Functionalization of Crumb Rubber Surface for the Incorporation into Asphalt Layers of Reduced Stiffness: An Overview of Existing Treatment Approaches

Abstract

The substitution of mineral aggregates with crumb rubber (CR) from waste end-of-life tires (ELTs) in the asphalt concretes, has been considered a sustainable paving industry approach. The rubber has been used to construct pavements with proven enhanced resilience and improved durability. However, some issues related to the rubber’s surface adhesion or swelling may arise with these practices and generate complications (binder consumption, temperatures, mixing times). One possible solution to overcome the materials’ compatibility problems is to pre-treat the CR’s surface before its incorporation into the asphalt mixes to allow a surface functionalization that can enhance coverage and cohesion inside the mixes. The physical treatments using radiations-based beam are already exploited in the plastic recycling industries avoiding the use of chemicals in considerable amounts. Such treatments permit the recovering of large quantities of polymer-based materials and the enhancement of interfacial properties. This article provides an overview of existing surface treatments of polymers and especially rubber, including gamma ray, UV-ozone, microwaves, and plasma. Several studies have shown an overall improvement of the rubber surface’s reactive properties due to contaminant removal or roughness enhancement attributed to cross-linking or scission reactions occurring on the rubber’s surface layer. With those properties, the asphalt mixes’ phase stability properties are increased when the pre-treated rubber is incorporated. The treatments would permit to increase the CR quantities, yet reduce the layer stiffness, and improve the durability and the sustainability of future advanced road pavements.

Particles formation due to the wear of tires and measures for the wear reduction: A review

“…88 Kim and Lee 89 have shown in their research that the TWP consists of great number of components: C, Al, Ca, Ba, Cl, Fe, Cu, Cr, K, Mn, Mg, Na, O, Ni, Si, S, Zn, and Ti, while according to the research, present components are C, Si, and S. 90 Table 3 shows the components which are present in the wear of tires products, according to the results of various researchers. It can be noticed that in all researches the main component that is always present is Zn, as proved by Johansson et al 91 For four Chinese towns (Tianjin, Beijing, Qingdao, and Zhengzhou) where the amount of PM 2.5 and PM 10 80 Pehlken and Essadiqi 81 Makoundou et al 82 Hoyer et al 83 Hamdi et al 84 Pehlken and Mu ¨ller 80 Pehlken and Essadiqi 81 Makoundou et al 82 Hoyer et al 83 Formela 85 Natural rubber, % is from 8.8 to 16.0 mg/(km veh) and 37.4 to 63.9 mg/ (km veh), respectively. 54 Reconstruction of the emission of the PM 10 shows 51%-64% soil and cement dust, 26%-40% tailpipe exhaust, 7%-9% tire wear, and 1%-3% brake wear, while for PM 2.5 it shows 59%-80% tailpipe exhaust, 11%-31% soil and cement dust, 4%-10% tire wear, and 1%-5% brake wear.…”

Life Cycle Assessment of Innovative Asphalt Mixtures Made with Crumb Rubber for Impact-Absorbing Pavements

“…The binders' properties are given in Table 2: After the production, all the samples were characterized in the laboratory with volumetric [22][23][24], mechanical [25][26][27], impact-attenuation [28,29], leaching [30], and natural ageing, and the values are shown in Makoundou et al [17,20] and Fathollahi et al [30]. The samples CCR, CRED and WCR also underwent freeze-thaw cycles analysis [17,31].…”

“…The concept was developed because a negligence of the risk of standard stiff surfaces to foster injuries was observed in the case of non-collision incidents or falls of VRUs-the users not protected by a shield-together with the necessity to manage an important amount of tyres at the end of their life. The IAPs' material is in fact designed to accommodate the everyday mobility of users on sidewalks and bike lanes, while reducing the risks of injuries due to impacts caused by potential falls [16,17].…”

“…Moreover, previous studies from the authors introduced the cold binder and demonstrated the feasibility of cold-mixed IAP, allowing the increase of workability, the diminution of externalities and the save in production energy (from 140-160 • C to ambient temperature) [17,20]. As the rubber holds a central role in the IAP formulation, further analysis and data collection is needed, related to the durability over time and weathering of the material and the potential impact on the environment [17,20].…”

Tests of rubber granules used as artificial turf for football fields in terms of toxicity to human health and the environment

“…After these processes, fragmented rubber materials: steel wires and textile cord are obtained. Depending on the degree of grinding, the rubber material can be used in various ways 11 – 16 . According to data from 2018, more than 1.5 million tons of car tires were processed in this way.…”