Physico-mechanical performance of fly ash based geopolymer brick: Influence of pressure- temperature- time

Trillions of masonry fired-clay bricks are being produced globally every year, however, their manufacturing process is far from eco-friendly. This work was designed to develop fly ash (FA) based geopolymer brick, a sustainable alternative to fired-clay brick. For the optimum manufacturing technique, physico-mechanical performance was assessed by molding pressure (0, 20, and 40 MPa), curing temperature (ambient, hot), and curing time (7 and28 days) as well as combined effect of these parameters. It was observed that the molding pressure densifies the mixture and results in decrease in porosity and water absorption. As a result, the strength was increased significantly (more than 180 %). For the curing temperature, the hot curing state was well collaborated with the higher molding pressure of 40 MPa to develop the compressive strength compared with the ambient-curing condition due to the high rate of geopolymerization. The curing time was found to be not significant for the strength development. The strength was enhanced more than 600 % when the combined effect of pressure temperature time was applied. Although, 40 MPa molding pressure showed higher strength, however, the 20 MPa molding pressure could sufficiently satisfy the ASTM strength criteria. The correlation matrix was developed, and it was observed that pressure temperature has 0.91 correlation with the strength and recommended as the optimum technique. The pilot-scale test confirmed that the physico-mechanical properties satisfied the standards. Furthermore, mechanical strength was found to be in good correspondence with the physical properties under all strength enhancing techniques, which was reconfirmed with the microstructural analysis using scanning electron microscope.