Cyclists, pedestrians and elderly people’s specific needs in urban road infrastructures are often neglected. They rarely benefit from safety measures or innovations. Inspired by playgrounds and aiming to reduce vulnerable road users (VRUs) injuries, the development of the rubber-based Impact-Absorbing Pavements (IAP) offers a possibility to rethink the design of urban pavements and address safety on roads, which constitutes a major challenge in terms of attaining more sustainable, resilient, and safe cities. Therefore, bituminous mixtures with four different crumb rubber contents, 0%, 14%, 28%, and 33% (in total weight), were produced by partial aggregates substitution using the dry process. After the assessment of the geometrical and volumetric properties, the mechanical performances were evaluated. Finally, the samples were tested to measure the abrasion and impact attenuation with the well-known Head Injury Criterion (HIC), at different temperatures from −10 to 40 °C, to obtain a wide range of values referring to possible weather conditions. A significant effect of the rubber percentage and layer thickness on impact attenuation was observed. All observations and results confirm the feasibility of the IAP concept and its positive effect on future injury-prevention applications.
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.
The road surface texture is responsible for controlling several quality/safety road indicators, such as friction, noise, and fuel consumption. Road texture can be classified into different wavelengths, and it is dependent on the material used in the paving solution. With the aim of evaluating and characterizing the surface texture of a microsurfacing road pavement, six microsurfacing samples were made in the laboratory with both traditional materials (basaltic aggregates and bituminous emulsion) and with innovative materials from recycling procedures (crumb rubber (CR) and artificial engineered aggregate (AEA)). The characterization was performed through the use of a conoscopic holography profilometer with high precision and post-processing of the profiles detected through consolidated algorithms (ISO standards). We found that the aggregate type plays a very important role in the pavement texture. The binder agent seems to be highly important, but more studies regarding this are necessary. The use of crumb rubber as an aggregate proved to be feasible, and the texture parameters that were obtained were in accordance with the benchmark ones. In addition, the study shows that the use of artificial engineered aggregates does not impair the surface texture. Finally, the use of the texture parameters defined by the ISO standards, together with a statistical analysis, could be useful for defining the surface texture characteristics of microsurfacing.
The present study has been developed to investigate the effect of freeze and thaw (F–T) cycles on the characteristics of highly rubberised asphalt materials to be used as impact-absorbing pavement (IAP) in urban road infrastructures. The tested samples were produced in the laboratory following the dry process incorporation. Two main types of crumb rubber particles in the range of 0–4 mm were used. Moreover, two types of binders, one warm and one cold, were utilised to prove the feasibility of cold-produced admixtures. The temperature range of the F–T procedure was comprised between −18 ± 2 °C (dry freezing), and 4 ± 2 °C (in water), and the cycles were repeated, on the samples, 10 times. At 0, 1, 5, and 10 cycles, the samples were tested with non-destructive and destructive testing methods, including air voids content, ITSM, ITS, and Cantabro loss. The waters of the thawing period were collected, and the pH, electric conductivity, and particle loss were measured. A consequent change in mechanical behaviour has been recorded between warm and cold produced samples. However, the tests found that the F–T cycles had limited influence on the deterioration of the highly rubberised samples. The loss of particles in the thaw waters were identified as being potentially caused by the temperature stresses. The research suggested various ways to optimise the material to enhance the cold-produced layer mechanical performances, aiming at a fume and smell-free industrialised solution and reducing the potential leaching and particle losses.
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