The objective of the presented study is to determine linear viscoelastic (LVE) properties of corresponding binders and mixes and to check how they change with reclaimed asphalt pavement (RAP) content. The investigation is part of a wider on-going research project, in the framework of a PhD thesis, in collaboration between Université de Lyon/École Nationale Travaux Publics de l’État (ENTPE), EIFFAGE Travaux Publics and Beyond Petroleum. Dynamic shear rheometer and tension/compression (using a Métravib device) complex modulus tests were performed on nine different bitumens, produced as blends of two different base bitumens and RAP-extracted bitumen in various proportions. LVE properties of six asphalt mixes, produced with the same materials and proportions of certain bitumen blends among the nine tested ones, were measured in tension/compression mode. 2 Springs, 2 Parabolic Elements, 1 Dashpot model was used to fit experimental data both for binders and mixes. Shift-Homothety-Shift in time-Shift transformation (developed at ENTPE) was applied to verify the correspondence of LVE behaviours of related binders and mixes.

The main issue with asphalt pavement recycling is the assessment of the influence of aged bitumen in reclaimed asphalt pavement (RAP) material on viscoelastic properties of a blended binder in the final mixture. Blending charts or empirical laws, such as the “log–log” rule, are currently used to estimate grading parameters for material characterisation. However, a true prediction method of linear viscoelastic properties is still missing. The presented study is part of a wider ongoing research effort in the framework of a Ph.D. thesis, in collaboration between University of Lyon/Ecole Nationale des Travaux Publics de l'Etat (ENTPE), EIFFAGE Travaux Publics (ETP) and Beyond Petroleum. The paper focuses on the influence of the RAP-extracted binder content on viscoelastic properties of bitumen blends obtained from different asphalt binders. Three unaged bitumens were blended with a binder extracted from a well-known RAP material in different proportions (20%, 40% and 60%) for a total of 13 different bitumen blends. Complex modulus Dynamic Shear Rheometer tests were performed on binders at the ETP Research Center. Experimental results were modelled by using the 2S2P1D model, previously developed at ENTPE. A method to estimate viscoelastic properties of bitumen blends over the whole range of frequency and temperature is proposed.

The paper focuses on the investigation of the effects of a recycling agent on mechanical performances of bituminous mixtures produced with reclaimed asphalt pavement (RAP). Twenty-one different bituminous mixtures were produced and tested, using three distinct virgin binders (15/25, 35/50 and 70/100 penetration grades), with RAP contents varying from 0% to 60%. Seven of the mixtures were produced by adding a recycling agent of vegetable origin (its content was fixed equal to 3.5% by weight of the RAP binder). One of the mixtures is a 100% RAP mixture, produced only with RAP-extracted binder and aggregates issued from RAP material. Another one is a “perfect” mixture, produced by perfectly blending 70/100 base binder with 60% RAP-extracted binder and using this blend to coat virgin and RAP aggregates. Material properties were investigated using classical tests commonly performed by the road paving industry in Europe, in order to assess the impact of the addition of the recycling agent according to the current standard procedures. In particular, complex modulus |E*| (at 15°C and 10 Hz) and fatigue parameters ₆ and 1/b (at 10°C and 25 Hz) were determined by means of two-point bending tests on trapezoidal samples. The addition of the recycling agent was observed to generally lower |E*| and improve fatigue performances of mixtures with a RAP content equal or greater than 40%.