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Summary

It has been shown that theoretical understanding of the microstructure:transport property relationships of concrete, from the cement paste up to the full composite, can be based on the ideas of pore size and connectivity, with connectivity defined rigorously using percolation concepts. These concepts give a fairly complete, although at present mainly qualitative, picture of how transport properties depend on microstructure in concrete. Percolation phenomena in concrete include the setting of cement paste, the connectivity of the C-S-H gel phase, the disconnection of the capillary pore space in cement paste, the effect of leaching of calcium hydroxide on the transport properties of cement paste, and the connection of the interfacial transition zones in concrete. Like the material itself, percolation phenomena are important over many length scales, and since more than one phase of the concrete composite is simultaneously percolated, concrete must be considered to be an interpenetrating phase composite [81].

The use of a set of multi-scale microstructure models to investigate transport and mechanical properties of concrete has been demonstrated. By relating microstructure to properties at all relevant size scales, a more complete understanding of the influence of microstructure and the underlying physical processes on the performance of these composite materials can be obtained. For the case of chloride diffusivity, a nearly complete set of results has been presented [83,84]. As the structural modelling and computational capabilities described herein continue to evolve, their use as a tool in the design of a concrete with desired properties and service life should become a reality.