Microwave Fast Sintering Production of Sustainable Lightweight Aggregates with Agroindustrial Waste

Abstract

This study aims at analyzing the influence of agroindustrial waste incorporation into red ceramics to produce lightweight aggregates sintered in a microwave oven. Sustainable artificial lightweight aggregates are sought out, particularly in the context of a circular economy. At first, red clay, sugarcane bagasse ash, and rice husk ash were characterized by means of X-ray fluorescence, loss on ignition, X-ray diffraction, grain sizing, true specific mass, and thermal gravimetric analysis. Three different ceramic masses were extruded: the reference, with no added waste; clay with 40% sugarcane bagasse ash; and clay with 40% rice husk ash. All samples were presintered in a conventional oven at 600°C for 60 min. Conventional sintering occurred at temperatures between 700°C and 1,100°C at a 10°C/min heating rate. Microwave sintering occurred for 5, 10, and 15 min, at a 50°C/min heating rate in a chamber coated with silicon carbide (susceptor). After sintering, specimens were characterized regarding linear shrinkage, water absorption, apparent porosity, apparent specific mass, X-ray diffraction, and scanning electron microscopy. Results showed that microwave sintering increased compressive strength, decreased water absorption, and provided microstructure refinement. The addition of waste reduced specimens’ specific mass after sintering. Sugarcane bagasse ash–added red ceramic specimens sintered in a microwave oven yielded values close to those of Brazilian expanded clay, thus appearing as an alternative for production of more sustainable lightweight aggregates, in view of greater agroindustrial waste utilization and lower energetic consumption during the sintering process.