Study on the physical mechanical properties and freeze-thaw resistance of artificial phase change aggregates

Abstract

Phase change material (PCM) is often mixed into concrete as artificial aggregate. Developing artificial phase change aggregates (APCA) with excellent freeze–thaw resistance is a key for the high-performance phase change concrete. In this paper, the APCA with controllable particle size, large apparent density, high strength, and well frost resistance was obtained by using a disc granulator. The microencapsulated phase change material (MPCM) was completely dispersed in the aggregates. The cement shell further protects the MPCM from leakage. The enthalpy, specific heat, microstructure, and product composition of APCA were measured and analyzed by differential scanning calorimeter, scanning electron microscope (SEM), and X-ray diffraction (XRD). The effects of the amount of MPCM on the strength and freeze–thaw resistance of the APCA were analyzed through single particle compressive strength test and freeze–thaw cycle test. The results indicate that the artificial aggregates with more MPCM have higher enthalpy. The MPCM can absorb the cement hydration heat, reduce the cement hydration rate, and then slow down the development of early strength of the artificial aggregates. With the increasing content of the MPCM, the apparent density and the strength of the APCA decrease, and the water absorption increases. At the same time, a large number of MPCM are added to increase the pore number of the APCA, which promotes the carbonation to develop inside the aggregates and generate a large number of calcite crystals, reducing the strength reduction caused by the increase of the pores. When the content of the MPCM is 10–30% of the mass of cement, the APCA have high freeze–thaw resistance. The maximum strength reached 66% of the 28 d strength after 200 freeze–thaw cycles, which is helpful to improve the freeze–thaw resistance of the phase change concrete.