The Société du Grand Paris, which is developing a mobility network for the 21st century, aims to reduce the consequences of the installation on the environment. A number of semi-directed interviews of stakeholders and a thorough literature review have been performed to acquire both a socio-economical and technical view on the subject. The results of this study begin with an analysis of the concrete sector from the raw material to the site to identify the existing and envisaged technical possibilities and the means available to the contracting authority to reduce its environmental impacts. Particular attention is paid to the carbon footprint, the main externality associated with this material. Some particularities developed by blends of Portland cements and calcined clays are then exposed on their mechanical aspects and their ability to resist certain attacks. Metakaolin, as it has been the most studied clay used in concrete, is often taken as an example, but the diversity and variability of such sedimentary materials make it so that reproducing the same tests for lower-grades clays would be justified for a possible use in building materials. This study discusses the results and highlights the organisational and technical problems that SGP could encounter if they decided to use the clayey excavated waste that they produce every year to make "low-carbon concrete".