Research On Compaction Mechanism Of Thermosetting Epoxy Asphalt Mixture For Steel Deck Pavement

In the compaction process of epoxy asphalt mixture,there are not only the wetting effect between asphalt binder and fillers,the viscous effect of asphalt mastic,the adhesion effect between asphalt mastic and aggregate particles and the contact effect between aggregate particles,but also the thermal curing reaction caused by the thermosetting epoxy asphalt.Due to the special design requirement and field construction conditions of steel deck pavement,over curing,uneven curing and mixture segregation occur in field construction and cause compaction quality problems.Therefore,to solve the problems,the mechanism of epoxy asphalt mixture compaction needs to be studied.Based on the current state of relative research,it can be found that in the area of multiscale research,the currently used 2-dimentional digital image process methods are not suitable for the mixtures with smaller particle size and finer gradation,the macroscale parameters and the mesoscale parameters are not significantly corresponded.In the area of mechanical analysis,the finite element method based on continuum hypothesis is not suitable while the DEM(Discrete Element Method)is under developing at irregular shape aggregate particle modeling method,mastic modeling method and hot mixed asphalt mixture modeling method.In the area of construction research,macroscale experiments are still the major study methods and there are few studies on the special field construction conditions of steel deck epoxy asphalt pavement and its effect on the compaction quality.Therefore,this article mainly focus on four research aspects including the multiscale method for the research of epoxy asphalt mixture compaction,the mesoscale tribology mechanism of asphalt mixture compaction,the DEM simulation and the field construction conditions analysis.Firstly,the asphalt binder rotary viscosity test,the mortar viscosity test based on dynamic shear rheometer and the Superpave gyratory compaction test was conducted to study the isothermal curing properties of asphalt binder(mortar)and macroscale compaction characteristics of asphalt mixture under the curing temperature of 100??110? and 120?.Then the Double-Arrhenius model was used to study the three stages of isothermal curing reaction of epoxy asphalt binder and mortar.The designed compaction stage was defined based on the densification curve.The CD IE(Construction Densification Index for Epoxy asphalt concrete)was presented and used to discover the quadratic function correlation between compaction effort and curing time.Then,the inner meso-structure image of compacted epoxy asphalt mixture was acquired using slicing-optical scanning method.An adaptive extremum suppression algorithm was developed to conduct stratified gray intensity extremum suppression on distance transformed gray image.And combined this algorithm with OTSU binarization method,morphological reconstruction method and watershed transform algorithm,a digital image segmentation recognition method was developed for epoxy asphalt mixture with smaller aggregate size and finer gradation,which solved the problems of particle connection and over segmentation in asphalt mixture digital image process.Thus a multiscale research method for the study of epoxy asphalt mixture compaction was established.Secondly,the solid-fluid-solid meso-structure of asphalt mixture was studied,three meso-structure characteristic parameters including the CAR(Contact Area Ratio),the ACA(Average Contact Angle)and the PMFT(Proximity Mastic Film Thickness)were presented and a boundary pixel window search algorithm was developed.The value variation of meso-structure parameters under continuous compaction load was studied and the correlation between asphalt binder(mortar)viscosity,design compaction effort,CDIE,CAR and PMFT was established.The Stribeck curve theory was introduced to discover how the mastic viscosity affect the lubrication state of meso contact structure thus affect the macro compaction characteristics.Then it was obtained that for the epoxy asphalt mixture compaction,the best asphalt binder viscosity for epoxy asphalt mixture compaction is 100cP-300cP,the best mortar viscosity is 100Pa·s?200Pa·s.Thirdly,the irregularly shaped aggregate particles were build based on the designed gradation using stochastic sphere vertex generating method and mid-surface ball filling method.The mixture particles were generated by extend the size of aggregate particle to the size of mastic coated aggregate particle.Then the loosely packed DEM model of asphalt mixture was built by gravity deposition.In addition,a two-stage contact model combined Burgers model with the parallel-bond model was designed,the value range of contact model's parameters for different curing conditions was obtained by conducting the trial simulation and parameter inversion based on the back propagation neural network algorithm.The DEM model was then used to simulate the Superpave gyratory compaction and study the particle movement,the air void distribution and the mechanics characteristics of hot epoxy asphalt mixture.Lastly,the phenomena including quality variation,mixture agglomeration,mixture friability and pavement surface bleeding that occurred in steel deck epoxy asphalt pavement field compaction was analyzed.By building the field compaction DEM simulation model,the velocity,displacement and mechanic properties of epoxy asphalt mixture particles under roller compactor was studied.The field compaction process of over cured mixture,uneven cured mixture and segregated mixture was simulated by changing the contact model parameters and conducting partition gravity deposition.Then the effects of these special conditions on the compaction quality was analyzed.The results shows that the same repeated compaction load is unable to improve the density of highly cured epoxy asphalt concrete.The agglomerated mixture particle can break the dense structure around it under compacion load and the upper agglomerated particle has greater impact on the compaction quality.Additionally,with the increasing of vertical segregation level,the instability of compaction mixture particels increases.As the compaction load attenuate vertically,over repeated compaction leads to the separation of mastic from aggragate on the upper part of mixture layer thus cause surface bleeding.