The effectiveness of the incineration of sewage sludge on the evolution of physicochemical and mechanical properties of Portland cement

Abstract

The influence of sewage sludge, treated at temperatures between 300 and 800°C, on cement-based materials has been studied in this paper. The clinker of CPJ45 cement was partially replaced by sewage sludge ash (SSA) admixture in mortar at various percentages. The sewage sludge ashes were characterized chemically, physically and mineralogically. In addition, the influences of SSA on mortar properties, including Blaine fineness, specific gravity, water demand, time of setting, compressive strength and degree of hydration were also investigated.Results show that calcination influences the microstructure of sewage sludge and increases its pozzolanic activity that reaches its maximum at 800°C. The presence of absorbed water and organic matter in sewage sludge calcined in temperature range 300–500°C prolongs strongly the setting time and affects negatively the compressive strength and the hydration degree of mortars. While the high amounts of P2O5 and SO3 in sewage sludge calcined in temperature range 700–800°C increase also water demand and setting time compared to the control mortar, however, the compressive strengths and the degree of hydration increase with time and become superior to the control mortar at 90days, for a replacement rate of 15%. The best mechanical results are obtained for the substitution of 5% of calcined sewage sludge at 28days.