The fundamental equations
The transport properties of concrete measure the ability of fluids to move through it. The equations for them were first documented by the end of the nineteeth century (Fick 1855; Darcy, 1856) and applied to concrete by the middle of the twentieth century (Powers et al., 1954). However, they remain difficult to measure, particularly if the common in situ tests are used.
Interest in these properties has increased as many structures built in the second half of the twentieth century have suffered durability problems, particularly corrosion of reinforcement. This corrosion was investigated by Knudson (1907) and was soon discovered to be caused by chloride transport through the cover layer (Rosa et al., 1912