Post-tensioning is a reinforced-concrete system that uses high-strength steel cables stressed after the concrete is cast to keep the slab in compression. In Miami-Dade, most parking decks built after 1975 are post-tensioned because it allows longer spans and thinner slabs. When a tendon fails, the slab loses a measurable portion of its design capacity — immediate inspection and repair is required. The three visual signs below are how our crews triage a parking deck on the first walk.
Sign 1 — Rust bleed at the anchor
Post-tension tendons terminate at anchor plates on the slab edge. When corrosion reaches the anchor, brown rust staining appears on the concrete face directly above or below it. Staining does not always mean the tendon has lost capacity — but it always means the protective anchor seal has failed. In a salt-air environment, that seal failure is the first domino. Action: inspection by the engineer of record, followed by anchor repair and re-sealing.
Sign 2 — Spalling along the tendon line
Tendons follow a shallow parabolic path through the slab. When the grout or sheathing around a tendon fails and water reaches the steel, the corrosion product expands and spalls the concrete above. A linear spall pattern that follows the tendon line is a near-certain sign of interior corrosion. Action: chloride testing, tendon exposure for inspection, and — if corrosion is confirmed — engineered de-stress and splice repair.
Sign 3 — Blown tendon
A blown tendon is the worst case. The cable has fractured under stress and the stored energy has released — violently. Concrete spalls outward, sometimes with visible cable protruding. This is a life-safety condition. Action: immediate closure of the affected area, emergency engineering inspection, and emergency repair mobilization. CORE Builder Group can mobilize a containment and assessment crew to Miami-Dade or Broward the same day.