| Double-layer asphalt paving is a common paving technique for roads where high durability is required.This technology can pave two layers of asphalt mix pavement at the same time and complete the construction in the same roll.Compared with the traditional single-layer paving technology,the double-layer paving technology of asphalt pavement has many advantages,such as improving the bonding effect between the pavement layers,optimising the pavement structure,saving construction time and cost,and so on.Using this technology in construction can effectively increase the life of the road,reduce maintenance and repair costs,and improve driving comfort and safety.However,it should be noted that there is relatively little research on the technology of dual-layer asphalt pavements both at home and abroad.In particular,there is a lack of systematic research into the specific interlayer bonding and compaction characteristics of the dual layer technology and their effect on road performance.These problems are the main bottlenecks restricting the further development of asphalt surfacing technology.Therefore,it is necessary to intensify research on this technology and to further investigate its characteristics and influencing factors in order to promote the development and application of this technology.Firstly,in order to more realistically simulate the compaction effect of the double-layer paving technology on the pavement,this study adopts the rotary compaction method to prepare the specimens.Based on the existing dual-layer asphalt pavement,this paper designs a variety of pavement structure combinations,simulates the compaction process of the fixed compaction work of the pavement by setting the number of rotary compactions,and determines the required value by making a single-layer test piece aggregate quality,thus providing a basis for the production of dual-layer specimens.The research results show that: under the same compaction conditions,the mass of aggregate required for double-layer specimens is greater than that for single-layer specimens,and the double-layer paving technology will change the compaction effect of the pavement layer.Secondly,this study uses image processing technology to evaluate the interlayer bonding effect of simulated double-layer paving specimens,and investigates the effect of different interlayer processing methods on the embedding depth of the pavement surface layer,while explaining the compaction characteristics of rotary compaction.The evaluation index and compaction characteristics of different surface layer structure combinations are investigated.The research results show that the combination effect between the pavement layers can be effectively improved by adopting the double-layer paving technology,and different surface layer gradations lead to different surface layer embedding depths.The embedding depth is relatively stable,but when SMA-13 is used as the top layer of the pavement,the embedding depth is deepened,but its distribution is not uniform.In addition,when studying the compaction characteristics of different pavement structures,it was found that the combination of 3cm+7cm has the best compaction characteristics and better compaction effect compared to the combinations of 4cm+6cm and5cm+5cm.The compaction work required is less,the bonding effect of the surface course is better and the performance is more stable under subsequent load.Considering different surface course materials,when AC-20 is used as the lower course gradation and SMA-13 is used as the upper course gradation,the early compaction effect is better,but it also requires more compaction work,and the later compaction effect is not as good as that of AC-13.13 asphalt mix is used as the surface course sample.Then,this paper then examines the method of analysing the mesostructure of a double-layer asphalt mix at different scales.Two-dimensional images of asphalt mix,mortar and cement were obtained by laser diffraction,electron microscopy and optical imaging.Using the digital image analysis method,combined with the thickness distribution curves of the dispersed phase at different scales,the spatial structure distribution of the dispersed phase was quantified,and structural parameters such as expectation,mode,maximum specific gravity and uniformity parameters were proposed and error control analysis was carried out.The research results show that the void ratio has no significant effect on the mortar thickness of the specimen.Within the target void ratio range,by comparing the mortar thickness of the double layer specimens with different structural combinations,it is found that the combination of 3+7 heights is due to the good compaction characteristics.Therefore,the mortar thickness distribution is more uniform and the mortar thickness is less than that of other combinations and single layer specimens.For different mixes,when SMA-13 is used as the top layer,the mortar thickness is greater but the uniformity of distribution is poor.Finally,this study extensively tested single layer and double layer rotationally compacted specimens under different height combinations and surface material combinations using direct shear tests,direct pull-out tests and three-point fatigue tests.The results of the research show that the dual layer paving technology improves the bond between the pavement layers,increases the shear strength between the pavement layers by 60% and increases the tensile strength by approximately 50%.At the same time,it has no significant effect on the high temperature performance of the specimen.Of the different height combinations,the 4cm+6cm combination has the best rideability and the most significant performance improvement.Of the combinations of different surfacing materials,when SMA-13 is used as the top layer,the pavement performance is most noticeably improved,but it requires more compaction work.Double-layer paving technology can also improve the anti-fatigue performance of the surface course and ensure the performance of the road after long-term use. |
