Toughness Enhancement Mechanism Of Graphene Modified Asphalt And The Self-Healing Behavior Of Its Mixtures

To improve the strength and toughness of asphalt and to reduce rutting,cracking,loosening and other diseases of asphalt pavement,different polymer modifiers are widely utilized in asphalt pavements for improving the performance and durability of asphalt pavement.The compatibility between the polymer modifiers and the asphalt or asphalt mixture is not easily controlled,resulting in a negative impact on the pavement performance during its service life.Graphene is a two-dimensional material with high mechanical strength and toughness that reconstructs the original structure and improves the original properties of asphalt after being added to it.In light of this,graphene is selected to modify asphalt in this paper,and the pretreated graphene modified asphalt is prepared.The conventional physical properties and anti-aging performance of graphene modified asphalt are evaluated to reveal the toughness enhancement mechanism of graphene modified asphalt.Finally,the effects of the graphene addition method on the conventional pavement performance of asphalt mixtures are discussed,and the multiple self-healing behaviors of graphene modified asphalt mixtures are clarified,which provides technological support to improve the pavement performance and durability of asphalt pavement.First,the dispersant solvents DMSO and NMP are utilized to pretreat graphene to obtain DG and NG,respectively.Fourier infrared spectroscopy,scanning electron microscopy and fluorescence microscopy are utilized to analyze the characteristics of the pretreated graphene and their modified asphalt,to solve the problem of uneven dispersion of graphene in asphalt.Results indicate that DG modified asphalt has better mechanical properties because of the high bond energy of the C=C double bond,and DG is more evenly dispersed in the asphalt,compared with NG and unpretreated graphene.Next,the conventional physical properties of DG modified asphalt are tested,and the changes in surface morphology,chemical functional groups,molecular weight distribution and light absorbance of the asphalt before and after aging are analyzed using scanning electron microscopy,Fourier infrared spectroscopy,gel permeation chromatography and UV-vis spectrophotometer.Results indicate that the penetration and ductility of asphalt are reduced after adding DG,and the softening point of asphalt is increased.When the DG content exceeds 0.4%,the compatibility between DG and asphalt decreases,but the compatibility of DG modified asphalt still meets the requirements of the specification.The formation of sulfoxide groups during the aging process of DG modified asphalt is effectively inhibited with 0.4%DG,which slows down the conversion of small and medium molecular weight molecules to large molecular weight molecules,and provides asphalt with low UV absorption and high UV reflection capacity.Accordingly,it is recommended to use 0.4%DG to modify asphalt.Then,the mechanical performance enhancement mechanism of DG modified asphalt is further investigated using asphalt direct tensile tests and atomic force microscopy,and the microscopic surface morphology,roughness,adhesion,Young’s modulus and energy dissipation of DG modified asphalt are tested to further investigate the mechanical performance enhancement mechanism of DG modified asphalt.Results indicate that the Young’s modulus of asphalt is increased by adding DG,making DG modified asphalt have better deformation resistance.Because of its large surface energy,DG adsorbs the light components of asphalt and forms the intercalation structure.The number of bee-like structures in DG modified asphalt is increased by the formation of intercalation structures,and the volume of the bee-like structures is smaller than that of 70~#pavement petroleum asphalt.The flow of light components is restricted by the intercalation structures,which show a reduction in adhesion and dissipation energy.When it is stressed in tension,the stress is concentrated in the large volume of the bee-like structure within 70~#pavement petroleum asphalt,which reduces its mechanical properties.While the small volume and large number of bee-like structures in DG modified asphalt disperse the stress,the mechanical properties of DG modified asphalt are enhanced.Meanwhile,the visco-toughness enhancement mechanism of DG modified asphalt is being further investigated in terms of visco-toughness change and energy absorption.X-ray diffraction tests,visco-toughness tests,rotational viscosity tests,Charpy impact tests and three-point bending fracture tests are utilized to investigate the toughening mechanism of DG modified asphalt.Results indicate that the formation of intercalation structure is confirmed by the increasing dimensional spacing of DG modified asphalt,and the viscosity and visco-toughness of the DG modified asphalt are also enhanced,giving DG modified asphalt better deformation resistance.The extension of cracks is hindered by increasing micro-cracking of DG modified asphalt,and part of the energy generated by impact is absorbed,resulting in DG modified asphalt with excellent visco-toughness at low temperatures.The visco-toughness enhancement of DG modified asphalt at low temperatures is more remarkable,which significantly improves the anti-cracking performance.Finally,based on the toughness enhancement mechanism of graphene on asphalt,the effects of DG addition methods on the pavement performance of asphalt mixtures are comparatively investigated.Also,multiple fracture-healing cycles are performed on the base asphalt mixture specimens and two kinds of graphene modified asphalt mixtures by using microwave heating to comprehensively evaluate the pavement performance and the multiple self-healing behaviors.Results indicate that the high temperature deformation resistance,low temperature anti-cracking performance and moisture stability of the asphalt mixture are improved after adding DG.Because of the high thermal conductivity of DG,it provides asphalt mixture specimens with a higher healing temperature after microwave heating,which increases the peak fracture force and healing efficiency after the fracture-healing cycles.In multiple fracture-healing cycles,the graphene modified asphalt mixture specimens made by DG modified asphalt have better thermal stability,and the stable high-temperature area on the surface guarantees its high healing efficiency after multiple fracture-healing cycles.In conclusion,the paper reveals the anti-aging mechanism of graphene modified asphalt,clarifies the mechanical enhancement mechanism and visco-toughness enhancement mechanism of graphene modified asphalt.The research results have important implications for improving the pavement performance of asphalt pavements,extending their service life,and promoting the development of graphene and other nanomaterial modified asphalt technologies.