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Concrete is one of the most widely used construction materials in the world. Throughout this extensive usage many concrete structures are subjected to high temperatures either by consequence of their intended function, for example as in nuclear reactor vessels or aircraft runways, or unintentionally, often as a result of accidental or deliberate fires. For both of these scenarios the structural behaviour of concrete under highly elevated temperatures is clearly very important.High temperature is known to have a number of easily observable effects on concrete including loss of strength, loss of stiffness and spalling, i.e. the fracturing and loss of material from the surface of concrete elements. Spalling, which is the focus of this project, varies considerably in occurrence, extent and severity, and manifestations, ranging from minor and non-violent, to severe and explosive, have been regularly observed. In all five distinct forms of spalling have been identified. In order of increasing violence these are Post Cooling spalling, Aggregate spalling, Corner spalling, Surface spalling and Explosive spalling.Whatever the form, spalling can have significant structural and safety implications depending on the structure that is affected. Where structural members, such as columns and walls, are exposed to elevated temperatures, spalling can result in a loss of load bearing cross-section and the exposure of steel reinforcement, which is highly susceptible to heat damage, and can ultimately lead to the collapse of the entire structure. Even where collapse does not occur there are significant economic implications associated with the time and cost of repair and this extends to situations where collapse is not an issue, for example in aircraft runways, where even minor spalling can have safety or (at the very least) serviceability implications and hence associated economic consequences.Despite its common occurence there is a fundamental lack of understanding of the phenomenon of spalling and the processes that control it. This is demonstrated by the results of numerous studies and the analyses of several high profile incidents including the Channel Tunnel fire, in which a range of hypotheses have been presented but no real consensus as to the exact mechanisms underlying the observed spalling behaviour has emerged.The aim of this work is to develop an advanced numerical tool that, by accounting for the physical processes at work within concrete exposed to elevated temperatures, will ultimately be capable of predicting the occurrence, type and extent of spalling that may be expected in any particular structure subjected to any combination of thermal and mechanical loading. The model will thus have significant applications in the structural and safety assessment of either existing or proposed new structures under actual, historical or hypothetical thermal and mechanical loading scenarios.Furthermore, by applying this model in an extensive series of numerical experiments the fundamental processes underlying and controlling spalling may be explored and a better understanding of the phenomenon can be achieved.The improved understanding of spalling behaviour and the application of the model will allow types of concrete, concrete structures and remedial or protective techniques to be designed such that their performance under severe conditions can be specifically addressed and optimised, and hence the structural, economic and safety implications of structural exposure to elevated temperatures can be minimised.
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