| Crumb rubber modified asphalt(RA)not only benefits environmental protection but also improves or enhances the performance of asphalt pavement,especially in terms of fatigue performance.However,RA has poor compatibility,which can cause stratification and affect the effectiveness and engineering quality of its use.Pre-treating the crumb rubber to improve its compatibility with asphalt and increase the storage stability of crumb rubber modified asphalt is a beneficial attempt.However,it is worth investigating whether pre-treated crumb rubber will have a negative impact on the performance of asphalt mixtures,particularly in terms of fatigue performance.Therefore,studying the self-healing characteristics of pre-treated crumb rubber modified asphalt(PRA)and mixture has practical significance and engineering reference value.Firstly,molecular dynamics simulation methods were used to establish models of pretreated crumb rubber,PRA,and crack,to explore the effects of asphalt type,healing temperature,and crack width on self-healing characteristics of PRA.Secondly,asphalt tests were conducted to study the impact of crumb rubber pre-treatment schemes on the basic technical properties and compatibility of PRA,supplemented by infrared spectroscopy,toluene extraction,thermogravimetric analysis,and scanning electron microscopy tests to explain the interaction mechanisms between pre-treated crumb rubber and asphalt.Finally,bitumen ductility tests,shear modulus tests,fatigue-rest-fatigue tests,tensile tests,and three-point bending fatigue tests of the mixture were carried out to analyze the impact of healing factors on the self-healing characteristics of PRA and mixture,and to evaluate the consistency between test results and molecular dynamics simulation results.The simulation results showed that furfural extract oil or naphthenic oil microwave treated crumb rubber modified asphalt(KWA or HWA)had strong diffusion ability,and van der Waals forces were the main driving force for self-healing of PRA,with electrostatic forces also having a strong driving force for KWA selfhealing behavior.Higher temperature is beneficial to the self-healing of PRA,and an increase in crack size will hinder self-healing behavior.The test results showed that oil pretreatment increased the solubility of crumb rubber in asphalt,increased the penetration and ductility of PRA,while lowering softening point,viscosity,and the difference between separation and softening points.Microwave treatment broke the covalent bonds between C and S atoms,increased the number of small molecules,and improved the compatibility between crumb rubber and asphalt.Under higher healing conditions such as 60℃,KWA asphalt had slightly better healing effects than HWA asphalt,while HWA asphalt had better healing effects under lower temperatures.The self-healing rate results of the fatigue-rest-fatigue test of PRA were consistent with the molecular dynamics simulation results,and the self-healing performance ranking was: KWA>HWA>WA.The fatigue healing rate of modified asphalt mixtures prepared by oil-microwave treated crumb rubber was at least 1.4 times higher,and the fatigue healing rate was closely related to the diffusion coefficient index of molecular dynamics simulation. |
