Study on Basic Performance and Drying Shrinkage Characteristics of Binary Solid Waste Geopolymer Mortar Prepared with Peanut Husk Ash and Slag

Abstract Geopolymer mortar (GM) is a sustainable alternative to cement with a low carbon footprint and excellent mechanical performance. However, its reliance on ground granulated blast-furnace slag (GGBFS) and natural sand, along with significant drying shrinkage, limits its sustainability and durability. In this study, peanut husk ash (PHA), an agricultural by-product, was utilized as a dual replacement material to partially replace GGBFS and natural sand in GM, thereby developing a novel green building mortar. A total of 17 mortar mixtures, prepared by employing PHA as a dual replacement material to partially replace GGBFS (0%–15% by weight) and natural sand (0%–30% by weight), respectively, were systematically investigated for properties including fresh state behavior, mechanical strength, drying shrinkage, and microstructure versus cement mortar (CM). The experimental results show that the volcanic ash effect and the microaggregate filling effect of PHA work synergistically to enhance the matrix performance. Compared with the reference group, when the total replacement rate was 20% by weight, the 28-day compressive strength of mortar increased by 21.7%, the 90-day drying shrinkage reduced by 31.2%, and the working performance met the construction requirements. Microstructural analysis reveals that highly active SiO 2 in PHA reacts with Ca ( OH ) 2 generated by GGBFS hydration to form gels, which improves the pore structure. This study offers new insights into using agricultural wastes efficiently in geopolymers, providing theoretical and engineering support for sustainable building materials.