Research On Salt Corrosion Mechanism Of Asphalt And Asphalt Mixture In Coastal Environment

The roads in the coastal area have been subjected to long-term salt erosion,and their service life is less than expected.To explore the mechanism of salt erosion damage to asphalt pavement in the coastal area,this article analyzes the characteristics of salt erosion damage in the coastal environment,simulates the coastal salt erosion environment indoors,and sets up a salt dry wet freeze-thaw cycle erosion model to accelerate the process of salt erosion damage to asphalt and asphalt mixtures.From three dimensions: the performance of salt corroded asphalt itself,the adhesion performance of salt corroded asphalt aggregate,and the water stability performance of salt corroded asphalt mixture,the damage law and internal damage mechanism of salt corrosion are studied.The 70 # base asphalt,SBS modified asphalt and TPS high viscosity asphalt were treated by salt corrosion cycle.The conventional properties,fatigue properties and cohesive properties of salt corrosion asphalt were characterized by three major indicators,rheological test(DSR)and tensile test;Atomic force microscope(AFM)was used to observe the microscopic morphological differences of asphalt before and after salt corrosion.The experimental results show that after salt corrosion damage of asphalt,its high-temperature performance increases,its deformation resistance enhances,and its low-temperature ductility weakens.The ductility has the strongest sensitivity to salt corrosion;Salt corrosion exacerbates the deterioration of asphalt’s fatigue resistance.After 20 salt corrosion cycles,the degree of fatigue performance degradation is as follows: matrix asphalt>SBS asphalt>TPS asphalt;Salt corrosion enhanced the tensile strength and self cohesion of asphalt.The basic value of tensile strength of TPS asphalt was the largest,and the increase in salt corrosion was the smallest,while that of base asphalt was the opposite;At the micro level,the surface roughness Ra of asphalt decreases after salt corrosion,and the adhesion and self-healing properties both decay.Using the hanging insertion method to coat asphalt film to form specimens,salt corrosion cycling treatment was carried out.Surface energy tests were conducted on the specimens after cycling,and the surface energy and its components,asphalt aggregate adhesion work,asphalt aggregate water three-phase system peeling work,and water stability index ER were calculated.A decay model of asphalt aggregate adhesion performance under salt corrosion environment was established.The results indicate that under corrosive environments,the surface energy of asphalt decreases,the adhesion work between asphalt and aggregate decreases,the absolute value of peeling work between asphalt aggregate water three-phase increases,and the ER value gradually decreases.The adhesion performance between asphalt and aggregates decreases,and aggregates with larger surface energy are more prone to wetting with water,gradually replacing the asphalt film coated on the surface of the aggregates with water.Design the mix proportions of PA-13 and SMA-13 asphalt mixtures according to the specifications,determine the aggregate gradation and optimal oil ratio,form standard Marshall specimens,and perform salt and water corrosion cycling treatment.The results show that the void ratio of asphalt mixture increases,and the splitting tensile strength and TSR value decrease under the salt corrosion environment,that is,the structural stability and water stability of asphalt mixture decrease;Salt erosion is greater than water freezing and thawing in salt erosion environment.Water stability in water erosion environment is closely related to asphalt mixture porosity.The larger the porosity,the weaker the water stability.Propose the forms of damage to salt corroded asphalt pavement,including chemical damage,physical damage,and mixed damage.Chemical damage refers to the chemical reaction between salt molecules and lightweight components of asphalt,which changes the hydrophobicity and adhesion of asphalt;Physical damage refers to the precipitation of crystals in the salt solution inside the asphalt mixture structure,which penetrate into the asphalt film,reducing the bonding effect of the asphalt,and reducing the strength and water stability of the asphalt mixture;Mixed destruction refers to physical destruction,which involves the dissolution of salt crystals in the asphalt film and partial chemical reaction with the asphalt,while expanding the contact area between the asphalt and the salt solution.