It is common practice to assume full blending of the aged binder of reclaimed asphalt (RA) within the design of new asphalt mixtures. Although being practical, this assumption has often led designers to asphalt mixtures lacking binder. Hence, going towards recycled asphalt mixtures (RAM) there is a need to have a better understanding of the blending phenomena, to have a general agreement on terminology and finally adapting RA classification and mix design procedures accordingly. This manuscript aims at being both a reference and stimulus for the scientific community to work in this direction and on this basis provides a nomenclature and a theoretical framework of the blending phenomena. The study is built upon a literature review on definitions, methods and influencing factors related with the blending phenomena and as a result, an intrinsic property of RA, the Degree of binder Activity (DoA), is introduced for the sake of improving RA classification. Furthermore, the two well-known concepts of the Degree of Blending (DoB) and the Degree of binder Availability (DoAv) are redefined, within the proposed framework, together with practical suggestions to introduce them in mix design procedures.

Cold recycled asphalt mixtures (CRAMs) are generally comprised by reclaimed asphalt pavement, virgin aggregates, bitumen stabilising agents (asphalt emulsion or foamed asphalt) and active filler (Portland cement or hydrated lime). Depending on the type and content of each mixture constituent, the CRAM may exhibit different mechanical behaviours. The aim of this study is to evaluate the influence of mixture composition on the mechanical behaviour of CRAMs. The materials used were collected during the construction of an experimental test section and were used as base course mixtures. From triaxial resilient modulus test and dynamic modulus test, it was found that the type and content of bitumen stabilising agent and active filler substantially influence the behaviour of the CRAM. From triaxial resilient modulus tests, it was observed that the mixtures with cement addition behaved similarly to cementitious materials (independent of the confining pressure), while the ones with hydrated lime resembled a granular material (dependent of the stress-state). The dynamic modulus test results indicated that the CRAMs also exhibit viscoelastic properties. Besides, the test provided a clear difference between mixtures stabilised with either asphalt emulsion or foamed asphalt.

Cold recycling with foamed asphalt stabilisation has been gaining acceptance and growing steadily. This study evaluates the performance of cold recycled mixes stabilised with foamed asphalt, with respect to the effects of confining stresses, and material moisture content. An experimental test section with a foamed stabilised recycled material used as the base course was monitored through quality control and quality assurance and falling weight deflectometer (FWD) tests. In laboratory, indirect tensile strength, triaxial resilient modulus, and permanent deformation tests were performed. Based on the results obtained, one can conclude that the curing is a critical consideration in terms of timing and its influence on pavement performance. Triaxial tests showed the stress dependency of this bitumen-stabilised material, while permanent deformation results indicated some potential for damage in early stages after construction. On the field evaluation, FWD data indicated the decrease in deflection with time, as a result of the increase in the layers stiffness.

Despite the importance of hysteresis of water diffusion in polymeric materials, only limited literature is available on this subject. The FT-IR-ATR spectroscopy technique was used to investigate the effect of cycling moisture boundary conditions on the diffusivity of moisture of three asphalt binders. Each sample passed through three hydration cycles and two dehydration cycles. The existence of hysteresis of moisture diffusivity in asphalt binders is validated. The increase in moisture diffusivity is primarily attributed to the change in microstructure of the asphalt binder after being exposed to moisture. This is supported by atomic force microscope images of asphalt binder before and after exposure to water. Evidence to an increase of water trapped in the form of vapour even after dehydration was observed, and this may also contribute to the increase in diffusivity. This topic is still under investigation by this research group.

The prediction of asphalt pavements performance in relation to the main distresses has been proposed by different researchers, by means of laboratory characterisation and field evaluation. With respect to fatigue, there are different approaches to determine what failure criterion to be considered, what testing conditions to be used and which specimens’ geometry to be produced. Tests performed in asphalt binders and mixtures have been recommended to characterise the fatigue resistance, and correlations among the several scales are proposed in order to make it more practical and more precise to predict the performance of asphalt layers. In terms of laboratory fatigue characterisation of asphalt mixtures, some of the most common tests are the four-point bending beam, diametral compression, the push-pull tests, among others. The characterisation of asphalt binders is also relevant, since fatigue is dependent on their rheological characteristics. Linear viscoelastic parameters of the binders, time sweep and amplitude sweep tests were used to rank three asphalt binders (one neat 30/45 penetration grade binder; one SBS-modified binder; and one highly modified asphalt, HiMA) in terms of fatigue behaviour. HiMA showed the highest fatigue resistance. One dense hot mix asphalt (HMA) mixture (prepared with the AC 30/45 neat binder) was characterised in terms of different fatigue test methods and correlated with binder tests, comparing the two scales approaches. The fatigue life of the asphalt mixture followed in agreement with results from the asphalt binder.