Study On Mechanical Properties And Crack Propagation Of Asphalt Pavement Under Low Temperatur

In the 1980 s,China began to develop asphalt pavement.Nowadays,asphalt pavement has become the preferred pavement method for high-grade highways,and the mileage has also been greatly improved.However,in China,the cold area accounts for about 43 % of the land area in China.In addition,there are low temperature phenomena in many areas of China,and asphalt pavement is prone to reflection cracks at low temperatures.In addition,there is also acid rain in many areas of our country.Acid rain will flow into cracks along the pavement and aggravate the corrosion damage of asphalt pavement.Reflection cracks are reflected from the cracks in the original bottom layer after road maintenance or reconstruction.The road ’ white to black ’(cement concrete pavement to asphalt pavement)is a typical case of reflection cracks.Nowadays,China ’s white cement concrete pavement still occupies a large proportion.Because black asphalt pavement has many advantages that white pavement does not have,many white pavements in China are facing the problem of ’ white to black ’.The reflection crack in the asphalt surface layer after the transformation is one of the key problems to be solved in the ’white to black ’ pavement,so it is of great practical significance to study the reflection crack of low temperature asphalt.The damage caused by low temperature of asphalt is mainly caused by tensile crack.Due to the lack of mechanical parameters such as tensile performance of asphalt mixture at low temperature,this paper carried out experimental work under the influence of low temperature.The overall goal of this paper is to consider the coupling of low temperature acid rain,so as to carry out the coupling experiment of low temperature acid rain.Because the numerical simulation research can observe the crack propagation and consider the advantages of the whole model,this paper carried out the numerical simulation of the white to black condition.The results are as follows :(1)The physical experiment of asphalt mixture samples under low temperature studied.By comparison,it is found that the low-temperature saturated sample reaches the peak value of splitting failure when the loading displacement is 2.8mm.The plastic deformation capacity and peak load are between the low-temperature natural sample and the normal-temperature natural sample,and the time to reach the peak value of splitting failure is later.It is speculated that micro-cracks are generated during the freezing process of the sample.These micro-cracks are closed during the failure of the sample,which consumes a lot of energy and makes it show better mechanical properties.(2)The mechanical properties of asphalt mixture samples after acid rain corrosion at low temperature were studied.It is found that acid rain has a corrosion effect on asphalt mixture,and causes the loss of some components in aggregate and the increase of porosity.A large number of bubbles were generated around the sample,and it was speculated that the acid solution entered the interior of the sample through the pores and corroded it.The longer the corrosion cycle,the more the uniaxial compressive strength of the sample decreases.With the decrease of PH,the flexural tensile strength of the sample decreases.In addition,the longer the corrosion cycle,the smaller the flexural tensile strength of the sample,and the splitting strength of the sample also shows a consistent law.(3)RFPA temperature plate is used to select the common "white to black" condition,and the numerical simulation of the low-temperature reflection crack shows that:(1)In the unbroken "white to black" pavement model,there is an obvious stress concentration phenomenon at the prefabricated crack tip near the interface of the upper two layers,indicating that the constraint of the surface layer leads to the stress at the top crack tip.With the increase of S/T value(the ratio of the precast crack spacing S to the surface thickness T),the stress at the lower end near the interface between two adjacent cracks gradually changes from 0 to compressive stress.The faster the cooling rate of the model is,the more AE will appear in the structure,resulting in more micro-crushing.By combining the three cooling rates,it can be concluded that the cumulative AE amount of asphalt pavement structure is the minimum when S/T=1,5 and 6.(2)In the "white to black" pavement model of fragmentation,the peak value of the overall AE and the overall stress level increase with the increase of the cooling rate.Through comparison,it is found that the base layer has a greater influence on the AE of reflected cracks,and the cumulative AE amount of asphalt pavement structure is the minimum when S/T=6,7,8.(3)The model after acid rain corrosion was simulated,and it was found that the stress peak and the amount of acoustic emission after corrosion showed an overall decrease compared with the non-corrosion state.(4)The study of the homogenization model shows that the maximum tensile stress always appears at the A and A points on the upper end of the prefabricated crack,indicating that the crack is more likely to develop along the crack tip.The maximum value of tensile force increases with the increase of S/T value,and drops sharply when S/T=0.5,and then keeps a slow increase with the increase of S/T value.According to the simulation results,the relevant prevention measures of asphalt pavement are put forward.