Air-Entrained Concrete for Freeze-Thaw Exposure
Why intentionally entrained microscopic air protects exterior concrete, how finishing affects the surface, and when exposure requirements govern the mixture.
Editorial review: 2026-09-29 · How we review technical content
Key takeaways
- Air entrainment creates a controlled system of small, well-distributed air voids in hardened concrete. In concrete exposed to cycles of freezing and thawing while sufficiently wet, those voids provide pressure-relief space as water freezes. This is fundamentally different from large accidental air pockets caused by poor consolidation.
- Identify freeze-thaw and deicing exposure before ordering. The ready-mix producer needs the required air range and exposure classification. Do not assume that simply specifying a high PSI compensates for missing air entrainment in severe freeze-thaw service.
- Test air content when required using the method appropriate to the aggregate and project specification. Protect the mixture from large changes in air caused by extended mixing, pumping, temperature, or admixture interactions. Consolidate sufficiently to remove large entrapped voids without attempting to eliminate the intentionally entrained microscopic system.
What entrained air does
Air entrainment creates a controlled system of small, well-distributed air voids in hardened concrete. In concrete exposed to cycles of freezing and thawing while sufficiently wet, those voids provide pressure-relief space as water freezes. This is fundamentally different from large accidental air pockets caused by poor consolidation.
Air requirements depend on exposure, aggregate size, mixture proportions, and the governing specification. Concrete that remains dry and protected indoors has different durability needs from exterior pavement that will be saturated and exposed to deicing salts.
Planning the mixture and finish
Identify freeze-thaw and deicing exposure before ordering. The ready-mix producer needs the required air range and exposure classification. Do not assume that simply specifying a high PSI compensates for missing air entrainment in severe freeze-thaw service.
Consider the finish. Air-entrained concrete can be more susceptible to blistering or delamination when aggressively hard-troweled, particularly if finishing traps bleed water or air beneath a densified surface. Exterior broom finishes and interior hard-troweled floors therefore have different considerations.
Field control
Test air content when required using the method appropriate to the aggregate and project specification. Protect the mixture from large changes in air caused by extended mixing, pumping, temperature, or admixture interactions. Consolidate sufficiently to remove large entrapped voids without attempting to eliminate the intentionally entrained microscopic system.
Finish only after the surface is ready. Do not close the surface while bleed water is still present, and begin curing promptly.
Typical problems
Common failures include exterior scaling where concrete was not suitable for exposure, surface delamination from premature or aggressive finishing, and inconsistent field air caused by uncontrolled mixture adjustments. Another mistake is confusing total fresh-concrete air with a complete evaluation of the hardened air-void system.
Deicing chemicals can make early exposure more demanding. New concrete should be cured and allowed to mature before harsh service according to project and material guidance.
Evaluation
Review the mix submittal, exposure classification, fresh-air test results, finishing method, curing record, and service environment. If distress develops, investigate moisture exposure, drainage, finishing, curing, and deicer history as well as the original mixture.
For structural and durability requirements, follow the adopted ACI code/specification and project documents.
References & further reading
- ACI CODE-318-25 Building Code Portal — Structural concrete code requirements and commentary.
- ACI SPEC-301-20 — Specifications for Concrete Construction — Specification framework for concrete construction.
- ACI PRC-302.1-15 — Guide to Concrete Floor and Slab Construction — Slabs, site preparation, jointing, finishing, curing, and floor construction.
- ACI SPEC-301-20 — Specifications for Concrete Construction — Reference specification used when incorporated into project specifications.
- ACI PRC-308-26 — Curing of Concrete—Guide — Current ACI guide to external curing practices, published in 2026.
- NRMCA Concrete In Practice (CIP) — Industry education covering common concrete field problems and practices.