Preparation Of Mesoporous Silicon-based Phase Change Materials And Its Application In Temperature Control Of Concrete Piers

As an important part of transportation,how to prevent temperature cracks during pouring and maintenance is a difficult problem for bridges.Piers belong to the category of mass concrete,and mass concrete will produce a lot of hydration heat in the early stage of pouring,and then produce temperature stress and cracks,and shorten its service life.The appearance of phase change concrete technology has solved the above problems to a certain extent.However,phase change concrete is facing many problems,such as easy leakage,easy corrosion,low compressive strength and short service life.Therefore,the preparation of shape-stabilized phase change materials suitable for mass concrete with suitable temperature range,high enthalpy of phase change,good thermal stability and thermal conductivity,not easy to leak and not affecting its strength has become the top priority.In order to solve the problems of easy leakage and poor thermal conductivity of phase change materials,myristic acid(MA)with suitable phase change temperature,high phase change enthalpy and good thermal stability was selected as core material,and wrinkled mesoporous silica nanoparticle(WMSN)with high strength,high surface area and strong adsorptive force was used as matrix.The MA/WMSN with good properties was prepared by vacuum impregnation method,and its performance characterization tests was carried out.The results showed that the maximum loading of MA/WMSN was 65 wt.%,the phase transition temperature ranged from 38 ℃ to 58 ℃,and the melting and crystallization enthalpies were 92 kJ/kg and 86 kJ/kg,respectively.Thermogravimetric analysis showed that it possessed of good thermal stability and no loss of weight below 180 ℃.It is suitable for the preparation of phase change concrete.The simulation analysis of ordinary concrete pier(OP)model and shape-stabilized phase change concrete pier(PCP)model was carried out by using ANSYS software.The temperature distribution cloud diagram and the temperaturetime curves of each node were obtained.The control of internal temperature field of concrete by MA/WMSN was analyzed,and the temperature control effect was evaluated.The addition of MA/WMSN was 5 %.The analsis results showed that shape-stabilized phase change materials would not disturb the internal temperature distribution of the piers during pouring and maintenance period,when the internal temperature of pier rose to its phase change temperature range,MA/WMSN begain to absorb the heat of hydration,which reduced the maximum temperature of concrete nodes by about 2~10 ℃.According to the temperature-time curves of each node,the shape-stabilized phase change materials could reduce the heating rate and cooling rate of the concrete,as well as lowering the maximum temperature of the concrete,delaying rise to the maximum temperature and reducing temperature difference.Moreover,it could effectively prevent temperature cracks in concrete bridges.