Concrete
How to scope corroded post-tension tendons in a parking structure
Identify the PT system, connect investigation findings to structural decisions, and measure tendon repairs with defined acceptance evidence.
Direct answer
Scope corroded post-tension tendons by identifying the installed system, mapping tendon distress and water entry, and commissioning tests that distinguish protection defects, broken steel, and lost prestress. Use PTI DC80.3-24/ICRI 320.6-2024 for single-strand unbonded systems, then turn the findings into an engineered load-management plan, measured repair quantities, and acceptance records for each tendon. Include drainage, joints, and anchorage protection in the scope so the repair addresses the route that admitted water.
On this page
What belongs in a tendon corrosion repair scope?Which post-tensioning system is installed?What does unbonded tendon corrosion look like?Which investigation tests answer the tendon question?How many tendons and anchorages should be investigated?What must the engineered load-management plan control?Repair, replace or strengthen: which decision does the evidence support?How should sheathing, anchorages and water entry be repaired?How do you price and phase a parking garage tendon repair scope?Worked examples from published parking structure repairsWhat evidence closes the repair scope?What should the owner inspect after tendon repairs?Open the related tool for the calculation, checklist, or packet.
FieldOS by AnvilfieldOffline-first FieldOS for job photos, proof packets, property memory, calculations, teams, billing, and owner-ready reports.What belongs in a tendon corrosion repair scope?
A tendon repair scope identifies affected tendons, evidence supporting each repair decision, permitted temporary conditions and records needed to release completed work.
Use the parking structure restoration and repair guide for the wider garage program. Here, keep tendon investigation and repair quantities distinct from ordinary concrete patching.
Define the deliverables before commissioning tests
Require a system schedule, condition maps, test plan, load-management drawings, repair quantities and inspection hold points. Carry one stable tendon ID through the plan, photographs, opening records, tests, repair detail and closeout. Mark each condition as verified, suspected or inaccessible; these are Anvilfield record conventions.
The owner supplies history and access; the investigating engineer selects the investigation and evaluates structural consequences; the repair designer specifies permanent repairs and temporary conditions; the PT specialist executes the specified work; the testing agency supplies traceable results. The Chester Street 2024 project manual shows how these responsibilities become submittals, measured items and acceptance records.
Include top and soffit access, occupied rooms, utilities, opening reinstatement and temporary water exclusion. State who authorizes supplemental testing, changed quantities and redesign after concealed conditions appear.
Which post-tensioning system is installed?
Identify tendon construction, corrosion protection and hardware separately. In an unbonded tendon, coated steel can move relative to its sheath and transfers force through anchorages; in a bonded tendon, cementitious grout bonds the steel within its duct. That distinction changes how a local defect affects the investigation and repair. PTI DC80.3-24/ICRI 320.6-2024 addresses evaluation and repair of single-strand unbonded post-tensioned structures; a cement-grouted multistrand or bar system requires the grouted-system investigation branch described by ACI PRC-423.8-21.
Match structural and PT placing drawings, shop drawings, material certificates and previous repair records to controlled observations of the installed details. Confirm that the member is post-tensioned before assigning a repair branch: a precast member can be pretensioned, post-tensioned or conventionally reinforced. Use its fabrication and connection records to establish which system is present.
Schedule mixed construction and successive repair generations by location. ACI PRC-423.4-14 is the separate unbonded single-strand corrosion and repair report.
| Installed system | Evidence to obtain | Protection to verify | Investigation/repair consequence | Source |
|---|---|---|---|---|
| Plastic-sheathed unbonded seven-wire strand | Strand and PT drawings; observed sheath and wedge anchorage; steel records | PT coating, sheath continuity, end caps and transitions | Trace the continuous tendon and both ends; distinguish steel condition from protection condition | S1, S2, S6 |
| Older paper-wrapped or loose-sheathed unbonded strand | Original detail and observed wrapping/seam; historical hardware | Actual remaining barrier and water paths | Test selection and replacement feasibility must match the old sheath; do not assume modern encapsulation | S2, S3 |
| Button-headed parallel-wire tendon | Wire bundle and end-bearing/button-head detail | Wrapping, anchorage enclosure, water entry | Separate hardware and strengthening design from seven-wire monostrand repair | S2, S7 |
| Cement-grouted multistrand or bar tendon | Duct, grout and anchorage records; observed construction | Grout continuity/condition, ducts and anchor protection | Use grouted-system investigation, including void/grout evidence; use ACI PRC-423.8-21 rather than applying the unbonded guide wholesale | S10, S15 |
| Mixed or previously modified system | Location-linked records for every system and repair generation | Each old-to-new interface | Schedule separate details and acceptance records; unresolved identity stays open in the design register | S6; Anvilfield synthesis |
Identify the steel as well as the sheath
PTI FAQ 18, July 2026 distinguishes 250 ksi and 270 ksi strand and normal-relaxation and low-relaxation steel; repair design needs both strength and relaxation type. Confirm diameter and net steel area from records or authorized testing. A newer replacement or one capped anchorage does not establish the identity or encapsulation of every tendon on the floor.
Record identity as observed-and-documented, records only, or unresolved. Account for sampling in the structural assessment. The post-tension slab stressing guide explains original system terminology and stressing records; retain those records as evidence for the repair-specific design.
What does unbonded tendon corrosion look like?
Protruding strand, displaced anchorage hardware, fresh anchor-zone spalls and a reported tendon release require immediate area control and structural assessment. PTI Journal’s July 2006 repair paper describes distress and legacy-system problems that warrant investigation; crack width alone does not establish permission to continue garage operations.
Map rust or grease stains, leaking pockets, tendon-line cracks and soffit damage as investigation evidence. Separate concrete delamination from observations of the strand, wires and anchorages. An intact-looking surface cannot establish the condition of embedded steel.
Trace water from deck surfaces, joints and drains to anchor pockets, tendon low points and repair transitions. Water can travel along a sheath, separating the visible entry point from the damaged steel. The potentially affected length follows the tendon route and water pathway rather than the edge of a visible patch.
Check competing causes: rust from conventional reinforcement, cracking away from tendon lines, damaged anchorage concrete and recent drilling. Visible rust extent does not establish residual strength; use fracture or material examination where the mechanism changes the repair decision [S2, S3].
| Evidence category | Location and measurement fields | What the finding supports | Next scope item | Source |
|---|---|---|---|---|
| Broken wire, protruding strand or displaced hardware | Level, grid, tendon ID, observed break/displacement, photo | A visible break confirms local discontinuity; displaced hardware needs its mechanism resolved | Immediate area control; engineering assessment of affected tendon/load path | S2, S6 |
| Anchor pocket rust/leakage | End ID, wet/dry state, stain/defect extent, photo | Suspected water access or hardware deterioration | Specified pocket investigation and adjacent-water-path review | S2, S5 |
| Grease staining/tendon-line cracking | Alignment, length in ft, width in in or mm, dated photo | Possible protection defect or tendon distress | Targeted investigation correlated with tendon layout | S2 |
| Spall/delamination | Top/soffit, measured sq ft and depth in in, steel encountered | Concrete deterioration footprint | Approved removal limits plus separate PT assessment where encountered | S6 |
| Failed joint/drain or ponding | Joint/drain ID, wet-weather photos, affected route | Source or concentration of water | Drainage/joint/waterproofing repair package | S4, S6 |
| Inaccessible zone | Exact boundary, reason, next access opportunity | Unassessed extent | Access allowance and investigation return point | Anvilfield record convention |
Use the crack monitoring guide for repeatable measurements. Tie each observation to the mapped tendon, date and prior repair boundary.
Which investigation tests answer the tendon question?
Choose each test for a specific question and decision: location, concrete distress, exposure, steel condition or force.
The 2017 NCHRP Research Report 848 describes differing NDE methods for bridge PT and stay-cable systems. Applying a method in a garage requires validation for its tendon construction and access. A GPR location scan alone cannot certify remaining tendon cross-section, effective prestress or structural capacity.
Use embedded-feature locating before designed openings to coordinate access and conflicts. The diagnostic test selection guide separates concrete material questions from tendon questions. Measurable tension can coexist with local steel damage.
| Investigation | Question answered | Evidence delivered | Limitation carried into the scope | Design/bid decision it supports | Source |
|---|---|---|---|---|---|
| Records reconciliation | What was installed and altered? | System, tendon routing, steel/hardware records, gaps | Records require correlation with actual construction | Which investigation and hardware package to specify | S1, S2, S6 |
| GPR/embedded-feature locating | Where are tendons/rebar and proposed opening conflicts? | Marked plan, depth interpretation, coverage limits | Congestion and depth affect interpretation; no direct strength/force certificate | Engineer's opening locations and access plan | S8 |
| Visual survey and concrete sounding | Where is visible distress or delamination? | Location-linked photos and concrete distress map | Cannot expose hidden steel condition | Survey quantities and target locations | S2, S6 |
| Designed inspection opening/pocket examination | What are local protection, water and hardware conditions? | Local images, steel/anchor observations, sample IDs | Local evidence; opening/restoration must be engineered | Protection-only work versus further steel/force investigation | S1, S2, S6 |
| Steel-condition examination and authorized laboratory testing | Is the exposed/sample steel pitted, fractured or of uncertain identity? | Measured condition, sample provenance, material/fracture results | Removed sample and accessible face are not the whole tendon population | Reuse, replacement, supplementation and investigation expansion | S2, S3 |
| Engineer-specified in-place force/lift-off testing | What force does the specified test infer at this location and stage? | Test method, calibration, location, load/displacement record, limitations | Feasibility depends on accessible compatible hardware; not residual strength or whole-length corrosion clearance | Analysis input and repair disposition | S1, S2; decision logic is Anvilfield synthesis |
| Half-cell survey of suitable rebar | Where does rebar potential indicate corrosion activity? | Electrode, continuity/circuit checks, conditions and potentials | No transfer of rebar probability bands to sheathed strand | Conventional reinforcement corrosion program | S9 |
| Concrete or grout chloride testing | What contamination is present at the sampled depth/material? | Method, depth, units, material/binder basis | Concrete, grout and tendon environments differ | Water-source control and material-specific durability interpretation | S11, S15 |
Why rebar tests do not become tendon acceptance tests
ASTM C876-22b estimates corrosion potential in uncoated reinforcing steel and expressly excludes using its results to estimate structural properties, so a rebar potential map does not establish the residual capacity of a sheathed tendon.
Read the half-cell potential definition and survey interpretation guide when specifying the separate rebar program. ASTM C1152/C1152M-20 measures acid-soluble chloride, generally total chloride, in mortar and concrete; record depth, sampled material and reporting basis. Chemistry describes exposure at the sample location, not tendon force.
FHWA-HRT-14-040, March 2014 studies chloride thresholds in cementitious tendon grout. Interpret a grout sample within that system; its thresholds do not transfer to grease-filled unbonded tendons.
How many tendons and anchorages should be investigated?
The Chester Street March 21, 2024 bid package allows 125 slab openings and 250 grout-pocket openings for its investigation. Use these as project-specific bid allowances; the initial count for another garage follows its systems, exposure, known failures, variability, access and structural consequences.
Group locations by system generation, level, tendon direction or band, anchorage type, repair history and water exposure. Include apparently unaffected comparison locations. Count distinct tendons separately from openings because several openings can examine the same tendon; a distress-only sample cannot establish garage-wide damage prevalence.
For every group, record the population, selected tendon IDs, selection reason, method, result and expansion authorization. Classify the outcome as accepted evidence supporting a stated disposition, adverse evidence requiring redesign or expansion, or inconclusive evidence requiring different access or testing. An inaccessible location stays unassessed.
Define what makes the investigation expand
Expand when damage extends beyond the assumed boundary, adjacent tendons share the same water entry, installed steel or hardware differs from records, or force/material findings change the structural model. The engineer identifies the next group and the decision it will settle. Price supplemental access, openings, laboratory work and reinstatement with that decision path.
Report findings by sampling group; deliberately selected wet pockets cannot represent all garage tendons.
End each investigation stage with a decision for every group: enough evidence for the specified repair, additional locations needed, or a changed investigation method. Keep wet and apparently dry groups separate when reviewing results. A satisfactory exposed segment does not clear an unexamined anchorage or an inaccessible portion of the same tendon.
What must the engineered load-management plan control?
The phase plan must control occupancy, affected levels, construction loads, removal limits, temporary supports, observation triggers and release conditions. Assess the full anchor-to-anchor tendon route and affected members before limiting restrictions to the visibly damaged bay. Include the temporary loss of tendon contribution during investigation and repair.
The structural review addresses flexure, shear and punching where applicable, anchorage-zone condition, serviceability and redistribution assumptions. Trace temporary supports through underlying floors to the final supporting structure. Closing parking stalls does not establish the capacity of that temporary load path.
ACI CODE-562, Assessment, Repair, and Rehabilitation of Existing Concrete Structures supplies an assessment and repair framework; the adopted edition, permit requirements and contract determine its project application. Put the applicable basis on the design documents.
| Condition/phase | Decision to record | Responsible decision | Evidence before work/occupancy changes | Release requirement | Basis |
|---|---|---|---|---|---|
| Known tendon failure or unknown structural effect | Defined restricted area and assessment extent | Structural assessment engineer | Condition map and affected tendon/load-path review | Written disposition for specified use | S1, S2 |
| Investigation opening | Location, depth/extent limits and temporary support requirement | Investigation/repair designer | Located embedded features and authorized opening detail | Opening inspected and restored as specified | S6, S8 |
| Concrete removal/PT repair | Permitted concurrent work and support sequence | Repair and temporary-works designers | Approved phase drawing and verified supports | Required repair strength and PT records accepted | S6 |
| Equipment/material/debris staging | Weights, wheel/contact loads, routes and allowed locations | Employer, using information from a person qualified in structural design | Equipment data and load evaluation | Load removed or next stage approved | S12(a) |
| Tendon stressing work zone | Barricade and access arrangement | Employer implementing design and safety plan | Signs, barriers and controlled access | Work zone released under the project plan | S12(c) |
| Adjacent occupied areas and lower levels | Parking/egress/debris separation and support implications | Designer plus owner/operator for access | Phase-specific access and protection plan | Approved phase transition | S6 |
| Return to service | Approved vehicle use and remaining restrictions | Repair designer; owner implements | Accepted repair package, specified strength and temporary-support disposition | Written authorization identifying area and use | S6 |
Separate operating restrictions from repair operations
Under 29 CFR 1926.701(a), the employer must determine that the affected concrete structure can support proposed construction loads, using information from a person qualified in structural design. Record equipment weights, wheel/contact loads, debris accumulations, material staging and permitted travel routes on the phase drawing.
Under 29 CFR 1926.701(c), employees behind the jack during tensioning must be essential to the post-tensioning operation, and signs and barriers must limit employee access to the post-tensioning area. Coordinate these work zones with parking, egress and protection of adjacent occupied areas.
The shoring and reshoring guide supports temporary-load-path coordination. Keep the repair designer’s authorization, temporary-works design and owner’s access arrangement under the same phase ID.
Repair, replace or strengthen: which decision does the evidence support?
Select the intervention from steel and hardware condition, remaining force, continuous tendon route, available access, compatible components and repair-stage capacity. Protection restoration and structural restoration have different evidence requirements. Renewing sheathing does not replace lost steel section or establish effective prestress.
| Scope alternative | Evidence needed | What the design must establish | Measured scope item | Basis |
|---|---|---|---|---|
| Protection restoration | Local steel/hardware condition accepted for reuse | Required barrier and acceptable retained structural role | Sheathing ft; pocket/anchor treatment each | S4, S6 |
| Local steel/splice repair | Damage extent and sound connection zones; compatible steel/hardware | Transfer of required force and repair-stage capacity | Strand ft; couplers each; stressing locations each | S1, S2, S6 |
| Complete tendon replacement | Existing tendon route, sheath usability and access feasibility | New tendon force, anchor zones, profile and transitions | Tendon/strand ft plus separate anchor/stressing items | S1, S2 |
| Supplemental strengthening | Existing system contribution and available attachment/load path | Force transfer, anchorage capacity, clearance, protection and temporary states | Designed system quantities | S2, S7 |
| Leave tendon out of service | Verified system condition and analysis of required strength/serviceability | Acceptable defined use without crediting that tendon | Analysis/disposition plus any protection work | S2 |
| Member/slab replacement | Extent and lifecycle comparison of alternatives | Permanent replacement and temporary load path | Area/volume and associated systems by design | S16 |
Compare future access and protection continuity alongside initial constructability. The published cases below show how system identity and damage extent change the repair choice.
Why repair force differs from new-construction force
PTI FAQ 18, July 2026 assigns repair jacking force to the licensed design professional because existing steel identity and the difference between original and post-repair losses determine the force needed to restore effective prestress.
For its 0.5 in, seven-wire, 270 ksi strand example with no new long-term losses, PTI FAQ 18, July 2026 reduces the original 33 kip jacking value by 1.9 kip for low-relaxation steel or 4.1 kip for normal-relaxation steel, giving rounded repair examples of 31 kip and 29 kip respectively. These values explain the loss calculation; the approved repair schedule supplies the project force.
New strand and substantial replacement concrete change long-term losses; degraded coating and paper wrapping change friction. PTI FAQ 18 permits the designer to retain the original jacking force when the resulting effective force is acceptable. The repair schedule must identify the steel, loss assumptions and selected force, rather than applying one reduced value to every tendon.
Set reuse criteria before exposed steel is accepted. Record broken wires, pitting, hardware damage and the extent actually examined; average visible section loss alone cannot establish the strength of a locally pitted strand. Require a written tendon disposition that reconciles steel condition, attainable force and structural analysis, as the 2006 PTI repair paper and 2026 repair-force FAQ frame those decisions.
How should sheathing, anchorages and water entry be repaired?
Specify continuous protection across old-to-new sheathing, couplers and anchorages, with inspection before concealment. PTI FAQ 16, July 2017 treats sheathing continuity and restored PT coating as corrosion defenses and explains that the repair also preserves the strand’s unbonded behavior. A painted pocket cannot replace the specified tendon protection assembly.
Which dimensions and manufacturer details belong in the specification?
The M10.3-16 Appendix C detail reproduced in PTI FAQ 16, July 2017 uses separate tubing and tape extension datums, as the comparison below records; the FAQ separately specifies tape at least 2 in wide.
Resolve the FAQ narrative and Chester specification against the approved detail before procurement. Distinguish access exposure, tubing overlap and tape extension in the takeoff.
| Issue | Verified instruction or product scope | Difference that matters | Which document governs the decision? | Source/version |
|---|---|---|---|---|
| Existing unbonded system | Joint evaluation guide is DC80.3-24/ICRI 320.6-2024 | Use the specified edition for existing single-strand unbonded PT | Project's specified/adopted documents plus identified current guidance | S1, S19 |
| Manual and specification editions | PTI lists field manual M10.3-26 and tendon specification M10.2-24 | FAQ 16 reproduces a detail from M10.3-16 | Approved project detail referencing the specified manual edition | S4, S19 |
| Sheath repair access versus overlap | Chester §3.6.A requires at least 6 in exposure beyond damage; FAQ 16's reproduced 2016 appendix shows tubing 3 in past damage and tape 3 in past tubing | Exposure, tubing overlap and tape extension have different datums; Chester §3.6.D describes tape 3 in onto existing sheathing | Dimension each interface in the approved project detail and resolve conflicting wording with the designer | S4 pp. 1 to 3; S6 §3.6 |
| Waterproof tape | FAQ 16 calls for compatible waterproof tape; ordinary duct tape is unsuitable | PTI's FAQ index retracts the old December 2002 tape qualification document | Current product technical data/testing and approved detail, not the retracted list | S4, S20 |
| Pocket fill | FAQ 11 specifies premixed cementitious chloride-free non-shrink repair grout, with manufacturer preparation, mixing and cure | Pocket fill and underlying anchor protection need separate acceptance | Approved pocket material and manufacturer's instructions | S5, revised July 2010 |
| GTI Zero Void intermediate coupler | 0.5 in product intended for construction-joint continuity or future extension | Catalog application is not approval as a corrosion-repair splice | Supplier's approved repair-specific assembly and engineer's design | S17, undated product page, checked 2026-11-05 |
| VSL unbonded monostrand | Product family lists 0.5 and 0.6 in systems and distinct anchor/coupler components | Same nominal strand diameter does not establish compatibility with legacy hardware or another manufacturer's seals | Selected system's submittal and approved interfaces | S18, undated product page, checked 2026-11-05 |
Congested bands, support bars, old wrapping and inaccessible undersides affect whether the specified transition can be sealed. Require interface details and clearances in the submittal. Coordinate the joint sealant work and traffic deck waterproofing with anchorages and repair edges so the water-entry correction reaches the actual source.
How do you price and phase a parking garage tendon repair scope?
Price a defined package with current project quotations for its access arrangement and PT system. Separate fixed investigation and temporary-work costs from remeasured concrete, sheathing, strand and hardware quantities. Put inclusions, separately paid work, measurement rules and authority for quantity changes beside each item.
The Chester Street 2024 bid form, items 32 through 40 provides published estimated bidding quantities and payment units. Use its work breakdown with explicit measurement rules and payment inclusions.
| Item | Description, paraphrased | Estimated bid quantity | Payment unit |
|---|---|---|---|
| 32 | Slab investigation opening | 125 | each |
| 33 | Grout pocket investigation opening | 250 | each |
| 34 | Tendon sheath repair | 1,000 | lin ft |
| 35 | New seven-wire strand | 2,500 | lin ft |
| 36 | Strand coupler | 100 | each |
| 37 | Central stressing coupler, including restressing | 50 | each |
| 38 | New fixed-end anchorage | 15 | each |
| 39 | Reseat tendon in existing end anchor | 5 | each |
| 40 | Reseat tendon in existing stressing-end anchor, including restressing | 10 | each |
Chester’s Section 01 22 00 includes locating and restoration in slab-opening item 32. Sheath-repair item 34 measures length while concrete work is separately measured; new-strand item 35 includes old-to-new sheath transitions; coupler item 36 includes coupler protection and exposed-sheath repair.
Central-stressing-coupler item 37 includes shoring, phasing and restressing, while concrete work and new strand are paid separately. New fixed-end item 38 also includes shoring; reseating items 39 and 40 include pocket restoration. Use those boundaries to check the project payment schedule before extending quantities. Separate shared temporary works from work already included in an individual repair item.
What cost and time should the estimate carry?
Build the budget from investigation and engineering, access, temporary works, measured tendon repairs, concrete reinstatement, testing and water exclusion. Obtain current quotations for the identified system and hardware. Include additional investigation locations and a review allowance for concealed conditions; keep owner closure costs separate from contractor work.
Anvilfield estimates 25 to 38 working days for 375 investigation openings if one crew completes an assumed 10 to 15 openings per working day, including local restoration. This planning calculation uses the Chester quantities and an estimator-selected production allowance. Divide openings by daily output and round up; replace the allowance with the specialist's proposed crew output for the actual access and repair details.
Schedule engineering reviews, material procurement, temporary supports, tendon repairs and cure holds as separate activities. Keep slow soffit access and pocket work as distinct production items when preparing the contractor schedule. Reopening follows specified strength, accepted PT records, temporary-support release and the surfacing manufacturer's traffic-release conditions.
Municipal owners can procure investigation separately to resolve concealed conditions before bidding repairs. Bid history helps an estimator identify the owner's purchasing pattern: PorchRocket Bid Control shows who won past public garage repair bids and for how much.
Worked examples from published parking structure repairs
Turn an investigation allowance into access quantities
Anvilfield estimates 375 scheduled openings and an allowance of 84 pocket-access locations from Chester Street’s March 21, 2024 quantities and pricing assumption.
| Input or calculated result | Quantity | Basis and estimating use |
|---|---|---|
| Slab investigation openings | 125 each | S6, bid item 32; includes locating and opening restoration |
| Grout-pocket investigation openings | 250 each | S6, bid item 33; includes cap and pocket restoration |
| Total scheduled openings | 375 each | Anvilfield estimate: sum the two distinct opening categories |
| Pocket openings per access location | Average 3 | S6, Section 01 22 00, item 33 pricing assumption |
| Pocket access-location allowance | 84 locations | Anvilfield estimate: divide 250 by 3 and round up |
| Access allowance at 2 pockets per location | 125 locations | Anvilfield estimate: changed grouping assumption for access sensitivity |
| Additional locations in that access case | 41 locations | Anvilfield estimate: 125 minus 84 |
Method: add the two opening categories, then divide pocket openings by the specified average grouping and round up. In symbols, 125 + 250 = 375 openings; ceiling(250 / 3) = 84 pocket-access locations. Changing to two pockets per location gives 125 locations, or 41 additional setups. Price those extra setups only where separately payable.
Associate every opening with a tendon and investigation decision. Access setups and distinct tendons need separate counts: moving a lift does not necessarily reach another tendon, and an opening allowance does not establish a replacement quantity.
Different members can require different repairs
The July/August 2001 ICRI Alexandria case found that almost all elevated-slab tendons needed replacement, while approximately 10% of the mat-foundation tendons needed repair. The selected scope replaced the elevated PT slab with conventionally reinforced concrete and repaired the mat slab and tendons.
The published case reports three weeks to remove the 37,000 sq ft elevated slab. That duration belongs to slab removal; procurement, reconstruction and reopening are separate schedule activities. Compare the affected members independently, including usable access, required capacity, protection restoration and continuing maintenance.
Why a wire count does not establish remaining structural capacity
PTI’s 2024 O’Hare presentation reports a column with three 42-wire tendons, at least ten failed wires and unknown condition of the remaining wires, followed by external PT strengthening. Anvilfield estimates a minimum observed failed-wire share of 7.94%: divide failed wires by the original wire count and express it as a percentage, 10 / (3 × 42) × 100 = 7.94%.
Carry that observed damage and the unresolved condition into analysis. The reusable case record is system identity, observations, unknowns, structural evaluation, selected strengthening and protection details.
What evidence closes the repair scope?
Accept the tendon record, protection assembly, concrete repair and operating state separately. The Chester Street 2024 specification, Section 03 01 24 §3.9 connects strength, stressing and as-built evidence to completion.
Set hold points before mobilization and assign a reviewer to each. Specify the required concrete strength, force and elongation acceptance ranges in the repair documents. Retain access until discrepancies are resolved, and inspect hardware, sheath transitions and anchorage protection while visible.
| Hold point | Required evidence | Who reviews/releases | What keeps the item open | Basis |
|---|---|---|---|---|
| System/design before mobilization | Verified steel/system schedule, repair details, approved temporary conditions | Repair designer | Unresolved material identity or load-path assumptions | S3, S6 |
| Exposed tendon before disposition | Photos, measured condition, sample/test results, location ID | Investigating/repair engineer | Unassessed pitting, fracture or hardware condition | S1, S6 |
| Hardware/material before installation | Product data, certificates, steel size/area/grade and approved compatibility | Repair designer under submittal process | Unapproved substitutions or missing interface detail | S6 |
| Stressing readiness | Specified versus actual concrete strength; approved loss calculations; matched jack/gauge calibration | Designated inspector and repair designer | Strength, equipment or calculation not accepted | S6 §3.9 |
| Force/elongation record | Tendon ID, force/pressure, calculated and measured elongation, conditions and disposition | Repair designer | Out-of-range or unexplained result under project criteria | S6 §3.9 |
| Protection before concealment | Sheath, coupler and anchorage continuity; caps; accepted transitions; photos | Engineer/testing agency as specified | Gaps, incompatible protection or incomplete inspection | S4, S6 |
| Concrete/material repair | Placement, curing, specified strength; pull-off result and failure mode where required | Specified testing agency/designer | Failed criterion or unclassified failure mode | S6, S13 |
| Waterproofing/closure | Joint/drain details and accepted deck protection; operating restrictions | Designer and owner for their respective scope | Unfinished water-entry correction or restricted phase | S6 |
| Return to service/turnover | As-built repair map; released supports and restrictions; maintenance schedule | Repair designer; owner implements | Missing release or incomplete structural evidence | S6 |
Keep concrete test results separate from tendon acceptance
ASTM C1583/C1583M-25 requires a failure mode for every pull-off result and permits averaging only results with the same failure mode; a repair-bond result does not establish restored tendon force. Locate embedded steel and approve test sites before drilling pull-off specimens in PT concrete.
Use the pull-off testing guide for that concrete evidence and the concrete repair and restoration guide for substrate, placement and curing scope after PT-specific details are established. Record every discrepancy and its written resolution.
The written service release identifies the area, permitted use and remaining access obligations.
What should the owner inspect after tendon repairs?
The University of Missouri System’s Parking Garage Evaluations and Maintenance Guidelines call for annual in-house visual inspections and suggest late winter or early spring. Use that owner-program example to establish a dated calendar for leaks, drains, sealants, pockets and repair interfaces; the repair engineer specifies closer tendon monitoring where findings require it.
Use closeout photographs and the repaired tendon map as the baseline. Salt, persistent leaks and legacy protection increase exposure; prior failures and active movement increase urgency. Record the observer, next review date and reason for any shortened interval.
New York City’s parking-structure program requires a condition assessment and filed report at least once every six years for covered structures, performed by a New York State licensed and registered professional engineer who is also a Qualified Parking Structure Inspector (QPSI). Keep that local statutory cycle separate from repair monitoring and prompt response to new distress. A new release or displaced hardware requires immediate area control and structural assessment.
Field checklist from investigation to turnover
- Identify every system and mark unresolved steel/hardware identity.
- Collect PT drawings, prior repairs and material certificates.
- Trace tendons, ends, intermediate anchors and inspection locations.
- Map distress, water routes and inaccessible zones with dated photographs.
- Assign each test a question, location, limitation and decision.
- Record sample groups, comparison locations and expansion triggers.
- Obtain engineered opening, removal and temporary-support requirements.
- Record equipment, debris and material loads and approved locations.
- Put area controls, public separation and egress on the phase plan.
- Give each tendon a written repair, replacement, strengthening or reuse disposition.
- Approve steel, hardware and protection interfaces before procurement.
- Define investigation, sheath, strand, hardware and stressing payment boundaries.
- Inspect and photograph exposed work before concealment.
- Accept strength, stressing and protection evidence; resolve deviations.
- Complete joint, drainage and waterproofing repairs.
- Issue the as-built register, service release and observation schedule.
Sources checked and how to cite this page
Anvilfield. Reviewed 2026-11-05. Update log: publication and article review, 2026-11-05. References below include PTI technical guidance, publisher descriptions, agency requirements and published project evidence.
Evidence tables are Anvilfield syntheses of the cited references.
How to cite this page: Anvilfield, How to scope corroded post-tension tendons in a parking structure, 2026, https://anvilfield.com/field-guides/concrete/post-tension-tendon-corrosion-repair/
FAQ
How do you investigate tendon corrosion in a parking garage?
Identify the system, map distress and water entry, then use designed openings and selected tests to answer steel-condition and force questions.
How do I identify the PT system in an existing garage?
Match structural and PT shop drawings to observed sheath, strand or wire, and anchorage details. Record protection and steel identity separately; one encapsulated repaired end does not establish the protection of the whole tendon.
What are signs of unbonded tendon corrosion?
Rust or grease staining, wet pockets, tendon-line cracking, anchor distress and released strand warrant location-linked investigation. A visible wire break establishes local discontinuity; staining alone does not establish fracture.
Can GPR prove a tendon is unbroken?
A location scan does not establish whole-tendon integrity, force or residual capacity. Use it to coordinate embedded-feature locations and engineered access, then obtain the condition and force evidence required by the investigation.
Can half-cell testing measure PT tendon corrosion?
ASTM C876-22b addresses uncoated reinforcing steel. Its rebar potential bands are not acceptance criteria for grease-filled sheathed tendons; keep rebar corrosion mapping separate from tendon-condition evidence.
How many tendons need testing?
Chester Street’s 2024 bid package allows 125 slab openings and 250 pocket openings. A project sampling plan sets its own count from system, exposure, failure history and structural consequences. Count distinct tendons separately, include comparison locations and define investigation expansion triggers.
Must a corroded tendon always be replaced?
The disposition follows steel and hardware condition plus structural analysis. Protection repair, local steel repair, replacement, supplemental strengthening and leaving a tendon out of service require different evidence and design checks.
Can a garage stay open during tendon repairs?
Operation is limited to the areas, loads and uses authorized by the engineered phase and support plan. Carry lower-level support implications, construction loads, public separation and egress into the same phase record.
Should an old tendon be restressed to the original jacking force?
PTI FAQ 18, July 2026, assigns a repair-specific force decision to the licensed design professional using existing steel identity, effective prestress and changed losses. Use the approved repair schedule for the project force.
What does parking garage tendon repair cost?
Build a current estimate from separate investigation, access, engineering, temporary works, tendon repairs, concrete reinstatement and waterproofing quantities. Obtain system-specific contractor quotations and define payment inclusions so sheath transitions, shoring and restressing are counted once.
How long does parking garage tendon repair take?
For 375 investigation openings, Anvilfield estimates 25 to 38 working days at an assumed crew output of 10 to 15 openings per day including local restoration. Add engineering review, procurement, tendon repairs and cure holds as separate scheduled activities; their durations follow the actual repair package.
What proves a tendon repair is complete?
The closeout package links each tendon to accepted material and hardware records, approved stressing results, inspected protection, concrete-strength evidence and an as-built repair map. Resolve deviations before concealment and obtain the written release for the specified use and area.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.
Sources checked
- S1: ICRI, 320.6-2024, joint PTI DC80.3-24, publisher page Checked 2026-11-05. Public publisher description: scope and 2024 joint edition; licensed clauses not reproduced.
- S2: PTI Journal, July 2006, Repairs, Modifications, and Strengthening with Post-Tensioning, manufacturer-hosted full paper Checked 2026-11-05. Full 2006 paper: legacy systems, distress and repair/strengthening alternatives.
- S3: PTI FAQ 18, Stressing single strand unbonded tendons in PT repair projects, July 2026 Checked 2026-11-05. July 2026 FAQ: steel identity, loss assumptions and repair force examples.
- S4: PTI FAQ 16, Sheathing Repairs, July 2017 Checked 2026-11-05. July 2017 FAQ, including reproduced M10.3-16 Appendix C: protection continuity and dimension reference points.
- S5: PTI FAQ 11, Proper Filling of Single-Strand Tendon Stressing Pockets, revised July 2010 Checked 2026-11-05. Revised July 2010: pocket grout and manufacturer preparation, mixing and curing.
- S6: City of Birmingham, Chester Street Parking Structure, 2024 Repairs, issued for bid March 21, 2024 Checked 2026-11-05. March 21, 2024 issued-for-bid manual: items 32 to 40, payment inclusions, protection details and acceptance evidence.
- S7: PTI Convention 2024, O'Hare International Airport Parking Garage: Assessment, Repair, and Strengthening Checked 2026-11-05. 2024 presentation: button-headed wire system, column wire observations and external PT strengthening.
- S8: NCHRP Research Report 848, Inspection Guidelines for Bridge Post-Tensioning and Stay Cable Systems Using NDE Methods, 2017, National Academies Checked 2026-11-05. Public publisher overview: system-specific NDE methods and differing investigation questions.
- S9: ASTM C876-22b, Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete Checked 2026-11-05. Public scope and significance: uncoated reinforcing steel and structural-property limitations.
- S10: ACI PRC-423.8-21, Corrosion and Repair of Grouted Post-Tensioning Tendon Systems, 2021 Checked 2026-11-05. Public description: 2021 grouted multistrand/bar investigation and repair scope.
- S11: ASTM C1152/C1152M-20, Acid-Soluble Chloride in Mortar and Concrete Checked 2026-11-05. Public scope: acid-soluble chloride in mortar and concrete.
- S12: OSHA, 29 CFR 1926.701(a) and (c), General requirements, current public text checked Checked 2026-11-05. Agency text: construction-load capacity determination and tensioning-area access controls.
- S13: ASTM C1583/C1583M-25, direct tension/pull-off method Checked 2026-11-05. Public scope/significance: direct-tension test and failure-mode reporting.
- S14: NYC Department of Buildings, Parking Structures, current program page Checked 2026-11-05. Agency program: local six-year minimum assessment cycle for covered parking structures.
- S15: FHWA-HRT-14-040, An FHWA Special Study: Post-Tensioning Tendon Grout Chloride Thresholds, March 2014 Checked 2026-11-05. March 2014 technical summary: normal-grout chloride thresholds and experimental conditions.
- S16: ICRI Concrete Repair Bulletin, Post-Tensioned Concrete Structure Evaluation, July/August 2001, pp. 14 to 15 Checked 2026-11-05. July/August 2001, pp. 14 to 15: Alexandria elevated-slab replacement, mat-tendon repairs, area and removal interval.
- S17: GTI, 0.5 in Zero Void Intermediate Coupler, current product page Checked 2026-11-05. Manufacturer application: construction-joint continuity or future extension; repair compatibility requires an approved assembly.
- S18: Structural Technologies, VSL Unbonded Monostrand Post-Tensioning, current product page Checked 2026-11-05. Manufacturer product family: nominal strand sizes and distinct anchor/coupler components.
- S19: PTI Publications catalog, current official PDF Checked 2026-11-05. Public catalog: joint repair guide and field-manual editions; catalog listings establish editions.
- S20: PTI FAQs & Technical Notes index, current official page Checked 2026-11-05. Official index: current FAQs and explicit retraction of the December 2002 tape-qualification document.
- S21: ACI PRC-423.4-14, Report on Corrosion and Repair of Unbonded Single-Strand Tendons, 2014 Checked 2026-11-05. Public description: 2014 unbonded single-strand corrosion and repair scope.
- S22: ACI repair code portal Checked 2026-11-05. Publisher repair-code framework; project adoption and contract application must be established.
- S23: University of Missouri System, Parking Garage Evaluations and Maintenance Guidelines, undated current agency page Checked 2026-11-05. Owner guidance: annual in-house visual inspection, seasonal timing and condition-based review.