Reinforced concrete infrastructure, Understanding the past, present and future

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The construction industry is of critical importance to the UK economy and typically represents between 6-8% of the national GDP. But the large scale of this output comes at an environmental cost. The efficient design and lifetime extension of structures is therefore a social, environmental and economic priority. The focus of this proposal is reinforced concrete where a major complication in delivering efficient, sustainable, low-maintenance solutions is that the performance of these structures reflects numerous factors including the initial design, the in-service conditions, the load history and any interventions during the service life. In service, one of the challenges is that there is an interaction between the concrete and the internal reinforcement and this behaviour is not currently well understood. This problem is exacerbated when considering how shear forces are transferred since questions still remain about how even a basic reinforced concrete structure carries these forces under static load conditions. Indeed, the 2006 collapse of the de la Concorde Overpass in Quebec is a tragic reminder of the impact of the initial design, in-service repairs and bridge management all contributed to the eventual collapse. It is therefore clear, considering the potential environmental and public safety issues, that a fundamental investigation to ascertain the types of structures and loadings which may be susceptible to time dependant changes in load sharing mechanisms that could be detrimental to the structural performance is overdue. The situation becomes even more complex when interventions to increase or re-establish the strength of an existing structure are required. For example, the application of additional external fibre reinforced polymer (FRP) reinforcement has been found to be an effective means to achieve the capacity increases required to keep existing structures in service. FRPs have a high strength to weight ratio and are lighter and more durable than equivalent steel strengthening systems. However, this additional reinforcement changes the load-sharing behaviour of the structure. Furthermore, in many cases, the provision of the additional reinforcement addresses an immediate strengthening need where speed and ease of installation are primary considerations. However while the initial motivation may be for a short-term intervention, it is likely that, due to the disruption and costs associated with demolition and reconstruction, many of these FRP strengthening systems will be in service for a considerable period of time. To date, the longer term in-service performance of strengthened RC structures has not been adequately addressed. Cost-effective approaches for extending the life of existing infrastructure are becoming increasingly important in the current era of financial constraints.This project seeks to address these identified gaps through the establishment of a high-level, enduring, international collaboration between the University of Toronto (U of T), Canada, Queen's University, Canada and the University of Cambridge, UK. The particular strength of this collaboration is that it brings together the necessary expertise to re-evaluate the time- and load-dependent baseline conditions in an existing reinforced concrete structure and to then assess and predict the long-term performance of both unstrengthened and FRP-strengthened structures. This enhanced understanding will inform asset owners and managers and lead to improved design and maintenance strategies.