Performance and strength mechanism of aeolian sand mortar solidified by coal gangue–slag geopolymers

This study systematically evaluated the workability and mechanical properties of coal gangue–slag-based geopolymer aeolian sand mortar (GPAM), with a focus on the effects of liquid-to-solid (L/S) ratio, aeolian sand (AS) content, alkali equivalent, and sodium silicate modulus on its performance. The evolution of microstructure and pore characteristics was investigated using XRD, SEM-EDS, FTIR, and LF NMR. The results showed that the incorporation of AS reduced the mortar flowability but improved early flexural and compressive strengths. When 100 % AS was used as a replacement, the 28-day flexural strength and compressive strength increased by 5.65 % and 6.29 %, respectively, compared to the control sample. Under conditions of low L/S ratio (0.40), low modulus (1.2), and high alkali equivalent (0.20), the mortar exhibited optimal strength and acceptable workability (flow spread >200 mm), with its 28-day compressive strengths exceeding 40 MPa. Microscopic analysis revealed that conditions of low L/S ratio, high alkali equivalent, and low modulus promoted the transformation of albite to anorthite and the formation of N(C)-A-S-H and C-A-S-H gels, resulting in a continuous and dense cementitious network. The dissolution of reactive Si, Al, and Fe from AS enhanced the interfacial bonding with the matrix, improved pore distribution, and reduced the total void ratio. The study results showed that the synergistic activation of coal gangue and slag, combined with the incorporation of AS, can significantly improve the mechanical properties and compactness of geopolymer mortar, providing both a theoretical and practical basis for the development of low-carbon building materials in wind-sandy regions. • Aeolian sand was used as fine aggregates to optimize the coal gangue-slag based geopolymer. • The incorporation of aeolian sand enhanced the early strength and promoted the densification of the geopolymer matrix. • The reactive Si, Al, and Fe in the aeolian sand improved interfacial bonding and pore structure. • Coal gangue-slag synergy is verified, aiding low-carbon materials in wind-sandy regions.