Co-Utilizationof Municipal Solid Waste Incineration Fly Ash and Bottom Ash in Alkali-Activated Concrete: Engineering Performance and Heavy Metal Leaching Characteristics

To promote the co-utilization of municipal solid waste incineration fly ash (MSWIFA) and size-fractionated bottom ash (MSWIBA), an alkali-activated binder was prepared from MSWIFA, ground granulated blast furnace slag, and coal fly ash. The 0–2.36 and 2.36–4.75 mm MSWIBA fractions were converted into cold-bonded artificial lightweight aggregate (ALA; 2.36–4.75 mm), whereas the 4.75–9.5 mm fraction was used directly as coarse aggregate. An L9 orthogonal experiment evaluated water-to-binder ratio, sand ratio, and ALA-to-coarse MSWIBA ratio. Slump and 28 d compressive strength ranged from 125 to 180 mm and from 17.5 to 30.0 MPa, respectively. A1 reached a 28 d strength of 30.00 ± 1.57 MPa across three independent batches. The ALA-to-coarse MSWIBA ratio was associated with the largest strength variation. At 175 freeze–thaw cycles, A1 had a relative dynamic elastic modulus of 56.37 ± 0.81% and mass loss of 4.94 ± 0.05%. Continuous immersion in 5 wt.% Na2SO4 for 180 d gave reported strength retention coefficients of 72.6–74.8%; all were below the adopted 75% criterion. Short-term ICP-MS measurements showed Cd, Pb, and Ni concentrations below the corresponding Class III groundwater reference values. These results identify A1 as the preferred formulation for further component-scale evaluation, with sulfate resistance requiring improvement.