Hazards of Post-Tensioned Slabs:

Post tension slab construction is common in areas with expansive soils. If your location is an area with expansive soils, always assume the slab is post tensioned. Once the concrete is poured and sets, the cables are tensioned. Once tensioned, the cables cannot be de-tensioned. The hazard exists when workers cut into the slab and rupture the tensioned cable. If there is the potential that a slab may be post tensioned, a competent or qualified person needs to identify the cable locations before any slab work begins.

Stucco and bricks may cover cable grout making it difficult to identify post tensioned slabs. If a slab is post tensioned there will be a hole in the foundation or slab that contains a cable end. Always look to see if the cable ends have been mudded over by some form of concrete patch filler. If the wall is load bearing, the footer under the wall is probably post tensioned. Corners typically contain cables. Cables typically run East to West or North to South.

Do NOT cut into a post tensioned slab if there is a chance you will rupture a cable. People have been dismembered and killed when cables are cut and burst out of the concrete.

Questions to start discussion:

1. Why should you identify post tensioned slabs?
2. How do you identify post tensioned slabs?