Regulation mechanism of autogenous shrinkage in high-strength cementitious composites by solid waste-based porous aggregate

To clarify the regulation effect of porous aggregate (PA) sintered from heavy metal sludge on the autogenous shrinkage of high-strength cementitious composites and its temperature-dependent mechanism, composites with PA volume replacement ratios of 0%, 10%, 20%, 30%, and 40% were prepared and cured at 10℃, 20℃, and 30℃. Fluidity, mechanical properties, and 7 d autogenous shrinkage were measured. XRD, FTIR, TG/DTG, and low-field proton nuclear magnetic resonance (¹H NMR) were used to analyze hydration products and moisture migration. The results show that PA decreases the fluidity from 312 mm to 143 mm, but increases the early compressive strength; the 1 d compressive strength of the composite with 40% PA is increased by 27.27%. At 20℃, the reference group exhibits a 7 d autogenous shrinkage of 523.87 με, whereas the composite with 40vol% PA compensates for shrinkage and shows an expansion of approximately 167 με. At 30 ℃, the expansion exceeds 200 με. Microstructural results indicate that PA promotes the consumption of C₃S and C₂S, increases the contents of Ca(OH)₂, AFt, and chemically bound water, and delays internal humidity reduction through continuous water release. The regulation of autogenous shrinkage by PA results from the synergistic effects of porous water storage, humidity-responsive water release, continuous hydration promotion, free-CaO hydration expansion, and skeleton restraint. These findings indicate that heavy-metal-sludge-derived PA can be used as a green internal curing aggregate for both solid waste utilization and shrinkage control.