Calcined clay, particularly when used in the form of metakaolin, is an important pozzolanic material that significantly enhances the properties of cement and concrete. The process of calcining clay involves heating natural clays at temperatures typically between 600 °C and 800 °C, which dehydroxylates the clay and alters its mineral structure, increasing its reactivity with cement hydrates. This pozzolanic reaction makes calcined clay a valuable addition to concrete, improving the mechanical properties and durability of the material. It is especially effective under severe environmental conditions, providing resistance to sulfate attack, reducing alkali-silica reaction (ASR), and enhancing the overall longevity and resilience of concrete structures in aggressive environments.