Monitoring durability of concrete lining of the bored 'Green Heart Tunnel"

Important concrete infrastructure is increasingly being designed for long service life. This is done by modelling of degradations and probabilistic assessment of uncertainties, e.g. using the DuraCrete method. In the design phase, this is necessarily based on past experience, simplified modelling and limited testing. Installing monitoring sensors provides the possibility of updating the service life design (SLD) with data from the structure during its exposure to its real environment. This paper presents first results of such an exercise. A high speed train link (HSL) between Amsterdam and Brussels is almost completed. Part of HSL is the Green Heart Tunnel (GHT), an 8.6 km long bored tunnel, whose precast concrete lining elements were designed using DuraCrete. Anode Ladder (AL) and Multi-Ring Electrodes (MRE) were embedded to monitor corrosion initiation due to chloride ingress (from saline ground water) or carbonation and moisture conditions in the concrete. In a laboratory environment, companion "dummy" lining elements were exposed to various saline solutions and AL and MRE readings were taken over several years. The paper will present the corrosion monitoring system, the first field and laboratory data and the approach to updating the SLD, aimed at improved service life predictions under real conditions and assessment of the risk of unexpected maintenance and repair