| Asphalt pavements are subjected to long-term effects of temperature and traffic loads to produce internal micro-cracks and gradually expand to form macro-cracking,which seriously affects the service life and service quality of the pavement.Advanced technology is urgently needed to contain and retard the expansion of microcracks at the early stage of damage.The healing ability of asphalt material itself is not enough to repair the internal microdamage effectively,so how to improve the self-healing performance of asphalt pavement has become a research hotspot in the field of road maintenance.Organic nano-montmorillonite(MMT)was used as the research object.By determining the preparation process of nano-modified asphalt,the effect of MMT on the multiple healing performance of asphalt and mixture was systematically quantified,the mechanism of MMT enhanced healing performance of asphalt was investigated from multiple angles,and the characteristics and changes of the healing performance of MMT modified asphalt and mixture were summarized.The aim is to apply nanomaterials to enhance the healing ability of asphalt and mixture to achieve long-term multiple micro-damage self-healing and delay the occurrence of cracking diseases.The main work and research results are as follows:First,the preparation process and properties of nano-modified asphalt were studied.The physical properties and storage stability of the nano-modified asphalt were well prepared by adding MMT with hydrophobic and lipophilic properties to the base asphalt and SBS modified asphalt according to the process of shear temperature 160℃,shear rate 5000 rpm and shear time60 min.The rheological test and viscoelastic master curve analysis showed that the MMT dose of more than 3% could improve the high temperature PG grade,viscosity and resistance to permanent deformation of asphalt under heavy traffic conditions.However,the doping amount up to 5% will weaken the creep recovery sensitivity under heavy load.Next,the self-healing performance of the nano-modified asphalt was investigated.The fatigue test with rest period was used to consider the influence of different influencing factors on the healing behavior of asphalt,and the modified healing index based on modulus and loading time was evaluated for the nano-modified asphalt,and the damage level was less than 50% and the healing time was more than 30 min at a healing temperature of 25°C.The addition of MMT could improve the healing index of asphalt by up to 22.5%.The ultimate slope of the asphalt healing master curve could be used as an index to judge the healing potential of asphalt,which proved that MMT could accelerate the healing rate of asphalt microdamage.In addition,MMT enhanced the optimal healing temperature and multiple healing capacity of the asphalt,and MMT formed a stable and dense structure in the SBS modified asphalt,so it was more effective in improving the multiple healing performance of the SBS modified asphalt than the base asphalt.Then,the healing mechanism of MMT-enhanced asphalt was investigated.The surface free energy theory was applied to reveal the reasons for the healing performance of MMT-enhanced asphalt,the microscopic morphology was observed to characterize the nanosphere spacing variation and analyze the distribution state of MMT in asphalt,the correlation between molecular structure index and molecular weight distribution and healing index was investigated,and the molecular dynamics was applied to construct a healing model to analyze the healing behavior of MMT-modified asphalt molecules.The study proved that MMT modified asphalt has high surface free energy.The cohesive work of asphalt and its adhesion work with aggregate is increased by MMT,which accelerates the efficiency of energy transfer in the self-healing process of asphalt.The intercalation and peeling structure formed in the asphalt enhances the intermolecular force of the asphalt,reduces the number of branched chains in the asphalt molecular structure,expands the molecular chain activity space,and increases the free volume share,thus enhancing the diffusion rate of asphalt molecules and making it easier to gather at the damage interface to enhance the self-healing ability.In addition,the stable intercalation structure also helps to promote the macromolecular composition and improve the fatigue damage resistance of asphalt.Finally,the self-healing performance of the nano-modified asphalt mixture was investigated.The healing ability of MMT-modified asphalt mixture was investigated by using semicircular bending and pulling test,multiple fatigue-healing simulation considering healing temperature,damage level and freeze-thaw action.The multiple healing index of the nanomodified asphalt mixture was proposed,and it was demonstrated that MMT effectively promoted the healing process of micro-damage of asphalt mixture,and the healing index of asphalt mixture with MMT added under certain healing conditions was 10%-15% higher than that of the mixture without MMT added,which effectively extended the fatigue life of the mixture.The polynomial fitting of the healing test results and the constructed healing surface equations determine the healing conditions that should be satisfied for MMT modified asphalt mixture to achieve a specific healing effect.The results of the study can provide a technical reference for the promotion of nanomaterials in road engineering and their application in the field of asphalt and mixture self-healing research. |
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