Evaluating cradle-to-gate environmental life cycle impacts of river gravel and limestone as concrete aggregates

Aggregates are the most widely extracted material, making up 60%–80% of concrete volume and strongly influencing its environmental footprint. This study conducts a cradle-to-gate life cycle assessment (LCA) comparing three structurally equivalent concrete mixtures differing in coarse aggregate type: 100% river gravel (RG), 100% crushed limestone (LS) and a 50–50 LS–RG blend. All mixtures were prepared with identical cement content and only minor variations in sand and batch water due to aggregate moisture and absorption corrections to isolate the effect of coarse aggregate type on environmental performance. The functional unit is 1 m³ of ready-mixed concrete. The system boundary includes U.S.-specific raw material extraction, regional transportation and concrete batching. It covers seven environmental impact categories, global warming potential, acidification, eutrophication, smog formation, ozone depletion, non-renewable energy demand and freshwater consumption. Portland cement dominates environmental burdens across all mixtures, accounting for 92%–94% of total global warming potential (GWP) and resulting in less than 2% variation in overall GWP among the three scenarios. At the aggregate production stage, crushed limestone exhibits approximately 100% higher GWP and 220%–235% greater acidification and smog formation emissions relative to river gravel, attributable to elevated fuel and electricity demands for blasting and crushing. In contrast, river gravel demands about 50% more freshwater and generates 200%–240% greater eutrophication potential, stemming from its intensive dredging and washing processes. These variations suggest that relative aggregate performance depends on local water availability, eutrophication sensitivity and energy-system carbon intensity. Crushed limestone is less favourable where energy is carbon-intensive, whereas river gravel poses greater concerns in water-limited areas. The findings highlight multi-criteria LCAs' importance for aggregate selection while confirming cement decarbonisation as concrete's primary emissions-reduction strategy.