Study On Rheological Properties And Inherent Mechanism Of TPU Modified Asphalt And Mastic

Thermoplastic polyurethane elastomer(TPU)as a new polymer material,which has been widely used in many fields due to its flexible formulation and wide adjustable range of properties.However,the research and application of TPU as asphalt modifier in the field of road engineering are rarely reported.As a new kind of polymer material,the study of TPU as asphalt modifier should not be focused on the single material and the mix ratio,and should also take the interface phase between heterogeneous materials which is difficult to capture and complex and changeable as the research object.The interaction between TPU modified asphalt and ore aggregate is the direct factor to produce the interfacial phase,and the asphalt mastic composed of asphalt with ore filler plays a bonding and filling role in the asphalt mixture,which has a significant impact on the pavement performance of asphalt mixture.For these reasons,a kind of TPU asphalt modifier was independently designed and synthesized.Based on physical and chemical characterization,rheological analysis and macroscopic interface tests,the appropriate parameters and content of TPU modifier were determined.The rheological properties and fatigue self-healing properties of TPU modified asphalt at high and low temperatures were studied based on the rheological method,the interaction and mechanism between TPU modified asphalt and different kinds of mineral filler.A micromechanical model of TPU modified asphalt mastic considering the interaction between asphalt and mineral filler was established.The internal mechanism affecting the rheological properties of TPU modified asphalt mastic was analyzed by using this model.The specific contents are described briefly below:(1)Polyester-based and polyether-based TPU were prepared by transesterification polycondensation,and the TPU modifiers with different composition of soft segment,content of hard segment(Ch),molecular weight and isocyanate index of the root index(r)were taken as the research objects.The polytetramethylene ether glycol(PTMEG)or poly(1,4-butylene adipate)(PBA)was as the soft segment,methylene diphenyl diisocyanate(MDI)was as the hard segment,and the 1,4-butanediol(BDO)was as chain extender.The influence of chemical structure of TPU modifier on its macroscopic physical properties was revealed from the aspects of chemical composition,molecular structure,thermal and physical mechanics.Fourier Transform Infrared Spectroscopy(FTIR),Elemental Analysis(EA),Gel Permeation Chromatography(GPC)and Nuclear Magnetic Resonance(NMR)were used to infer the structure sequence and composition ratio of soft and hard segments of the synthesized TPU.The thermal properties of the synthetic modifier were studied by Vicat Softening Temperature(VST),Thermogravimetric(TG)and Differential Scanning Calorimetry(DSC).The mechanical properties of TPU were tested by means of manual Shore hardness tester,pendulum impact testing machine and servo universal testing machine.The results indicated that the chemical structure of TPU can be changed through the selection of soft segment structure and the design of Ch and r,and the mechanical properties of TPU modifier can be adjusted.(2)The suitability processing parameters of TPU modified asphalt were taken into consideration on reaction temperature,shearing time and shearing revolution as investigation factors according to the orthogonal grey correlation analysis method.The mixing scheme of TPU was optimized by experiments of penetration,softening point,ductility and rotational viscosity,and the appropriate dosage of TPU modifier was obtained.FTIR,Fluorescence Microscopy,Scanning Electron Microscopy(SEM),Atomic Force Microscopy(AFM),DSC and TG were used to qualitatively analyze the effects of soft segment structure,Ch and r on the chemical properties,microstructure and thermal properties of TPU modified asphalt were analyzed,and the internal chemical reaction mechanism of TPU modified asphalt is revealed.It could be concluded from the results that both kinds of TPU modifier with the content of 5%,the performance of modified asphalt is the best.The isocyanate in TPU can react with the active functional groups such as carbonyl group,phenol and carboxylic acid in the base asphalt to form new compounds.The modified asphalt of polyether-based TPU asphalt exhibited lower glass transition temperature.(3)Dynamic Shear Rheometer(DSR)and Bending Beam Rheometer(BBR)were used to analyze the effects of different soft segment composition,Ch and r on the rheological properties at high and low temperatures,permanent deformation resistance and fatigue self-healing properties of TPU modified asphalt.Through time,temperature and frequency scanning rheological tests of TPU modified asphalt binder,the fatigue self-healing properties of TPU modified asphalt in a wider range of temperature and loading frequency were evaluated.The accuracy of the criterion of fatigue failure of TPU modified asphalt was improved,and the main synthesis parameters of TPU modifier were defined.It is applied to the fatigue performance evaluation and life evaluation of TPU modified asphalt.The criterion of fatigue failure suitable for TPU modified asphalt is put forward.On the whole,it can be seen that When the normalized modulus drop to 0.5,the corresponding load action times(NF50)can be used as an indicator to evaluate the fatigue life of TPU modified asphalt.The healing time is the key factor affecting the self-healing performance of TPU modified asphalt,and the suitable synthesis parameters of TPU asphalt modifier are as follows:soft segment composition is PTMEG,Ch=40%,r=1.05.(4)Different kinds of mineral filler were selected to prepare TPU modified asphalt mastic.The rheological properties of TPU modified asphalt mastic at high and low temperature were compared and analyzed by DSR and BBR tests.The master curves of complex shear modulus(|G~*|)and stiffness modulus(S)of TPU modified asphalt mastic were constructed.Based on the analysis of rheological properties of TPU modified asphalt mastic,the evaluation method and index of interaction between TPU modified asphalt and ore filler were put forward,and the influence rule of ore powder type on the interaction between TPU.The micromorphology,particle size distribution and specific surface area of different kinds of mineral filler were measured and analyzed by SEM,laser particle size analyzer and BET,and the interaction between TPU modified asphalt and mineral filler was discussed.modified asphalt and ore filler was analyzed in detail by using the interaction index.The chemical composition of TPU modified asphalt and mastic was analyzed by X-ray diffraction(XRD)and FTIR,and the influence of chemical reaction between TPU modified asphalt and mineral filler on its interaction was analyzed.The interaction mechanism between TPU modified asphalt and ore filler was investigated from physical and chemical aspects.The results showed that the fitting method of interaction parameters between ore filler and asphalt can eliminate the dependence of interaction parameters on the volume fraction of ore filler.(5)According to the mesomechanical theory of composite materials,the|G~*|of asphalt mastic with different powder/binder ratios was calculated by H-MRP model.The ratio of powder to binder which is close to the test result is determined.After considering the structure of asphalt layer thickness,the TPU modified asphalt mastic four phase H-MRP model had established.The|G~*|of TPU modified asphalt mastic was predicted by using this model.The effects of complex shear modulus and Poisson’s ratio of TPU modified asphalt,modulus of mineral powder,Poisson’s ratio,particle size of mineral powder and thickness of structural asphalt layer on the|G~*|of TPU modified asphalt mastic were analyzed.The internal mechanism on the|G~*|of TPU modified asphalt mastic was analyzed.The calculations indicated that the appropriate thickness of structural asphalt layer after choosing,the predicted value of|G~*|calculated by the four phase H-MRP model is close to the experimental value.In this study,the chemical structure and mechanical properties of the TPU modifier can be adjusted.The polyether-based TPU modified asphalt developed can effectively solve the problem of poor compatibility between the modifier and the matrix asphalt,and has excellent high,low temperature and fatigue self-healing properties.In addition,some suggestions on the composition design of TPU modified asphalt mastic are put forward,which has a positive role in guiding the composition design of asphalt mastic or mixture and improving the road performance of asphalt mixtures.