Sewage Sludge Ash as a Partial Replacement of Cement in Concrete

Abstract

Sewage sludge ash (SSA) is the by-product obtained from incinerating mechanically sewage sludge. By using the small amount of sewage sludge ash (SSA) mortars of comparable strength can be produced to replace cement. However, information on how SSA affects the properties of cement mortars is limited to given the Pozzolanic activities of most SSA being modest. This study identified the mechanisms behind some beneficial effects of the SSA on the strength development of mortars through a comparison study with fine sewage sludge ash (FSSA) and pulverized fly ash (PFA). The findings of this study indicated that the presence of SSA accelerates the rate of heat evolution from cement hydration while PFA does not produce this effect (Chen Z, Poon CS, Constr Build Mater 154:791–803, 2017). A higher content of SSA or FSSA produces a greater effect. Replacing cement by SSA or FSSA up to 10% did not induce significant changes to the pore structure of the pastes. The strength of the mortars, PFA reduces the drying shrinkage of the mortars, but SSA causes greater drying shrinkage due to increasing content of mesopores with sizes less than 0.025 mm. This harmful effect is greater with FSSA.