Effects of curing temperature on early-age mechanical property and microstructure of lunar regolith simulant geopolymer

The utilization of in-situ resources is of significant importance for the construction of lunar bases, considering the high cost of transportation between Earth and the Moon. Lunar regolith simulant geopolymer (LRSG) is considered a viable construction material based on in-situ resources. Due to the significant temperature variations between day and night on the lunar surface, curing temperature has a notable impact on the physical and mechanical properties of LRSG. Therefore, investigating the effects of different curing temperatures on LRSG is of great importance, providing a theoretical foundation for the construction of lunar bases utilizing in-situ resources. In light of this, the present study explores the influence of curing temperatures of 40℃, 60℃, and 80℃ on the early-age mechanical properties and microstructure of LRSG. Through microscopic characterization techniques such as SEM-EDS, 29 Si MAS NMR, and MIP, the study analyzes the micro-morphology, elemental composition, chemical shifts, and porosity of LRSG. The results indicate that within a curing temperature range of 40℃ to 80℃, both compressive and flexural strengths of the LRSGs increased in correlation with the rising curing temperature. Specifically, at a curing temperature of 80℃ and a curing time of 72 h, the LRSG demonstrated the highest compressive and flexural strengths of 48.57 MPa and 3.52 MPa, respectively, marking increases of 1171.47 % and 345.57 % over those achieved by counterparts cured at 40℃ and 72 h. Microscopic analyses revealed that an increase in curing temperature significantly enhanced the alkaline activation reaction extent, leading to a rise in the generated hydration products N-A-S-H and C-A-S-H gels. These hydration products rapidly filled the LRSG interior, improving the structure density and reducing its porosity.