Building Construction: Concrete Mixes and Placing Notes

Concrete Mixes and Placing

• Maximum size aggregate is 20mm with a maximum concrete slump of 100mm
• Minimum concrete cover for reinforcing steel:
  • Directly against earth: 75mm
  • Suspended slab: 20mm
  • Slab on grade: 40mm
• Minimum days for stripping of forms and shores:
  • Foundation: 1 day
  • Suspended slab: 8 days
  • Beams: 14 days
  • Walls and columns: 21 days
• Contractor must submit pouring schedule and construction joint locations to the structural engineer at least 4 days prior to pouring for approval

Footings

• Footings are designed for an allowance soil bearing pressure of 96 kPa (2000psf)
• Footings shall rest at least 1.50m below natural grade line
• Minimum concrete protection for reinforcement: 75mm clear for concrete deposited in the ground and 50mm for concrete deposited against a formwork

Reinforcements

• Yield strength of reinforcing steel bars: 414 MPa or 60,000 psi
• Re-bars sizes 10mm or larger shall be deformed, and smaller than 10mm may be plain

Concrete Slabs

• All slab reinforcements shall be 20mm clear minimum from the bottom and top of the slab
• Spacing of bars at column strips shall not be more than 1% slab thickness
• Bedded slabs shall be reinforced with 10mm @ 250mm O.C each way to the center of the slab, and construction joints shall be at least 3.65m apart

Columns

• Provide extra sets of ties at 100 O.C for tied column reinforcement above and below beam-column connections
• Column ties shall be protected everywhere by a covering of concrete cast slope monolithically with the core with a minimum thickness of 40mm and not less than 40 times MSA
• Alternate bars shall be welded or mechanically spliced at any level, with vertical distances between welds or splices of adjacent bars not less than 600mm