Development And Performance Study Of Low Temperature Phase Change Material For Anti-freezing Cement Pavement

In some areas of China,freezing phenomenon often occurs on the road surface in winter,and the friction coefficient of the road surface decreases,which seriously affects road safety.In view of this phenomenon,this paper puts forward adding phase change materials in cement concrete pavement to adjust temperature and preventing pavement frozen.This paper summarizes the characteristics of various types of phase change materials and the climatic characteristics of pavement frozen areas in China.The suitable range of anti-freezing phase change materials is determined as organic solid-liquid phase change materials with phase change temperature of 0-5 ℃.The common phase change materials such as organic polyols,fatty acids and alkanes were screened from three aspects of phase change performance,thermal stability and long-term use stability.Finally,the initial temperature of phase transformation is 2.3 ℃,the latent heat of phase transformation is 227.9 J/g,the initial temperature of phase transformation is 2.5 ℃,and the octanoic-decanoic acid eutectic with latent heat of phase transformation is 104 J/g is chosen as the main phase change material for further research.Expanded graphite was chosen as the carrier of liquid phase change material from the aspects of pore size and physical compatibility.Phase change material was encapsulated by physical adsorption.The adsorption rates of tetradecane and octanoic-decanoic acid eutectic were 90.71% and 87.69%,respectively.Tetradecane-expanded graphite was chosen as the composite phase change material for the final study from the point of view of higher enthalpy of phase change.The effect of temperature and pressure on the adsorption rate of Tetradecane-Expanded Graphite was studied.It was determined that temperature had little effect on the adsorption rate when the phase change material was liquid.The final adsorption mode was water bath at 60 C and atmospheric pressure.Tetradecane and expanded graphite are physically adsorbed in the composite phase change materials.The initial temperature of phase change is 4.1 C,and the enthalpy of phase change is 198.9J/g.The adsorption stability is good.The influence of mixing mode and content of composite phase change materials on the strength of mortar was studied.The lower strength of PCM weakens the skeleton of cement mortar.The 28-day flexural strength of PCM equivalent volume replacement sand and PCM direct admixture specimens are 61.2% and 68.8% of the standard specimens respectively,and the compressive strength is 42% and 56% of the standard specimens,respectively.The optimum mixing mode of PCM composite is determined to be direct admixture.In addition,the strength of cement mortar decreases with the increase of phase change material content.Because expanded graphite has certain toughness,the effect of composite phase change material on flexural strength is less than that of compressive strength.Multiple phase change cycles have little effect on mortar strength.After 25 phase change cycles,the flexural strength of the specimens decreases by 0.05 MPa,while the compressive strength increases by 1.93 MPa,which can ensure the long-term service strength of phase change cement mortar.By improving the design strength grade,phase-change concrete with flexural strength of 4.6 MPa was poured to meet the requirements of medium traffic load grade.Through the temperature regulation performance test of concrete slab and simulated freezing test,it is determined that phase change concrete has certain temperature regulation ability.The addition of composite phase change materials can reduce the cooling rate of concrete,delay the time of concrete reaching 0 ℃,and have a certain anti-freezing effect.