Hydrolysis-modified secondary aluminum dross as an additive for supersulfated cement: Early-age strength enhancement and leaching evaluation.

The disposal of secondary aluminum dross (SAD), a major industrial solid waste, poses significant environmental challenges due to its low utilization rate. This study explores the potential of modified SAD (MSAD) as an additive to improve the early-age strength of supersulfated cement (SSC). Optimal hydrolysis conditions for SAD were determined as an ultrasonic power of 250 W, a liquid-to-solid ratio of 8:1, a duration of 4 h, a temperature of 70°C, and a pH of 13. Microstructural analysis revealed that the hydration products of the MSAD-reinforced SSC primarily consist of ettringite and C-(A)-S-H gel. The specimen incorporating 10% MSAD demonstrated superior performance, exhibiting the highest compressive strength with remarkable enhancements of 93.7%, 20.2%, 14.1%, and 11.19% at curing ages of 1, 3, 7, and 28 days, respectively. Combined phase and microstructural evidence suggests that this improvement is associated with enhanced early ettringite formation and pore refinement. Furthermore, leaching evaluation of the 10% MSAD-reinforced SSC specimen showed that the leaching concentrations of the tested heavy metals and fluoride were within the limits specified in the referenced Chinese standards under the adopted test conditions.