Investigating the Ability of Road Specifications to Discriminate the Rutting Behavior of Rubberized Asphalt Mixtures in Italy

Despite its worldwide adoption in many countries, rubberized asphalt mixtures are not fully incorporated as an alternative paving material in current Italian road specifications. This reluctance stems from a lack of experience, resistance to change in established work practices, and, sometimes, insufficient evidence demonstrating tangible benefits with local specifications. Furthermore, conventional characterization methods such as void checks and indirect tensile strength testing by means of IDT may not accurately capture the true benefits of using alternative paving materials. This study introduces performance-driven characterization approaches with the final aim of evaluating whether more advanced procedures may provide additional information compared to current practices and, in turn, promote the use of alternative paving materials. Hence, an investigation has been conducted to compare the rutting behavior of conventional asphalt mixtures with those modified with engineered crumb rubber (ECR). This comparison utilized performance-driven characterization approaches, including a basic IDT-based methodology at higher temperatures (HT-IDT), as well as two more sophisticated approaches, the Stress Sweep Rutting (SSR) and Flow Number (FN) tests, using the asphalt mixture performance tester (AMPT). Finally, the results were compared with those obtained using the IDT, a conventional method as specified by the major Italian road authority. As a result, the addition of ECR proves beneficial in enhancing the qualities of dense mixtures tailored for use on urban and secondary roads; however, only performance-driven characterization, with both basic and advanced methodologies, can clearly describe the pivotal role of ECR in achieving discernible enhancements in the rutting behavior of asphalt mixtures.