Study On Crack Resistance Of Semi-rigid Base In High Altitude Mountainous Areas

Semi-rigid base asphalt pavement is prone to reflect cracks in use,especially in high altitude mountainous areas.In this paper,the temperature field,stress field and stress intensity factor of semi-rigid base asphalt pavement are analyzed in detail by finite element software under the background of climate in high altitude mountainous area,and corresponding anti-cracking measures are put forward.At the same time,according to the cracking characteristics of semi-rigid base and the anti-cracking measures of semi-rigid base proposed by finite element analysis,the influence of coarse aggregate content,fine aggregate content and cement content on drying shrinkage coefficient and temperature shrinkage coefficient is studied through laboratory tests.The composition of semi-rigid base material is optimized.And the gradation of cement stabilized macadam base and cement content which are suitable for semi-rigid base asphalt pavement in high altitude mountainous areas are obtained.Firstly,the temperature field and temperature stress model of semi-rigid base asphalt pavement in high altitude mountainous area is established based on the historical climate data of Malkang to analyze the temperature field and temperature stress state of structure layer of pavement,and the influencing factors of temperature stress are analyzed quantitatively and significantly.The results show that the pavement depth affected by solar radiation and atmospheric temperature in high altitude mountainous areas ranges from 0 cm to 71 cm,and the semi-rigid base and asphalt surface course are the main structural layers affected by solar radiation and atmospheric temperature.In winter,the maximum temperature tensile stress of asphalt pavement surface reaches2.56 MPa,and the maximum temperature tensile stress of top of base layer is 0.34 MPa.The stress is close to the tensile strength.Both base and surface layers have the risk of temperature shrinkage cracking.The expansion coefficient of base layer has a significant effect on the temperature stress of base layer,and reducing the expansion coefficient of base layer can reduce the temperature stress of base layer.Secondly,the stress intensity factors of temperature-type and load-type reflective cracks are calculated,and the primary and secondary factors of stress intensity factors are analyzed by orthogonal test method.The results show that with the increase of reflective crack depth,the cracks stress intensity factor of K_I of temperature-type and load-type increases significantly;with the increase of pavement temperature,the peak value of K_I of load-type reflective cracks decreases gradually,the peak value of K_III increases gradually,and the contribution proportion of type II cracks to the expansion of reflective cracks increases rapidly;the primary factor of the stress intensity factor K_I of temperature-type reflective cracks is the expansion coefficient of the surface layer.The next factors are surface modulus and the expansion coefficient of the base layer,but the difference of the extreme values of the three is not obvious.Finally,the main conclusion is that the expansion coefficient is the main influencing factor of temperature stress and temperature-type reflective crack stress intensity factor based on finite element method.For cement stabilized macadam base,this paper analyzes the effects of coarse aggregate content,fine aggregate content and cement content on drying shrinkage coefficient and temperature shrinkage coefficient of cement-stabilized macadam.The results show that when the pass rate of 4.75 mm is30%³5%and 0.075 mm is 1%³%,the shrinkage coefficient of cement stabilized macadam base is low,and 4%cement dosage is the reasonable content of cement stabilized macadam.The results of optimization verification of cement stabilized macadam base show that the temperature tensile stress of optimized cement stabilized macadam base is 0.217 MPa,which is 36.9%lower than that before optimization.The peak value of temperature-type stress intensity factor K_I at different reflective crack depths is lower than that before optimization.When the reflective crack depth is 0 cm?that means only base crack?,the peak value of K_I decreases the most,reaching 27.0%.