Recycling of bottom ash and fly ash wastes in eco-friendly clay brick production

The use of waste-based materials in the construction industry has received significant attention in recent years to develop environmentally-friendly construction materials. This paper presents an experimental study on the properties of bricks containing clay, fly ash (FA), and bottom ash (BA). A total of 12 batches of bricks were manufactured and experimental tests were conducted at two firing temperature of 950 and 1050 °C to determine the apparent porosity, water absorption, apparent specific gravity, bulk density, compressive strength, and thermal conductivity. Microstructural analysis was undertaken to describe the reasons for the obtained experimental results. The results show that the bricks fired at 1050 °C exhibit slightly lower apparent porosity and water absorption but slightly higher bulk density and thermal conductivity than those fired at 950 °C. The results also show that an increase in the FA content leads to an increase in the apparent porosity and water absorption but a decrease in bulk density and thermal conductivity of the bricks. BA content does not have any significant influence of the properties of the bricks. It is also shown that bricks containing 5% FA, 5% BA, and 10% BA exhibit a similar compressive strength to those containing only clay. The leaching results show that the leaching of heavy metals from fired bricks is significantly lower than that of the limit concentrations. The leaching concentrations of the samples show that the heavy metals were immobilized in the ceramic structures of all fired bricks. These highly promising findings suggest that up to 30% replacement of wastes with ashes can provide bricks to reduce the environmental impact of abundant waste products and conserve non-renewable natural resources.