Experimental study and performance improvement of recycled building bricks based on microwave sintering technology

Abstract

The preparation of recycled building bricks (RBB) from construction spoil with microwave technology is a green, highly efficient, and energy-saving method. However, the low dielectric loss and high sintering temperature of construction spoil result in a long continuous heating time, which is not conducive to energy conservation or the lifespan of microwave equipment. This study proposes the use of hematite tailings as an auxiliary sintering material to enhance the response of RBB to microwave radiation. Orthogonal experiments were used to analyze the influence of the mass fraction of hematite tailings, the mass fraction fly ash, forming pressure and sintering temperature on the sintering efficiency, mechanical properties, and other basic properties of RBB. The optimum materials and process parameters for manufacturing RBB were obtained. These results indicated that hematite tailings can effectively improve the sintering efficiency of RBB under microwave radiation. The mass fraction of tailings is the most important factor affecting the sintering efficiency, and sintering efficiency increases with an increase in the tailings mass fraction. These four factors have a significant impact on the mechanical properties of RBB. Higher sintering temperature and forming pressure improve the compressive strength, which will decrease with the increasing mass fraction of tailings and fly ash. The average compressive strength of the samples in No. 9 group was the highest, reaching 34.44 MPa. The No. 9 group (30 wt% hematite tailings, 4 wt% fly ash, 66 wt% construction spoil, 20 MPa forming pressure and 800 °C sintering temperature) is considered the best material and process parameter combination for manufacturing RBB with microwave technology due to its highest strength, high solid waste content, good sintering efficiency and performance.