| Cracks is one of the main diseases of flexible pavement systems,which seriously affects the durability of asphalt concrete.At present,there are many test methods to evaluate the crack resistance of asphalt mixture.The size and parameters of each test sample are different,resulting in different evaluation indexes of crack resistance.In the fracture test,the test parameters will have a magnificent effect on the test results.Using the asphalt bending creep test,in the condition of low temperature,the evaluation indexes of matrix asphalt mixture,SBS modified asphalt and rubber modified asphalt were studied.The stiffness modulus and m value obtained from the test were analyzed.The test results show that the rubber modified asphalt has the best performance under the low temperature,followed by SBS modified asphalt.The indirect tensile test,beam bending test and semicircle bending test of three kinds of AC-13 asphalt mixtures were carried out under the low temperature of-10 ℃.The maximum load,tensile strength and fracture work obtained from the test were compared.Combined with the failure characteristics of the failure specimens,the results showed that the indirect tensile test has certain defects,and the evaluation indicators show different size relationships.The results obtained from the trabecular bending test and the semicircular bending test showed the crack resistance of these three types materials(rubber modified asphalt mixture> SBS asphalt mixture> matrix asphalt mixture).which is consistent with performance of asphalt under the low temperature.It is also found that the trabecular bending test and the semicircular bending test can be converted into each other under certain conditions.Subsequently,the repeatability,variability and on-site applicability of the evaluation index were further analyzed,which showed that the semicircular bending test was the most reasonable method to evaluate the crack resistance of the asphalt mixture.Based on the semi-circular bending test of matrix asphalt mixture and SBS asphalt mixture,the reliability of the three anti-cracking performance evaluation indexes of JIC,KIC and fracture energy(Gf)was analyzed.In addition,the influence of different cutting depths,loading rates and temperature on the three anti-cracking performance evaluation indexes was studied.The results of the study showed that the three types of indexes can clearly distinguish different asphalt mixtures with enough reliability.When the toughness of the test piece fails,JIC shows an increase with increasing loading rate and temperature.The performance of KIC decreases with the increase of incision depth and temperature,and increases with the increase of loading rate.The loading rate and temperature have a significant effect on KIC,and the influence of incision depth on KIC is relatively small.Gf decreases with increasing cut depth.When the asphalt mixture has ductile fracture,Gf increases with increasing loading rate.When the rate is 5mm / min or 0.5mm / min,the maximum value of Gf was obtained at the temperature of 15℃.The effect of loading rate and temperature on Gf was significant.When the test is performed at a loading rate of 50 mm / min,the sensitivity of Gf to temperature(not greater than 25℃)was greatly reduced.Additionally,it was found that if the loading rate is lower than 5mm / min,the results of the cracking behavior of asphalt mixture was closer to reality. |
