Placement Methods
| Method | Rate | Best For |
|---|
| Boom pump | 60–150 m³/hr | Foundations, slabs, reach 32–63 m |
| Line pump | 15–60 m³/hr | Interior, long runs, small pours |
| Crane & bucket | Variable | Stiff mixes, high-rise, no pump access |
| Direct chute | Truck speed | Close access, chute reach 3.5–6 m |
Cold Joints (CSA A23.1 Cl. 7.4.2)
Each layer must be placed before preceding layer takes initial set (60–90 min typ.). Pre-calculate pour rate and truck count.
Max Free-Fall
1.5 m max drop to avoid segregation. Use tremie or elephant trunk for deep pours.
Vibration & Consolidation
| Head Dia. | Radius | Spacing (1.5×r) | Use |
|---|
| 25 mm | 75–150 | 110–225 mm | Thin, tight rebar |
| 38 mm | 130–250 | 200–375 mm | General work |
| 50 mm | 200–350 | 300–525 mm | Footings, thick |
| 75 mm | 300–500 | 450–750 mm | Mass concrete |
Technique
- Insert vertically; let head sink under own weight
- Penetrate previous lift 75–150 mm
- Hold 5–15 sec until paste sheen & bubbles stop
- Withdraw slowly (~75 mm/sec)
- Keep head 75 mm from form face (no burn marks)
- External form vibrators: 1.0–1.5 m c/c, 30–60 sec/cycle
Power Trowelling Sequence
| Pass | Tool | Pitch |
|---|
| 1 — Float | Float pan | Flat (0°) |
| 2 — 1st trowel | Trowel blades | Low (5–10°) |
| 3 — 2nd trowel | Trowel blades | Medium (15–25°) |
| 4 — Final burn | Trowel blades | High (30–40°) |
NEVER trowel bleed water into surface. Wait for sheen to disappear and ~5 mm footprint.
Screeding Tolerance
±6 mm over 3 m straightedge for hard-trowel slabs. Laser screed: ±3 mm.
Curing (CSA A23.1 Table 19)
| Exposure | Min. Cure | Strength |
|---|
| C-1, C-2 (structural) | 3 days | 70% f'c |
| F-1 (freeze-thaw mod.) | 3 days | 70% f'c |
| F-2 (freeze-thaw severe) | 7 days | 70% f'c |
| C-XL (extended life) | 7 days | 70% f'c |
Curing Methods
- Compound: 5 m²/L, two passes at right angles. Type 1 (dissipating) or Type 2 (permanent).
- Wet burlap: Gold standard; keep continuously wet.
- Poly sheeting: 6-mil; causes mottling — avoid on architectural surfaces.
Sawcut Control Joints
| Parameter | 150 mm Slab |
|---|
| Depth (early-entry) | ≥1/4 slab = 38 mm |
| Depth (conventional) | ≥1/3 slab = 50 mm |
| Max spacing | 3.6–5.4 m (24–36 × thickness) |
| Ideal timing (20°C) | 6–18 hrs; early-entry 4–6 hrs |
| Panel aspect ratio | ≤1.5:1 |
When in doubt, cut sooner. Plan joints at all re-entrant corners and column block-outs.
Temperature Protocols
Hot Weather (>27°C)
- Evaporation retarder if rate >1.0 kg/m²/hr
- Erect windbreaks; begin curing immediately after finishing
Cold Weather (<5°C)
- Maintain >10°C for first 72 hrs (CSA A23.1 Cl. 7.7.4)
- Insulated blankets / heated enclosures / hydronic
- Cold Weather Plan required 48 hrs before pour
- Min 3 temperature sensors per 100 m²
- Never let fresh concrete freeze — 50% strength loss
Safety — Do Not Forget
- Boom pump: 3 m min clearance from power lines <750 V. No workers in swing radius. Signal person mandatory.
- Concrete burns: pH 12–13. Rubber boots, long sleeves, gloves, safety glasses. Wash skin immediately.
- Line pump: Clamp all joints — blowout at 15 MPa can send fitting through a wall. End hose max 3 m, two crew members.
- Crane & bucket: Critical lift. No workers under suspended load. Barricaded exclusion zone.
- Air-entrained concrete: Do NOT hard-trowel — collapses protective air voids. Broom/float finish only for exterior.
Pro Tips
- Pre-calculate pour rate: m³/hr needed, truck count, and cycle time. Gaps = cold joints.
- Broom texture: Pull perpendicular to traffic flow. Medium bristle (1–2 mm) for most exterior. Test by running palm across.
- Truck spotter: Mandatory for every reversing ready-mix truck. Driver must have visual contact with spotter.