Evaluation Method Of High Temperature Stability Of Asphalt Mixture

Rutting is one of the damage forms of asphalt pavement.As the overload phenomenon appears continuously and the temperature of the pavement environment rises,the rutting phenomenon is becoming more and more prominent.The modified asphalt can improve the high temperature performance of the asphalt mixtures and the rutting damage of asphalt mixtures.There are many tests to evaluate the high temperature performance of asphalt mixtures.The dynamic stability(DS)based on the equation of wheel-track tester is currently the most commonly used indicator for evaluating the rutting-resistance performance of asphalt mixtures.When using the dynamic stability to evaluate the rutting-resistance performance of modified asphalt mixtures,large measurement and calculation errors often occur.The main purpose of this paper is examine the evaluation method of the hightemperature behavior of modified asphalt mixture.To this end,firstly,rutting tests of two different gradations of modified asphalt mixture(Superpave-13,SMA-13)and an asphalt mixtures with unmodified asphalt binders as a control were carried out at 45 ℃,60 ℃ and70 ℃ test temperatures with and without water by lab rutting tester;Secondly,the trend of rutting-load repetition curve of various asphalt mixtures under different conditions are studied.The shortcomings of current dynamic stability index in evaluating anti-rutting performance of asphalt mixtures under different environments are analyzed,and a new rutting evaluation method for modified asphalt mixtures is proposed.(1)When the test temperature is 45℃、60℃,there is a relatively big fluctuantion in evaluating the rutting-resistance performance of the modified asphalt mixture with the dynamic stability value obtained by the current DS calculation method;When the test temperature is 70℃ or the immersion rutting test is 60℃,the coefficient of variation between the same group of specimens and the degree of dispersion are small when the DS value is used to evaluate the rutting-resistance ability of the modified asphalt mixture.However,under this circumstance,the trend of rutting curve development is fast.(2)Rutting development curve showed two sections of compaction in the beginning and flow of aggregates in the later phase.Comparing with unmodified asphalt mixtures,modified asphalt mixtures performed much stronger in flow-resistance in the later phase making a flatter curve.The difference between the rutting curves of the mixtures with modified and unmodified binders was if inflection point are obviously appeared.The current DS calculation method thus produces large measurement and calculation errors.Theconcept of dynamic stability DS1 obtained by replacing the d60-d45 with the rutting curve area of the whole process is reasonable and scientific,and the error is greatly reduced.(3)The variability analysis method is used to analyze the degree of dispersion of the index values between the same group of specimens.The method of variance analysis is used to analyze the discrimination between the two indicators to evaluate the anti-rutting performance of asphalt mixture,and the method of gray absolute correlation analysis is used to analyze the index value is similar to the change trend of the asphalt mixture rut depth.The analysis results show that the improved calculation method index DS1 is more suitable for evaluating the anti-rutting performance of the modified asphalt mixture than the evaluation index DS.