Reuse of Secondary Treated Wastewater and Fly Ash for the Manufacturing of Concrete: A Sustainable Approach

Urbanization and rapid improvement in infrastructure have increased the demand for potable water in all metro cities. It is very important to provide potable water to people and to decrease the utilization of potable water for non-potable use. In this regard, concrete production needs a significant amount of water for mixing and curing. This water can otherwise be used by secondary treated wastewater from sewage treatment plants. In this research, the secondary treated recycled wastewater from three secondary-level wastewater processing plants was used to manufacture concrete, and the same wastewater was compared with that of concrete manufactured using potable water. Concrete mixtures prepared using tap water showed greater workability, with slump test values ranging from 80 to 190 mm, compared to mixtures made with secondary treated wastewater, which had a workability range of 80 to 180 mm. These mixtures also incorporated different percentages of fly ash. The addition of 10% to 30% fly ash improved workability across all mixtures, particularly those with secondary treated wastewater. Strength testing revealed that tap water mixtures had compressive strengths ranging from 43.6 to 32.4 MPa, split tensile strengths from 2.76 to 5.82 MPa, and flexural strengths from 3.55 to 2.76 MPa. In contrast, mixtures with secondary treated wastewater showed compressive strengths from 38.5 to 28.4 MPa, split tensile strengths from 2.95 to 2.15 MPa, and flexural strengths from 4.80 to 2.9 MPa. Incorporating fly ash into the secondary treated wastewater mixtures resulted in decreased strength properties, regardless of the dosage. Nevertheless, all mixtures met the M30 grade concrete requirements at 28 days. Furthermore, scanning electron microscopy (SEM) analysis was conducted on the concrete specimens to analyze the microstructural composition. The workability, strength, and durability properties of concrete were significantly affected by the fly ash content, while the water type used in the preparation of the concrete mixtures did not have a notable impact. In conclusion, secondary processed wastewater may be considered a feasible substitute for the construction water usage sector, particularly in the context of rapid urbanization. Indian standards should prioritize the development of health-centric, chemical-focused, economically viable, and ecologically conscious guidelines for the purpose of reuse.