The feasibility of utilizing sewage sludge as a source of aluminosilicate to synthesise geopolymer cement

The purpose of this study was to evaluate the feasibility of utilizing sewage sludge as a source of aluminosilicate to synthesise geopolymer cement. Sewage sludge was calcined at various temperatures to enhance its geopolymer reactivity. Sodium hydroxide and sodium silicate solution mixture was used as an alkaline activator. The geopolymer mortars' setting time, flow workability, unconfined compressive strength (UCS), pore volume, and water absorption characteristics, wet-dry cycles and TCLP characteristics were measured. X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used for microstructural analysis. The results showed that the highest 7-day UCS of up to 18.9 MPa was obtained, corresponding to a 270.6% strength increase over the control. The microstructural analysis showed that the optimal mechanical and physical properties were obtained when the sewage sludge was calcined at 750 degrees C showing that calcining the sewage sludge increases the geopolymer reactivity. The UCS decreases with the increase in wet dry cycles but the geopolymer composites were still within the minimum strength requirement of 3.5 MPa. TCLP showed that the leachability of the produced geopolymers is below the permissible limit. Geopolymer mortar made from sewage sludge ash can be utilized for various concrete and building applications without the risk of short- or long-term environmental contamination. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The study evaluated the feasibility of using sewage sludge to synthesize geopolymer cement. It was found that calcining the sludge increased the geopolymer reactivity and improved the mechanical and physical properties of the geopolymer composites. The geopolymer mortar made from sewage sludge ash can be utilized in various construction applications without environmental contamination.