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We report on the novel application of quasi-elastic neutron spectroscopy to study the reaction mechanism between tricalcium silicate and water. The in situ data taken at a series of fixed temperatures varying from 10 to 40 °C show that the amount of free water in the system remains relatively constant for an initial period, ranging from 1 h at 40 °C to 16 h at 10 °C. This is followed by an exponential decrease in the amount of free water that crosses over to a diffusion-limited behavior for later times. Fits to an Avrami type behavior allow us to determine an activation energy for the hydration process on the order of 30 kJ/mol.

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In internal curing, pre-wetted lightweight aggregates (LWA) serve as internal reservoirs to supply the extra water needed by the cementitious and pozzolanic components of the concrete during their hydration processes. Due to their porous nature and reasonably high absorption capacity, the LWA can also be filled with other materials, such as phase change materials (PCMs). In this paper, three potential applications of PCM-filled LWA in concrete technology are presented. In addition to the previously explored application of increasing the energy storage capacity of concrete in residential and commercial construction by using a PCM with a transition temperature near room temperature, applications for higher and lower temperature PCMs also exist. In the former case, a PCM can be used to reduce the temperature rise (and subsequent rate of temperature decrease) of a large concrete section during (semi)adiabatic curing, to minimize thermal cracking, etc. In the latter case, a PCM can perhaps reduce the number or intensity of freeze/thaw cycles experienced by a bridge deck or other concrete exposed to a winter environment. In this paper, these latter two applications are preliminarily explored from both experimental and modeling viewpoints.

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