Study On Interfacial Effects And Influences Of Moisture On Rubberized Asphalt-aggregate Interface

Rubberized asphalt has been widely applied in the field of engineering due to its good performance,development prospect and environmental benefits.The existing researches focus mostly on the macro performance of rubberized asphalt mixture but ignore the interface between rubberized asphalt and aggregate.However,for multi-phases materials,rupture occurs easily on the weak interface phase.As one of the most common types of asphalt pavement distress,water damage,is caused by the stripping of asphalt on the interface.Thus,to deeply understand the interface reactions is of profound significance to promote the interface performances between rubberized asphalt and aggregate.For these reasons,the complete process of interface reactions,from the adhesion forming to failure between asphalt and aggregate,and the effects of moisture were taken into account in this study.The research proceeded as followed:（1）The rheological properties of binders were investigated under various conditions.（2）Molecular dynamics models were constructed to simulate the molecular behaviors of interface between asphalt and aggregate and evaluate the adhesion between them.（3）The Disk-shaped compact tension（DCT）test was employed to analyze the failure process and characteristics of interface and image processing was used to identify and quantify different failure types.Meanwhile,the effects of moisture on interface behaviors at different scale were studied.Firstly,Thermal Gravity（TG）,Infrared Spectrum Experiment（FTIR）and Differential Scanning Calorimeter（DSC）tests were conducted on rubber to characterize its physiochemical properties.Then Dynamic Shear rheometer（DSR）and Bending Beam Rheometer（BBR）tests were adopted to determine the rheological and viscoelastic performances of rubberized binder at different temperature,fatigue and aging status.The results showed that the treatment on rubber lowered the viscosity of binders at high temperatures.Rubberized binder has better high temperature performances for its higher failure temperature and more elastic components than virgin binder.Meanwhile,the treatment on rubber was found to be the most significant factor affecting the high temperature performance of binder.The rheological properties of virgin binder were closely correlated to the low temperature performance of rubberized binder.The viscoelasticity of rubberized binder was sensitive to short aging procedure.The rubberized binders used in this research had improved performance and would thus contribute to the interface performance.The molecular behaviors of interface between rubberized binder and aggregate were investigated from molecular scope.The molecules of asphalt and representative aggregate oxide were established and verified first.After that,the cohesion of asphalt,adhesion between asphalt and aggregate oxide and concentration distribution of asphalt on the surface of aggregate oxide were determined to evaluate the performance of interface.The results showed that:（1）The cohesion of rubberized binder,the adhesion between it and CaO/MgO were better than that of the virgin binder.（2）The aggregate oxides greatly influenced the interface binding behavior.The aggregates with more CaO and MgO content generally had better adhesion with asphalt while aggregates with more SiO₂ and Al₂O₃ had poor adhesion.（3）The stronger molecular interactions and better adhesion between asphalt and aggregate were formed when the asphalt with more concentrate distribution and higher peak value of concentration.（4）Aging had no obvious effect on the asphalt concentration but effectively influenced the cohesion of asphalt and adhesion at interface.Moisture was introduced to evaluate its effect on interface molecular behaviors through constructing the model under moisture condition.And the concentration of moisture was obtained and analyzed as well.The results showed that:when moisture intruded in the interface system,it existed not only in asphalt but also in the interface between asphalt and aggregate.The diffusion rate of moisture increased with temperature and the moisture diffused faster in virgin asphalt than in rubberized asphalt.Besides,asphalt aging mitigated the diffusion of moisture.The cohesion of rubberized asphalt under moisture condition was greater than that of virgin asphalt.And asphalt aging would result in a greater difference of cohesion between rubberized and virgin asphalt.Asphalt under moisture condition has improved cohesion,especially for the aged asphalt.Interface formed by asphalt and aggregates with higher CaO/MgO content has better moisture resistance while that formed by aggregates with more SiO₂/Al₂O₃ content were more sensitive to moisture,especially for the rubberized asphalt.Moisture had adverse effect on adhesion between asphalt and aggregate.The aggregates with more CaO showed better resistance whereas aggregates with more SiO₂ tended to cause moisture damage.The disk-shaped compact tension test（DCT）was employed and critical indexes obtained from LOAD-Crack Mouth Opening Displacement（CMOD）curves were proposed to analyze the failure process,characteristics of interface between rubberized asphalt and aggregate,and the effect of several factors.The results showed that:in most cases,higher asphalt stiffness and aggregate strength would improve the fracture performances of interface.When formed by alkaline aggregate,the interface performed better to resist fracture.Smaller rubber size would result in better fracture resistance and the addition of Styrene-Butadiene-Styrene（SBS）had more positive effect than rubber.Anti-stripping additives were found to improve the interface performances.MATLAB software was employed to identify the fracture characteristics of DCT samples and to distinguish three different failure types.Meanwhile,the proportion of various failure types was determined and the effect of moisture was considered.The results showed that Red-Green-Blue（RGB）method could effectively and accurately identify the aggregate and the parameter used in MATLAB was verified to be rational.The proportion of different failure types was ranked from high to low as cohesive failure,adhesive failure and aggregate fracture failure.In most cases,moisture would result in a decreased portion of asphalt cohesive and aggregate fracture failure but increased portion of adhesive failure.And similar to the results of molecular dynamics,the cohesion of rubberized asphalts was lower than SBS modified asphalt and the interface formed by alkaline aggregate had better moisture resistance.The addition of anti-stripping additive improved the adhesion between asphalt and aggregates to a certain extent.