Delayed ettringite formation (DEF) refers to a detrimental chemical reaction in hardened concrete, occurring under certain conditions which can significantly impair its structural integrity. Initially, ettringite is a naturally occurring mineral that forms during the early stages of cement hydration and is generally benign or even beneficial in small amounts, contributing to the initial strength gain of concrete. However, under specific circumstances, particularly under high temperature curing scenarios which disrupt normal ettringite formation, it can form at a later stage. This delayed formation can cause substantial internal stress within the concrete, leading to cracking, spalling, and other forms of deterioration.