Compressive Strength and Microstructure of Microwave-Cured Waste Brick Powder-Based Geopolymer Mortars

In this study, the compressive strength, microstructure and energy consumption of conventional oven- and microwave-cured waste brick powder-based geopolymers were investigated. For this purpose, the bricks that emerged as defective products during the factory production process were broken, ground, and used as aluminosilicate source. Samples with varying water contents were produced to examine the effect of the water/binder ratio. An alkali solution prepared with sodium silicate and sodium hydroxide was used as activator, and natural river sand was utilized as aggregate. The mixtures were cured in a household microwave oven at 300-W power level for 30, 45 and 60 min. Additionally, oven-cured specimen prepared at 90 degrees C for 1, 3 and 5 days was used for the sake of comparison. Samples with different water contents (ranging from 0.35 to 0.60) were produced to examine the effect of the water/binder ratio. The highest compressive strengths obtained in conventional and microwave curing mortars were 32 MPa and 36 MPa, respectively. The optimum water/binder ratio for oven and microwave curing was 0.4 regarding compressive strength, and lower rates reduced workability and strength. SEM images demonstrated that the microwave-cured paste had a more homogeneous structure and contained fewer cracks and pores than that of the oven-cured specimen at the same water/binder ratio. The results indicated that microwave-cured waste brick powder-based geopolymers with appropriate mixing ratios and curing regimes have higher compressive strengths and more homogeneous microstructures than their conventionally cured counterparts, with 94% energy savings.