Microwave-assisted heating of cementitious materials: Relative dielectric properties, mechanical property, and experimental and numerical heat transfer characteristics

The characteristics of cementitious materials subjected to microwave energy are presented. First, the dielectric properties of cementitious materials during a 24-hour first-hydration period were measured at a frequency of 2.45 GHz. Second, the characteristics of hardened cement paste as subjected to heating for a short period (without loss of moisture) by microwave energy with a single-mode rectangular wave guide, with specific attention to temperature rise, compressive strength, and the use of the maturity function was investigated experimentally and theoretically. The obtained results show that dielectric properties are relatively high and remain constant during the dormant period. After this period, the hydration reaction resumes and dielectric properties decrease rapidly. With the use of microwave heating, early-age strength increases during the first 14 days; however, during the next 14 days, early-age strength decreases slightly, until it reaches its lowest at the 28-day mark. The temperature rise as actually recorded at the center of the sample during microwave heating in our experiment consistently agreed with figures calculated by a mathematical model.