What is a post-tension concrete slab? Why did AFT Construction use this method for the slab at our Whitewing at Higley build?
A concrete slab is susceptible to soil expansion and contraction, which can lead to cracking. Post-tensioning is a form of pre-stressing concrete to provide reinforcement and overcome concrete’s weaknesses.
Post-tension concrete slabs are used to create a monolithic (single pour) slab that is stronger than a traditional slab without reinforcement. This is achieved by laying out high-strength steel cables in a crisscrossed grid pattern throughout the foundation prior to pouring the concrete.
Steel cables have a high capacity to resist the tensile forces (e.g., the weight of a structure) that concrete can be vulnerable to. After the steel cable grid is complete, the concrete is poured over the grid and the cables are embedded in the concrete. The newly poured concrete is allowed to cure to approximately 75%, at which time the cables are tensioned (i.e., stretched) using hydraulic jacks and then anchored to the concrete.
The result is a more compressed, reinforced concrete slab that spreads the load of the structure over a wider area and helps reduce cracking. The tensioning process is analogous to the Chinese finger trap toy in that when a person pulls their fingers outward in an attempt to remove them from the trap, it actually tightens the trap. Other added benefits are a post-tension slab will often times require less excavation and grading work, which can shorten your construction schedule, and the monolithic pour can assist in preventing termite penetration.
Why did we use a post-tension slab at our Whitewing at Higley build? While Arizona may be best known for its climate and desert landscape, its soils can also be poor, unstable, and expansive. These unstable conditions can lead to heaving, settling and expansion issues when a structure is built.
Post-tension concrete slabs reduce these settling issues and reduce the possibility of cracks in the home’s foundation.