Concrete durability is adversely affected by deicing agents and sulphate solutions. Sodium chloride and calcium chloride are the commonly used deicing agents—salts thrown on roads and other pavements to help ice melt in winter. Sulphates are common in soils and clays in Britain, Europe, the Middle East, western North America and elsewhere, while chlorides and sulphates are also present in sea-water. Scanning electron micrographs of limestones (used quite commonly as aggregate in concrete) show that the surfaces of limestones scale and disintegrate when soaked in solutions of sodium chloride, calcium chloride and magnesium sulphate. The morphology of both calcite and dolomite is changed, but calcite is attacked most rapidly, the progress of the reactions being observed to be controlled by cleavages and grain boundaries; the morphological results depend on the angle between the plane of weakness and the surface. Some limestones show dimensional change during continuous soaking in salt solutions at constant temperature. The adverse effect on concrete durability of deicers and sulphate solutions may thus result from attack on limestone aggregate as well as on cement paste.