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Tunneling for road and rail infrastructure enables expansion of networks beneath our cities and limits encroachment of these networks into existing developed surface sites. But this is not without its challenges – particularly when it comes to ensuring these tunnels can achieve design lives of 100 years or more with very limited opportunities for maintenance.
Reinforced concrete is the key material used for lining of tunnel bores. The completed lining must resist water ingress and potentially aggressive ground conditions. It must also resist the effects tunnels operations may have on the internal tunnel environment as well as the anthropogenic impacts of atmospheric pollution and resultant climate change.
This paper discusses key factors that have been considered in the development of durability assessments and concrete specifications for tunnels across Australia over the past few years and touches on some key concepts that impact the durability of concrete in tunnels, some familiar, some less-so. These include carbonation and the dilemma of trying to improve carbonation resistance while reducing project related CO2 emissions by using high levels of supplementary cementitious materials; improving sulphate-resistance while enabling high early strengths; and defining wick action effects with appropriate measures for confirming adequate performance. The paper considers the design approaches that can be adopted to define performance requirements and the practicalities of various performance measures for these factors for specifiers, constructors and asset owners.