Study On Temperature Control And Crack Resistance Of Early Age Concrete With Composite Phase Change Materials

The temperature crack of early age concrete is one of the important factors that affect the service life of concrete structure.Temperature cracks provide the possibility for harmful media to attack the concrete,accelerating the deterioration process and affecting the safety of the structure in severe cases.Since the phase change material(PCM)can stably complete the process of heat absorption and heat release at a fixed temperature,this research expects to utilize the PCM to make the concrete itself have the ability to control the temperature.PCMs are used to slow down the rate of temperature rise,and reduce the hydration temperature to control the temperature of the concrete within a certain range,thereby alleviating the risk of temperature cracking.First,the thesis selected four different types of PCMs.By studying the thermal properties of different phase change materials,it was determined that paraffin is most suitable for temperature control of concrete at early age.The PCM was adsorbed by porous materials.The results showed that the adsorption rate of ceramsite to paraffin reached 73.5 % The surface of the paraffin/ceramsite PCM could not be treated in the study,it was observed that there was no obviously leakage problem in the paraffin/ceramsite PCM.The stability and thermal properties of paraffin/ceramsite PCM have been explored,it was proved to have good stability and compatibility with cement-based materials.Then,the paraffin/ceramsite PCM was mixed into the concrete as a raw material,and study the cracking risk of the paraffin/ceramsite phase change concrete at early age.The temperature control performance and early age mechanical properties of the phase change concrete were mainly studied in this research.The results of adiabatic conditions and semi-adiabatic conditions show that PCM can effectively control the early hydration temperature of concrete,and the heat absorption performance increases linearly with the increase of the amount of PCMs.Since the strength of concrete decreases with the increase of paraffin/ceramsite PCM,a comprehensive assessment of the early age cracking tendency of phase change concrete is needed.In the study,the uniaxial experiment was used to study the deformation and stress development of phase change concrete at early age.The research results found that,the temperature expansion of phase change concrete increased,and the temperature shrinkage value decreased compared with ordinary concrete.The growth rate of thermal stress in phase change concrete decreases with the amount of PCMs.By comparing performance parameters of early age concrete,it was found that the cracking sensitivity of paraffin/ceramsite phase change concrete is lower than ordinary concrete.Comparing with different macro encapsulation methods,it was found that paraffin/ceramsite phase change concrete is more suitable for controlling the temperature cracks of concrete.Finally,the research was based on finite element software(COMSOL Multiphysics)to study the effect of phase change temperature,enthalpy and transition interval on the temperature control.From the perspective of economy,it hopes that PCM can effectively control the heat of hydration Through comprehensive analysis of various factors,the basis for optimal selection of PCMs is proposed,which provides a certain reference for improving the utilization rate of phase change materials.