Innovative hybrid curing method for accelerating the strength of high-performance cement paste using microwave heating coupling with low-pressure processing Natt Makul Building Technology Program, Faculty of Industrial Technology, Phranakhon Rajabhat University, 3 Moo 6 Changwattane Road, Anusaowari Sub District, Bang Khen District, Bangkok, Thailand highlights  A high-performance cement paste was manufactured in accelerated conditions.  Accelerated conditions using microwave-assisted low-pressure processing (MW-LP).  MW-LP can process the paste almost a day faster than water curing.  MW-LP improved the paste’s mechanical properties.  MW-LP can significantly reduce the production time in the manufacture. article info Article history: Received 19 November 2015 Received in revised form 11 December 2015 Accepted 12 December 2015 Available online 17 December 2015 Keywords: Cementitious Material Microwave Processing Pressure Properties abstract In this study, cementitious materials (here defined as a high-performance cement paste produced by mixing Type 1 Portland cement with an effective amount of water) were manufactured in accelerated conditions using microwave-assisted low-pressure processing (i.e., accelerated curing). Based on the con- cept that the hydration reaction of cementitious materials comprises three main periods—a dormant per- iod, an acceleration period, and a deceleration period—process parameters were determined for the most effective period (acceleration) for producing paste via microwave processing. The time-dependent dielec- tric characteristics of the cementitious paste and the water–cement ratio by mass influenced the temper- ature, i.e., caused it to increase, and the properties of the microwave-cured paste. The results show that the use of microwave-assisted low-pressure processing improved the paste’s mechanical properties. Specifically, microwave energy can accelerate compressive strength development 15 min after the com- pletion of microwave-assisted low-pressure curing. With a delay time of 60 min, microwave energy can process the paste almost a day faster than water curing, which is the standard method for curing paste. The use of microwave energy, therefore, can significantly reduce the required energy and production time in the manufacture of high-performance paste. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Currently, microwave (MW) processing is employed in indus- trial manufacturing processes [1–4] for various materials, such as foodstuffs [5–7], wood products [8,9], ceramics [10–12], biological organisms [13,14], and chemical reactions [15,16]. MW processing involves volumetric (bulk) rapid heating and dipole interactions in dielectric materials, including polar molecules. The interactions instantaneously convert electromagnetic (EM) radiation in the dielectric materials to thermal energy [17,18]. Theoretically, MW energy can be applied to cementitious (CM)- based materials. Water, which is a main component that reacts with cement particles in a hydration reaction, has a dielectric per- mittivity at room temperature that is higher than the dielectric permittivity of concrete’s other constituents. Consequently, when an electric field is penetrated by concrete components, energy is transferred from the electromagnetic (electric) field to the water’s molecular bonds (which comprise MW-irradiated materials) via friction among the positive and negative ions in compressed and uncompressed conditions. As a result, any heat that is generated is dissipated and transferred within the concrete to be processed, and the temperature of the concrete is elevated. Thus, an acceler- ated hydration reaction occurs. Instantaneously, free water http://dx.doi.org/10.1016/j.conbuildmat.2015.12.084 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved. E-mail address: shinomomo7@gmail.com Construction and Building Materials 105 (2016) 245–252 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat