Performance of sustainable concrete incorporating treated domestic wastewater, RCA, and fly ash

This study evaluates the impact of using treated wastewater (TWW), recycled concrete aggregates (RCA), and fly ash (FA) on the mechanical, durability, and microstructural properties of concrete. A total of eight concrete mixes were manufactured and tested. Fresh mixing water and natural gabbro aggregates were completely replaced with TWW and RCA, respectively, whereas 20% of cement was substituted by FA. Test results revealed that TWW slightly reduced concrete mechanical properties by 6% to 12%, while it drastically reduced the chloride permeability by 77% in comparison with freshwater concrete. In addition, RCA decreased concrete compressive and flexural strengths by 21% and 10%, respectively, compared to natural aggregate concrete. Moreover, TWW concrete mixes with RCA had 16% to 42% lower porosity and chloride permeability than their counterparts with gabbro aggregates. Furthermore, concrete mixes with TWW, RCA, and FA exhibited the lowest chloride permeability among the investigated mixes. It was also shown that the interfacial transition zones between RCA and cement matrix were improved by replacing FA for 20% of cement. Analytically, aggregate and concrete morphological images and chemical composition were investigated to support the experimental results.