in this study. Based on the pore structure, we identified the influence of pore structure on efflorescence behavior and compressive strength evolution. Those results showed that long-term and initial high-temperature curing played a negative role in mitigating efflorescence. Long-term curing refined the pore size, facilitating alkali salt migration to the surface. Initial high-temperature curing enhanced pore connectivity, which facilitated alkali salt movement. The number of pores below 20 nm governs the effect of efflorescence on compressive strength. Crystallization degrades geopolymer with a large number of pores below 20 nm. This study provides a new understanding of the effect of pore structure on efflorescence and the evolution of compressive strength during efflorescence and facilitates optimization of geopolymer formulations to relieve efflorescence.