Thames Tideway Tunnel – Use of a Decisional Carbon Footprint Tool for Determining Concrete Mixes

Thames Tideway Tunnel is the biggest infrastructure project ever undertaken by the UK water industry and has been designed to upgrade London’s 150-year-old sewer network. The under-construction 25 km tunnel will intercept wastewater and stormwater and divert them into treatment plants to prevent the release of untreated effluents into River Thames. The East Section consist of six worksites, including 10 km of tunnel, deep shafts, maritime works and structures connected with the existing system. Even though the project is already an environmentally beneficial project, we aspire to deliver it with the lowest possible contribution to greenhouse gas emissions. For each of the concrete mixes used on Eastern Section of Thames Tideway Tunnel (“Tideway East”), we have estimated the carbon footprint using the VINCI Construction tool CO2CRETE IMPACT®, taking into account the volume of concrete, the composition of each mix and the transportation before and after the batching plant. Thereafter, we have evaluated carbon footprint of all these mixes using the EXEGY® matrix (VINCI’s brand for promoting low carbon concrete). This became a useful decisional tool for determining concrete mixes to be used on site based on both properties and CO2 emissions. Furthermore, this study has highlighted several opportunities for reducing embodied concrete carbon emissions for both permanent and temporary works. Reduced carbon concrete mixes were then designed and used on site which led to significant savings. Where reducing embodied carbon emissions of concrete was not achievable (due to required early age strength), we sought alternative savings by challenging design and construction methods. Thanks to that strategy, a design optimization was implemented on site reducing the thickness of the tunnel secondary linings and thus the volume of concrete by more than 11,000 m3 leading to a massive CO2 saving. This paper details the analysis of greenhouse gas emissions due to concrete and highlights the main savings achieved.