The post-tension slabs are the primary slab-on-grade foundation type used when building over our expansive soils here in central Texas. Post-tension concrete foundations are an evolution in traditional concrete slabs. It’s a technique where foundations are reinforced with steel cables commonly referred to as tendons. These steel cables are positioned before the concrete is poured. The tension is added after the concrete has hardened. Since concrete has excellent abilities for dealing with compression forces and the steel is ideal for handling tensile forces, this combination allows for the use of thinner slabs and can cut down on curing time and, ultimately, a reduction in construction costs.
Although post-tension foundations are an improvement, they do not solve all foundation problems. To determine if you have a post-tension cable foundation, look for the circular blemishes on your foundation. This is where the stressing end pockets were filled with a high strength non-shrink grout, which leaves a visible circular pattern at the perimeter of the exposed foundation. If you can see the metal of the post-tension cable, then you need maintenance. Ignoring the exposed cable end pockets can expose the ends to moisture, which will cause a significant amount of rust to the steel. This condition can cause several problems, ranging from catastrophic cable failure to persistent cracking of the concrete slab as the rusting steel expands.
Remember, check annually for changes in your foundation.