Evaluation Method Of Low Temperature Performance Of Asphalt And Asphalt Mixture Based On EBBR And SCB

As the concept of highway full life cycle is proposed,the problem of low temperature cracks has become one of the hot spots and key directions of asphalt pavement research,and scholars in related fields have proposed a large number of low temperature performance test evaluation methods.However,engineering practice shows that the commonly used trabecular bending test,low temperature split test,and cracking on site are not highly correlated;the BBR test(Bending beam rheological test)has a general effect on the prediction of cracking ability.Based on this background,this topic uses the existing pavement core samples and different types of asphalt commonly used in Jilin Province to perform the improved BBR test(EBBR test)and semi-circular bending test(SCB test),using the EBBR and SCB results of recycled asphalt Through mutual verification,the comparison between the recovered asphalt and fresh asphalt EBBR results verified the ability of these two tests to evaluate the low temperature performance of asphalt pavement.Discrete element simulation was used to establish the SCB virtual test system,linking the EBBR and SCB test results,providing a way to directly predict the low-temperature performance of the mixture through the test results of the binder,and further revealing the numerical relationship between the EBBR test and the SCB test.First,the recycled materials and freshly mixed asphalt are processed.The core samples taken from the four cracking sections of Changji Expressway are cut and pre-cut to complete the SCB test loading.After loading,the test piece was crushed.After extraction and distillation treatment,four types of recycled asphalt were separated.The three major indexes of recycled asphalt were tested,and they were subjected to TFOT aging treatment and reserved for EBBR loading.Six types of matrix asphalt and aging asphalt mixed according to the requirements of Jilin Province are selected for short-term TOFT aging and long-term aging treatment,and the changes of the three major indexes before and after aging are tested,and the remaining asphalt is reserved for EBBR test analysis.The low-temperature PG classification is carried out on the freshly mixed asphalt.After a simple analysis of the PG grading,the aging types and asphalt varieties have an influence on the low-temperature performance.The common low-temperature evaluation methods and indicators of asphalt binders are analyzed,and the EBBR test is used to evaluate the performance of aging asphalt.Since the BBR test is included in the EBBR system,the rheological behavior under BBR conditions is analyzed first.Through the relationship between the stiffness modulus and its rate of change,the degree of influence of the three types of aging on the crack resistance of the asphalt material was determined,and the effect of the modifier type on the low temperature performance of the asphalt was judged.Introduce the Delta T index,and draw the relationship between the low-temperature relaxation capacity of freshly mixed asphalt.Because the traditional indicators rely on PG classification,the data analysis and processing methods do not match the actual needs of my country,the asphalt low temperature design temperature index is proposed,and its data stability and evaluation ability are verified.Aiming at the 180 s stiffness modulus proposed in the current asphalt pavement specifications,the fitting calculation method is obtained based on the Burgers model,and the low-temperature cracking index prediction values of various asphalts are proposed accordingly.Based on the EBBR test loading mode,the low-temperature grade loss of extracted asphalt,common matrix asphalt,and modified asphalt in four typical road sections was obtained,and the effect of physical hardening on the low-temperature performance of asphalt binder was quantitatively analyzed.It is concluded that the grade loss of extracted asphalt is about 2～3℃,and that of freshly mixed asphalt is about 1～8℃.According to the index distribution rule,it is considered that the EBBR test has a wider application range and higher evaluation requirements than BBR.It can be used to evaluate the low temperature performance of recycled asphalt,various types of aging asphalt,and common modified asphalt.After that,the SCB test method and its characterization rules were analyzed.With reference to the AASHTO specification and the IL-SCB test,a test mold for 100 mm diameter and 150 mm diameter samples was designed,which improved the test control method and further enhanced the applicability of the test.The analysis of the fracture energy of the pavement core sample shows that the results of the 100 mm SCB test can be quantitatively related to the cracking degree of the pavement in service.For the section with greater cracking degree,the corresponding fracture energy value is lower and the crack resistance of the structure is worse.After statistical analysis,it was found that the SCB test data had less variability and better data stability.The low-temperature evaluation capabilities of peak load,fracture energy,fracture toughness,stiffness,and flexibility factor indexes were tested separately.It is considered that except for the peak load,the other indicators can obtain the expected laws.The numerical laws obtained by these indicators confirm the conclusions obtained in the analysis of fracture energy,and also support the prediction level of the SCB test for the low temperature crack resistance of asphalt pavement.The SCB test can be echoed with the recovered asphalt EBBR results,which also proves the accuracy of the test method.Finally,the discrete element PFC software was used to complete the threedimensional discrete element virtual test of asphalt mixture.According to the mesomechanical characteristics of the discrete element model of asphalt mixture,the simplified modeling method is selected to simplify the FAM into contact keys.The softened parallel bond model is selected as the contact model between spherical particles.With reference to the method of predicting the dynamic modulus of the mixture with mortar,the three-phase model was used to predict the flexural modulus of the mortar for the four recycled materials.Using frequency domain analysis methods and linear elasticity-related principles,the asphalt BBR test stiffness modulus is converted into relaxation modulus,bulk modulus,and shear modulus main curves.Combined with composite materials and theory,the equivalent coating film thickness,Single particle size equivalent modulus and FAM equivalent bending modulus.Through the comparison of curves and lines,and the comparison of data,the SCB virtual test setup proposed in this paper was verified,and the construction of the virtual test simulation architecture of the test was completed.A preliminary prediction method for obtaining the low-temperature performance of the mixture directly through the asphalt binder test was initially constructed.