Mechanical effects of recycled packaging plastic in bituminous binders and mixtures

The inclusion of alternative materials (AM) in road construction is one current practice that supports politics of Green Transition. The incorporation of the food packaging recycled plastic studied in this research addresses minimizing the creation of disposals and a more efficient use of this resource. However, there are still uncertainties about the mechanical performance of this material. In this context, this research aims to explore the mechanical effects of the incorporation of plastic in bituminous mixture in two scales, either in bitumen as a binder modifier or in wearing course, in replacement of a part of the aggregate content. For this purpose, an experimental plan divided in two phases was proposed aiming to investigate: (i) the mechanical changes observed in bitumens that interacted with recycled plastic; and (ii) the mechanical characterization of mixtures produced with this material through dry process. For the first phase a procedure using High Shear Mixer (HSM) and filtering at 150 ℃ was formulated in order to induce conditions of interaction similar to those found during the mixing process. After separated from the plastic, the obtained binder was chemically and mechanically characterized using, respectively, Fourier-Transform Infrared (FTIR) and Dynamic Shear Rheometer (DSR) techniques. The characterization of these materials allowed infer that in some mixing conditions such as time of exposure to high temperatures and rotation speed of the tank might be favourable for particles from the plastic being incorporated in the bitumen. This is particularly interesting knowing that this interaction might be experienced by modified mixtures even when the plastic is aimed to function as an aggregate. For the purpose of the second phase, five different mixtures were produced, with different plastic contents of 0, 2.5, 5 and 7 %. Cylindrical specimens were extracted from slabs of 50 × 50 cm mixed and compacted in laboratory. Thermo-mechanical tests were performed in tension-compression. The results suggested that the stiffness and the elasticity of the samples is significatively changed and influenced by the plastic content. In contrast, the plastic content seems to influence the workability and level of compaction. When 5% of the aggregates were replaced by plastic the performance of the material was improved in comparison to the reference sample without plastic. The Complex Modulus (|E*|) increased at lower frequencies and decreased in the higher, while similar results were found in 15 ℃. This particular result reveals that at 5% not only the recycled plastic can be employed as a replacement for mineral aggregates but also it is possible to achieve effects of modification of bitumen using a dry process.