Utilization of Sintered Sludge Ash with Different Mechanical–Thermal Activation Parameters as a Supplementary Cementitious Material: Mechanical Properties and Life Cycle Assessment of Cement-Based Paste

The proposal of sintered sludge cement (SSC) paste aligns with the low-carbon development goals of building materials. However, there is a lack of scientific guidance for the preparation of sintered sludge ash (SSA). Herein, this study systematically investigates the influence mechanism of mechanical-thermal activation parameters of SSA on the mechanical properties and life cycle assessment (LCA) of SSC paste, and conducts a comprehensive evaluation using a radar chart and the TOPSIS method. The results show that with the increase in calcination temperature and duration, the compressive and flexural strengths of the SSC paste are improved, especially at 600 °C and above, increasing by 57.92% and 62.52%, respectively. The longer calcination time at 1000 °C results in a decrease in its mechanical properties. The addition of SSA significantly reduces the LCA indicators of cement paste. Specifically, 30% SSA only contributes 8.1% to the global warming potential. Compared to calcination, the LCA indicators have less sensitivity to ball milling, and prolonging the time hardly increases them. Based on performance and environmental impact, the optimal SSA is obtained by calcining at 800 °C for 2 h and ball milling for 10 min. This study can provide theoretical guidance for efficient building material utilization of dredged sludge.