Alkali–silica reaction
The alkali–silica reaction (ASR), also commonly known as concrete cancer, is a deleterious internal swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (i.e., non-crystalline) silica found in many common aggregates, given sufficient moisture. This deleterious chemical reaction causes the expansion of the altered aggregate by the formation of a soluble and viscous gel of sodium silicate (Na2SiO3 · n H2O, also noted Na2H2SiO4 · n H2O, or N-S-H (sodium silicate hydrate), depending on the adopted convention).