Preparation and performance evaluation of aeolian sand mortar with internal addition of wet-modified fly ash by stearic acid

It is of significance to realize the resource utilization of large-volume solid waste and prepare hydrophobic mortar materials. Aeolian sand (AS) was used as fine aggregate to prepare aeolian sand mortar (ASM) with the addition of fly ash (FA) modified by stearic acid (SA). The effect of modified FA (SF) replacement rate (SFR) on the water absorption and mechanical properties of ASM was assessed. The modification mechanism of SA on FA and the effect mechanism by which SFR affects the water absorption and mechanical properties of ASM were revealed combining with scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). The results indicate that the surface water contact angle of SF "first increases and then decreases" with increasing SA dosage (SAD), achieving superhydrophobicity at a dosage of 7% under both the dry and wet modification processes. SFR exerts a significant influence on the water absorption and mechanical properties of ASM, both the water absorption rate and capillary water absorption (CWA) of the mortar decrease with increasing SAD, and the pores with size ranges of 20–30 nm and 30–40 nm exhibit the most significant impact on the CWA of ASM based on grey relational analysis (GRA). The strength of ASM first increases and then decreases with increasing SAD, reaching its maximum when the SAD of 5% and SFR of 10%.