Microstructures and mechanical properties of Portland cement at an early age when subjected to microwave accelerated-curing

This paper presents an investigation of microstructural development and mechanical properties of cement pastes when subjected to microwave energy. The microstructures of hydration products of cement pastes were examined by SEM/EDX and XRD. Compressive strengths of the cured samples were also measured. The results obtained show that the temperature increases monotonically during the microwave curing process. Significantly, the rate of temperature rise in the paste with a lower water-to-cement ratio was quite high. Calcium silicate hydrate (Ca₃SiO₅), calcium hydroxide (Ca(OH)₂) and xenotile (Ca₆(SiO₃)₆(H₂O)) were identified by XRD in the cured samples. When cured at elevated temperatures, pastes develop strength quite rapidly. At an age of 8 hours after microwave curing at 100 °C, 0.25-w/c paste attained a strength of 25.1 MPa (240% higher than the lime-saturated water-cured paste); at 24 hours curing the strength was 68.3 MPa, and at 7 and 28 days the strength values were 74.9 and 75.2 MPa, respectively.