Workability, mechanical, durability, and microstructural investigation of sustainable concrete utilizing secondary treated wastewater, fly ash, and sodium nitrite

The present study focused on utilizing secondary treated wastewater (STW) from three secondary-level wastewater treatment plants, fly ash (FA), and sodium nitrite (SN), to manufacture sustainable concrete and compared the results with those of concrete manufactured using tap water. The workability (slump cone), strength (compressive, split tensile, and flexural strength), and durability (rapid chloride permeability and efflorescence test) properties of the materials were examined. Furthermore, scanning electron microscopy (SEM) analysis was conducted on the concrete samples to analyse the microstructure. The workability, mechanical, and durability properties of the concrete mixtures were significantly affected by the FA and SN content, while the water type used in the preparation of the concrete mixtures had no significant effect. Based on durability tests, the penetrability of concrete mixtures is low to moderate, indicating the better quality of the mixtures, and the efflorescence in concrete mixtures was found to be nil. Finally, it can be concluded that STW from three secondary-level wastewater treatment plants with 10% FA and 2% SN had comparable results to those of concrete manufactured using tap water. HIGHLIGHTS Secondary treated wastewater (STW), fly ash (FA), and sodium nitrite (SN) were utilized to manufacture sustainable concrete. Workability, strength, durability, and microstructural analysis properties of the concrete mixtures were significantly affected by the FA and SN contents, but STW had no significant effect. STW with 10% FA and 2% SN had comparable results with those of concrete manufactured using tap water.