Amedeo Virgili

New method to estimate the “re-activated” binder amount in recycled hot-mix asphalt

The magnitude of the binder re-activation within the reclaimed asphalt pavement (RAP) fraction is a major concern when recycled hot-mix asphalt (HMA) is produced, since it directly affects the final performance of the mix. Currently, no reliable methods to predict the RAP binder re-activation are available and the lack of such information prevents the quantification of the proper amount of virgin binder to be added to the recycled HMA.This study proposes a new method to estimate the re-activated binder amount based on the surface area (SA) of RAP aggregates. Laboratory results demonstrated the effectiveness of the SA approach in the case of RAP amounts typically used for hot-recycled HMA. Moreover, the experimental investigation suggested that revised coefficients are needed for the evaluation of the SA to account for the presence of clumps when high amounts of fine RAP aggregates are used.

In Plant Production of Hot Recycled Mixtures with High Reclaimed Asphalt Pavement Content: A Performance Evaluation

Nevertheless hot recycling process is nowadays a widespread technique, many doubts related to the in plant recycling process effects on the performance of recycled mixtures still exist and limit the maximum allowable amount of Reclaimed Asphalt Pavement (RAP). Therefore, the feasibility of an efficient production of plant hot recycled mixtures characterized by high RAP content and suitable performance should be properly addressed. To this aim, the overall performance of hot recycled asphalt mixtures produced in asphalt plant and containing high RAP content were assessed in this study. The mixtures were prepared with two different bitumens (high and low content of SBS polymer modifier) and 40 % of RAP only deriving from asphalt layers containing polymer modified bitumens. The aggregate grading curve was previously optimized through a specific laboratory study by applying the Bailey Method and using selected RAP. A third mixture, currently used for binder layers in motorway pavements, was also studied for comparative purposes. Compactability, stiffness, cracking and rutting resistance and fatigue behavior were investigated. Results of the mechanical tests suggest that mixtures containing 40 % RAP are suitable for the production of new asphalt pavements, especially when low modified bitumens are used. In fact, the performance of such mixtures were comparable or even higher than those of the reference mixture. In particular, the specific and accurate mix design allowed the potential drawbacks due to higher RAP content to be balanced.

Performance Assessment of Plant-Produced Warm Recycled Mixtures for Open-Graded Wearing Courses

Sustainable solutions, such as the combination of reclaimed asphalt pavement (RAP) as a partial substitution of virgin materials and warm-mix asphalt (WMA) additives to decrease production temperatures, represent the new research frontier in the asphalt industry. Specific investigations must evaluate the consequences of recycled WMA performance, especially in the case of open-graded (OG) mixtures, given that lower production temperatures can affect the adhesion properties and durability of those materials. This paper describes an experimental effort that involved OG mixtures produced in plant at warm temperatures (130°C) with two WMA chemical additives characterized by different compositions. In addition, an equivalent mixture (used as a control for comparison purposes) was produced at standard temperatures. Each material was prepared with a polymer-modified binder and 15% RAP. The main objective of the study was to characterize volumetric and mechanical properties of the investigated mixtures with particular attention paid to compactability aptitude and durability. To this end, gyratory-compacted specimens were subjected to several laboratory tests after dry and wet conditioning (i.e., indirect tensile strength, Cantabro test, semicircular bending, and repeated indirect tensile loading). Moreover, plant production of the investigated mixtures made it possible to evaluate the feasibility of large-scale processes. The WMA mixtures showed significant water susceptibility, although they guaranteed good compactability and satisfied mechanical acceptance requirements and international recommendations for raveling resistance in dry conditions. The chemical composition of the WMA additives was found essential to reduce the water damage. Surfactants and adhesion enhancers included within one of the investigated WMA additives ensured better water resistance than the other additive classified as a viscous regulator.

Influence of different fillers and SBS modified bituminous blends on fatigue, self-healing and thixotropic performance of mastics

The prediction of asphalt pavement performance is closely linked to the behaviour of mastic, consisting of filler and bitumen, which can be modelled as viscoelastic material. The purpose of this study is to investigate the effect of different fillers and bituminous blends on mastic fatigue response, considering recoverable phenomena in viscoelastic materials (thixotropy and self-healing) that concurrently occur. Three fillers (limestone, basalt and Portland cement) and three aged polymer modified bitumen contents (0%, 45% and 100%) were blended with a virgin polymer modified bitumen obtaining nine mastics characterised in terms of fatigue, self-healing and thixotropy using a Dynamic Shear Rheometer. Data obtained are analysed through a model previously adopted for polymer modified bitumens and mastics, allowing the determination of the fatigue endurance limit. Results show that the presence of filler with increasing particle density and/or Rigden voids causes a higher mastic stiffness without a clear trend on fatigue performance. In fact, great attention should be put on filler-bitumen interactions based on the physicochemical nature of filler. Moreover, whatever the filler considered, an enhancement in the fatigue endurance limit is detected in the mastics blended with a percentage of aged polymer modified bitumen (up to 45%), promoting the addition of Reclaimed Asphalt to obtain more performing and sustainable recycled mixtures.