Experimental study on cementitious reactivity of MSTP sludge incineration ash

One of the main objectives of this study was to activate the pozzolanic activity of sludge, produced by municipal sewage treatment plants (MSTP), which makes it become an admixture to replace a part of cement in cement-based materials. Nowadays, a significant quantity of MSTP sludge is obtained in China, and the disposal of sludge presents a rising challenge for the environment, which is the reason why this paper examines the possibility of adding this waste product to cement-based materials. MSTP sludge was activated by thermal (Incineration) and mechanical (Grinding) treatment. Meanwhile, the changes in the crystalline structure of MSTP sludge incineration ash (MSA) were evaluated using X-Ray Diffraction (XRD), and mortar strength tests were carried out on the mortars containing MSA to investigate the reactivity of the produced materials. The obtained results revealed that the optimal activation conditions of MSA were as follows: incinerated at 800 C for 2.5 hours followed by fast cooling in air and then ground until 60 minutes. Moreover, we have observed that MSA has an appreciable effect on the increase in compressive strength of the mortars and using of 20% MSA as a replacement of part of cement could be considered the optimum content. More importantly, the tests showed that extract toxicity of heavy metals in MSA were much lower than the national standard though some heavy metals existed in MSA. These results demonstrate the feasibility of recycling MSTP sludge has become an admixture in cement-based materials for construction engineering.