Expansion in cement and concrete refers to the increase in volume of these materials, which can occur due to various chemical reactions and physical processes. Common causes of expansion include the hydration of expansive agents, such as ettringite and calcium oxide, and physical effects like thermal expansion. Chemical expansion is often due to reactions such as alkali-silica reaction (ASR) or delayed ettringite formation (DEF), where new phases with larger volumes are formed within the concrete. These reactions can be exacerbated under severe environmental conditions such as high moisture, temperature changes, and chemical exposure, leading to significant structural problems.