Recycling MSTP Sludge as an Admixture in Concrete

Abstract

One of the main objectives of this study was to activate the pozzolanic activity of sludge, produced by municipal sewage treatment plants (MSTP), make it become an admixture to replace a part of cement in concrete. Nowadays, a significant quantity of MSTP sludge is obtained in China. That is why this paper examines the possibility of adding this waste product to plain concrete with Portland cement. Preliminary studies are carried out on using MSTP sludge as an admixture by thermal (calcining) and mechanical (grinding) treatment. The pozzolanic activity of the calcined sludge ash (CSA) evaluated by Cement Mortar test. The CSA-blended cement concrete was formed into specimens of cubic concrete with 100 mm×100 mm×100 mm. They are with 30 wt. % cement replaced by CSA, which was prepared by the optimal activation conditions. The Cement Mortar test results revealed that the optimal activation conditions of CSA were as follows: calcined at 800°C for 2.5 hours followed by fast cooling in air and then ground until 60 minutes. Besides, the compressive strengths of concrete specimens with added 30% CSA were 103.6% and 105.3% of those of the ordinary Portland cement concrete specimens at 7 and 28 days, respectively. These results demonstrate the feasibility of recycling MSTP sludge as an admixture in concrete for construction engineering.