Influence of microstructure on the transport properties of concrete

Most of the world's infrastructure is built in concrete with more than 1m3 of concrete being produced every year for every person on the planet. However, concrete structures gradually deteriorate and this is a major problem around the world. All of the commonly occurring deterioration processes are controlled by the penetration of water and aggressive agents via pores and microcracks inherent in the microstructure. An ability to predict this transport would allow more reliable prediction of remaining life and would facilitate the development of more durable structures. This project aims to develop an understanding of how the microstructure of concrete controls penetration of water and aggressive agents and then to develop models for predicting transport properties. Concrete microstructure will be quantified using a multi-scale approach combining optical, field emission electron and 3D laser scanning confocal microscopy. This will allow all relevant phases to be characterised at the appropriate length scale giving global information (volume fraction, specific surface), morphology (shape), topology (tortuosity, connectivity, constrictivity) and spatial variability. A range of samples will be tested to establish the effect of different ingredients, proportions, processing and exposure history on the microstructure. The transport properties most important to concrete durability will be measured on parallel samples and correlated to the microstructure, to identify the influence and relative contribution of different types and sizes of pore, microcrack and other phases. A multi-scale model of the microstructure will be reconstructed using data from microscopy and models for predicting transport properties will be developed from classical transport theories, effective medium approximation and flow simulation using network models. This will facilitate future development of more durable materials and more reliable service life prediction models and will also be relevant to the storage of radioactive waste.