Self Regulating Temperature Mechanism And Experimental Study Of Bridge Phase Change Material

Since the 13th Five-Year Plan,China's highway construction is still in a period of rapid development.Concrete box structure has been widely used for its advantages of fast construction,high structural stiffness and smooth driving.It is the preferred structural form of urban expressway and expressway bridges.However,because of the poor thermal conductivity of concrete,concrete box girder structure is prone to form large temperature gradient stress under the action of temperature loads such as sunshine radiation,air convection and thermal radiation,which seriously affects the safety and durability of bridge operation.This paper breaks the conventional idea of temperature crack control and proposes a new method to improve the temperature field distribution of box girder structure by using phase change materials.From the mechanism,it is verified that the thermal storage characteristics of phase change materials can reduce the process of heat absorption and self-regulating temperature of concrete.Firstly,based on the theory of phase change heat storage,the expression form of heat storage stage of composite phase change materials is analyzed,and the calculation method of self-regulating mechanism of phase change heat storage concrete under ideal adiabatic conditions is deduced by combining with the theory of heat absorption temperature rise of concrete structure.It is verified from the mechanism that the self-regulating effect of concrete can be reduced by using the thermal storage characteristics of phase change materials.Secondly,the phase change characteristics,thermal stability,chemical compatibility,economy and other aspects of phase change materials were classified and screened.Two kinds of phase change raw materials,LA and PEG,were selected.According to the preparation and properties of the composite phase change materials,the porous adsorption and sol-gel method were used to prepare them.Lauric acid/expanded graphite?LA/EG-CPCMs?and polyethylene glycol/silica sol?PEG/SiO₂-CPCMs?are two kinds of composite shape-stable phase change materials.The adsorption effect,compatibility,DSC characteristics and thermal cycle stability of these two materials are tested by SEM scanning electron microscopy,infrared spectroscopy,comprehensive thermal analyzer and blast dryer.Then,LA/EG-CPCMs and PEG/SiO₂-CPCMs were directly added into C50 concrete by absolute volume method,and seven mix ratios of ordinary concrete,LA/EG and PEG/SiO₂ phase change concrete with 5%¹5% volume content were designed respectively.During pouring,the slump and forming density of concrete were tested.The cubic specimens after demoulding were tested at room temperature for 3 days,7 days,28 days and 28 days at high temperature.Compressive strength test and comparative analysis of the test results;the thermal conductivity of each group of concrete was measured by intelligent plate thermal conductivity tester,and the specific heat capacity of PEG/SiO₂ phase change concrete was calculated.The indoor cooling test of PEG/SiO₂ phase change concrete was carried out.Finally,based on the experimental data and relying on the Lao Tuanpo No.1 Bridge,the temperature-stress coupling model of multi-scale Beam-Solid element is established by using ANSYS finite element software.The temperature and stress fields of the mid-span section in the period of 5:00 to 18:00 are analyzed and calculated,the results show that the maximum temperature drop range of phase change concrete on bridge temperature field distribution is about 2 C,and the maximum stress drop range is 19.01%..