To What Extent Does Decreasing the Proportion of Clinker in Cement Production Effectively Decrease Its Carbon Footprint?

The current context of global warming requires urgent action to reduce carbon emissions from all industries, including the concrete production. To meet this challenge, the European cement standard, EN 197–5, has been implemented to introduce CEM II/C-M low-carbon Portland cements incorporating a higher percentage of mineral additions (up to 50%), and a new family CEM VI cements with a very low clinker content, ranging from 35 to 49%. This work focuses on these new cements, mainly ternary mixtures based on clinker, slag and limestone filler for high clinker replacement rates. This choice is based on the exploitation of the synergy between limestone and mineral additions containing aluminates which has been established in the literature. This study is focused on concretes based on these new ternary clinker-slag-limestone cements, to compare them with existing binary cements in terms of durability with respect to corrosion induced by carbonation. Two main tests were performed: accelerated carbonation that reveals corrosion initiation time, and electrical resistivity that provides insights into corrosion propagation time. Additional microstructural characterization was also carried out to understand the link between the macroscopic durability properties and the microstructure. A service life prediction model was used to quantify the service life of the concrete cover from material properties. Concretes were then compared on the basis of two carbon efficiency indicators corresponding respectively to the carbon cost of 1 MPa and one year of service life. Opposite trends are observed on the carbonation resistance and electrical resistivity. Good durability can be expected for low carbon cements, as they have high electrical resistivity and therefore a long corrosion propagation time, despite their relatively low carbonation resistance,. The carbon footprint indicator related to service life is more relevant than the one related to mechanical performance since it takes into account an important function of concrete which is durability.