Minimising the Carbon Footprint of Standard-Compliant Structural Concrete by Adopting Low-Binder LC³ Mix Designs

Concrete is, as a matter of fact, the only construction material able to globally meet the growing demand for new structures and infrastructure. Hence, CO₂ emissions related to the construction sector, mainly attributable to Ordinary Portland Cement (OPC), are expected to increase. Rapid and effective solutions are needed to meet future demands sustainably and achieve carbon neutrality by 2050. Among these, reducing clinker in cement and reducing cement in concrete are considered the most promising and ready-to-use. Limestone Calcined Clay Cement (LC³) is widely recognised as the most feasible blended cement addressing the former. Whereas the latter is currently prevented by the requirement of a minimum binder content in concrete in most existing prescriptive-based Standards. This work aims to minimize the CO₂ emissions of standard-compliant structural concretes by suggesting a low-carbon and low-binder concrete design, thus providing evidence for an update of prescriptive codes. LC³ concrete mixes were designed to reduce the clinker content by up to -75% and binder content to 250 kg/m³ while targeting normal-use strength classes (C25/30, C30/37). The mechanical and durability properties of the low-binder LC³ mixes were compared to equivalent OPC mixes designed according to European codes. A life cycle analysis highlighted the CO₂ reduction potential of the new systems while ensuring good mechanical properties and improved resistance to chloride penetration. Imposing a minimum cement content resulted in a conservative approach leading to overconsumption of cement (+30 to +70 kg/m³) and higher CO₂ emissions (+45%) compared to an efficient mix design of blended cement concrete.