Post-tensioning is a method used in construction to strengthen concrete structures. It involves placing high-strength steel tendons inside ducts within the concrete. After the concrete has cured, these tendons are tensioned, or pulled tight, and then anchored to the concrete, which helps to compress the material and improve its load-bearing capacity. This technique is commonly used in bridges, parking garages, and large buildings, allowing for longer spans and thinner slabs. By reducing the amount of concrete needed, post-tensioning can also lead to cost savings and lighter structures. Overall, it enhances the durability and performance of concrete constructions.