A novel rapid microwave-thermal process for accelerated curing of concrete: Prototype design, optimal process and experimental investigations

In this work, a mobile microwave (MW)-assisted curing unit for the accelerated curing of concrete work piece is designed based on coupled electromagnetic (MW)-thermal analysis. The design of this unit is described together with experimental investigations into the heating characteristics of concrete work piece subjected to the MW-accelerated curing process. Mathematical models are applied to design a horn-shaped MW cavity and as a basis for constructing a stationary and a moving MW-accelerated curing unit that uses MW energy at an operating frequency of 2.45 +/- 0.05 GHz and at powers of 400 W and 800 W. The experiments included the effects of MW curing on the temperature evolution, moisture content variation, and compressive strength development properties of the concrete. Also, the concrete workpiece was compared to water-cured conventional concretes and air-cured conventional concretes on the basis of these properties. Based on the concept of antenna, a rectangular horn-shaped cavity of. 246.7 mm wide x 333.68 mm long is designed showing a uniform thermal distribution for concrete curing. From the experiments, it was found that the application period for curing using the mobile MW-curing unit was considerably shorter than for conventional, curing methods. The appropriate pre-heating interval is 30 min, and MW energizing for 15 min/time and a paused duration of 60 min produces maximum compressive strength. However, the time needed for curing was considerable. When concrete was heated using MW energy for more than 90 min at over 80 degrees C, the effect was a continuous decrease in compressive strength. Further, at early age, the compressive strength development of the concrete work piece subjected to MW curing was greater than that achieved by air curing or water wet-curing. (C) 2016 Elsevier Ltd. All rights reserved.