Pour Strip Zero
Post-tensioned concrete slab on a commercial jobsite where a pour strip leave-out would traditionally sit open at the construction joint

The Post-Tensioned Concrete Slab, and How to Eliminate Its Pour Strip

What a PT slab is, why post-tensioned slabs shorten so much at stressing that they rely on pour strips, and the mechanical rebar splice that keeps the reinforcement continuous across the seam.

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ICC Approved Mechanical Rebar Splice | ACI 318 Type 1 & Type 2 Compliant | Engineered for Reinforced & Post-Tensioned Work | 45+ Years of Engineering Expertise
The Engineering View

Most PT guides explain the tendons. We attack the leave-out those tendons force you to detail.

A post-tensioned concrete slab is reinforced with high-strength tendons that are stressed after curing so they actively compress the concrete, which is what lets a PT slab span farther and stay thinner than a conventionally reinforced one. Every other explainer walks through tendon layout, anchor detailing, and stressing sequence, then stops. Ours starts from the detail those guides skip: the moment you stress a PT slab it shortens, and it keeps shortening through creep and drying shrinkage, which is exactly why PT structures rely so heavily on pour strips and delay strips to release that shortening before the reinforcement is tied continuous. That open leave-out is the thing PS=Ø was built to remove. Our couplers and closure strip go in where the pour strip would sit, so the slab still shortens naturally but the crew is never leaving an open joint. PS=Ø is an ICC Approved, ACI 318 Type 1 and Type 2 compliant mechanical rebar splice engineered over 45 years to keep reinforcement continuous across that seam.

What is a post-tensioned concrete slab?

A post-tensioned concrete slab uses steel tendons that are tensioned after the concrete has cured, then anchored so they hold the slab in compression. Because the concrete is compressed before any load arrives, it resists cracking rather than waiting to crack in tension the way passive rebar allows. That is why PT slabs dominate long-span floor plates, podium decks, and parking structures where thickness and column spacing matter. The reinforcement that has to stay continuous across a construction joint is the mild steel, and that is the reinforcement a pour strip or closure pour interrupts.

That shortening is the opening PS=Ø was built for. Instead of leaving the strip open and coming back to fill it, the mild reinforcement is spliced mechanically across the seam. The slab is still stressed, still shortens, and still cures on its own timeline, then the couplers are grouted to complete a continuous connection. You can see the full assembly on our system page, where the couplers and closure strip replace the traditional pour strip.

Why do post-tensioned slabs need pour strips?

A post-tensioned slab needs a pour strip because it shortens more than a reinforced one, and it does most of that shortening in the first weeks after stressing. The tendons compress the concrete, the slab shortens elastically at once, then creep and drying shrinkage carry it further. If stiff cores, shear walls, and columns restrain that movement, restraint-to-shortening forces build up and crack the slab. The pour strip leaves a gap so each side shortens on its own before the reinforcement is tied continuous. The specific movements a PT pour strip has to release:

  • Elastic shortening. The instant the tendons are stressed, the compressed slab shortens. This is the movement conventionally reinforced slabs do not have.
  • Creep. Under sustained compression the concrete continues to shorten slowly over weeks, adding to the total movement at the seam.
  • Drying shrinkage. The same volume change every slab goes through as it cures, layered on top of the PT-specific movement.
  • Restraint at stiff elements. Cores and walls fight all of the above, so the stiffer the restraint the more shortening relief the detailing has to provide.
"The pour strip on a PT slab is not there for shrinkage alone. It is there because stressing the tendons shortens the slab the moment the jack releases, and that movement has to go somewhere."

That is why PT structures lean on pour strips harder than any other slab type, and why designing the strip out has to preserve the shortening, not just close the gap. Our engineers can review your stressing sequence and delegated design. Read how they approach it on the engineer impact page, or call (800) 355-8414 to talk through a specific layout.

Post-tensioned vs reinforced concrete slab

Both are reinforced concrete, but they carry load and move differently, and the difference in movement is what drives the pour-strip decision. A reinforced slab shortens mainly from drying shrinkage. A PT slab adds elastic shortening at stressing and creep on top of that, so it moves more and needs more shortening relief. Here is how the two compare on the points that matter to a detailer.

Factor Conventionally reinforced slab Post-tensioned slab
How load is carried Passive rebar resists tension after the concrete has already cracked High-strength tendons are stressed to actively compress the concrete before it is loaded
Movement at the seam Drying shrinkage only Elastic shortening from stressing, plus creep and drying shrinkage, so the slab moves more
Why a pour strip is used Relieve restraint-to-shortening from drying shrinkage before tying the slabs together Release elastic shortening and creep at stressing before locking the reinforcement across the seam
Reinforcement across the joint Lapped or doweled once the strip is cast Must be made continuous after stressing, which is where the leave-out sits open
With PS=Ø Splice carries mild reinforcement across the seam, no open strip Slab still shortens at stressing, splice keeps the rebar continuous, leave-out eliminated

The takeaway is that the PT pour strip exists because of movement, not because the concrete could not be poured continuously. Keep the movement, remove the open gap, and the reason for the leave-out is satisfied without the schedule cost. For the broader family this detail belongs to, see concrete movement joints.

How PS=Ø eliminates the pour strip in a PT slab

PS=Ø replaces the open pour strip with a self-supporting mechanical splice. The slab is still stressed, still shortens through elastic shortening, creep, and drying shrinkage, so you keep the movement the delay strip was there to provide, but the mild reinforcement stays continuous and the joint closes with a grout, not a return pour. Here is the sequence at a high level.

  1. 1

    Engineered shop drawings

    Our engineers detail the splice into your structural design so it works with the tendon layout and stressing sequence, carrying the mild reinforcement across the seam where a pour strip would otherwise interrupt it.

  2. 2

    Couplers set where the leave-out would sit

    The couplers and closure strip go in exactly where the pour strip would sit, so crews are not leaving an open gap and exposed rebar across the deck for the trades to work around.

  3. 3

    Stress the slab and let it shorten naturally

    The tendons are stressed on the engineer of record schedule and the slab goes through its elastic shortening, creep, and drying shrinkage off the critical path. No 30 to 60 day open strip waiting to be poured back.

  4. 4

    Grout the couplers to close the seam

    Once shortening is complete, the couplers are grouted to finish a continuous, ICC Approved, ACI 318 Type 1 and Type 2 compliant connection. The pour strip is gone.

End view of a PS=Ø mechanical rebar coupler that replaces the pour strip in a post-tensioned concrete slab

The method has been used to eliminate pour strips and delay strips on live commercial jobsites including Gaylord Pacific, The Ottawa Hospital, and IU Health Downtown. See more on the case studies page, then call (800) 355-8414 to talk through your structure.

What removing the pour strip changes on a PT project

Taking the pour strip out of a post-tensioned sequence changes the day for everyone who touches the deck. Engineers hold structural intent without detailing an open leave-out across the tendon field. Placement and finishing crews pour and stress continuously, then skip the return trip to close the strip. For a crew-level view of how that plays out, read what eliminating the leave-out means for placement and finishing crews.

Want the full mechanics of the seam, the couplers, the closure strip, and the grouting that replace the pour strip on reinforced and post-tensioned work? Our system page walks through the couplers and closure strip that replace the leave-out and how the whole assembly installs.

Questions Engineers Ask

Post-tensioned concrete slab FAQ

What is a post-tensioned concrete slab? +
A post-tensioned concrete slab is a slab reinforced with high-strength steel tendons that are tensioned after the concrete has cured, then anchored so they actively compress the concrete. That compression lets a PT slab span farther and stay thinner than a conventionally reinforced slab of the same capacity, because the concrete is held in compression instead of waiting to crack in tension. The trade-off is movement: when the tendons are stressed, the slab shortens elastically right away, and continues to shorten through creep and drying shrinkage. That shortening is exactly why PT slabs lean so heavily on pour strips and delay strips, and it is the movement PS=Ø is engineered to accommodate without leaving the joint open.
Why do post-tensioned slabs need pour strips? +
Because a post-tensioned slab moves more than a conventionally reinforced one. When the tendons are stressed, the slab shortens elastically at once, then keeps shortening through creep and drying shrinkage over weeks. If that shortening is fully restrained by stiff cores, shear walls, or columns, restraint-to-shortening forces build up and crack the slab. A pour strip, also called a delay strip or closure strip, leaves a gap open so each side can shorten independently before the reinforcement is tied continuous across the seam. PS=Ø keeps that same shortening allowance but carries the reinforcement across the seam with a mechanical splice, so the movement still happens and the open leave-out does not have to.
What is the difference between a post-tensioned and a reinforced concrete slab? +
A conventionally reinforced slab relies on passive rebar that only resists tension after the concrete has cracked. A post-tensioned slab uses high-strength tendons that are stressed after curing to actively compress the concrete, so it resists cracking before load is applied. PT slabs can therefore span farther and run thinner. The difference that matters for the pour strip is movement: a reinforced slab shortens mainly from drying shrinkage, while a PT slab also shortens elastically at stressing and keeps moving through creep, so PT structures demand more shortening relief and rely more heavily on delay strips and pour strips.
Can you eliminate the pour strip in a post-tensioned slab? +
Yes. PS=Ø is engineered for reinforced and post-tensioned work. The couplers and closure strip go in where the leave-out would sit, the slab is stressed and allowed to shorten and cure naturally, then the couplers are grouted to complete a continuous connection. That keeps the shortening allowance the pour strip was there to provide, but removes the open gap with exposed rebar sitting on the critical path. It is an ICC Approved, ACI 318 Type 1 and Type 2 compliant mechanical rebar splice.
Does PS=Ø interfere with the tendon layout or the stressing sequence? +
No. PS=Ø splices the mild reinforcement that has to be carried continuous across the seam, which is the reinforcement a pour strip normally interrupts. It is detailed into the structural design by our engineers so it works with the stressing sequence rather than against it. The slab is still stressed on the engineer of record schedule and still shortens as designed. What changes is that the reinforcement stays continuous across the seam instead of sitting in an open leave-out waiting for a return pour.
How long does a pour strip stay open in a post-tensioned slab? +
Traditionally a pour strip or delay strip is left open for weeks, commonly cited as 30 to 60 days, so the slab can complete most of its elastic shortening, creep, and drying shrinkage before the strip is cast. The exact window depends on the mix, stressing sequence, span, and how much restraint-to-shortening the engineer of record needs to relieve, so the final number belongs to the design team. During that period the leave-out sits open on the critical path with exposed rebar. PS=Ø removes that wait by carrying the reinforcement across the seam with a mechanical splice, so the slab still shortens but the joint does not sit open blocking the schedule.
Let's Talk

Design the Pour Strip Out of Your Next PT Slab.

Tell us about your project and our engineers will walk you through detailing and where PS=Ø can take a pour strip or delay strip off the critical path on post-tensioned work.

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