## 2 Materials and Methods  
In this study, two recycled materials (i.e., the powdered rubber from ELTs and the re-refined engine oil bottom (REOB)) were used to produce bitumen extenders that were able to replace a specific amount of petroleum bitumen obtaining extended bitumens. The 50/70 penetration grade bitumen (B-50/70) was used as the reference material and base constituent of the extended bitumen. The powdered rubber (R) was produced from the trituration processes at an ambient temperature of waste tires from cars and trucks after the separation phase of textile and metallic parts of the tires themselves. The maximum dimension of rubber particles was 0.40 mm, while the density was 1.01 g/cm\({}^{3}\). The Italian consortium, Ecopneus Scpa, to promote the recycle and the reuse of waste tires, provided the material. The REOB is the by-product of a vacuum tower in a re-refinery plant of exhausted engine oil supplied by Itelyum Srl. This research used and compared two recycled oils (hereinafter called O1 and O2, or Ox if both or one of them were considered alternatively) that were produced in two distinct refinery plants of the same company. Both REOB had a density approximately equal to 1.00 g/cm\({}^{3}\). Five mixes were prepared per each REOB (i.e., O1 and O2) by varying the mass of each recycled materials. In particular, the considered R-REOB ratios were:  
1. R:Ox = 3:1
2. R:Ox = 2:1
3. R:Ox = 1:1
4. R:Ox = 1:2
5. R:Ox = 1:3  
All extenders were prepared by mixing the pre-heated materials. The first step consisted of warming up both materials at 130 \({}^{\circ}\)C in the oven; the Ox for at least 1 h 30', while R for 15'. Then, the Ox was added to the R portion and the recycled materials were mixed by the use of a propeller mixer at a rate of about 600 \(\div\) 650 rpm for 15'. The mixing phase was performed at a temperature equal to 130 \({}^{\circ}\)C. In order to keep the blend at a constant temperature during the mixing process, the container was immersed in a glycerine bath, which was continuously warmed up by a heating plate. The resulting blends underwent nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) analysis to establish the optimum R-REOB ratio, which has been considered as the maximum amount of REOB that can be absorbed by R. The optimal proportion aims to maximize the use of both recycled materials. The spectroscopic analysis was carried out by two NMR instruments that operated at two different proton frequencies: a low resolution NMR (L-NMR) at 15 MHz and high resolution NMR (H-NMR) at 300 MHz [19]. The L-NMR is a homemade instrument, which has been used to perform relaxation experiments at ambient temperature; while, the H-NMR is a Bruker Avance 300 (Germany) that allowed the analysis of diffusion. Thanks to the software Mathematica, the collected data were post-processed and the spin-spin relaxation time (T\({}_{2}\)) of all extenders were determined by fitting with an exponential equation. This relaxation time is concerned with the exchange of energy among spins without being affected by the surrounding environment [20]. The H-NMR spectra and diffusion properties of all samples were evaluated at the production temperature of 130 \({}^{\circ}\)C. The specimens do not need any specific conditioning before performing the tests. The scanning electron microscope (SEM, JEOL JXA-8230, Japan) allowed the investigation of the R-REOB blends' morphological structure. The tests were run in vacuum mode on the pre-conditioned samples, which were sputter coated with a thin film of graphite. Various magnifications were considered to collect the images of all specimens. Thanks to the definition of the optima R-REOB ratios (that is 1:1 and 1:2), the extenders were used to produce four extended bitumens replacing 25% by the total weight of the binder, and their rheological response was investigated.