Durability of concrete — Degradation phenomena involving detrimental chemical reactions

While interacting with its service environment, concrete often undergoes significant alterations that often have significant adverse consequences on its engineering properties. As a result, the durability of hydrated cement systems and their constituent phases has received significant attention from scientists and engineers. Cement paste deterioration by detrimental chemical reactions is discussed. First, the mechanisms that govern the transport of ions, moisture and gas are described. Then, different chemical degradation phenomena are reviewed. Microstructural alterations resulting from exposure to chlorides and carbon dioxide are discussed. Sulfate attack from external sources is described including processes resulting in the formation of ettringite and thaumasite. The mineralogy of Portland cement is sensitive to temperature and thermal cycling, particularly during the early hydration period.