Study On The Macro Fracture And Self-Healing Property Of Asphalt Mixture Based On SCB Test

In order to study the macroscopic fracture performance and self-healing properties of bituminous mixture.In this paper,the stress intensity factor K and the J-integral fracture toughness,obtained from loading test in laboratory,are used to analyze the fracture performance of semi-circular specimens.Besides,the ratios of tensile strength,fracture energy,and Jic fracture toughness obtained loading test before and after healing were defined as the self-healing indexes,and they are used to characterize the self-healing properties of the fracture specimens after induction heating in different temperature ovens.The finite element software was used to analyze the two-dimensional and three-dimensional mechanical responses of the semi-circular specimens of bituminous mixtures.The research on fracture resistance of bituminous mixture focuses on the experimental methods and evaluation index.The experimental methods for the fracture resistance of bituminous mixtures mainly include splitting test(indirect tensile test),bending test of beam,semi-circular bending test(SCB),and disk-shaped compact tension(DCT).In this paper,the SCB test was used from the comparison and analysis of the specimen making,the testing difficulty and evaluating index and so on.By analyzing the two-dimensional and three-dimensional mechanical responses of the semi-circular specimens,it was indicated that the tensile stress of semi-circular specimens was mainly distributed between two pivot points,and the maximum tensile stress mainly appeared at the center of the bottom of the specimen and decreased along the diameter and thickness direction.Besides,the compressive stress was mainly distributed at the pivot and the loading point,and an arched pressure belt was formed at the periphery of the semicircular specimen along the branch point.Furthermore,the vertical displacement was axisymmetric analysis along the load line,and gradually decreased.with the diameter direction,but increased with the thickness direction.Under the assumption of plane stress and plane strain,the stress coefficient equation and displacement coefficient equation of the semi-circular specimen with diameter 100mm and diameter 150mm were established.When the pivot spacing is 0.8 times the diameter,the stress coefficient at the bottom of the semi-circular specimen was 4.899 and 4.835,respectively.In addition,the fitting equation of stress intensity factor with the depth of slit of the notched semicircle specimen was established under the assumption of plane strain.It was demonstrated that the tensile strength,KIC value and Jic value of AC-20 mixture and SMA-13 mixture are greater than that of AC-13 mixtures,through SCB testing result of five kinds of mixtures,which shows that the asphalt mixture designed with coarse gradation has better cracking resistance.Besides,the KIC value and Jic value of AC-13 mixtures prepared in 70#base bitumen,SBS modified bitumen and composite modified bitumen,has no significant difference,that is,bitumen has little effect on the crack resistance of the mixture at low temperature.The results of induction heating of the same batch of fractured specimens in a certain environment indicated that the macro-fracture of the asphalt mixture could occur self-healing,and the self-healing index was less than 1.0,indicating that the performance of the asphalt mixture could not be completely recovered,but the healing index could reach 50%?80%when healed eight hours in 100‰ environmental.The healing temperature and healing time promoted the self-healing properties of the asphalt mixture,and the self-healing index accelerated with the increase of the healing temperature and healing time.There was an optimal healing temperature and optimal healing time in the healing process.When the optimal healing condition is exceeded,the effect of improving healing performance is not significant.In this paper,the optimal healing temperature and the optimal healing time of the asphalt mixture at a specific time and temperature environment were 60?,and 8 h,respectively.The self-healing index of asphalt mixture decreased with the notch depth of the specimen.The notch depth could indirectly indicate the degree of damage before healing.The deeper the notch depth,the greater the degree of fracture and the lower the self-healing ability.The self-healing performance of bituminous mixtures prepared different kinds of bitumen and grades were different.In this paper,the self-healing performance of the fine grade asphalt mixture prepared by SBS,which is SBS AC-13mixture,was best,and AC-20 mixture's Self-healing performance is the worst,which is mainly due to the different particle size of the gradation of the mixture and the different self-healing mechanism of the bitumen.According to the capillary flow principle,the fitting relationship between the self healing index and the healing time could be established,and the fitting correlation coefficient R2 is generally greater than 0.9.According to the time-temperature conversion effect of asphalt material,the relationship between healing time and healing temperature was established in the same healing index.