Effect of microwave curing on metakaolin-quartz-based geopolymer bricks

Abstract

In this paper, the effect of microwave curing on the mechanical strength and microstructure of metakaolin geopolymers with quartz sand was investigated. Depending on the heat transfer from the surface to the core of the specimens, conventional heating is non-uniform and lasts longer. In contrast, volumetric heating generated by microwave heating leads to faster strength development. Firstly, the impact of microwave power on geopolymers was investigated. Then, the effects of various curing methods, including only microwave curing, traditional curing, and/or microwave curing, on the strength development of geopolymers were compared. This research proposed a mixed curing process for metakaolin-quartz geopolymers: curing in oven at 80℃ for 7 h and then 160 W microwave radiation for 12 min and the bending strength was 16.5 MPa. It was found that extending the curing time has a positive effect on geopolymer bending strength under all curing conditions. When microwave curing with high power was used directly, it was not conducive to the dissolution stage of geopolymerization, resulting in incomplete reaction. After being cured in oven at 80℃ for 7 h and then cured in the microwave 160 W for 12 min, the bending strength of the geopolymer pastes exhibited the same bending strength as that of the specimens cured at 80℃ for 24 h; however the time was shortened by one third. In addition, mercury intrusion porosimetry(MIP) showed that compared to conventional curing, microwave curing led to specimens with high porosity. The pore size range was divided into two parts: 0.05–0.1 μm and near 20 μm.