Concrete Specifications

All concrete work shall conform to the latest edition of ACI 301 – Specifications for Structural Concrete, unless otherwise noted (UNO) in these construction documents.

All concrete mixes shall be designed by a qualified registered engineer. Mix design data must comply with either field experience or the trial mixture method per ACI 301/318.
Mix proportions shall:
1. Ensure workability and consistency for proper placement around reinforcement and in forms without segregation or excessive bleeding.
2. Meet the required exposure conditions.
3. Meet or exceed the required f'c.
4. Not exceed the maximum water/cement (w/c) ratio.
The contractor shall indicate the planned placement method for each concrete mix.
Retempering (adding water on-site) is prohibited unless the special inspector is present to verify compliance with the w/c ratio and design slump. The ready-mix supplier must provide the maximum water withheld at the plant. Concrete exceeding these limits shall be rejected.
Slump tests shall be performed at the point of placement, except when:
- The point of delivery is the same as the point of placement, or
- The contractor has an approved correlation between fresh concrete properties at delivery and placement.
Air-entrained concrete shall not be used in normal-weight floor slabs intended for hard-troweled finishes.

Hydraulic Cement:

Fly Ash:

May replace a portion of Portland cement with approval from the architect and structural engineer.
Must comply with ASTM C618 Class C or F.
Maximum replacement amounts are provided in the concrete table.

Normal-Weight Aggregate:

Must comply with ASTM C33.
Material certificates from the supplier must be submitted with the concrete mix design.
River rock or pea stone aggregates are not allowed.

Water:

To protect reinforcement from corrosion, maximum water-soluble chloride ion concentrations in hardened concrete (28–42 days), contributed from all ingredients, must not exceed limits shown in the concrete table.

Concrete shall be placed carefully to avoid displacing reinforcement.
Proper vibration is required, especially around post-tensioned anchorages and congested areas (e.g., column joints).
Placement shall be completed within 90 minutes of adding mixing water, per ASTM C94.
Tolerances shall conform to the latest edition of ACI 117 – Specifications for Tolerances for Concrete Construction and Materials.

Element	f'c (psi)	Exposure Category	Max CL	Max Fly Ash	Max W/CM Ratio	Max Coarse Aggregate Size	Min Air Content
Interior Slabs on Ground	3,500	F0,S0,P(W)0,C1	0.30	20%	0.45	1"	N/A

Bull floating shall be completed before accumulation of bleed water on the surface.
Final finishing should only begin after the bleed water has evaporated and the surface sheen disappears.
Wet trowelling may weaken the surface and cause crazing and dusting.
Follow architectural requirements for final finishing (e.g., steel trowel, broom finish).

Bleed water (free water at the surface) must be removed to avoid dilution of cement near the surface, which reduces strength.
Methods include dragging the surface with a garden hose.

Saw-cut control joints, if required, shall be made as soon as the concrete can support the weight of workers and equipment.

Slabs must be cured for minimum 7 days immediately after finishing:
1. Curing Compound: Apply a water-based dissipating resin type that breaks down after ~4 weeks. Must conform to ASTM C309 Type O or 1D, Class B. Apply in two coats at right angles for complete coverage.
2. Wet Cure: Keep the surface continuously wet after finishing.

All concrete will crack, even with proper design and construction.
Plastic shrinkage cracks occur within the first few days; they may widen up to 50% of final size within ~30 days and continue to develop for up to one year.
Cracks smaller than 0.06" are usually inconsequential.
Cracks wider than 0.06" may indicate issues with mix, placement, finishing, or curing and may require epoxy repair or replacement.

Causes of plastic shrinkage cracks: Rapid drying due to hot weather, high wind, low humidity, or delayed curing application.

No water shall be added to mix trucks in excess of the volume withheld by the ready-mix supplier.
Before adding water, confirm that the slump is below tolerance and the ready-mix supplier had indicated the withheld water volume.