Air-Entrained Concrete in Ontario: Essential OBC Requirements for Durability

Ontario’s concrete structures face extreme environmental challenges — from constant freeze-thaw cycles to de-icing salts and moisture exposure. Without proper protection, these factors can cause cracking and surface scaling over time.

To ensure long-term performance, the Ontario Building Code (OBC) requires the use of air-entrained concrete in exposed applications. By introducing microscopic air bubbles into the mix, water can expand safely during freezing, improving durability and lifespan.

Why Air-Entrained Concrete Matters

In cold climates, water freezing inside concrete pores expands by about 9%, creating internal pressure that damages the surface. Air-entrained concrete solves this by providing space for expansion.

Key benefits:

• Prevents Cracking & Scaling – Resists repeated freeze-thaw cycles.

• Improves Durability – Protects against de-icing salts and sulfates.

• Maintains Integrity – Extends the service life of slabs and foundations.

OBC & CSA Requirements

Compliance with the Ontario Building Code and CSA A23.1 is mandatory for all exterior concrete exposed to moisture or freezing conditions.

Minimum Air Content by Aggregate Size:

Nominal Max. Aggregate Size	Min. Air Content	Tolerance
≤ 19 mm (¾ in)	6 %	± 1.5 %
20–37 mm (¾–1½ in)	5.5 %	± 1.5 %
> 37 mm (1½ in)	5 %	± 1.5 %

Additional Requirements:

• Garage Floors & Exterior Flatwork: 5–8 % air content.

• Freeze-Thaw Exposure: Air-entrainment mandatory.

• Exposure Class C-2: Required for contact with de-icing salts.

• Testing: Conduct on-site using CSA A23.2-4C (Pressure Method).

  
  

How Air-Entrainment Works

Air-entraining agents (AEA) form microscopic bubbles — 10 to 100 microns — that act as pressure-relief chambers. This allows frozen water to expand safely without damaging the concrete matrix.

Best practices:

• Balance durability and strength in the mix design.

• Avoid over-vibration or over-finishing, which can remove protective air voids.

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Ensure Your Concrete Meets Ontario’s Durability Standards

We help engineers and contractors design, inspect, and optimize concrete mixes to meet OBC durability standards and structural reliability.

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Applications & Exceptions

Typical uses:

• Exterior slabs, sidewalks, driveways

• Garage floors, patios, and steps

• Foundations, footings, grade beams

Exceptions:

• Interior slabs not exposed to freezing.

• High-finish surfaces (with engineer approval) where lower air content is desired.

Factors Affecting Air Content

• Cement Type: High Alkali → More Air; High Fineness → Less air.

• Aggregates: Clean, rounded sand helps; dust or clay reduces air.

• Water Quality: Soft water and detergents increase air.

• Temperature: Cooler concrete holds more air; warm mixes lose it.

• Mixing & Vibration: Over-mixing or worn blades can reduce air content.

For Contractors: Quick Recommendations

• Test air content for each delivered batch.

• Use proper AEA dosage per approved mix design.

• Avoid excessive vibration during placement.

• Use sealers or waterproof coatings for added surface protection.

  
  

Conclusion: Building Durable Concrete with Confidence

Air-entrainment isn’t optional in Ontario — it’s an OBC requirement for long-lasting, resilient concrete. Proper mix design, testing, and quality control ensure your projects meet both structural and durability standards.

Our team at Parsways Inc. ensures each design meets Ontario’s durability standards — not just on paper, but in performance.

Co-authored by Yousef Davari and Negin Amani.