Preparation And Cooling Mechanism Of Composite Phase Change Heat Storage Asphalt Pavement Materials

The asphalt pavement in hot climates easily causes heat stability diseases, such rutting, translation, and so on. At the same time, it not only pollutes environment but also aggregates the urban heat island effect, that is because it releases VOCs and releasing to rise environment temperature and worsen human being reside environment at high temperature. The research supported by the National Natural Science Fund project of China（Grant No. 51178491）. Based on phase change heat storage theory, composite shape-stabilized phase change materials（CPCM） were prepared, that were applicable to asphalt pavement engineering, and asphalt pavement materials with phase change heat storage were prepared by CPCM replaced fine aggregates, which could initiative to cooling the temperature of asphalt pavement in hot climates.Firstly, combined selection rules of phase change heat storage materials（PCM） and technical requirements of asphalt pavement engineering materials, the technical properties of PCM applied to asphalt pavement engineering were anlysised; the structures and characterizations of normal and low temperature solid-liquid PCM were investigated to select out polyethylene glycol（PEG） as PCM, that has suitable phase chagne temperature, high latent heat, excellent thermostability and stability of phase change cycles, good crystallinity and chemical stability. Step cooling curve and DSC（differential scanning calorimetry） were used for the phase change behavior of binary PEG systems, results showed that the phase change temperature of binary PEG systems distributed a certain temperature range and was adjusted to adapt to different temperature of the practical applications. The influence of PEG on the performance of asphalt and asphalt mixture is studied after PEG was directly doped in asphalt and asphalt mixture. The results showed that PEG direct doping phase change asphalts and its asphalt mixtures have lower temperature susceptibility, 20% PEG2000 of direct doping phase change asphalt could cooling about 10 ℃, and 0.6%,0.8% PEG2000 of direct doping phase change asphalt mixtures could respectively lower temperature actively 1.3℃and 1.4℃. In addition, the action mechanism of polyethylene glycol and asphalt was physical action. But the dosage of PEG2000 was directly influenced the technical performances of direct doping phase change asphalts and its asphalt mixtures, so the dosage of PEG2000 should not be exorbitant and the cooling was limited.Secondly, PEG/SiO₂ CPCM were prepared by coagulant-assisted sol-gel method and temperature-assisted sol-gel method, the influences of two kinds methods on heat storage properties of CPCM were compared, results indicated that Ca²⁺ and PEG formed coordination compounds and the parts PEG have lossed phase change heat storage function, enthaly loss rate of Ca-CPCM was higher. Temperature-assisted sol-gel method was adopted to prepare CPCM in this paper. DSC, XRD（X-ray diffraction）, FT-IR（Fourier Transform Infrared Spectoscopy）, TG（Thermogravimetry）, POM（Polarizingmicroscope） and SEM（scanning electron microscope） et al analysis methods were employed to investigate heat storage property, store/release heat efficiency, thermophysical properties, thermostability, stability of phase change cycling, crystallinity, phase change behaviour and surface topography of CPCM, the influence of PEG with different molecular weight and different mass fraction acted on the properties of CPCM. Phase change onset temperature of PEG/SiO₂ CPCM were 39.5℃⁴9.4℃, melting enthaly and crystallization enthalpy were respectively 98.1J/g¹08.1J/g, 95.2J/g¹08.9J/g. With the increase of PEG molecular weight, phase change onset temperature of CPCM rised, and latent heat of CPCM increased first and then slowly. Phase change onset temperature of 30%⁸0% PEG/SiO₂ CPCM were 37.0℃³9.8℃, melting enthaly and crystallization enthalpy were respectively 27.0J/g ¹18.3J/g, 27.2J/g ¹18.2J/g; phase change onset temperature and latent heat of CPCM were both increased with increaseing mass fraction of PEG. CPCM had excellent thermostability and stability of phase change cycling, higher store/release heat efficiency. 30%⁷0% PEG/SiO₂ CPCM had good stabilized shape and the composite sturcture formed by PEG as nuclear and SiO₂ gel as carrier backbone.Then, PEG/SiO₂ CPCM were grinded into phase change particles less than 0.6mmand and added to the asphalt, the effect of phase change particles on the basic properties, dynamic rheological properties and cooling performances of asphalt were disscussed. Results indicated that phase change particles were similar to inorganic particles, high temperature stability of asphalt mortar was improved after added phase change particles, 5%²0% phase change particles could cooling 3.6℃⁷.9℃. Asphalt shape-stabilized PCM possessed good heat storage property, thermostability, chemical compatibility and crystallization performance, and PEG/SiO₂ and asphalt was physical adsorption.Finally, phase change particles were added to hot mix asphalt mixture by volume replaced fine aggregates and composite phase change heat storage asphalt mixture（CPAM）. Cooling effects of were measured by outdoor measurement and indoor simulation, which was related the dosage of phase change particles. 5% phase change particles could cooling more than 5℃; Gradation cooling effect has little effect. Indoor accelerated thermal cycling test showed that CPAM had excellent stability of phase change cycling. Dislocation phase change heat storage in differenet temperature range took placed by phase change particles blends of PEG with different molecular weight. The dosage of phase change particles effected pavement performances, with the increase of dosage, in the equivalent temperature, dynamic stability improved 2.9%³5.6%, dynamic stability of framework dense gradation was higher than that of the suspended dense gradation. Low temperature anti-cracking and water stability of CPAM is good. Cooling mechanism of CPAM was analysised based on the phase change heat transfer theory.According to the engineering technology requirements of asphalt pavement, CPCM were independently prepared for asphalt pavement, and appled in hot mix asphalt mixture. It was not only achieves the independent innovation of new pavement materials, but also expands the application field of PCM, the theoretic foundation and technical support would be provided for the applications of CPAM.