Effects of 3-aminopropyltriethoxysilane and EVA incorporation sequence on alkali-activated stainless steel slag–ground granulated blast-furnace slag binders: Strength, toughness, microstructure and heavy-metal safety

To develop alkali-activated stainless steel slag (SSS) – ground granulated blast furnace slag (GGBFS) materials with high compressive strength and enhanced toughness, 3-aminopropyltriethoxysilane (APTES) and ethylene vinyl acetate copolymer (EVA) redispersible polymer powder were incorporated. The effects on the mechanical properties, microstructure, and environmental risk associated with heavy metals were investigated under three incorporation routes, namely single addition, direct hybrid addition, and pretreatment-assisted hybrid addition. The results show that EVA mainly improved post-peak energy dissipation and material toughness, but adversely affected matrix densification and compressive strength. In contrast, APTES enhanced matrix strength by promoting the formation of C-A-S-H gels, regulating the Si–O–T network structure, and refining the pore structure, but provided limited toughening. Direct hybrid addition of APTES and EVA exhibited a pronounced antagonistic effect on compressive strength. Pretreatment altered the interaction sequence and initial distribution of APTES, thereby mitigating the unfavorable interfacial interactions arising from direct hybrid addition and enabling more effective coordination between APTES-induced matrix strengthening and EVA-induced toughening. Although the alkali activation reaction and pretreatment process increased the proportion of labile Cr and Ni species, their leaching concentrations remained below the regulatory limits, indicating a low environmental risk. The pretreated hybrid sample exhibited a 28 d compressive strength of 88.56 MPa and showed increases of 18.33%, 20.51%, and 36.97% in total fracture energy, CMOD energy ratio, and post-peak sustained energy dissipation parameter, respectively.