Designing the incineration process for improving the cementitious performance of sewage sludge ash in Portland and blended cement systems

Abstract

Currently, there is little doubt that the global temperature increase is a consequence of the concentrations of manmade greenhouse gases. Sustainable alternatives such as the use of supplementary cementitious materials and the reduction of sanitary landfills through the incineration of sewage sludge hold promise for the reduction of these gases.An experimental design is proposed to make the incineration of sewage sludge (SS) more efficient, thereby improving the sewage slush ash (SSA) produced as a supplementary cementitious material. Different maximum temperatures and residence times were studied in the partial replacement of Portland and blended cements; the resulting SSAs contributed to the mechanical behavior of concrete through improved hydraulic and pozzolanic activity in addition to intense interactions with cement.The particle size distributions of the SSAs were similar to those of the cements, but the specific surface areas of the SSAs were up to 18 times higher than those of the cements. This vast difference is explained by the presence of micropores after the incineration process. Consequently, the specific surface area of the SSA particles was the most important property explaining the pozzolanic activity and interaction effects with cement. Lower incineration temperatures and higher incineration times increased the specific surface area, therefore increasing the cementitious performance of SSA. The SSA cementitious performance was lower in blended cement than in Portland cement; however, the replacement of blended cement by SSA increased the compressive strength at early and late ages.