Influence of processing methods on the strength activity index for sludge as a supplementary cementitious material

Utilizing activated sludge as a partial substitute for cement can both curb cement consumption and address sludge reuse in an economically and environmentally-friendly manner. This study delves into the pozzolanic activity of mechanically-thermal (MT) activated sludge and alkali-mechanical-thermal (AMT) activated sludge, employing the strength activity index (SAI) method. Microscopic insights provided by X-ray diffraction (XRD), scanning electron microscopy (SEM), and laser particle size analysis aid in the interpretation of observed phenomena. The findings underscore the superiority of MT activation over AMT activation, with an SAI of 97 %. Optimal pozzolanic activity is achieved through a 2-hours holding time, slow heating at 10 °C/min, and rapid cooling. A calcination temperature of 800 °C effectively promotes the decomposition of active minerals and enhances the sludge's pozzolanic activity. Additionally, a ball milling time of 2 minutes proves sufficient to meet practical demands, as prolonged ball milling has a limited impact on sludge pozzolanic activity.