Air Content in Concrete: Why Polycarboxylate Superplasticizer (PCE) Entrains Air and How to Control It

Sep. 28, 2026

Concrete Admixture Technical Guide · No. 15

Fresh concrete always contains some air. A small amount is harmless, and in freezing climates it is even essential. But too much air weakens the concrete — and polycarboxylate superplasticizer (PCE) naturally entrains some air. Controlling air content is therefore a skill every PCE user should have.

What Air Does in Concrete

Effect	Benefit or Risk
Freeze–thaw Resistance	Tiny, well-spaced bubbles absorb the pressure of freezing water — essential in cold climates
Workability	Bubbles act like ball bearings, making the mix easier to place
Strength	Every extra 1% of air reduces compressive strength by roughly 5%
Surface Finish	Too much air leaves a rough or porous surface

Air is therefore a trade-off: good for durability and workability, but bad for strength.

Why PCE Entrains Air

PCE is a polymer surfactant. Like all surfactants, it lowers the surface tension of water and stabilises the bubbles that form during mixing, so the bubbles do not simply collapse.

Two points follow:

1.Most PCE will entrain a little air even when you do not want it.

2.A high slump-retention PCE (such as PC 6020RT) tends to entrain more air, which is why it is often used with a defoamer.

How Much Air Is Right

Concrete Type	Typical Target Air Content
Ordinary concrete (no freeze–thaw exposure)	2% to 4%
Freeze–thaw Resistant Concrete	4% to 7%
High-Strength Concrete	Usually kept low (≤ 2%) to protect strength

The exact target depends on the maximum aggregate size and the exposure, but these ranges are a sound guide.

How to Control It

The air content is adjusted with two small additives:

Additive	What It Does	Typical Dosage
Air-Entraining Agent	Creates fine, stable bubbles for freeze–thaw resistance	0.005% to 0.05% of cement weight
Defoamer	Breaks down excess or unwanted air	0.01% to 0.05% of cement weight

If the air is too high, add a defoamer.

If the concrete must resist freeze–thaw and the air is too low, add an air-entraining agent.

Measure the air content, then adjust — do not dose blind.

Troubleshooting

Symptom	Likely Cause	Remedy
Concrete Weaker than Expected	Air content too high	Add a defoamer
Rough, Porous Surface	Too much air, or large bubbles	Add a defoamer, or check the PCE dosage
Freeze–thaw Damage in Service	Air content too low, or bubbles poorly spaced	Add an air-entraining agent
Air creeps up with a high slump-retention PCE	Retention PCE entrains air	Use a defoamer together with the retention PCE

The Key Point

Air content is not an accident — it is a variable you can control. Because PCE entrains air on its own, always measure it in the trial mix and adjust with a defoamer or an air-entraining agent as needed. A few tenths of a percent make a real difference to strength.