Degree of blending between asphalt binders in recycled asphalt mixtures produced in laboratory and in asphalt plant

Abstract

Aligned with the economic aspect, with the changes in the environmental scenario, given the climatic variations and other impacts resultant from anthropic actions, milled material or Reclaimed Asphalt Pavement (RAP), prevenient from the milling of deteriorated asphaltic coatings, proved to be environmentally advantageous in restoring and building new pavement. Its reuse allows a reduction in expenses from raw material extraction, such as asphalt and mineral aggregates, and transportation. Environmentally, the benefits may be related to the decrease in pollutant gas emission rates and fuel consumption generated by extraction, processing, and transportation. Nevertheless, the application of RAP in asphaltic mixtures still presents some limiting factors, especially concerning percentages considered as high. Difficulties in defining more precise dosage methods tend to inhibit the maximization of RAP usage, due to the lack of knowledge about its characteristics and the mechanisms involved in the process of mixing with the other recycled Hot Mix Asphalt (HMA) components. Assuming, for instance, that the residual binder of the RAP will be entirely mixed with the new asphalt binder (full blending hypothesis) is still common practice for recycled HMA dosage. Supposing this condition may lead the designer to adopt an insufficient amount of binder to be added to the new mixture, resulting in an asphalt concrete more susceptible to cracking due to early fatigue or to the breakdown of the asphaltic mass. However, it is known that the interaction, which occurs between reheated aged binder and the new binder, happens only partially. There does not exist, however, a consensual method that allows determining precisely this degree of interaction. It should also be highlighted the importance of distinguishing between the two mechanisms involved in the interaction - the level of activation, or Degree of Binder Activity (DoA), and the level of interaction, or Degree of Blending (DoB) - discerning the quantity of binder available within the RAP from the efficiency of interaction between the aged asphalt binder and the recycling agent (RA), and how both may affect the dosage of recycled HMA. Thus, the objective of this research is to evaluate the DoB between aged binders from different types of RAP and the RA, after recycled HMA confection. Different types of RAP, previously characterized, will be selected for the recycled HMA production in the laboratory, under controlled conditions, considering different percentages of RAP. Furthermore, two recycled mixtures will be evaluated, composed of 10 and 30% of RAP, as well as a reference mixture without RAP, produced in an adapted volumetric plant. The Asphalt Analyzer Rubber will be used to extract binders, along with tetrachlorethylene solvent, acquired with resources from the present research project, linked to the "Fundação de Amparo à Pesquisa do Estado de São Paulo" (FAPESP). Three stages of extraction were proposed to analyze what would be considered the three binders "layers" recovering the aggregates. This procedure was already evaluated in Gustavo dos Santos Pinheiro dissertation, which integrates this research project. The solution originated from each extraction stage will undergo the asphalt binder recovery utilizing a rotary evaporator. To characterize the rheological behavior of the binders obtained in each stage of extraction, frequency and temperature sweep tests will be conducted in order to obtain linear viscoelastic properties and determine different rheological parameters. From these results, the aim of this study is to evaluate the degree of interaction between binders (DoB) as well as to verify the rheological changes to the different "layers" of recovered binders, evaluating the homogeneity of the mixture between binders.(AU)