Strength evolution and microscopic mechanisms of cementitious materials prepared from industrial and municipal solid wastes under the influence of sulfates

Solid waste-based cementitious materials represent a promising alternative to conventional Portland cement, contributing to a reduction in carbon dioxide emissions and enhancing the recycling of industrial and municipal waste. However, these materials are susceptible to harsh environmental conditions, such as sulphate attack, which may result in expansion, strength degradation, and alterations in permeability. This study systematically investigated the effects of sulphate exposure on the mechanical properties and permeability of cementitious materials derived from industrial and municipal solid wastes, such as blast furnace slag, desulphurization gypsum, construction waste, and municipal sludge. Microstructural and chemical characterisation was performed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). In sulphate solutions ranging from 0.2 to 50 g/L, the unconfined compressive strength of these materials increased by 5.8 %–24.8 % during the initial 10 days of exposure, before decreasing to 4.13–9.18 MPa after 90 days. Sulphate reactions with industrial waste components resulted in the formation of expansive phases, such as ettringite and gypsum dihydrate, leading to structural degradation. The particle size of construction waste and the slag content significantly influenced the rate of sulphate-induced degradation.