Research On Anti-cracking Mechanism Of Open-graded Large Stone Asphalt Mixes Of Asphalt Pavement

In order to solve the problem of the reflective cracking in the semi-rigid base asphaltpavement, the asphalt overlay on old concrete pavement and the rigid base asphaltpavement, as well as the water damage problem of the semi-rigid base asphalt pavement,OLSM(Open-graded Large Stone Asphalt Mixes) relief layer has been put forward by someChinese scholars, it has been set below the asphalt surface layer and paved on the semi-rigidbase, the old concrete pavement, and the rigid base with cracks (or joints) in recent years inChina. The research on OLSM of asphalt pavement is still in the stage of the indoor test andthe test road construction. In this dissertation, on the basis of the existing research, thematerial composed design of OLSM and its road performance test have been continued, themesostructure and the macroscopic mechanical response of OLSM of asphalt pavementhave been thoroughly and systematically analyzed. On the basis of theoretical calculationsand combined with the test roads construction, the structure design steps and processes ofOLSM cracking relief layer of asphalt pavement have been proposed.In this dissertation, on the basis of the reference gradation of OLSM-25in the domesticand international, by using of the variable I principle, the gradation of OLSM-25has beendesigned. Combined with the requirements of the porosity (15%to20%), the recommendedgradation range of OLSM-25has been proposed. the mechanical property, the hightemperature performance, the low temperature performance and the water stability ofOLSM-25have been tested, and the technical specifications of OLSM-25have beenproposed. By using of the discrete element method, the numerical simulation of the indirecttensile (splitting) test of AC-16, AC-20and OLSM-25have been carried out. Combinedwith the test roads construction, the discrete element model of asphalt pavement structurewith OLSM-25cracking relief layer has been established. Under the action of theasymmetric traffic load, the comparative analysis of the mesostructure with two differenttypes of cracking relief layer, and the mesostructure with three different gradationsOLSM-25cracking relief layer have been carried out. By using of the finite element method,the finite element model of asphalt pavement structure with OLSM-25cracking relief layer has been established, the stress and fatigue analysis on asphalt pavement with two differenttypes of cracking relief layer, and three different gradations OLSM-25cracking relief layerhave been carried out. On the basis of the analysis of structural design method of asphaltpavement in the domestic and international, considering the actual situation ofearly-cracking destruction in the base of asphalt pavement in our country, the constructionrecommendations, the design steps and processes of OLSM of asphalt pavement structurehave been proposed. On the basis of the anti-cracking mechanism, the reasonable structureof OLSM of asphalt pavement have been recommended.The research indicates that as follows:(1) Under the action of the peak axial force,when the cylinder specimen of asphalt mixture is cracking, the number of micro-crackswithin the specimen reduces gradually. as compared with the AC-16and AC-20, theanti-cracking effect of the indirect tensile test of OLSM-25is significant.(2) Under theaction of the asymmetric traffic load, when two cracking relief layers have the samethickness, the vertical contact force, the speed of the vertical movement and the verticaldisplacement of A point particle in the bottom of OLSM-25cracking relief layer were lessthan the corresponding values of the ordinary AC-25cracking relief layer. The anti-crackingeffect of OLSM-25cracking relief layer is better than ordinary AC-25cracking relief layer.(3) The coupling stress is less than the traffic load stress and the temperature stress. For thestructural design of the rigid base asphalt pavement with OLSM cracking relief layer, itstraffic load stress or temperature stress should not exceed its own allowable anti-tensilestrength. On the above design basis, the reasonable thickness of OLSM cracking relief layerwill be calculated and determined.(4) Compared to the ordinary AC-25cracking relief layerwith the same thickness, OLSM-25cracking relief layer has higher carrying capacity andbetter stress relief performance. By using the cracking relief layer of OLSM-25, thepropagating speed of the reflective crack will slow down effectively, and the fatigue life ofthe asphalt pavement structure will be improved significantly.(5) In practical engineeringapplications, considering the stress relief effect, deformation capacity, slowing down thepropagating speed of the reflective crack, extending the fatigue life of asphalt pavement,and the mixture segregation problem in the construction, the2#gradation OLSM-25withrelative coarse aggregates and medium porosity should be taken as the cracking relief layer, not only the purpose of the stress relief effect, slowing down the propagating speed of thereflective crack should be achieved, its road performance requirements should be met and ithas a certain degree of deformation capacity, but also the life of the asphalt pavementstructure should be extended.