Analysis And Research On Fatigue Characteristics Of Semi-rigid Base Of Permanent Pavement

Semi-rigid base asphalt pavement is the most widely used pavement structure in China,which has the advantages of strong slab,low cost and high strength.With the rapid development of China’s economy,the traffic volume is increasing day by day,the overload problem is increasing day by day,the road surface has been seriously damaged,and the service life has been reduced.Therefore,the concept of permanent pavement design is gradually concerned,which is aimed at improving the service life of the road and reducing the total economic input.The key to avoid structural damage is to control the tensile stress at the bottom of the base layer,which is closely related to the mechanical and fatigue properties of the base material.In order to study the fatigue performance of permanent pavement,this paper relies on the science and technology project of Hebei Provincial Department of Transportation’Reliability Analysis and Evaluation of Permanent Asphalt Pavement with Semi-rigid Base’.Based on the permanent asphalt pavement of Jingde Expressway,the raw materials,gradation and cement dosage of cement stabilized macadam base of actual pavement are adopted.The single factor test method is used to study the mechanical and fatigue properties of cement stabilized macadam materials.（1）The mechanical properties of cement stabilized crushed stone materials were tested by different factors.The results show that the flexural strength and splitting strength of cement stabilized crushed stone materials are basically the same with the influence of cement dosage,compaction degree and age.However,the flexural strength and splitting strength increase linearly with the increase of cement dosage and compactness.The flexural strength and splitting strength increase logarithmically with the increase of age.In the first 28 days of curing age,the flexural strength and splitting strength of cement stabilized macadam material increase rapidly.After 28 days,the growth rate is greatly reduced and gradually tends to be gentle.Therefore,in actual construction,attention should be paid to the protection of cement stabilized macadam base within 28 days after paving.（2）The freeze-thaw compressive strength of cement stabilized macadam materials with different freeze-thaw cycles was tested.The results showed that the freeze-thaw cycle reduced the compressive strength of the material,and the more freeze-thaw cycles,the lower the compressive strength.At the same time,with the increase of freeze-thaw cycles,the change range of compressive strength of cement stabilized gravel materials gradually decreases.The change of compressive strength of materials with higher compressive strength before freeze-thaw cycle after freeze-thaw cycle is significantly lower than that of materials with lower compressive strength before freeze-thaw cycle.Therefore,freeze-thaw cycle has a higher degree of weakening the compressive strength of materials with higher compressive strength.（3）The fatigue properties of cement stabilized macadam materials with different cement dosages were studied,and the fatigue properties of the materials were analyzed by scanning electron microscopy.The results show that the fatigue life of the materials increases with the increase of cement dosage.The fatigue equation of cement stabilized gravel material is established and corrected.From the microscopic point of view,compared with the cement stabilized crushed stone material with higher cement dosage,the interfacial transition zone of the material with low cement dosage is more loose,and the cement hydration products in ITZ are less.After fatigue failure,due to the effect of repeated load,the internal damage of the material continues to occur.The ITZ of the cement stabilized gravel material with low cement dosage is more loose and has more voids.Therefore,its ability to resist bending and splitting is lower than that of the material with higher cement dosage.The ability to resist repeated load is low,and the fatigue life is relatively low.（4）The three-dimensional finite element model of the dynamic response of the pavement structure of Jingde Expressway is established,and the stress at different positions of the semi-rigid layer is obtained.The fatigue life of the semi-rigid layer is estimated:the fatigue life of the upper base is 3.60×10¹¹ times,the fatigue life of the lower base is 6.46×10¹⁰ times,and the fatigue life of the subbase is 1.53×10¹⁰ times.