Study On The Adhesion Characteristics Of Warm Mix Recycled Asphalt And Aggregate

Asphalt pavements are widely used in road surfacing in China,and the large amount of old material generated during maintenance and repair is called recycled asphalt pavement（RAP）.In recent years,the recycling technology of asphalt pavement and how to improve the recycling rate of RAP have attracted the attention of domestic and international researchers.In order to improve the utilisation rate of RAP and to reduce the construction temperature,warm mix technology is considered for the regeneration of RAP.The adhesion between asphalt and aggregate is one of the most important properties of asphalt pavements,and its strength and durability are greatly influenced by the nature of the aggregate,but also by the nature of the asphalt.Due to the complexity of the blending components of warm mix recycled asphalt,the interaction with various types of aggregates is not yet clear.For this reason,it is necessary to examine the adhesion of warm mix recycled asphalt to the aggregates in order to judge the applicability of warm mix recycling technology.In this paper,three kinds of aggregates,basalt,granite and limestone,90#base asphalt and SBS modified bitumen,were used in the new asphalt with different proportions（15%,30%,45%,60%）of aged asphalt to obtain miscible asphalt,and warm mix,regenerant and both regenerant and warm mix were added to the miscible asphalt to prepare warm mix miscible asphalt.The warm-mix asphalt,recycled asphalt and warm-mix recycled asphalt were prepared by adding warm-mix,recycled and warm-mix asphalt.Contact angle tests,pull-out tests and Atomic Force Microscope（AFM）tests were used to study the effects of ageing asphalt,rejuvenator,warm mix and different types of aggregates on the adhesion properties of the asphalt-aggregate interface from both macro and micro perspectives:（1）Contact angle tests show that ageing weakens the cohesive power of asphalt and the cohesive power of asphalt and aggregate,and that the cohesive power of miscible asphalt and its cohesive power with each aggregate gradually decreases as the amount of ageing asphalt increases.Under dry conditions,the cohesive power of the warm mix miscible asphalt and the aggregates recovered to above the original asphalt level for all the ageing asphalt dosing conditions,while the cohesive power of the warm mix SBS asphalt and the aggregates did not recover to the original asphalt level at 60%of the ageing asphalt dosing;with the addition of the regenerating agent,the cohesive power of the regenerating asphalt and the aggregates increased and was better than that of the warm mix miscible asphalt,which recovered to above the original asphalt level.The adhesion between warm mix and recycled asphalt and aggregate is the strongest with the synergistic effect of warm mix and recycler.Under wet conditions,the adhesion of asphalt to aggregate was significantly reduced compared to dry conditions.The warm mix had a negative effect on the adhesion of asphalt to aggregate,the regenerant had a negative effect on the adhesion of SBS modified asphalt to aggregate and a positive effect on the adhesion of matrix asphalt to aggregate.（2）AFM observations showed that the addition of warm mix and regenerating agent improved the microscopic morphology and adhesion of the aged asphalt,with the microscopic morphology of the warm mix regenerated asphalt being closest to the level of the as-built asphalt.The regenerating agent improved the microscopic adhesion of the miscible asphalt more than the warm mix,where the adhesion of the warm mix miscible asphalt recovered to above the original asphalt level at 15%and 30%of the aged asphalt,while the adhesion of the warm mix SBS modified asphalt did not recover to the original asphalt level at all aged asphalt dosing levels.The results of Pearson correlation analysis showed that the surface energy and adhesion work of the asphalt obtained from the microscopic AFM test showed a high correlation with the surface energy and asphalt-aggregate adhesion obtained from the macroscopic contact angle test.（3）The pull-out test results show that the interfacial damage energy of asphalt and aggregate decreases with the increase of ageing asphalt admixture,the adhesion of granite to asphalt is more affected by the admixture of ageing asphalt,limestone is less affected by it,the addition of warm mix and regenerating agent can weaken the effect of increasing admixture of ageing asphalt on adhesion.The addition of regenerating agent and warm mix agent can help to improve the interfacial damage of asphalt and aggregate,but the interfacial damage of warm mix SBS modified asphalt and aggregate did not recover to the original asphalt level,the interfacial damage of warm mix matrix asphalt and aggregate only recovered to the original asphalt level at 15%of aged asphalt,the interfacial damage of regenerated asphalt and aggregate all recovered to the original asphalt level or more,the interfacial damage of warm mix regenerated asphalt and aggregate The interfacial damage energy of warm mix recycled asphalt and aggregate was the largest.After linear fitting of the results of the contact angle test,AFM test and pull-out test,it was found that the interfacial damage energy E of asphalt and aggregate showed a high positive correlation with the adhesion work W_as and adhesion force F.（4）Both the contact angle test and the pull-out test showed that limestone showed good adhesion to all types of asphalt,followed by basalt,and granite showed relatively poor adhesion.In summary,Under dry conditions,the addition of warm mix and regenerant can improve the adhesion of old and new miscible asphalt to aggregate,where the addition of warm mix is not as effective as regenerant in improving the adhesion of asphalt to aggregate,the use of warm mix alone has limited ability to improve the adhesion of SBS modified asphalt,warm mix and regenerant synergistic effect of warm mix regeneration of asphalt and aggregate adhesion to achieve the best results,therefore,warm mix regeneration is good regeneration method.At low levels of ageing matrix asphalt（15%）,warm mixes can be used directly to regenerate the asphalt;at high levels of ageing asphalt（45%,60%）,especially for SBS modified asphalt,warm mixes and regenerants are needed to achieve effective regeneration.