Ecological mortar using dried and burnt WWTP sludge

Abstract

In order to create alternatives for the disposal of sludge generated in wastewater treatment plants and contribute to reducing the environmental impacts generated by the construction industry, the aim of this work was to evaluate the technical feasibility of partially replacing cement in the production of mortars by the sludge produced at the Bragança WWTP. The sludge was characterized in relation to pH, moisture, total solids, and organic matter content, and underwent different preparation processes (4) before being incorporated into the mortar. M1: The previously dried sludge was burnt for 0.5 hour at 300 °C and for 3 h at 900 °C. M2: The sludge was dried for 24 h at 105 °C. M3: The sludge was dried for seven days by solar exposure. M4: The sludge was dried for 15 d by solar exposure. After sludge preparation, it was triturated and incorporated into the mortar mixture; the proportions of sand and water were 54 and 14%, respectively. The slurry was incorporated at concentrations of 0, 3, 5, 7 and 10%. The specimens were molded for the flexural and compressive strength tests. The specimen with 7% sludge of the M1 treatment obtained the best resistance, surpassing the standard; the specimens with sludge of the M2, M3, and M4 treatments showed similar results. The incorporation of sludge resulted in mortars within the specification of the EN 998-1:2018 norm in relation to compressive strength and, consequently, has technical feasibility.