Impacts of microwave on hydration evolution of Portland cement in the perspective of composition and microstructure of hydrates

• Effects of microwave curing on composition of hydrates were analyzed. • Effects of microwave on microstructure of hydrates were studies. • Three curing regimes, including microwave, normal, steam, were compared. Effects of microwave curing on the hydration evolution of Portland cement were analyzed, compared with normal curing and steam curing. Hydration products, microstructure of cement paste, and the underlying mechanism were investigated. Results showed that the hydration degree of Portland cement under microwave curing for 45-min radiation was higher than that under steam curing at 80 °C for 4 h and normal curing for 12 h. Steam curing promoted the hydration of C 3 S, and microwave curing accelerated the hydration of C 2 S. The main hydration products of C 3 A under normal, steam, and microwave curing, were AFt, katoite, and AFm, respectively. Microwave curing reduced the content of portlandite (CH), decreased the normal size of the face (0 0 1) of CH, and increased the preferred orientation of CH. In comparison with steam curing, microwave curing generated granular C–S–H gel with a high Ca/Si atom ratio in hydrated Portland cement.