Direct incorporation of paraffin wax as phase change material into mass concrete for temperature control:mechanical and thermal properties

Taking advantage of heat absorbing and releasing capability of phase change material (PCM), Paraffin wax-based concrete was prepared to assess its automatic temperature control performance. The mechanical properties of PCM concrete with eight different Paraffin wax contents were tested by the cube compression test and four-point bending test. The more Paraffin wax incorporated, the greater loss of the compressive strength and bending strength. Based on the mechanical results, four contents of Paraffin wax were chosen for studying PCM concrete's thermal properties, including thermal conductivity, thermal diffusivity, specific heat capacity, thermal expansion coefficient and adiabatic temperature rise. When the Paraffin wax content increases from 10% to 20%, the thermal conductivity and the thermal diffusivity decrease from 7.31 kJ/(m·h·°C) to 7.10 kJ/(m·h·°C) and from 3.03×10^-3 m²/h to 2.44×10^-3 m²/h, respectively. Meanwhile the specific heat capacity and thermal expansion coefficient rise from 5.38×10^-1 kJ/(kg·°C) to 5.76×10^-1 kJ/(kg·°C) and from 9.63×10^-6/°C to 14.02×10^-6/°C, respectively. The adiabatic temperature rise is found to decrease with an increasing Paraffin wax content. Considering both the mechanical and thermal properties, 15% of Paraffin wax was elected for the mass concrete model test, and the model test results confirm the effect of Paraffin wax in automatic mass concrete temperature control.