Influence Mechanism of Chemically Modified Alumina on the Hydration of Gypsum-Based Self-Leveling Mortar

This study investigates the effect of γ-aminopropyltriethoxysilane (KH550)-functionalized nano-active Al₂O₃ (KH-Al) on the properties of gypsum-based self-leveling mortar (GSL) prepared from industrial by-product gypsum. First, the effects of incorporating KH-Al at dosages of 0.05%, 0.1%, 0.25%, 0.5%, and 1% on the fluidity, setting time, and mechanical properties of GSL were analyzed. Subsequently, using X-ray diffraction (XRD), hydration heat analysis, thermogravimetric analysis (TG), and scanning electron microscopy (SEM), the influences of the nanomaterial on the mortar’s morphology, hydration characteristics, and crystal forms of hydration products were thoroughly examined. Finally, by comparing the modified GSL with ordinary GSL, the mechanism of KH-Al’s action on GSL was elucidated. The results demonstrate that nano-active Al₂O₃ modified with KH550 exhibits excellent dispersibility in the GSL paste. As the dosage of KH-Al increases, both the fluidity and setting time of GSL decrease. Upon incorporating KH-Al, the mechanical properties of GSL initially improve and then decline, with optimal mechanical performance observed at a 0.5% KH-Al addition. However, when the KH-Al dosage exceeds 0.5%, excess nano-active Al₂O₃ causes nanoparticle agglomeration, which impedes the hydration process. The nucleation effect of KH-Al promotes the formation of CŜH₂ and AFt, refines the crystals of hydration products, and enhances the phase transformation efficiency of the mortar. These findings indicate that KH-Al has significant potential to improve the mechanical strength and hydration kinetics of gypsum mortar and provide theoretical support for the application of nanomaterials in gypsum building materials.