Understanding the environmental impacts of virgin aggregates: Critical literature review and primary comprehensive life cycle assessments

Despite the ever-growing massive consumption of aggregates, knowledge about their environmental footprint is limited. My literature review on virgin aggregate Life Cycle Assessments (LCA) highlighted many shortcomings, such as low-quality inputs and fragmented system boundaries, and estimated that gravel consumption is responsible for 0.17-1.8% of the global carbon footprint. I thus developed comprehensive LCAs, based on field data collected in Quebec's quarries producing annually 7 million tons of aggregates, representing different types of rocks, productions (mobile, fixed), and energies consumed, using ecoinvent 3.7 and TRACI characterization method. Results show that the often-forgotten blasting and machinery are major contributors to several impact categories, along with diesel consumption. The link between the nature of the rock and the aggregate's environmental impacts is demonstrated for the first time: the harder it is, the more explosive it requires, thus increasing the impacts. Moreover, the more abrasive the rock is, the faster it wears out machinery, generating higher maintenance that increases human and ecosystem toxicities. A pronounced sensitivity of the impacts to the electricity mix is also shown based on a scenario analysis carried on Europe, China, and different Canadian and American regions. Additionally, aggregate transportation to the consumer, modeled with tailored inventories, can more than double the impact of the aggregate at quarry's gate, with strong regional variability. In a near future, I call for considering consistent system boundaries in aggregate LCA, refining blasting, energy consumption, machinery manufacturing and maintenance, as well as customizing truck transportation models, for more reliable aggregate LCAs.