SERVICE LIFE VERIFICATION FOR THE NEW QUEENSFERRY CROSSING

摘要

A new stay cable roadway bridge is being built outside Edinburgh, Scotland.The 2090 m long main bridge has 3 concrete towers and the approach viaducts have 6 concrete piers standing in shallow seawater.The normal way of ensuring the design service life for concrete structures in severe environment is by controlling the binder composition of the concrete, the maximum w/c ratio, the minimum cover thickness and applying crack width limitations.The Employer's Requirements demand for minimum 120 years of intended working life for all permanent structures.Therefore, an extensive investigation has been carried out by the Contractor Joint Venture and the Design team in order to ensure this in a well-documented way.The paper describes the durability requirements and the means by which these are fulfilled.The main focus is placed on the durability against chloride ingress and corrosion in the splash zone of the towers.The concrete used for the tower structures is made from slag cement, giving relatively low diffusion coefficients against chloride ingress.The simulation of chloride ingress is based on models suggested by the UK Concrete Society and the fib model code for durability design.These are based on the error function and applying an ageing factor on the diffusion coefficient.Material data and model simulation results are given to exemplify the design verification approach.Furthermore, the durability design parameters are explained and the sensitivity of the result is evaluated.