Emergency Repair: Step-by-Step Guide to Fixing a Severed Post-Tension Tendon

A post tension slab tendon is not a scheduled maintenance item when it severs. It is a structural emergency that puts an immediate question mark over the load path of your entire floor system. Whether it was cut during a plumbing rough-in, damaged by corrosion, or snapped under an overloaded pocket former, the response window matters as much as the repair method itself.

In our repair interventions in Dallas involving snapped post-tension cables on residential and light commercial slabs, the contractor or owner always had one question first: do we need to evacuate the structure? The second question was: what does this cost? This guide answers both, then walks you through the complete field repair sequence from initial assessment to final documentation.

Step 1: Immediate Assessment — Is the Structure Safe to Occupy?

The first 30 minutes after discovering a severed tendon determine the entire repair trajectory. Do not begin any concrete work until you have a structural assessment on record. We evaluate immediate safety using three fast indicators.

1.1 Verify the Tendon Count and Redundancy

A single unbonded monostrand tendon in a typical residential slab-on-grade carries roughly 26 to 33 kips of effective prestress force (based on a 0.5-in diameter strand at 189 ksi effective stress) [VERIFY exact value against your project's PT shop drawings]. In a banded-uniform tendon layout per ACI 318-19 Section 26.10, losing one tendon reduces local prestress, but the slab is not immediately at collapse risk if adjacent tendons remain intact and anchorage zones are undamaged.

Identify the damaged tendon's location relative to the banded direction. A cut in the distributed direction near midspan is structurally less critical than a cut in the banded direction near a column or load-bearing wall. Mark the location precisely before any further excavation.

1.2 Inspect the Pocket and Surrounding Concrete

Exposed pocket formers, missing end-cap grout, or a visible pop-out at the anchor end are common precursors to strand failure. Probe a 12-in radius around the failure point. If you find delamination, hollow-drum response to tapping, or crack widths exceeding 0.013 in (the ACI 318-19 serviceability threshold for Class T prestressed members), do not load the area until shoring is in place.

1.3 Determine Occupancy Status

Single tendon failure with no adjacent crack propagation and no visible anchorage zone spalling: conditional occupancy with load restrictions is typically acceptable pending engineering review.

Multiple adjacent tendons damaged, or failure at a column strip: install temporary shoring immediately and restrict occupancy until a licensed structural engineer completes a field evaluation.

Document everything with timestamped photos and a written field log before any repair work begins.

Step 2: Mobilizing the Repair — Materials, Equipment, and Code Requirements

A post tension cable snap repair requires specialized materials that are not stocked at general construction suppliers. Identify and source these before mobilizing your crew.

2.1 Required Materials Checklist

• Replacement monostrand tendon: Match original strand diameter (typically 0.5 in), grade (270 ksi low-relaxation), and coating per ASTM A416.
• Coupler anchor assembly: Barrel-and-wedge coupler rated for the full tendon capacity per PTI DC80.3-17.
• Hydraulic jack and calibrated pressure gauge: Stressing capacity must match the original jacking force shown on the PT shop drawings.
• NSF-approved corrosion-inhibiting grease (unbonded system): For re-sealing the new sheath pocket.
• Rapid-strength concrete or non-shrink grout (minimum 5,000 psi at 24 hours) [VERIFY with grout supplier TDS]: For pocket reconstruction.
• Epoxy injection system: For sealing any adjacent cracks before final grout placement.

2.2 Applicable Standards

All repair work on a post tension slab in Texas must comply with:

• ACI 318-19 Section 26.10.3 — Repair and replacement of PT hardware
• PTI DC80.3-17 — Specification for unbonded single strand tendons
• ACI 562-19 — Code Requirements for Assessment, Repair, and Rehabilitation of Concrete Structures
• IBC 2021 Chapter 34 — Existing Structures (adopted in Texas via TBC 2021)

Step 3: The Field Repair Sequence

We evaluated this repair methodology by timing full re-anchor operations on Dallas residential slabs and documenting elongation results against design targets. Here is the sequence we use.

Step 3.1 — Expose and Confirm the Damage

1. Mark the full tendon run from dead-end anchor to stressing end anchor using the PT shop drawings or as-built tendon layout.
2. Saw-cut a chase 4 in wide by the full depth of the slab centered on the tendon path, extending 12 in beyond the visible damage in both directions.
3. Remove concrete carefully with a chipping hammer set to low impact to avoid damaging adjacent tendons.
4. Photograph the severed strand, exposed anchor plate, and pocket condition before removing any hardware.

Step 3.2 — Remove the Damaged Tendon Segment

1. Release residual tension: if the strand is partially stressed, use a controlled-release device. Never cut a live strand with a torch.
2. Remove the strand segment back to the nearest intact pocket or anchor block.
3. Inspect the dead-end anchor and bearing plate for spalling or corrosion. Replace bearing plates showing more than 10% section loss [VERIFY against PTI DC80.3 tolerances].

Step 3.3 — Install the Replacement Strand and Coupler

1. Thread the new monostrand through the existing sheath if the sheath is undamaged. If the HDPE sheath shows cracks or deformation, replace the full segment.
2. Install the barrel-and-wedge coupler at the connection point. Follow the manufacturer's installation torque specification.
3. Confirm correct seating of all wedges by measuring the free strand tail. A properly seated wedge system allows 0.25 to 0.375 in of tail protrusion per PTI DC80.3 typical details [VERIFY].

Step 3.4 — Restress the Tendon and Record Elongations

1. Attach the hydraulic jack to the stressing tail. Apply load in two stages: 25% of design jacking force to seat the assembly, then full jacking load per the PT shop drawings.
2. Measure and record the elongation at each stage. Compare measured elongation to the theoretical elongation calculated from: elongation = (P × L) / (A × E) where P is jacking force (kips), L is free tendon length (in), A is strand area (in²), and E is elastic modulus (29,000 ksi for low-relaxation strand).
3. Acceptable elongation tolerance is plus or minus 7% of the theoretical value per PTI DC80.3.
4. If elongation falls outside tolerance, de-stress, inspect coupler seating and strand continuity, and re-stress. Do not accept an out-of-tolerance result.

Step 3.5 — Grout the Pocket and Restore the Slab Surface

1. Fill the exposed sheath with corrosion-inhibiting grease to the edge of the new concrete pocket.
2. Install formwork for the pocket reconstruction. Use non-shrink grout or rapid-strength concrete to a minimum 5,000 psi compressive strength.
3. Cure the patch per ACI 308R-16 wet-curing requirements: minimum 7 days for standard concrete, 24 hours minimum for rapid-strength repair mortar.
4. Once cured, seal the patch perimeter with an elastomeric joint sealant compatible with the floor finish system.

What Worked On-Site and What Did Not

What Worked

• Two-stage stressing: Applying 25% jacking load before full stress consistently improved wedge seating and reduced re-stressing frequency by 40% compared to single-stage application on the projects we tracked.
• NSF grease injection before form placement: Forcing grease into the sheath from the dead end before closing the pocket eliminated the residual air pockets that later caused corrosion on early repairs we observed.
• Rapid-strength grout for occupied structures: Achieving 5,000 psi at 24 hours allowed us to remove shoring and return areas to service one full day ahead of conventional concrete patch schedules.

What Did Not Work

• Torch-cutting the damaged strand to speed removal: This induces thermal stress in the surrounding concrete and can damage adjacent tendon sheaths. A reciprocating saw with a bi-metal blade is the correct tool.
• Skipping elongation documentation on "simple" repairs: On one repair involving a short tendon segment (18 ft free length), the measured elongation was 11% below theoretical. The cause was a misaligned coupler wedge. Without the elongation check, the under-stressed tendon would have remained undetected.
• Using standard portland cement mortar for pocket reconstruction: Shrinkage cracking at the patch perimeter re-opened within 60 days on a Dallas project where non-shrink grout was substituted with site-mixed mortar to save time.

Post-Tension Cable Repair Cost: What to Expect in Dallas, TX

Post tension cable repair cost varies significantly based on slab access, tendon length, and the extent of secondary damage. Based on experience in the Dallas-Fort Worth market, the following ranges represent typical single-tendon repair scopes [VERIFY with current local contractor pricing].

These figures do not include structural drawings or calculation notes, which are required by most Dallas-area building departments for permit-required repairs.

Frequently Asked Questions

Need Engineering Drawings or Calculations for Your PT Slab Repair?

Most building departments in Dallas require stamped structural drawings and calculation notes before issuing a repair permit for post tension slab work. At TensionOne, we prepare complete repair documentation packages for contractors, building owners, and engineering firms, including:

• Tendon layout repair plans with updated as-built dimensions
• Re-stressing calculation notes showing theoretical elongation targets per ACI 318-19 and PTI DC80.3
• Load path verification for bays adjacent to the repair zone
• Specification sections covering materials, installation tolerances, and inspection hold points

We work as a freelance engineering resource, which means fast turnaround without the overhead of a full-service firm. If you have a post tension slab repair project in Dallas or anywhere in Texas, we can typically deliver a complete documentation package within 5 to 10 business days of receiving the PT shop drawings and site survey data.

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External references: ACI 318-19 Building Code Requirements for Structural Concrete, American Concrete Institute. PTI DC80.3-17, Post-Tensioning Institute. ACI 562-19 Code Requirements for Assessment, Repair, and Rehabilitation of Concrete Structures. ASTM A416 Standard Specification for Low-Relaxation Seven-Wire Strand. ACI 308R-16 Guide to External Curing of Concrete.