Advances in the in-situ assessment of construction materials

The deterioration of concrete in structures is a major problem throughout the world. This has prompted research on methods of predicting the service life of both existing and new structures. Current prediction methods are still very basic and, before they can be used with confidence more reliable information on the properties of the concrete in these structures is needed. In this paper a range of test methods for determining the strength and transport properties of concrete are discussed from the perspective of research at Queen's University Belfast on advances made over the past thirty years. The initial focus was on in-situ strength testing and this led to the pull-off test and the development of the LIMPET. However when it became apparent that durability was a matter of much greater concern to practising engineers, measurement of permeation properties became a priority. This led to the development of the AUTOCLAM which was found to give extremely useful correlation in the laboratory and on site between the air and water permeability and durability. Subsequently problems associated with the ingress of chlorides into concrete have been recognised and in response the PERMIT has been developed which allows the diffusion characteristics of the "covercrete" to be determined. Using a combination of such approaches simple durability based criteria can be developed for concrete and the remaining life of existing structures estimated. As far as new construction is concerned the above methods can be used to develop durability related design criteria and in the future continuous monitoring techniques could prove to be useful. In the context of the latter, chemical fibre optic sensors are currently being developed to detect pH changes in concrete. However their long term reliability is yet to be proven.