Study On Temperature Control Mechanism And Performance Of Paraffin Phase Change Concrete

Mass concrete has been widely used in large foundation,dam,pier,port,building component and other infrastructures.In the process of solidification and maintenance of mass concrete,hydration reaction of cement produces a large amount of hydration heat in a short time,resulting in temperature cracks.In the construction period,due to the formation of large temperature difference between inside and outside of concrete,tensile stress occurs,leading to concrete cracking.Phase change temperature control concrete provides a new way to solve the temperature cracks of mass concrete,which has received extensive attention in recent years,but its temperature control mechanism and performance have not been well understood.In this paper,paraffin was used as phase change material(PCM)to prepare paraffin phase change concrete with addition contents of 0%,10%,20%,30%,40%,50%,60% and 70% respectively.The mechanical properties of paraffin phase change concrete,such as cubic compressive strength,axial compressive strength,elastic modulus and flexural strength,were studied by using the MTS universal testing machine.By analyzing the mechanical properties,contents of 0%,10%,15% and 20% were selected for studying the thermal properties of PCM concrete.Thermal properties,such as thermal conductivity,thermal conductivity,specific heat,linear expansion coefficient and adiabatic temperature rise were tested by using the thermophysical parameter tester.Based on the results of thermomechanical properties of phase change concrete with different paraffin content.By combining the mechanical properties and thermal properties,content of 15% was elected as the best.PCM concrete with 15% of Paraffin added and ordinary concrete without PCM were prepared for studying the effect of PCM on the mechanical properties of concrete at different ages.The mechanical properties of concrete at different ages,such as cubic compressive strength,axial compressive strength,elastic modulus and splitting tensile strength,were tested by using the MTS universal testing machine.The mechanical properties of PCM concrete and ordinary concrete increased with the increasing of age.The increasing rate of the mechanical properties for PCM concrete was slower than the ordinary concrete.The relationship between the mechanical properties and the age of the PCM concrete was fitted by using the empirical function.The changes of mechanical properties of PCM concrete could be precisesly estimated by the empirical function.The temperature control model test of paraffin phase change concrete was carried out using large-scale concrete specimens.The temperatuere distribution and changes with age were monitored and analyzed.Adding paraffin reduced the peak value of the internal temperature of the PCM concrete,by 6.61% compared to the ordinary concrete.The rising of the temperature in PCM concrete was slower than in the ordinary.The rate of temperature drop was obviously smaller than that of temperature drop of the ordinary concrete.The addition of paraffin also delayed the occurrence of the peak value of temperature and reduced the temperature gradient.It is confirmed that the temperature change of concrete can be controlled by incorporating paraffin,which can reduced the risk of temperature induced crack.