Experimental Investigation on the Strength, Durability, Microstructural, and Leaching Characteristics of the Fly Ash Bricks Made from Hazardous Brine Sludge and Industrial Wastes

Abstract The present study aims to develop sustainable fly ash bricks from hazardous brine sludge and industrial waste. The performance of the developed brick was evaluated for different mix proportions of fly ash, bottom ash, brine sludge, and cement. The green bricks were cured by sprinkling tap water once a day for 28 days. Thereafter, the bricks were investigated for different strengths, durability, microstructure, and leaching characteristics. The developed bricks achieved the highest average compressive strength of 28 MPa, and the water absorption was less than 20% after 28 days of curing, which satisfies the criteria for Class 12.5 bricks, i.e., structural bricks. The bricks exhibited an initial rate of absorption (IRA) of 0.03 g / cm 2 / min and a sorptivity value of 0.025 mm / s 0.5 and were suitable for deployment in exterior construction applications. The microstructural characterization tests, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) revealed the formation of complex linkages (barite, calcite, and C─S─H gel) in morphology and new crystalline and amorphous entities relative to the individual raw materials, supporting the strength and durability performances. Further, a toxicity characteristic leaching procedure (TCLP) test conducted on the bricks confirmed the effective immobilization of toxic metal ions (chromium, copper, vanadium, and zinc) from the brine sludge within the C─S─H gel matrix. The results suggested that the inclusion of 25% brine sludge and 25% (and more) bottom ash in the mix significantly enhanced the strength and durability performance of the developed bricks. It was concluded that the use of brine sludge together with industrial waste in brick production contributes toward sustainable development of construction materials.