Feasibility of producing non-fired compressed masonry units from brick clay mill residues by alkali activation

Brick clay mill residues are a type of particulate by-product that can cause environmental and health issues due to the content of fine particulate matter. The present research investigated the viability of using the brick clay mill residue to produce non-fired masonry units by sodium hydroxide and sodium silicate solutions. The compressive strength, linear shrinkage, bulk density and microstructure have been examined. It was found that the adoption of low-temperature (50 °C) moist-curing (90% relative humidity) significantly improved the strength of samples and prevent samples from the issue of surface cracking. The best time for moist curing was 48 h, and the optimal elevated curing temperature was 155 °C. The duration required to achieve ultimate compressive strengths for the samples cured at 200, 155, 110 and 65 °C was 24, 24, 48 and 120 h, respectively. The results showed that the compressive strength of brick samples ranged from 24 to 48 MPa, complying with ASTM C62 and ASTM C55. In addition, the FTIR and SEM-EDX results indicated that the strength gain was attributed to the formation of new network of aluminosilicate. The comparison of this alkali-activated and fired bricks showed that the bricks of this study had the potential to conserve energy and reduce emissions. In conclusion, this study revealed that the brick clay mill residues can be used to produce alkali-activated bricks.