Pre-stressing is a technique used in construction to enhance the strength and durability of concrete structures. It involves applying a compressive force to the concrete before it is subjected to external loads. This is typically achieved by using high-strength steel tendons or cables that are tensioned and anchored within the concrete. There are two main methods of pre-stressing: pre-tensioning and post-tensioning. In pre-tensioning, the tendons are stretched before the concrete is poured, while in post-tensioning, the tendons are tensioned after the concrete has cured. Both methods help to reduce cracking and improve the overall performance of structures like bridges and buildings.