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Post-tensioned slab formwork with tendon layout
PT Compatible

Post-Tensioned Slab Formwork

Aluminum beam formwork systems engineered for post-tensioned concrete slab construction. Joist layouts provide tendon clearance, drophead technology enables 3-day stripping, and reshoring supports slabs during stressing operations. Optimized for residential and commercial PT projects across Ontario.

3

Day Strip

2,500 psi

Strip Strength

PT

Compatible

PT System Features

Post-Tensioning Formwork Advantages

Aluminum beam systems designed specifically for the unique requirements of post-tensioned concrete construction.

Tendon Clearance

Joist spacing and layout coordinated with PT strand locations. Tendons pass between joists in open space. No contact between formwork and ducts. Prevents damage to plastic sheathing during concrete placement.

Early Strip Capability

Strip formwork at 3 days when slab reaches 2,500 psi (17 MPa). This strength is sufficient for PT stressing operations which typically occur days 3-5. Aluminum dropheads release joists while reshoring remains.

Drophead Technology

Aluminum dropheads connect joists to shores. After 3-day strip, dropheads lower 150 mm to release formwork. Reshoring remains supporting slab during tendon stressing and until full strength. Critical for PT safety.

Strand Layout Accommodation

Formwork layouts account for PT strand banding (concentrated tendons at column strips) and distributed tendons in middle strips. Joist spacing widens at middle strips, tightens at column strips to clear tendon groups.

Deflection Control

PT slabs are typically thinner than conventional slabs (200-250 mm vs 250-300 mm). Formwork must limit deflection to prevent cracking before stressing. Aluminum beams sized for L/360 deflection under wet concrete load.

Reusability

200+ reuses typical for aluminum PT formwork. Coordinate joist layout with PT engineer so same formwork pattern repeats on each floor. Standardized layouts maximize equipment reuse across multiple levels.

Formwork Coordination

PT Slab Formwork Cross-Section

Aluminum joist layout coordinated with post-tensioning strand locations for clearance and support.

  • Column strip coordination — Banded tendons (4-8 strands) at column centerlines require 900-1200 mm joist spacing to clear tendon bundles, with larger beam sizes for wider spacing.
  • Middle strip layout — Distributed single-strand tendons at 600-900 mm spacing with standard 6.5" aluminum joists at 450-600 mm intervals positioned between tendon paths.
  • Thinner slab advantage — PT slabs at 200-250 mm (8-10") thickness reduce dead load compared to conventional 250-300 mm slabs, with draped tendon profiles requiring variable vertical clearance in formwork.
  • Pre-construction coordination — Formwork supplier overlays joist layout on PT strand drawings, resolving all conflicts in a pre-construction meeting before slab pour to ensure zero tendon contact.
Post-tensioned slab formwork showing tendon clearance between joists
System Comparison

PT vs Conventional Slab Forming

Formwork considerations and cycle time comparison for post-tensioned versus conventionally reinforced concrete slabs.

Based on 1,000 m² floor plate, residential tower construction. PT slab 225 mm thick, conventional slab 275 mm thick.
Specification Factor PT Slab Formwork Conventional Slab Difference
Slab Thickness 225 mm (9") 275 mm (11") PT: 18% thinner
Concrete Volume 225 m³ 275 m³ PT: 50 m³ savings
Strip Timing Day 3 @ 2,500 psi Day 7-10 @ full cure PT: strip 4-7 days earlier
Formwork Complexity Coordinated joist layout Standard joist spacing PT: more coordination required
Reshoring Duration 10-14 days (through stressing) 7-10 days (until cure) PT: 3-4 days longer reshoring
Floor Cycle Time 5-7 days 7-10 days PT: 30% faster cycle
Total Slab Cost $165/m² ($15.3/ft²) $180/m² ($16.7/ft²) PT: 8% cheaper overall
Structural Span 10-12 m (33-40 ft) 8-9 m (26-30 ft) PT: 25% longer spans
PT Slab Cycle

Post-Tensioned Slab Construction Process

Typical 7-day cycle from formwork setup through tendon stressing. Day 0 is concrete placement.

  1. 1

    Formwork and Rebar (Day -2 to 0)

    Set aluminum formwork with joists coordinated to PT layout. Install bottom rebar mat and chairs. PT crew places tendon ducts and anchors per shop drawings. Install top rebar. Pre-pour inspection. Pour concrete day 0.

  2. 2

    Concrete Curing (Day 1-3)

    Concrete cures to 2,500 psi minimum at 72 hours. Take field cylinders at pour and test at 3 days. Cold weather or low-cement mixes may require 4 days to reach strength. Hot weather accelerates to 2 days.

  3. 3

    Strip Formwork (Day 3)

    At 2,500 psi, lower aluminum dropheads to release joists. Remove beams, joists, and plywood deck. Reshoring remains in place supporting slab. Formwork ready to reset at next level. 6-8 hours with 4-person crew.

  4. 4

    Tendon Stressing (Day 3-5)

    PT crew stresses tendons using hydraulic jacks at anchor pockets. Strand elongation monitored and recorded per engineering. Stressing introduces compression into slab. Cut and grout pockets after stressing complete.

PT Slab Formwork FAQs

Common questions about formwork systems for post-tensioned concrete slab construction.

PT slabs only need sufficient strength for tendon stressing operations (2,500 psi at 3 days). The reshoring system supports the slab during stressing and until full cure. Conventional slabs must wait for full strength before stripping because no prestress is introduced. Early stripping allows formwork to cycle to the next floor 4-7 days sooner.
PT engineer provides strand layout showing tendon locations in plan and profile. Formwork supplier overlays joist layout and adjusts spacing so tendons pass between joists. Pre-construction coordination meeting resolves conflicts. Final coordinated drawings issued to contractor showing both PT and formwork together.
If test cylinders show less than 2,500 psi at day 3, delay stripping and stressing for 24 hours and re-test. Winter projects often plan 4-day minimum to account for slower curing. Do not stress tendons until minimum strength is achieved - premature stressing can crack the slab.
Yes, for buildings with repetitive floor plates. PT strand layout is typically identical on each typical floor (column strips and middle strips in same locations). Formwork joist pattern repeats exactly. This maximizes equipment reuse and minimizes field layout time. Podium levels or penthouses with different layouts may need custom formwork.
Reshoring typically remains 10-14 days after pour. Standard practice is to maintain reshoring through two cycles: current pour (day 0), previous pour (day 7), and second previous pour (day 14). Day 21 slab has reached full strength plus benefit of post-tensioning and reshores can be removed. Slightly longer than conventional (7-10 days) but offset by faster formwork cycling.
Yes. PT tendons anchor in pockets at slab edges. Edge forms must have blockouts for anchor pockets (typically 150 x 150 mm). Pocket locations match tendon layout. After stressing, pockets are grouted flush. Balcony edges and cantilevers often have exposed anchors requiring architectural covers.

Related Solutions

Elevated Slab Forming

Multi-story formwork systems with drophead technology for conventional reinforced concrete slabs.

Slab Formwork Tables

Crane-lifted flying form tables for high-rise PT construction with repetitive floor plates.

High-Rise Reshoring

Multi-level reshoring systems for safe load transfer during PT stressing and concrete curing.

PT Formwork Coordination

Avema's engineering team will coordinate formwork layouts with your PT engineer and provide complete shop drawings for approval.

Call PT Specialist Request PT Layout
PT Coordination Included Shop Drawings Provided Pre-Construction Meeting