Valorizing Municipal Solid Waste Incineration and Electric Arc Furnace Slags in Alkali-Activated Mortars: Durability and Mechanical Property Mapping and Practical Limits

The increasing scarcity of coal fly ash (FA) motivates the development of waste-valorized binders. In this paper, municipal solid-waste incineration slag (MSWIS) and electric-arc furnace slag (EAFS) were co-activated as partial/total FA substitutes in alkali-activated pastes and mortars. Binary/ternary mixes (waterglass + NaOH + superplasticizer) were assessed for fresh behavior, strength and stiffness, porosity and capillary absorption, and screening durability (sulfate immersion, freeze–thaw, high temperature). Pastes reached 28-day and 90-day uniaxial compressive strength (UCS) up to 35 and 52 MPa; mortars reached 15 and 25 MPa, respectively. MSWIS contributed with its higher reactivity, while EAFS acted mainly as a filler. The superplasticizer showed a nonmonotonic response, linked to a coarser pore structure. The 25%FA-25%MSWIS-50%EAFS mortar outperformed 50%FA at freeze–thaw and high temperature. However, MSWIS-rich mixes were sulfate-sensitive and contained chlorides; until leaching/corrosion resistance is verified, applications should be limited to non-reinforced, low-sulfate exposure. These results demonstrate a feasible waste-valorization route and define the performance window and practical limits for cleaner production deployment.