Post-Tension Slab

High-strength steel cables, called tendons, are what set a post-tension slab apart from an ordinary concrete pour: they get pulled tight after the concrete has cured. The crew lays the tendons in a grid before the pour, sheathed in plastic so they can move. Once the concrete reaches strength, usually a few days later, a hydraulic jack stretches each cable and locks it. That squeeze, or compression, holds the slab together as one stiff plate.

The method matters in Arizona because of the ground. Much of Maricopa and Pinal County sits on expansive soil, clay that swells when wet and shrinks when it dries. That movement cracks a plain concrete slab and the home above it. A post-tension slab spreads loads and resists the soil's push and pull far better than a standard slab with rebar alone. The Post-Tensioning Institute notes this is why the design dominates residential foundations across the Southwest.

For example, a custom home in Casa Grande or Queen Creek, where clay soils and land subsidence are common, will almost always sit on a post-tension slab engineered to the specific soil report. A geotechnical engineer tests the lot, and the slab design is stamped before the AHJ approves the permit.

Post-tension differs from a rebar-only slab, where steel bars resist cracking but the concrete is never actively compressed. It also differs from pre-tension, used in factory-made beams where cables are tensioned before the concrete is poured. One practical note for owners: the live cables run through the slab, so you never cut, core, or drill into a post-tension foundation without locating the tendons first.