Analysis of Extensive Durability Test Data for Validating 120-Year Design Life of the Thames TidewayTunnel

Thames Tideway Tunnel, the biggest infrastructure project ever undertaken by the UK water industry, 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 effluent into the River Thames. The Eastern Section consists of six worksites, including 10 km of tunnel, deep shafts, maritime works and structures connected with the existing system. A design life of 120 years is required by the Tideway Specification. Parameters which can impact on the service life of the main reinforced structural elements with respect to reinforcement corrosion were considered in the probabilistic service life modelling done according to fib Bul. 34. It was conducted as a rational approach for determining limiting values for concrete properties and specification requirements. Thus, all mixes were tested prior to use in construction to demonstrate compliance with the concrete specifications including durability properties: accelerated carbonation; chloride ion migration; and additionally, water penetration. During the construction phase, numerous regular tests have been carried out to ensure compliance of the durability properties of these mixes to the specified requirements, and thus to ensure 120-year service life for the main civil works structures. This paper summarizes the results gathered on several concrete mixes over the last 5 years of construction. With more than 200 durability test results, this analysis highlights very high variability in considered durability parameters (Racc−1, DRCM, WP) that needs to be anticipated when implementing a Performance-Based Approach for concrete mix design.