Towards very high RAP content asphalt mixes:A comprehensive performance-based study of rejuvenated binders

Hot recycling of reclaimed asphalt pavement(RAP)from replacement of deteriorated asphalt pavements is a widespread technique,and able to ensure clear economic and environmental benefits.For this reason,paving industries,agencies and researchers are spending significant efforts in order to maximize such advantages by increasing the amount of RAP within new asphalt mixtures.Nevertheless,adequate performance of recycled mixtures must be guaranteed despite the re-use of high amounts of RAP which involves the presence of aged,oxidized and stiffened binder.In this perspective,the present study aimed at evaluating the rheological properties at mid-service and high-service temperatures of bituminous blends composed by 40%of virgin binder and 60%of aged rejuvenated bitumen(simulating the aged hard bitumen coming from the RAP).Such proportion was selected to represent a high recycling rate of RAP(about 60%of the total weight of aggregates,RAP included).A chemical commercial additive at the liquid state was selected as rejuvenator;it was dosed at the optimum content based on empirical and rheological preliminary characterization.The performance of the recycled blend was then compared to that of a virgin reference bitumen.Dynamic shear rheometer tests were carried out to determine the master curves and the failure characteristics(at mid and high service temperatures)of the selected binders.The effect of aging(related to the durability over the material lifetime)was also studied analyzing binders’responses in unaged,shortterm and long-term aged conditions.Overall,experimental findings demonstrated the efficacy of the rejuvenation of recycled binders containing very high amount of aged bitumen.

Numerical visco-elastoplastic constitutive modelization of creep recovery tests on hot mix asphalt

This paper discusses a visco-elastoplastic constitutive model to analyze the creep deformability of asphalt concretes at high service temperatures, finalized to improve the interpretation of permanent deformation phenomenon and performance design of road pavements. A three dimensional constitutive visco-elastoplastic model is introduced, in tensor as well as in numerical form. The associated uniaxial model is used to arrange a plastic element in series with the viscoelastic component. The latter is defined by an elastic spring placed in parallel with three Maxwell elements. Three different hardening laws, namely isotropic, kinematic and mixed hardening, are included in the constitutive model to compare the creep deformability. The proposed constitutive model has been calibrated and validated on the basis of uniaxial creep-recovery test results at 40℃. This is performed with a high performance hot mix asphalt concrete （HP-HMA） at different stresses and loading times. Depending on the hardening law considered, permanent deformation data predicted by the proposed model results are reasonably consistent with the experimental creep-recovery data. A rational constitutive model that is physically congruent with the creep phenomenon of asphalt concretes was developed and calibrated to achieve a deeper understanding of the stress-strain response of such materials. The fundamental relevance of an appropriate plastic response modeling, in the study of the creep behavior of asphalt concretes for highway and road pavements.