Rice Husk Ash (RHA) Recycling in Brick Manufacture: Effects on Physical and Microstructural Properties

In this study RHA was used as silica source in the obtainment of clay bricks. Different compositions were prepared, substituting the clays with diverse percentages of RHA (0–20 wt%) and requested water contents. The pastes obtained were extruded in laboratory, dried and then fired in an industrial camera kiln. Technological tests were performed after drying (linear shrinkage and naphtha absorption) and firing [(24-h immersion) water absorption, linear shrinkage, weight loss, average flexural strength] steps. Besides, to analyze the effect on the microstructure and mineralogy, SEM/EDS and XRD analysis of the fired bricks were performed. From the tests conducted it is possible to note that RHA content contributes to reduce the linear shrinkage during drying while an opposite effect is observed for the water absorption. Regarding mechanical test, the products containing up to 5 wt% of RHA are in according to the recommended values for roof. Bricks containing higher amounts of RHA could be used in building manufacturing (light weighted faced load bearing walls) where moderate strengths and penetration protection (porosity/permeability) are required. The carbon unburned present in the RHA contributes to increase the final porosity and the weight loss of the bricks.