Gabriella Buttitta

Any Life Cycle Assessment (LCA) aims to evaluate a product system, which is made of interconnected unit processes. Within the selected system boundaries, the processes can specifically pertain to the selected product system or can be more generic and applicable across different other product systems. This distinction is fundamental, and it consists of differentiating them into foreground and background processes. The former, specific to the product system, are largely modeled using primary data, directly provided by the suppliers or the producers. The latter, more generic, are usually modeled using database and/or literature. This distinction can be helpful during the Life Cycle Inventory, guiding the data collection and the interpretation of results, helping to provide recommendations and possible improvements. It follows that the distinction of foreground and background processes is a key concept in carrying out an LCA to help the practitioners toward a more robust study. The product system is the object of the assessment in any Life Cycle Assessment (LCA), and it is composed of interconnected unit processes.

The demand for reliable Environmental Product Declarations (EPDs) of asphalt mixtures is growing, particularly as they are increasingly used in public road construction tenders across Europe. However, the reliability and comparability of EPDs remain limited due to two main challenges: (i) significant variability in dataset selection for key materials such as bitumen and aggregates, and (ii) uncertainty regarding the influence of operational factors, including aggregate moisture, mixing temperature, and transportation. The objective of this research is to assess the influence of dataset selection and operational parameters on the environmental performance of an asphalt mixture, focusing on improving the reliability of EPDs. Within this research, a Life Cycle Assessment (LCA) was conducted using a cradle-to-gate approach (A1–A3), including modules C1–C4 and D, in compliance with EN 15804:2019+A2:2020. Primary data were collected from an asphalt plant in Lithuania, while secondary data were obtained from the Ecoinvent database. The sensitivity analyses were performed to investigate the variation of data set choices and key operational factors that influence the environmental impact. The assessment was carried out using the Simapro 9.6 software and the EF 3.1 impact assessment method. The results indicate significant sensitivity to dataset selection, particularly for bitumen and dolomite production, leading to environmental impact variations of up to 41.8% and 35.3%, respectively. Among operational factors, reducing aggregate moisture from 5% to 3% by sheltering stockpiles helps achieve the highest environmental impact reduction (3.2% under the Aggregate Single Score), while lowering mixing temperatures to 130 °C resulted in a 1.6% decrease. Transportation mode selection contributed to emission variations between 1.8% and 6.7%, with long-distance aggregate transport increasing emissions by up to 14.6%. The research findings underscore the critical need for harmonizing dataset selection and optimizing operational processes to improve asphalt sustainability. Standardizing datasets is essential for ensuring fair and transparent EPD generation for asphalt mixtures, particularly when used in road construction tenders, as seen in several European countries. Future research should explore the integration of reclaimed asphalt (RA) and assess its potential environmental benefits.

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.

The road pavement industry, worldwide, has often shown reluctance in quickly implementing innovative practices; however, in the case of raw material consumption, a cultural change is necessary and, in this sense, sustainability assessment could play a major role. Along these lines, this research study aims to provide evidence to all the involved stakeholders (material producers, pavement contractors, and road authorities) of how life cycle-based techniques can be crucial in evaluating whether the adoption of asphalt mixtures with high contents of reclaimed asphalt (RA) for wearing courses is actually a sustainable practice for major European roads. An evaluation framework composed of a life cycle assessment, to calculate the carbon footprint of both pavement materials and pavement activities, and a life cycle cost assessment, performed to determine the overall economic burden of the related road pavement surface courses and maintenance strategies over a sixty-year analysis period, is presented and applied to selected case studies. These were developed together with three major European national road authorities and include scenarios involving the construction of road surfaces with asphalt mixtures containing up to 90% RA. Results have shown that whenever high-content RA mixes do not under-perform against conventional mixtures, up to 50% CO₂eq savings can be registered and up to 60% economic cost reductions can be reported. The durability of road pavement layers remains a key parameter for any road pavement sustainability assessment exercises; therefore, in order to adapt the obtained results to other contexts, researchers should always consider conducting a sensitivity analysis of the reference service life and/or road authorities should somehow request road pavement durability as a pre-requisite within procurement practices.

Even though alternative paving materials, like rubberized asphalt, are sometimes present in specifications, these are still not widely adopted from road agencies mainly due to a lack of experience, reticence in changing work habits and, often, a lack of evidence of real gains in the change. Authors believe that performance-based laboratory characterization is a solution to highlight differences with conventional asphalt mixtures. Hence, this research wants to highlight the differences between designing asphalt mixtures modified with engineered crumb rubber (ECR) on the basis of conventional indirect tensile testing (ITS), as prescribed by Italian specifications, and by means of performance-related characterization. ECR allows to asphalt mixtures to be modified through a dry process without inconveniences such as uncontrolled swelling and the generation of fumes; on the other hand, performance-related characterization focuses on highlighting rutting behavior by using a basic approach, still based on ITS, and a more advanced viscoplastic methodology using the asphalt mixture performance tester (AMPT). As a result, performance-related characterization is necessary to highlight clear gains in the rutting behavior of the asphalt mixtures modified with ECR. Advanced methodology by means of AMPT provides a fine-tuned characterization; however, the basic approach by means of ITS already highlights the differences in performance. ECR could be widely used to improve the properties of dense mixtures for roads with low traffic; in fact, it solves many of the practical issues of adding crumb rubber through a dry process and greatly improves paving material properties compared to conventional asphalt mixtures, with an increase in cost of only 10%.