An experimental study of microwave drying under low pressure to accelerate the curing of Portland cement pastes using a combined unsymmetrical double-fed microwave and vacuum system

An experimental study was conducted on the use of microwave-assisted drying (MD) to accelerate the curing of Portland cement pastes (CM) under a low pressure by using a combined unsymmetrical double-fed microwave and vacuum system. The effects of microwave power (800 and 1600 W) and pressure level (30 and 50 kPa) on the temperature, moisture content, and gained compressive strength of CM were examined. The CM specimens were prepared with standard CM at water-cement ratios (w/c) by mass (0.38 (38% moisture content), 0.45 (45% moisture content), and 0.75 (75% moisture content)) before applying MD. In the experiments, when the CM specimens were dried using MD, the increases in was faster because of the high level of humidity. As it became less humid, the specimens could absorb less microwave energy and eventually remained at a stable temperature. A low pressure level affected the moisture content in CM, as a lower pressure resulted in a lower boiling point. The moisture in CM evaporated quickly, and the moisture content decreased faster than the high pressure did. Further, the w/c affected the temperature because a low w/c caused the CM temperature to be higher than that observed for a high w/c. Finally, the CM specimen that was dried using a microwave at 50 kPa and a 0.45-w/c attained the highest compressive strength.