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Placement

The process of depositing and distributing freshly mixed concrete into forms or final position

Placement is the process of depositing and distributing freshly mixed concrete into forms or final position. Proper placement ensures concrete reaches all areas of the form, surrounds reinforcement completely, and maintains uniform consistency without segregation. It's the critical transition from mixing to finishing that sets up everything that follows.

Why It Matters

Poor placement creates problems that no amount of finishing can fix. Concrete dropped from excessive height segregates—aggregate sinks, weak paste rises. Concrete dumped in piles requires excessive raking that brings water and paste to the surface, weakening it. Proper placement deposits concrete near its final position, minimizes handling, and maintains mix uniformity.

Timing is critical. Concrete begins stiffening within 90 minutes of mixing. Delays between batches create cold joints—weak planes where old and new concrete meet. Professional crews plan placement to maintain continuous flow, finishing one section before the next arrives.

Technical Details

Proper placement techniques:

Delivery and distribution:

  • Discharge directly into forms when possible
  • Drop from minimum height (under 5 feet) to prevent segregation
  • Place as close to final position as practical
  • Use chutes, conveyors, or pumps for long distances
  • Avoid dragging across reinforcement (causes segregation)

Placement sequence:

  • Start at far end, work toward exit
  • Place against previously placed concrete while still plastic
  • Avoid restarting in middle of slab
  • Plan pour to avoid isolated pockets or corners

Consolidation during placement:

  • Spade or rake around edges and reinforcement
  • Vibrate systematically as placement progresses
  • Don't vibrate in one spot too long (causes segregation)
  • Work concrete around embedments and into corners

Cold weather considerations:

  • Heated concrete and enclosures may be required
  • Protect from freezing for minimum 7 days
  • Slower setting time allows longer workable period

Hot weather concerns:

  • Faster setting reduces workable time
  • Higher water demand—add superplasticizers rather than water
  • Fog spray and windbreaks slow evaporation
  • Schedule pours for cooler parts of day

Maximum placement rates:

  • Depends on finishing crew size and experience
  • Typical residential: 10-20 cubic yards per hour
  • Must finish before concrete stiffens
  • Better to order multiple small loads than one oversize load you can't finish

Placement problems and solutions:

  • Segregation: Minimize drop height, avoid over-handling
  • Cold joints: Maintain continuous placement, use bonding agents if necessary
  • Voids: Proper consolidation, adequate slump for congested areas
  • Surface water: Result of excessive handling and finishing too early

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