Engineering properties of waste-based alkali activated concrete brick containing low calcium fly ash and rice husk ash: A comparison with traditional Portland cement concrete brick

Abstract

Alkali activated concrete bricks manufactured from waste materials are an alternative to replace PC as the principal binder in brick manufacture. The current study reports the mechanical and durability properties of blended fly ash and 20% rice husk ash (20RHA) alkali activated bricks and compares with Portland cement (PC) bricks (100PC). The 20RHA brick showed a compressive strength growth rate of 4% between 7 and 28 days as compared to 13.8% for 100PC bricks. Both achieved similar 28 days compressive strength (approximately 17 MPa). High tensile strength was observed in 20RHA this is attributed to the high bond strength at the interface of the 20RHA alkali activated binder and aggregates. In microstructural investigation, 20RHA brick displayed a stronger bond within the interfacial transition zone (ITZ) boundary compared to 100PC bricks at all ages. This makes the fracture plane more prone to pass through the aggregates than through the bond interface. Lower capillary suction near the surface for 20RHA concrete is hypothesized as the reason for the lower initial rate of absorption obtained for 20RHA when compared with 100PC. The addition of RHA makes the bricks more vulnerable to efflorescence when exposed to moisture due to the combined effect of the high porosity, a high Na2O/Al2O3 ratio and greater leaching of sodium ions.