Study On Construction Quality Evaluation In Hot In-place Recycling Of Asphalt Pavement

Hot in-place recycling（HIR）of asphalt pavement is widely used in the maintenance of high-grade highways in China due to its 100%utilization of old materials,fast construction speed and effective repair of pavement diseases such as rutting and looseness.HIR equipment recovers the pavement performance by heating,loosening,regenerating,re-mixing,paving and rolling.The construction process is complicated and the construction quality is greatly affected by the construction process and technology.Based on the HIR Project for asphalt pavement of Jiangsu expressway,this paper makes an in-depth study on the quality and uniformity of recycling construction through field investigations and core sample detection.First of all,use infrared thermal imaging camera to monitor the temperature field of HIR heating,milling and paving process.Propose evaluation indicators from mean temperature,uniformity,over-heating and conduct a quantitative analysis of temperature field during key construction process.And put forward improvement measures of temperature control.Secondly,use MATLAB-based image processing technology to process the color image of asphalt pavement texture into a binary map representing the positive and negative texture of the pavement.Negative texture area ratio（NTR）and negative texture X and Y axis distribution coefficients(C_VX,C_VY)are proposed as quantitative evaluation indexes of segregation,and the evaluation criteria for segregation of SMA-13 HIR pavement are determined.Combined with specific examples,the uniformity of road surface texture after HIR is evaluated to provide a reference for quantitative evaluation of segregation.Then,do non-destructive testing of road surface compaction,water permeability and structural depth after regeneration.Compared with milling and resurfacing,the compaction of HIR is lower,the distribution of longitudinal compaction is more uniform,and the lateral compaction is affected by compaction process.The water seepage coefficient and anti-skid performance of most regeneration sections reach the level of milling and resurfacing sections,but the quality fluctuates more.Finally,collect mixes during construction,experimental results point out that the old asphalt has different degrees of aging in the construction process.The higher the road temperature,the better the uniformity of temperature,the lower the fineness of grading in the Milling process.In-situ coring is carried out for the original road surface and the recycled road surface.After recycling,the compactness and rutting resistance of the mixture are reduced,the anti flying performance and the low-temperature cracking resistance are not significantly improved.The core taking research is carried out for the regeneration road section with different years of regeneration and similar working conditions,which approximately reflects the impact of the use time on the performance of the recycled mixture.The research indicates that the compaction of the recycled mixture continues to increase with the use of time,and it is the most uniform when used for 2-4 years.In two years,the rutting resistance recovered to the level of the original pavement and continued to grow,with no obvious regularity in the anti flying ability,low-temperature crack resistance and service time;for the regeneration process of changing the gradation type of the original pavement mixture,the performance variation of the recycled mixture material is large.Through a large number of field investigations,laboratory tests and theoretical analysis,the paper systematically studies the temperature field distribution,pavement performance changes,and material property changes during HIR construction.The study results are helpful to further improve the quality control of HIR construction.