Development of compressive strength of cement paste under accelerated curing by using a continuous microwave thermal processor

A high rate of strength development in mortar and concrete can benefit a number of important operations in the construction industry, such as concrete precasting, pavement repair and concrete decontamination. In this study, the acceleration of cement paste curing with microwave energy by using continuous belt drier is investigated. The microwave power was generated by means of 14 compressed air-cooled magnetrons of 800 W each for a maximum of 11.2 kW. The power setting could be adjusted individually in 800 W steps. This study included the heat transfer analysis taking place during the curing of cement paste with microwave energy and the compressive strength development of cement paste. The tested results were compared with those of the conventional cement paste that were cured in water and air. Internal structures of cement paste were investigated for analyzing the mechanical properties after curing. The variables emphasized on the thermal influences from using microwave energy, properties of cement paste, and time of curing. The test results showed that microwave energy accelerated the early-aged compressive strength of cement paste and not affect upon later-aged strength; for instance, the growth rate of compressive strength of 30 min-cured and water-to-cement ratio of 0.4 microwave-cured mortar after 3 days was 103% while 101 and 95% for specimens at the ages of 7 and 28 days, respectively. Furthermore, microwave curing can be saved profitably on energy consumption and reduced time of curing.