Life-Cycle Assessment of road pavements containing marginal materials: comparative analysis based on a real case study

The Life-Cycle Assessment (LCA) is a standardized procedure generally used, in Italy, in industrial engineering to evaluate the economic-environmental efficiency of production processes. LCA is aimed at optimizing the design, with special emphasis on environmental sustainability. Also in the construction sector, LCA has recently gained a fundamental role as a quantitative measurement tool able to take into account correctly the environmental and economic benefits achievable adopting different alternatives (most of them uncommon) based on the entire service life, maintenance and end-of-life procedures included. As far as pavement engineering is concerned, the use of marginal materials (such as, for example, reclaimed asphalt pavement, crumb rubber, slags, etc.) is becoming of strategic importance due to the decreasing availability of virgin natural resources and the consequent increasing public consciousness addressed to environmental protection and preservation. In this regard, the LCA applied to road pavements constructed using marginal aggregates probably represents the only effective tool able to evidence the crucial aspects on which the design choices should be based, taking also into account longterm parameters. Given this background, the present research illustrates one real case study of LCA analysis applied to asphalt pavements of a motorway. The use of industrial by-products (i.e. steel slags) instead of natural mineral aggregates is considered. Comparative evaluation of different scenarios has been carried out using specifically developed spreadsheets. The research study demonstrates that LCA is able to highlight potentialities and issues related to the different analyzed scenarios, representing a valid tool for designers and decision-makers. Moreover, the obtained results contribute to enlarge the worldwide database about the implementation of LCA for pavements. 1.2 The standards for LCA methodology Life Cycle Assessment is defined and described in ISO 14040 and ISO 14044 (ISO 2006a, b) standards. LCA framework (Fig. 1) can be divided in the following steps: 1) goal and scope definitions; 2) inventory collection and analysis; 3) environmental impact assessment; 4) obtained results interpretation. ISO standards describe in detail principles, framework, requirements and guidelines for the LCA, including: a) the goal and scope definition of the LCA; b) the life cycle inventory analysis (LCI) phase; c) the life cycle impact assessment (LCIA) phase; d) the life cycle interpretation phase; e) reporting and critical review of the LCA; f) limitations of the LCA; g) relationship between the LCA phases; h) conditions for use of value choices and optional elements. However, these standards do not state specific prescriptions to perform a LCA or defined methodologies for the specific LCA phase. Further, LCI phase can be performed separately from a specific LCA study, because LCI inputs/outputs introduction and quantification are not closely linked with the specific product or service evaluated with the LCA. Figure 1. Life Cycle Assessment framework (from the ISO 14040 (ISO 2006b)). 1.3 LCA in road engineering The attention addressed to the minimization of impacts related to the construction inclusion in the environment defines a general trend concerning the study of ecological characteristics throughout the different infrastructure project hypothesis (from design to maintenance, from use to end-oflife). LCA can be applied to several civil engineering sectors, such as the transport infrastructure one. In this sense, many researchers already ventured in LCA implementation to evaluate the environmental impacts connected to transport infrastructures, facing the most important problems related to the material type and its transport, that strongly represent onerous items in road construction and maintenance (Jullien et al. 2009, Santero et al. 2011, Azarijafari et al. 2016). The increasing expensiveness of road design (in terms of energy request and environmental impacts) involves the need to reduce work emissions and costs during its lifetime. In this sense, even more researchers, management and construction companies develop sustainable project and utilize LCA in decision procedures which affect several environmental aspects (such as impacts of different pavement types and materials). Also the decision-makers, with an accurate life cycle cost analysis, can use LCA to evaluate the project or policy impacts (Santero et al. 2011). Many studies evaluate the environmental issues and the effects on road construction, management/maintenance and rehabilitation. Amini et al. (2012) compared conventional and perpetual pavement (i.e. not requesting structural maintenance) and their different effects on environment and costs. Others researchers suggested to take into account the effect on the environment and infrastructure caused by road traffic (Zaabar & Chatti 2010, Santos et al. 2015a). For example, Bryce et al. (2014) evaluated through LCA the possibility to reduce the road maintenance activities considering the pavement damage and the related tire vehicles consumption (the surface type affects the vehicles pollution). Yang et al. (2015) assessed the use of Reclaimed Asphalt Pavement – RAP and Recycled Asphalt Shingle – RAS in partial substitution of virgin aggregates to check the different environmental impacts, considering also the vehicles fuel consumes as a function of the IRI index. Others authors studied LCA applied to road infrastructure materials. DeDene & Marasteanu (2012) examined the possibility to reduce production costs and harmful emissions of asphalt pavement with 15% of RAP. Butt et al. (2014) applied LCA to bituminous mixtures assessing the energy consumption and the environmental sustainability. In this case, the analysis of significant 1 Goal and scope definition 2 Life Cycle Inventory analysis (LCI) 3 Life Cycle Impact Assessment