Study On The Thermoregulation,Rheological Properties And Modification Mechanism Of Asphalt Modified With Polyurethane Solid-Solid Phase Change Materials

Phase change materials spontaneously reduce the adverse effects of temperature on asphalt pavements through thermal storage,reducing the incidence of temperature damage on pavements,but their violent phase change behavior during thermal storage also impairs the road performance of asphalt and its mixtures.Polyurethane solid-solid phase change materials(PUSSP)exhibit a solid phase state and adapt to the ambient temperature of asphalt pavements.Currently,the application of PUSSP to asphalt pavement is still in the exploratory period,research on the road performance of PUSSP-modified asphalt and mixtures is relatively restricted,particularly due to the lack of the mechanism of PUSSP and asphalt,and the main problem is that the thermal properties of PUSSP are insufficient and damage the lowtemperature creep performance of asphalt,which makes it difficult to be applied to asphalt pavements.As a result,this study developed PUSSP as an asphalt modifier with higher thermal storage capabilities while lowering damage to asphalt road performance,resulting in a more suitable for application on asphalt pavements.The thermodynamic test methods were used to demonstrate the phase change behavior,thermal storage,and micromechanical properties of PUSSP.The rheological methods were utilized to study the effect of PUSSP on the thermoregulation and rheological properties of asphalt.The establishment of asphalt macroscopic and microscopic indexes indicated the mechanism of macroscopic properties transformation for PUSSP-modified asphalt.The thermoregulation and road properties of PUSSP-modified asphalt mixtures were used to evaluate the adaptability of PUSSP with asphalt pavement.The major study contents are as follows:(1)Study on synthesis,thermal storage properties and micromechanical characterization of PUSSP.PUSSP asphalt modifier was developed,and the thermodynamic properties of PUSSP could be adjusted by controlling the synthesis process.The evolution of characteristic peaks of functional groups for reactants and products of PUSSP was analyzed with infrared spectroscopy(FTIR),and the synthesis results of PUSSP could be inferred from this.The phase change behavior and the mechanism of PUSSP were clarified with the help of an adsorption test,polarized optical microscope(POM),and X-ray diffraction(XRD).Based on differential scanning calorimetry(DSC)and thermogravimetry(TG),the thermal storage properties and thermal stability of PUSSP were investigated,and the effect of soft segment mass fraction of PUSSP on thermophysical properties was clarified.The soft and hard segment distribution and mechanical properties of PUSSP at the microscopic scale were clarified by atomic force microscopy(AFM).The results show that PUSSP has a solid phase state,and the thermal storage property is enhanced with an increase in soft segment mass fraction,while its thermal stability and elasticity decrease.(2)The preparation,thermal storage and thermoregulation properties of PUSSP-modified asphalt were investigated.Orthogonal design and gray correlation analysis were used to propose the optimal preparation process for PUSSP-modified asphalt,the basic physical properties of PUSSP-modified asphalt were evaluated with three major index tests of asphalt.The thermal storage properties and stability of PUSSP-modified asphalt were investigated using DSC and TG tests,a testing method and evaluation indexes of asphalt thermoregulation properties were proposed to clarify the thermoregulation properties of PUSSP-modified asphalt.The intrinsic link between the thermoregulation and thermal storage properties of PUSSP-modified asphalt was established.The results show that the maximum temperature difference between PUSSPmodified asphalt and base asphalt is 7.9 ℃,which exhibits better thermoregulation and thermal storage properties,these properties are enhanced with the increase of the soft segments mass fraction and content of PUSSP.(3)The rheological properties of PUSSP-modified asphalt were studied.Based on the dynamic shear rheometer(DSR)temperature scanning and bending beam rheometer(BBR)tests,the high and low-temperature rheological properties of PUSSP-modified asphalt were elucidated,and the high and low-temperature grades were determined by the PG grading.The rheological properties of PUSSP-modified asphalt under high temperature and high-frequency conditions were characterized by the Black curve and the dynamic complex modulus master curve plotted through the frequency scanning of DSR,and the correlation between G* master curves and CA model was verified.The MSCR test was used to clarify the permanent deformation resistance and stress sensitivity of PUSSP-modified asphalt.The high-temperature storage stability of PUSSP-modified asphalt was analyzed by the DSR segregation test.These results show that PUSSP-modified asphalt provides better elasticity,high-temperature rutting resistance,and permanent deformation resistance than that of base asphalt,and the lowtemperature creep performance is improved with the increase of the mass fraction of PUSSP soft segments.(4)Study on the modification mechanism of PUSSP-modified asphalt.The reaction mechanism between PUSSP and asphalt was analyzed using the FTIR test.The effect of PUSSP on asphalt’s microscopic morphology was clarified by fluorescence microscopy(FM)and scanning electron microscopy(SEM)tests,and the evolution role of the macro-properties of PUSSP-modified asphalt was revealed.Atomic force microscopy(AFM)tests were used to measure the roughness and Young’s modulus on the microscopic surface of PUSSP-modified asphalt,the effect of PUSSP on the microscopic morphology and properties of asphalt was quantified,and the association of asphalt macro and micro properties was established.A molecular model of PUSSP-modified asphalt was constructed by MD to clarify the interaction between PUSSP and asphalt.The results indicate that PUSSP-modified asphalt is physically modified and well compatible,the effect of PUSSP on the micro-morphological properties of asphalt induced a transformation of the macroscopic properties of asphalt.(5)The thermoregulation and road properties of PUSSP-modified asphalt mixtures were investigated.Based on the temperature monitoring test and its evaluation indexes,the thermoregulation properties of PUSSP-modified asphalt mixtures were elucidated.The road performance of PUSSP-modified asphalt mixtures was evaluated using the tests of hightemperature rutting,beam bending,Marshall stability and freeze-thaw splitting,etc.,the effects of PUSSP on the high and low-temperature performance and water stability for asphalt mixtures were clarified.The results show that PUSSP confers thermoregulation properties and improvement of high-temperature rutting resistance to asphalt mixtures,with a maximum temperature difference of 4.2 °C from the base asphalt mixtures.As the mass fraction of PUSSP soft segments decreases,the low-temperature cracking resistance and water stability of PUSSPmodified asphalt mixtures increase.