Concrete is one of the principal construction materials. Depending on the use to which it is put, concrete eventually fails as a material due to excessive loading, stresses, weathering and chemical action, or a combination of these. In compression it becomes stiffer and stronger when subjected to repeated loading; but it can be weakened if critical tensile stresses arise under loading conditions, and it may soften or crack. Concrete volume contains about 15% of minute empty spaces. It is therefore liable to absorb destructive substances such as acid rain, and in the case of concrete roadways and bridge decks, de-icing salts. When used over steel, expansion of the metal due to rusting creates pressure on the concrete. Another source of stress on concrete is during the sway of tall buildings.
Expenditure on the repair and upgrade of Australia's infrastructure made of reinforced concrete, was estimated in 1993 at $200 million to $500 million annually. As these structures age, maintenance costs and replacement costs will rise.