Microstructure and mechanical properties of phase change cloud concrete stone cementitious composites

In this study, a novel kind of phase-change cementitious composites with cloud concrete stone (CCS) as aggregate were prepared and studied. The CCS was synthesized with fly ash, slag, and other construction waste through water heat and autoclaving. The phase-change paraffin was absorbed into the CCS using the vacuum impreg-nation technique, and then the epoxy resin combined with cement powder was applied to the aggregate surface to prevent the leakage of phase-change materials (PCMs). The composite aggregate with phase change function was, thus, fabricated. A series of experiments were carried out to study and evaluate the molecular structure, physical phase, and phase transition temperature of encapsulated composite aggregate with the means of Fourier infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The PCM-cement composites were prepared by replacing coarse aggregates with the composite aggregate in proportions of 25%, 50%, 75%, and 100% in volume. To explore the strength degradation in view of the microscopic perspective, scanning electron microscopy (SEM), XRD, and Image-Pro-Plus (IPP) were used. The experimental results revealed that the effect of the micropores of CCS on the melting temperature of the phase-change ag-gregates (24.84 degrees C) is higher than that of the paraffin (22.91 degrees C). The mechanical experiments results demon-strated that the compressive strength and splitting strength losses in the PCM-cement composite with replacement ratios of 75% were 24% and 39%, respectively. The XRD results revealed that with the incorpo-ration of PCM, the calcium silicate hydrate (C-S-H) in the hydration products decreased and the Ca/Si value in C-S-H decreased from 9.05 to 2.13, which is one of the reasons for the strength decline of the PCM-cement composites. The cracks in the interfacial transition zone between the aggregate and matrix became large with increasing admixture, and the pore characteristics gradually became more apparent. The strength of the PCM-cement composite decreased with the increase in the average porosity, pore size, and perimeter of the matrix material.