Investigation On Semi-flexible Pavement Material Prepared By Cold Mix Asphalt

Semi-flexible pavement is a new type of composite pavement structure formed by the macropore asphalt mixture filled with the certain mechanical strength cement mortar.The material shows a high degree of driving comfort and construction integrity which the cement pavement was lack of and it effectively overcome the defects of the traditional asphalt pavement in the high temperature environment,such as weak resistance to deformation and strength reduction.However,domestic research on semi-flexible pavement materials was still in initial stage,lacking the systematic study.This research evaluated the high-performance semi-flexible pavement material systematically with low energy consumption,low environmental pollution and convenient construction combined with self-researched reactive cold mix asphalt.The main research contents are as follows:(1)The strength mechanism of semi-flexible pavement material was revealed from the interaction between asphalt and mineral material and the interaction between asphalt and cement basing on analysis of the formation mechanism of hot asphalt mixture strength.(2)The single factor and orthogonal experiments were carried out with control indicators including softening point,60? dynamic viscosity and 25? Brookfield viscosity.The optimal ratio of cold mix asphalt was determined with 2%SBS and 0.5%carbon nanotubes,which were characterized by softening point of 90.7?,60? dynamic viscosity of 34376Pa-s,25? Brookfield viscosity of 22.6Pa·s.And the dynamical shear rheology(DSR)and bending beam rheology(BBR)results showed that its performance grading could reach PG88-22.Scanning electron microscopy(SEM)and infrared spectroscopy(IR)were used to analyze the enhancement effect of microscopic products on asphalt performance.(3)The cement mortars samples were prepared with different water-to-binder ratio and sand-binder ratio.The optimum ratio of cement mortars was determined with 100%cementitious material,25%water-to-binder ratio,25%sand-binder ratio,and 1%water reducing agent,which were characterized by 7d compressive strength of 73.7MPa,7d flexural strength of 7.48MPa,fluidity of 12.26s,and 28d contraction of 0.81‰,indicating good mechanical properties.(4)The gradation of the macropore asphalt mixture of semi-flexible pavement materials was designed by volumetric method,the target void ratio of which was 23%,25%,28%and 30%and the optimum asphalt dosage was 4%,4.5%,5%,5%,respectively,according to the Japanese standard and the domestic standard JTG E20-2011 of OGFC grade optimum asphalt dosage.The drainage loss rate(Schellenberg Binder Drainage Test)of the macropore asphalt mixture was lower than the specification requirement of 3%,but the scattering loss rate(Cantabro Test)was high.The perfusion effect of cement mortars was evaluated by indicators of the connected void ratio,theoretical maximum grouting amount,actual grouting amount,grouting rate and filling rate,which the target void ratio of 23%,25%,30%mixed gradation showed a better grouting rate and the target void ratio of 28%had a relatively low grouting rate.The higher the target void ratio,the higher the fill rate of the cement mortars.(5)The performances of the reactive cold mix asphalt semi-flexible pavement material were evaluated by the water immersion Marshall test the freeze-thaw split test,the rutting test,the trabecular bending test and the slip resistant test.The pavement performances proved favorable:Marshall stability could reach 25.46kN,the residual stability was higher than 85%of the requirements of the modified asphalt mixture and the freeze-thaw splitting strength ratio was higher than 75%of the requirements of the common asphalt mixture in the specification,indicating a favorable water stability.In the rutting test,the dynamic stability of the material reached 57272.727 times/mm,and the deformation was merely 0.011mm-0.037mm,which could be regarded as non-rutting pavement materials.With the target void ratio increasing,the low-temperature crack resistance of the semi-flexible pavement material was firstly increased and then decreased,and the 25%void fraction grading material showed a better low-temperature crack resistance.The semi-flexible pavement material had better anti-sliding performance than the unfilled asphalt mixture which hardly be affected by void ratio.Consequently,the reactive cold mix asphalt semi-flexible pavement material proved favorable road performance,especially the high temperature deformation resistance and water damage resistance.