Compressive strength development and hydration of cement–fly ash composite treated with microwave irradiation

In order to investigate the relations between the microstructure and compressive strength of cement–fly ash-based material treated with microwave irradiation, the specimens microwave irradiated for 45 min was compared against that cured using (a) normal curing at 20 ± 1 °C, > 90% RH, (b) steam curing at 40 °C for 10 h and (c) steam curing at 80 °C for 4 h by performing compressive strength, X-ray diffraction, thermogravimetry–differential scanning calorimetry, scanning electron microscope–energy-dispersive spectroscopy and mercury intrusion porosimetry. The results show that although the early hydration degree of the microwave-cured composite is lower than that under steam curing, the microwave can significantly reduce the porosity, especially the pores less than 100 nm, to improve the early strength of mortar. The hydration degree of composite binder is similar to that under steam curing, and the porosity (especially the pores larger than 50 nm) of mortar under microwave curing is still the lowest, which makes compressive strength of mortar under microwave curing is the highest at later age.