Life Cycle Assessment of Asphalt Mixtures with WMR

This study aimed at providing pavement specialists with international average values of greenhouse gas emissions (GHG) and energy consumption related to the manufacturing of asphalt mixtures (cradle-to-gate), with and without waste and secondary materials for roads (WMRs). In order to achieve this goal, TG leaders first referred to current standards to define a methodology for obtaining benchmark values according to ISO 21678:2020. Then, a data collection tool was designed and provided to a group of international partners to build a life cycle inventory for asphalt mixtures including data from materials up to plant manufacturing (A1–A3). Partners were asked to provide information for any type of available mixtures with and without WMRs. A total of 16 case studies were collected and subsequently energy consumption values were recorded, and several cradle-to-gate life cycle assessment exercises were performed to obtain GHG emissions values. This set of results was used to develop benchmark values for reference (conventional) asphalt mixtures, namely asphalt concretes (ACs) and stone matrix asphalts (SMAs). Finally, in order to assess how environmentally-friendly it is to incorporate WMRs into asphalt mixtures, the benchmark values of the reference asphalt concrete and stone matrix asphalt mixtures were compared with the GHG and energy consumptions of asphalt mixtures manufactured with selected WMRs. As a result: (1) SMA seems to have higher impact than ACs, (2) Asphalt mixtures engineered with selected WMRs seem to be always a more environmentally friendly option when compared to benchmark values of reference SMA. However, this does not always hold true when the comparison is made with conventional ACs.