Understanding the environmental impacts of virgin aggregates: critical literature review and primary comprehensive Life Cycle Assessments

TL;DR

This paper critically reviews existing literature and presents comprehensive life cycle assessments of virgin aggregates, highlighting key environmental impacts, the influence of rock properties, and regional transportation effects to improve sustainability evaluations.

Contribution

It introduces detailed LCAs based on field data, demonstrating the impact of rock hardness, abrasiveness, and transportation on aggregate environmental footprints, addressing previous research shortcomings.

Findings

Blasting and machinery are major impact contributors.

Harder rocks increase environmental impacts due to more explosive use.

Transportation can more than double aggregate impact, with regional variability.

Abstract

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 to 1.8 percent of the global carbon footprint. I thus developed comprehensive LCAs, based on field data collected from quarries in Quebec 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 environmental impacts of aggregates is demonstrated for the first time: the harder it is, the more exposive 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 the gates of the quarry, 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.