Post-Tensioned Concrete

This specification covers the materials, fabrication, installation, stressing, grouting, and field quality control of cast-in-place post-tensioned concrete for buildings and parking structures. Post-tensioning is a method of prestressing in which high-strength steel strand is installed in the forms in an unstressed condition, the concrete is placed and cured around it, and the strand is then tensioned (stressed) against the hardened concrete and locked off at anchorages cast into the member. The resulting compressive force counteracts the tensile stresses that service loads would otherwise produce, allowing thinner sections, longer spans, reduced deflection, and controlled cracking. All work shall conform to the prestressed-concrete provisions of ACI CODE-318-25, Building Code Requirements for Structural Concrete, and to the applicable Post-Tensioning Institute (PTI) and ACI specifications referenced herein. The concrete itself — its materials, mix design, placement, consolidation, and curing — shall additionally conform to Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete; this standard governs only the requirements unique to post-tensioning.

Post-tensioning differs fundamentally from both ordinary reinforced concrete and from pretensioned precast. Unlike ordinary reinforcement, the prestressing steel is an actively stressed element carrying a large permanent force — a half-inch strand is routinely tensioned to over 30,000 lbf — so a failure of the strand, anchorage, or its corrosion protection is a release of stored energy, not merely a loss of passive reinforcement. Unlike pretensioned precast, where the force transfers into the member by bond as the strand is detensioned in a plant, post-tensioning transfers the force into the member through mechanical anchorages bearing on the concrete at the member ends, and the stressing happens in the field on the project. This shifts a set of controls — concrete strength at the time of stressing, anchorage bearing capacity, the stressing sequence, elongation verification, and (for bonded systems) grouting of the ducts — into the field, where they are this standard's central concern.

The most important conceptual distinction in this standard is between unbonded and bonded systems. In an unbonded single-strand system, each seven-wire strand is coated with corrosion-inhibiting grease and encased in a continuous plastic sheath for its full length; the strand remains permanently free to move relative to the concrete, and its force is held only by the end anchorages. This is the dominant system for elevated building floor slabs, beams, and parking decks because it is economical, the tendons are light and flexible, and no grouting operation is required. In a bonded multistrand system, several strands are grouped in a metal or plastic duct cast into the member, tensioned together by a multistrand jack, anchored, and then the duct is filled with cementitious grout; after the grout cures, the strand is bonded to the concrete along its length and is also protected from corrosion by the grout. Bonded systems are used where the higher force per tendon and the structural advantages of bond are needed — transfer girders, heavily loaded beams, and longer spans — and where the redundancy of bond (a localized strand failure does not unload the entire tendon) is desired. Many parking structures and most building floor slabs use unbonded tendons; many transfer girders and post-tensioned beams use bonded multistrand. A single project frequently contains both, and each system shall satisfy its own requirements in this standard.

Corrosion protection is the governing durability concern for both systems and is treated with particular emphasis for parking structures and other chloride-exposed work. Prestressing strand is far more sensitive to corrosion than ordinary reinforcement: it is highly stressed, cold-drawn, and can fail by hydrogen embrittlement or stress-corrosion cracking at a fraction of the section loss that a passive bar would tolerate, and the failure can be sudden and brittle. For unbonded tendons in aggressive exposure this standard requires encapsulated tendons — a fully sealed system in which the sheath, the anchorage, and the strand tail are continuously enclosed so that the strand is never exposed to the environment — and, where specified, electrically isolated tendons that permit the corrosion protection to be monitored. For bonded tendons the grout is both a structural and a corrosion-protection element, and its quality, completeness of fill, and freedom from bleed voids are critical.

Coordinate the concrete work with Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete. Coordinate non-prestressed reinforcement — the conventional mild-steel reinforcing that supplements the tendons at anchorages, in the bursting zone behind anchorages, and as bonded reinforcement required by code — with Concrete ReinforcementConcrete ReinforcementResolves to the current adopted revision.sync/concrete-reinforcement. Where post-tensioned members bear on or connect to precast or pretensioned elements, coordinate with Precast ConcretePrecast ConcreteResolves to the current adopted revision.sync/precast-concrete.

This standard does not govern pretensioned precast (see Precast ConcretePrecast ConcreteResolves to the current adopted revision.sync/precast-concrete), post-tensioned slab-on-ground residential foundations, bridge and other infrastructure post-tensioning, or external post-tensioning for repair and strengthening.

Materials, fabrication, installation, stressing, grouting, testing, and quality control shall comply with the latest adopted edition of the following standards and codes. Where the contract documents, the adopted building code, a referenced standard, or the post-tensioning supplier's engineering conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

The Contractor shall submit the following for the Engineer's review before any post-tensioning materials are fabricated or installed. No tendon shall be placed and no concrete shall be cast around tendons until the corresponding submittals have been reviewed and accepted. Submittals shall be complete and internally coordinated; piecemeal submissions shall be rejected.

The post-tensioning supplier shall prepare and submit placing (shop) drawings showing, for each member, the tendon layout in plan and the tendon profile in elevation, the number and size of strands per tendon, the high and low points of the profile and the support-bar heights or chair heights that establish the profile, the anchorage and coupler locations and types, the stressing-end and dead-end designations, the calculated jacking force and the calculated theoretical elongation for each tendon, the stressing sequence, the bursting and anchorage-zone reinforcement, and the location of all tendon penetrations, blockouts, and pour-strip closures. Placing drawings shall reconcile the tendon profile against the non-prestressed reinforcement and any embedded items so that the tendons can actually be placed at the specified profile without conflict.

Product data and the manufacturer's qualification documentation shall be submitted for the strand, the sheathing and corrosion-protection system, the anchorages, the wedges, and any couplers, demonstrating that the anchorage assembly meets the static, fatigue, and (for unbonded systems) the corrosion-protection acceptance tests of ACI CODE-318-25 and the applicable PTI specification.

Where the post-tensioning design or any portion of it (for example, the anchorage-zone reinforcement, the tendon profile detailing, or the stressing sequence) is delegated to the supplier, signed and sealed calculations shall be submitted, prepared by a registered professional engineer licensed in the jurisdiction of the project. Calculations shall address the effective prestress after all losses, the concrete stresses at transfer (stressing), the stresses in service, and the anchorage-zone (bursting and spalling) forces.

A written stressing procedure shall be submitted stating the stressing sequence, the calculated jacking force and gauge pressure for each tendon group, the calibrated jack and gauge identification, the anticipated wedge seating (anchor set) loss, and the elongation-acceptance basis. For bonded systems, a written grouting procedure conforming to PTI M55.1 shall be submitted stating the grout material and mix proportions, the injection and venting sequence, the equipment, and the procedures for verifying complete duct fill.

• Certified mill test reports for the prestressing strand (ASTM A416) or bar (ASTM A722), reporting the actual modulus of elasticity used to compute theoretical elongation.
• Jack and pressure-gauge calibration certificates from an accredited laboratory, dated within the calibration validity period (commonly six months or 1,000 cycles, whichever is sooner), with the jack and gauge calibrated as a unit.
• The qualifications and certification of the field personnel performing stressing and (for bonded systems) grouting.
• The post-tensioning supplier's quality-control plan.

• Stressing records for every tendon: the gauge pressure applied, the measured elongation, the calculated theoretical elongation, the percent difference, the wedge seating measured, and the date and personnel — reconciled and accepted by the Engineer.
• For bonded systems: grouting records for every duct, including grout batch, flow-cone time, bleed and set verification, injection pressure, the sequence of vents closed, and confirmation of complete fill.
• Records of any tendon that was re-stressed, replaced, or accepted under an engineered variance, with the supporting evaluation.
• As-built tendon layout noting any field-authorized profile or anchorage modifications.
• Warranty documentation.

The post-tensioning materials and the supplier's field services shall be furnished by a supplier regularly engaged in the production and installation of the specified system and able to demonstrate that its anchorage assemblies have passed the acceptance tests required by ACI CODE-318-25 and the applicable PTI specification. The Contractor shall furnish evidence of qualification before any post-tensioning material is delivered.

Personnel performing stressing operations shall be trained and certified in the specified system, and shall be qualified to read and reconcile elongation against gauge pressure. For bonded systems, personnel performing grouting shall be certified under a recognized grouting certification program (such as the ACI/PTI bonded post-tensioning grouting certification). Certification records shall be available at the site.

Post-tensioned concrete is a structural element requiring special inspection under IBC Chapter 17. The special inspector shall verify the tendon material and placement against the accepted placing drawings before concrete placement, witness and record stressing operations, verify elongation acceptance, and (for bonded systems) inspect grouting for complete fill. The special inspector is engaged by and reports to the Owner; the inspector's presence does not relieve the Contractor of responsibility for conforming work.

A pre-installation conference shall be held before the first post-tensioned element is cast, attended by the Contractor's superintendent, the post-tensioning supplier's field representative, the concrete subcontractor, the testing and special-inspection agencies, and the Engineer. The agenda shall cover tendon placement and profile control, anchorage-zone reinforcement, the concrete strength required before stressing and how it will be verified, the stressing sequence, elongation acceptance and the response to out-of-tolerance results, protection of tendons before and after stressing, and (for bonded systems) the grouting procedure and schedule.

No tendon shall be stressed until field-cured cylinders, cured under the same conditions as the member they represent, confirm that the concrete has attained the specified minimum compressive strength at stressing. This is the single most important hold point in the work: stressing against concrete that has not reached the required strength crushes the concrete behind the anchorage, fails the anchorage zone in bursting, and can cause progressive failure. Verification shall be by ASTM C39 cylinder breaks, not by maturity or rebound estimates alone unless those methods have been correlated to cylinder data and accepted by the Engineer.

The corrosion protection required for the tendons is governed by the service exposure, and parking structures are the controlling case for buildings because their decks are exposed to chloride-laden water tracked in from deiced roads. ACI CODE-318-25 Chapter 19 exposure categories apply to the concrete, and the post-tensioning system's corrosion protection shall be selected to match.

The C exposure category drives the corrosion-protection system. In C0 and C1 exposure, standard greased-and-sheathed unbonded tendons or standard grouted bonded tendons are adequate. In C2 exposure — the parking-structure case — this standard requires encapsulated unbonded tendons (or, for bonded systems, a fully grouted plastic-duct system with sealed anchorages) so that the strand is continuously enclosed and isolated from the chloride source. The cover over the tendons and the watertightness of the deck (membrane or traffic-bearing coating, specified separately) are additional controls in C2 exposure.

Prestressing strand for both unbonded and bonded systems shall be uncoated, low-relaxation, seven-wire steel strand conforming to ASTM A416/A416M, Grade 270 (270,000 psi specified minimum tensile strength), unless the design requires a different grade. Low-relaxation strand shall be used in lieu of stress-relieved (normal-relaxation) strand because its much lower long-term relaxation — not more than 2.5% at 1,000 hours from an initial load of 70% of specified minimum breaking strength — preserves more of the effective prestress over the life of the structure and is the current production standard. Strand shall be free of loose rust, pitting, and bond-reducing contaminants; tightly adhered surface rust without pitting is acceptable.

The half-inch (0.5 in.) diameter strand is the standard for unbonded building floor and parking deck tendons; the 0.6 in. strand is common in bonded multistrand tendons where higher force per strand reduces the number of strands and ducts. The strand diameter, the number of strands per tendon, and the tendon force are determined by the structural design and shown on the contract drawings.

Where post-tensioning bars are used (for short, straight tendons, for anchorage to existing construction, or for transverse stressing), they shall conform to ASTM A722/A722M. Bar systems use threaded ends and nut anchorages rather than wedges.

The jacking force and the resulting effective prestress are structural design values shown on the contract drawings and the accepted placing drawings. The temporary stress in the strand during jacking shall not exceed the limit of ACI CODE-318-25 (commonly 0.80 times the specified minimum breaking strength at jacking, reducing to 0.74 immediately after anchorage seating), and the contractor shall not increase the jacking force above the design value in an attempt to compensate for low measured elongation without the Engineer's evaluation.

In an unbonded single-strand tendon, the strand shall be continuously coated with a corrosion-inhibiting grease and encased in a seamless, watertight plastic (typically high-density polyethylene or polypropylene) sheath conforming to the materials requirements of ACI SPEC-423.7 and PTI M10.2. The grease shall fill the annular space between the strand and the sheath for the full length, providing both corrosion protection and lubrication so the strand can elongate freely within the sheath during stressing. The sheath shall have a minimum wall thickness adequate to resist damage during handling and concrete placement; a sheath punctured during placement leaves the strand exposed to the concrete and to any moisture that reaches it, and is the most common origin of unbonded-tendon corrosion. Damaged sheathing shall be repaired with a sealed, waterproof wrap before concrete placement.

The level of corrosion protection of an unbonded tendon shall match the service exposure. A standard (non-encapsulated) tendon protects the strand along its length with grease and sheath but does not fully seal the anchorage and the strand tail. An encapsulated tendon extends the watertight enclosure continuously through the anchorage: the anchorage casting is a sealed plastic or plastic-coated unit, a watertight connection joins the sheath to the anchorage, and a sealed cap encloses the stressed strand tail and the wedges, with the cap filled with corrosion-inhibiting grease. The encapsulated system creates a continuous, sealed envelope around the strand from end to end, with no point at which the strand is exposed to the environment.

Encapsulated tendons shall be used for all tendons in C2 (chloride) exposure — most importantly parking structures — and are recommended wherever the tendon is exposed to moisture. For interior, dry building floors (C0/C1), standard tendons are acceptable, although ACI now requires encapsulated tendons for tendons in structures designed under ACI CODE-318 in many editions; the specifier shall verify the current code requirement for the project and default to encapsulated tendons where there is any doubt about future exposure.

Where the corrosion protection is to be monitored or where an impressed-current cathodic protection strategy is anticipated, electrically isolated tendons shall be used, in which the strand and its anchorage are electrically isolated from the surrounding concrete and reinforcement by non-conductive components so that the integrity of the encapsulation can be verified by an electrical resistance measurement and monitored over the life of the structure. Electrically isolated tendons are a specialized requirement and shall be specified only where the design calls for them.

Unbonded tendons shall be anchored at each stressing end by a casting that bears on the concrete and grips the strand with hardened steel wedges, and at the dead end by a pre-seated wedge anchorage or a swaged/button-headed dead-end fitting. The anchorage assembly (casting, wedges, and, for encapsulated systems, the sealing components) shall be a qualified assembly that has passed the static and fatigue acceptance tests of ACI CODE-318-25 and PTI M10.2. The anchorage casting bears a concentrated force on the concrete and shall be installed with the manufacturer's anchorage-zone (bursting) reinforcement detailed on the placing drawings; omitting or mislocating the bursting reinforcement causes the concrete behind the anchorage to split when the tendon is stressed.

In a bonded multistrand system, the strands of each tendon shall be installed in a duct cast into the member, sized to allow the strands to be placed and later to allow grout to surround every strand. Ducts shall be of corrugated galvanized steel or, for aggressive exposure and where specified, of corrugated plastic (polyethylene or polypropylene) conforming to PTI/ASBI M50.3; plastic ducts provide an additional barrier against chloride ingress and electrical isolation and are preferred for parking and coastal structures. Ducts shall be mortar-tight at all joints and connections so that cement paste from the surrounding concrete cannot enter and block the duct, and shall be supported at the spacing required to hold the tendon profile and to resist flotation and displacement during concrete placement.

Bonded multistrand tendons shall be anchored by a bearing-plate anchorage with a wedge plate gripping each strand, qualified by the static, fatigue, and load-transfer acceptance tests of ACI CODE-318-25 and PTI/ASBI M50.3. Couplers, where used to splice tendons at construction joints or stage-stressing locations, shall develop the specified breaking strength of the tendon and shall be located and detailed on the placing drawings; couplers concentrate force and require their own anchorage-zone reinforcement. For aggressive exposure, the anchorage shall be a sealed (encapsulated) anchorage compatible with the plastic-duct system so that the corrosion-protection envelope is continuous through the anchorage.

Each duct shall be provided with grout inlets and with vents at all high points, at anchorages, and at any location where air or bleed water could be trapped, so that the duct can be completely filled and air and water displaced during grouting. The location of inlets and vents shall be shown on the placing drawings and shall reflect the tendon profile, because an un-vented high point traps a void that leaves strand ungrouted and unprotected.

The tendon profile — the vertical position of the tendon along its length — is the geometric basis of the entire post-tensioning design: it determines the eccentricity of the prestress force and therefore the balancing load the tendons apply to the member. Tendons shall be supported at the heights shown on the placing drawings using support bars, chairs, or bolster strips at the specified spacing so that the as-placed profile matches the design profile within tolerance. A tendon placed too low at midspan, or too high over a support, does not balance the load the design relied on and can produce cracking and excessive deflection that are difficult to remedy after stressing.

The tendon high points, low points, and support-bar heights are as indicated on the post-tensioning placing drawings and structural drawings.

The vertical placing tolerance for tendons controls how closely the as-built eccentricity matches the design. The tolerance shall conform to ACI CODE-318-25 and the placing drawings, and is tighter for thin members where a small vertical deviation is a large fraction of the available depth.

Concrete cover over tendons, ducts, and anchorages shall conform to ACI CODE-318-25 for the service exposure and shall not be reduced below the value the design requires for the C exposure category. In parking and chloride exposure, cover is a primary corrosion-protection control and is frequently increased above the code minimum.

Tendons and their sheathing or ducts shall be protected from damage during placement of concrete and from heat, sparks, and weld spatter during adjacent work. Sheathing damaged before concrete placement shall be repaired and sealed; a tendon with a torn sheath cast into the concrete is a corrosion liability that cannot be remedied without removing and replacing the tendon. Anchorage pockets and stressing-end hardware shall be kept clean and free of concrete that would prevent the jack from seating.

The concrete shall conform to Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete for its materials, mix design, placement, consolidation, and curing. Two requirements specific to post-tensioning are added here.

The concrete shall attain a specified minimum compressive strength before any tendon is stressed, verified by field-cured cylinder breaks. This strength-at-stressing requirement governs the construction schedule, because the member cannot be stressed — and therefore cannot be partially de-shored and put to work — until it is reached. Stressing against under-strength concrete crushes the concrete at the anchorage and fails the anchorage zone. The required strength at stressing is set by the design for the anchorage bearing and the member stresses at transfer, and is commonly in the range of 3,000 to 4,000 psi for slabs but shall be taken from the contract documents where stated.

Where the design permits partial stressing at a lower strength followed by full stressing once the concrete gains strength, the partial- and full-stressing strengths and the corresponding forces shall be stated on the placing drawings and reflected in the stressing procedure.

Tendons shall be stressed with hydraulic jacks calibrated as a unit with their pressure gauges by an accredited laboratory within the calibration validity period. The calibration relates gauge pressure to the actual force delivered by the jack; an out-of-calibration jack or gauge is the most common cause of the entire tendon population being over- or under-stressed without the elongation check revealing it, because the gauge reading is the contractor's primary force control. Calibration records shall be at the site and the calibration shall remain valid for the duration of stressing.

Tendons shall be stressed in the sequence shown on the placing drawings. The sequence matters because stressing one tendon shortens and cambers the member and changes the force in tendons already stressed, and because stressing introduces large eccentric forces that the partially loaded member and its shoring must accommodate. An out-of-sequence stressing operation can overload the member, the shoring, or the supporting structure, and can crack the member. The member shall be free to shorten and camber as it is stressed — forms and shoring that restrain the movement shall be loosened as the stressing procedure requires — so that the prestress goes into the member rather than into the formwork.

The delivered prestress force shall be verified at every tendon by two independent means: the jack gauge pressure (giving the applied force from the calibration) and the measured strand elongation (giving the force from the strand modulus and the stretch). Reconciling the two is the fundamental quality check of post-tensioning. A gauge reading alone can be wrong because of a faulty gauge, jack friction, or a blocked tendon; an elongation reading alone can be wrong because of anchorage slip, a misread reference mark, or an incorrect assumed modulus. When the measured elongation agrees with the calculated theoretical elongation within tolerance, both the force and the friction losses the design assumed are confirmed.

The measured elongation shall agree with the calculated theoretical elongation within ±7% for tendons in buildings, per ACI CODE-318-25. For short tendons, where a small absolute discrepancy is a large percentage, the tolerance may be assessed in absolute terms per the applicable PTI specification rather than as a percentage. Where the difference exceeds the tolerance, the cause shall be investigated and resolved with the Engineer before the tendon is accepted — common causes are an incorrect assumed modulus, friction higher than assumed (a kinked or blocked tendon), gauge error, or a misrecorded measurement — and the tendon shall not be over-stressed beyond the code jacking limit to force the elongation into tolerance.

When the jack releases the strand and the wedges seat into the anchorage, the strand draws back a small distance — the anchor set or wedge seating, commonly on the order of 1/4 in. — and a corresponding loss of force occurs at the anchorage. The expected seating loss shall be accounted for in the design and in the calculated elongation, and the measured draw-in shall be within the supplier's expected range. Excessive draw-in indicates a wedge that did not seat properly and a tendon that has lost more force than the design assumed; such a tendon shall be evaluated and, if required, re-stressed or replaced.

A stressing record shall be completed for every tendon at the time of stressing, documenting the gauge pressure, the corresponding force, the measured elongation, the calculated theoretical elongation, the percent difference, the measured wedge seating, the jack and gauge identification, and the date and operator. The records shall be reviewed and accepted by the special inspector and the Engineer as a hold point before the tendons are cut and the pockets are sealed.

The stressed strand tails projecting beyond the anchorage shall not be cut until the stressing records for those tendons have been reviewed and accepted, because once cut the tendon cannot be re-stressed. Tails shall be cut by an abrasive saw or shear, leaving the minimum projection the anchorage requires; tails shall not be cut by an oxy-fuel torch or by any method that heats the strand, because heat can release the wedges or anneal and weaken the strand at the anchorage.

After the tails are cut, the anchorage pocket shall be cleaned and sealed to protect the anchorage and the strand tail from corrosion. For encapsulated unbonded tendons, the sealed cap shall be installed over the wedges and tail and filled with corrosion-inhibiting grease, and the pocket shall be filled with a non-shrink, low-permeability patching mortar that bonds to the surrounding concrete. For bonded systems, the anchorage shall be capped and the pocket filled after grouting. The pocket treatment completes the corrosion-protection envelope at the most vulnerable point of the tendon — the anchorage — and an unsealed or poorly patched pocket is a frequent origin of anchorage corrosion and of unsightly rust staining on parking-structure faces.

Grouting applies only to bonded multistrand systems. After the tendons are stressed and accepted, each duct shall be filled with cementitious grout that bonds the strand to the surrounding concrete and provides corrosion protection. Grouting shall conform to PTI M55.1, Specification for Grouting of Post-Tensioned Structures. Incomplete grouting — leaving voids where air or bleed water was trapped — is the principal durability failure of bonded post-tensioning, because the ungrouted strand has no corrosion protection and the bond the design relied on is absent; the voids are hidden inside the duct and cannot be detected after the fact without specialized testing.

The grout shall be a prepackaged or job-proportioned cementitious grout that is non-bleed and thixotropic, with low permeability and minimal shrinkage, conforming to PTI M55.1. A non-bleed, thixotropic grout is required for all but non-aggressive interior exposure because ordinary cement grout bleeds water that rises to high points and leaves voids when the bleed water is later reabsorbed or evaporates; the thixotropic, anti-bleed formulation holds the water in the mix and fills the duct completely. The grout shall be tested for flow (ASTM C939 flow cone), bleed and volume stability (ASTM C1741), and compressive strength (ASTM C942 cubes).

Grout shall be injected from the lowest inlet of each duct and shall be pumped continuously until grout of the same consistency as that injected flows from each vent in sequence from low to high, at which point each vent is closed. The grout shall be injected at a controlled rate and pressure that fills the duct without segregating the grout or rupturing the duct. Grouting shall not be performed when the duct or the ambient temperature is below the minimum stated in the grouting procedure, and the grout shall be protected from freezing until it has set and gained strength. The grouting record shall confirm, vent by vent, that the duct was completely filled.

Bonded tendons shall be grouted as soon as practicable after stressing and acceptance, within the maximum time the grouting procedure and PTI M55.1 allow, to limit the period during which the stressed but ungrouted strand is exposed to moisture and corrosion inside the duct. Where grouting cannot follow promptly, the ducts shall be protected against moisture entry in the interim.

The concrete immediately behind each anchorage carries a large concentrated force that spreads into the member, producing bursting tension transverse to the tendon and spalling tension at the loaded face. This zone shall be reinforced with the anchorage-zone (bursting and spalling) reinforcement detailed on the placing drawings, in conformance with ACI CODE-318-25. The reinforcement shall be in place and inspected before concrete placement; it is the reinforcement that prevents the concrete from splitting when the tendon is stressed, and it cannot be added after the fact. Where the anchorage-zone reinforcement is welded, welding shall conform to AWS D1.4.

Dimensional tolerances for the concrete members shall conform to ACI 117-10 and Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete. Tolerances specific to post-tensioning are the tendon vertical placing tolerance (addressed under Tendon Profile and Placement) and the anchorage location and angularity tolerance, which shall be held so that the jack can be aligned with the tendon and seat squarely on the anchorage; an anchorage cast out of square forces the strand over an edge and produces a friction and seating anomaly at the most highly stressed point.

Concrete compressive strength shall be tested per ASTM C39 and Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete. In addition, field-cured cylinders cured alongside each post-tensioned member shall be tested to confirm the concrete has reached the specified strength at stressing before any tendon in that member is stressed. The field-cured cylinders reflect the actual in-place strength under the member's temperature history, which is the strength that matters for the stressing decision.

Every tendon's stressing operation shall be witnessed and recorded by the special inspector, and the elongation reconciled against the gauge force within tolerance before acceptance. The aggregate elongation results shall also be reviewed for systematic bias: if the entire population of tendons reads consistently high or low against theoretical, the cause is more likely a systematic error (an out-of-calibration jack, a wrong assumed modulus, or a calculation error) than a series of individual tendon problems, and the systematic cause shall be found before the results are accepted.

For bonded systems, the grout shall be tested for flow, bleed, and strength as specified, and each duct's grouting shall be recorded and confirmed complete. Where the contract documents or the building code require, post-grouting verification of fill (such as impact-echo or borescope inspection at vents) shall be performed on a sampling of ducts to confirm the absence of voids.

After stressing and before cutting and pocket sealing, the projecting tails and anchorages shall be protected from damage and from moisture. After pocket sealing (and, for bonded systems, after grouting), the corrosion-protection envelope shall be complete; any subsequent coring, drilling, or cutting of a post-tensioned member shall not be performed without the Engineer's review of the tendon layout, because cutting a stressed tendon releases its force suddenly and can injure personnel and damage the structure. The locations of tendons shall be recorded on the as-built drawings precisely for this reason.

A tendon with a damaged sheath discovered before stressing shall have the sheath repaired and sealed. A strand found broken, corroded, or with a damaged anchorage shall be evaluated by the Engineer; depending on the system, the remedy may be re-stressing, replacement of the tendon, or an engineered supplemental tendon, and the evaluation shall account for the redistribution of force to adjacent tendons. Repairs to unbonded tendons follow the principles of ACI 423.4R.

Concrete defects in post-tensioned members — honeycombing, anchorage-zone cracking, or low-strength concrete — shall be evaluated and repaired in accordance with Cast In Place ConcreteCast-in-Place ConcreteResolves to the current adopted revision.sync/cast-in-place-concrete and the Engineer's direction, with particular attention to anchorage-zone defects, which compromise the ability of the concrete to carry the anchorage force and may preclude stressing until repaired.

The Contractor shall warrant the post-tensioned concrete work against defects in materials and workmanship — including anchorage failure, corrosion of strand or anchorage attributable to a defective or incomplete corrosion-protection system, incomplete grouting of bonded tendons, anchorage-zone cracking, and loss of prestress attributable to construction defect — for a period of not less than one year from substantial completion, or for the period stated in the contract documents if longer. Material warranties provided by the post-tensioning supplier and any deck-membrane or coating manufacturer shall be passed through to the Owner and included in the closeout submittals. The warranty shall not limit the Engineer's right to require corrective work for nonconforming conditions discovered during the warranty period.