| Semi flexible pavement(SFP)material is a kind of composite pavement material formed by pouring high-performance cement mortar into the large gap asphalt mixture.Because of its high bearing capacity and high temperature stability,it can be set as the surface layer to solve the problems such as rutting caused by the lack of high temperature stability of asphalt mixture,so it has been widely concerned in recent years.However,in the actual engineering,the cracking of semi flexible materials has become the main reason that restricts its popularization.This is because the actual stress state of the pavement is complex,in addition,it is a three-phase heterogeneous material,and the quality of grouting is difficult to control during the construction.At present,the understanding of cracking performance and mechanism of semi flexible materials is limited.The optimization of material performance is usually based on the results of macro test.The skeleton structure of semi flexible materials can bear the load transfer stress and prevent the development of microcracks.The increase of oil stone ratio can enhance the crack resistance of materials,but it also affects the grouting of cement mortar.At present,the research on these two main factors affecting the crack is still blank.Therefore,based on the open fund of the State Key Laboratory of high performance civil engineering materials research on macro and micro structure design method of semi flexible composite pavement,this paper uses digital image processing technology to obtain the internal structure component information of semi flexible materials from the micro perspective,and studies the relationship between the micro index of internal structure and the macro performance of materials The optimization of crack resistance of materials provides a new way of thinking,which lays a foundation for the establishment of semi flexible composite pavement structure design system considering micro structure.Firstly,the fracture energy in fracture mechanics is used as an index to evaluate the crack resistance of semi flexible materials.In this paper,the application of SCB at home and abroad is summarized,and the test method of SCB is the main test method,and the fracture energy is the macro index to evaluate the crack resistance.Five kinds of semi flexible materials with different asphalt and additives were designed and manufactured.The failure mode and process were analyzed by testing the specimens at 25 ℃ and-10 ℃.The results show that in the low temperature environment,the semi flexible material appears brittle fracture when it breaks.At this time,the one with higher peak load,larger fracture energy and better cracking resistance in the low temperature environment,such as the semi flexible material with high asphalt.At room temperature,the viscosity deformation ability of the semi flexible material increases and retains a certain toughness.At this time,the material with slow fracture rate will have a larger extended fracture energy.For example,the semi flexible material with interface modifier and fiber is better in the environment with higher temperature.Secondly,with the help of digital image technology,the contact characteristics of semi flexible material skeleton structure are statistically analyzed,and the average coordination number is used as the micro evaluation index of semi flexible material skeleton structure.The results show that the distribution of the contact points is not uniform,there are more contact points in the middle and less contact points at both ends of the rotary compaction specimen;the average coordination number of the micro index and the macro crack resistance have a good correlation under the conditions of different compaction times,and properly increasing the compaction times is conducive to enhancing the stability of the semi flexible material skeleton structure,improving the crack resistance of the material;under the different oil stone ratio The average coordination number increases first and then decreases with the increase of the oil stone ratio,while the fracture energy of the semi flexible material is proportional to the oil stone ratio.When the oil stone ratio is 4.4%,the average coordination number is the largest,but the macro crack resistance is not the best at this time,which shows that under different oil stone ratio,it is not appropriate to characterize the stability of the semi flexible material skeleton structure by the average coordination number.Finally,based on the digital image processing technology,considering the role of coarse aggregate,cement mortar and voids in semi flexible materials,an evaluation method for the distribution uniformity of internal structural components of semi flexible materials is proposed.Five materials with different oil stone ratio are used to quantitatively evaluate the uniformity degree.At the same time,the cracking resistance and fatigue cracking resistance of five kinds of semi flexible materials with oil stone ratio at room temperature were evaluated by semicircle bending test,and the relationship between macro cracking resistance and micro internal structure uniformity was explored.The results show that the uniformity degree evaluation parameters proposed by imusm can quantitatively evaluate the homogeneity of the internal structure of the semi flexible material.When the homogeneity of the internal structure of the semi flexible material is the best,the asphalt content increases properly,but the influence on the cement mortar grouting is low,which can ensure the increase of the proportion of the overall asphalt content of the material and make the cement mortar fully It is suggested that the ratio of oil to stone should be between 4.4% and 4.7%based on the test results. |
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