Combined effects of treated domestic wastewater, fly ash, and calcium nitrite toward concrete sustainability

The drastic increase in freshwater and ordinary Portland cement (OPC) consumption poses severe environmental and economic challenges worldwide. This study; therefore, explores the mechanical and durability properties of concrete incorporating treated domestic wastewater (TWW), class F fly ash (FA), and calcium nitrite-based corrosion inhibitor (CN). OPC paste and mortar with TWW were first prepared and compared with the permissible limits specified in ASTM C1602/C1602M - 18 provisions. After that, ten concrete mixes were prepared with different ratios of TWW (0%, 25%, 50%, and 100%), FA (0%, 20%, and 35%), and CN (0% and 3%) and tested for fresh slump and density, compressive and flexural strengths, electrical resistivity, porosity, and chloride permeability. All concrete specimens were cured with fresh water. Concrete hardened properties were tested at 7, 28, and 90 days. Test results revealed that TWW slightly decreased concrete compressive and flexural strengths by 5%-12%, whereas it dramatically increased the porosity and chloride permeability by about 40%. It was also shown that the addition of FA significantly decreased the chloride permeability of TWW concrete by 55%-71%. The optimum FA replacement ratio was observed at 20 wt%. The addition of CN was shown to deteriorate the strength and durability properties of freshwater concrete by 10%-39%. However, combining TWW and CN has improved concrete resistivity, porosity, chloride permeability by 32%, 28%, and 32%, respectively. The optimum concrete properties were obtained using 20 wt% FA and 0% CN. The obtained results were analytically supported by scanning electron microscopy (SEM), energy-dispersive X-ray microanalysis (EDX), and X-ray diffraction (XRD) tests. Moreover, Pearson correlation and linear regressions were performed on the experimental data.