Concrete Admixtures: The Complete Guide — Functions, Dosage and When to Use Each

Sep. 23, 2026

Concrete Admixture Technical Guide · No. 09

This is a complete guide to the common concrete admixtures. For each one it covers the function, the mechanism, the dosage, the situations where it is used, and the problems to watch for.

Every dosage below is a starting point. The cement, the sand, and the weather all change the real number. Always run a trial mix.

1. Water Reducers (superplasticizers)

Function. A water reducer makes concrete flow better with less water. Less water means higher strength and better durability.

Mechanism. The main type is polycarboxylate superplasticizer (PCE), a comb-shaped polymer. Its carboxyl groups adsorb onto the cement particle, while its long side chains separate the particles through steric hindrance. This dispersion is what makes the mix flow.

Three forms. PCE is supplied as liquid, flake, or powder.

Form	Active Content	Notes
Liquid Mother Liquor	40% to 55%	The rest is water; you ship the water too
Flake	97% to 100%	Dissolve it in water yourself
Powder	Varies	Two types: spray-dried (loses performance) and flake-milled (keeps full performance)

Typical dosage. 0.1% to 0.5% of cement weight, by active content.

What can go wrong. The dose is not fixed. Cement with high tricalcium aluminate (C3A), clay in the sand, and heat all consume PCE. If the mix is stiff at the start, raise the standard reducer. If it loses slump rapidly after about 30 minutes, raise the high slump-retention PCE. An excessive dose causes segregation, bleeding, or delayed setting.

2. High Slump-Retention Water Reducer

This is a specialised water reducer. Do not confuse it with a standard water reducer plus a retarder.

Function. It keeps the concrete workable for two to four hours.

Mechanism. Its molecule is designed to release its dispersing action slowly. A portion of its acid groups are protected as esters, which hydrolyse gradually in the alkaline concrete. This is slow release — it keeps re-dispersing the cement over time.

Why it is not "reducer + retarder":

	Set Retarder	High Slump-Retention PCE
Primary Action	Slows the whole hydration reaction	Releases dispersion gradually
Net Effect	Concrete sets later	Concrete stays workable, sets on schedule

Typical use. Combine it with your main water reducer. The ratio is usually 9:1 to 3:1 (water reducer to slump-retention PCE). The correct ratio depends on how long the slump must hold and on the cement. Test to find it.

A practical note. A high slump-retention PCE often entrains some air, so it is frequently used together with a small amount of defoamer.

3. Set Retarders

Function. A retarder slows the setting of the concrete, giving more time to place and finish.

Mechanism. A retarder delays cement hydration, especially the fast reaction of C3A. It does not add dispersing power; it simply makes the reaction slower.

Common retarders and typical dosages:

Retarder	Typical Dosage (of Cement Weight)
Sodium Gluconate	0.05% to 0.2%
Sugar (sucrose)	0.03% to 0.15%
Citric Acid	0.05% to 0.2%
Sodium Lignosulfonate	0.1% to 0.3%

The warning. Too much retarder, and the concrete may not set for a long time — or may never set. Start low and test.

4. Early-Strength Agents

Function. They accelerate the early strength gain, so the concrete reaches strength sooner.

Mechanism. An early-strength PCE is built with amino and sulfonic acid groups that promote early cement hydration. It keeps the high water reduction of a standard PCE while adding faster early strength.

Real data (PC 6030E):

Property	Value
Water Reduction	≥ 25%
Chloride	≤ 0.06%
1-day strength ratio (C25)	≥ 180%
3-day strength ratio (C25)	≥ 170%
Dosage	0.2% to 0.5%

The low chloride content makes it safe for reinforced concrete.

When to use. Precast components, cold weather, emergency repair.

The warning. Avoid calcium chloride based accelerators in reinforced concrete — their chloride corrodes the steel. Calcium formate is a safer choice.

5. Air-Entraining Agents

Function. They introduce millions of tiny air bubbles, which protect the concrete from freeze–thaw damage and improve workability.

Mechanism. The agent stabilises micro-bubbles in the paste. These bubbles give the water a place to expand when it freezes, so the concrete does not crack.

Typical dosage. Very small, about 0.005% to 0.05% of cement weight. Target air content is usually 4% to 7%.

The warning. Too much air reduces strength. Each 1% of extra air can reduce strength by about 5%.

6. Defoamers

Function. They remove or control air bubbles.

When to use. When the air content is too high, or when a high slump-retention PCE entrains too much air.

Typical dosage. About 0.01% to 0.05% of cement weight.

7. How They Combine

A real admixture is rarely a single chemical. It is usually several of these combined — for example, a water reducer plus a defoamer plus a retarder.

Compatibility matters. The additives must work well together. A good PCE is compatible with the other small additives, which lets you adjust the mix freely for your local cement and sand.

The practical rule — read the timing:

Symptom	Timing	Remedy
Concrete stiff from the start	Immediately	Raise the standard reducer (PC 6010)
Was good, then slumped fast	After ~30 min	Raise the high slump-retention PCE (PC 6020RT)
Weak Mix, Visible Bubbles	Any time	Add a defoamer

Always test the combination before a large pour.

Our PCE Models

Model	Type	Notes
PC 6010F (flake) / PC 6010P (powder)	Standard high water reduction	The main reducer
PC 6030E	Early strength	For precast and cold weather
PC 6020RT	High slump retention	Slow-release; use with the 6010 series, ratio 9:1 to 3:1

Quick Reference Table

Admixture	Function	Typical Dosage (of Cement Weight)	When to Use
Water Reducer (PCE)	Less water, more strength	0.1%–0.5% (active)	Almost every concrete
High Slump-Retention PCE	Keeps workability 2–4 h	Combine with reducer, 9:1 to 3:1	Long transport, hot weather
Set Retarder	Slows setting	0.05%–0.3%	Hot weather, large pours
Early-Strength Agent	Faster early strength	0.2%–0.5%	Precast, cold weather
Air-Entraining Agent	Freeze–thaw resistance	0.005%–0.05%	Cold climates
Defoamer	Controls air	0.01%–0.05%	Too much air, or with slump-retention PCE

FAQ

What is the most important concrete admixture?

The water reducer (PCE). Almost every modern concrete uses one.

Is a high slump-retention PCE just a water reducer plus a retarder?

No. It is a specialised water reducer with a slow-release design. A retarder delays setting; a high slump-retention PCE slowly releases water-reducing power. They are different.

Do I need a defoamer with a high slump-retention PCE?

Often yes. A high slump-retention PCE can entrain some air, so a small amount of defoamer helps.

My mix is stiff. Do I raise the standard reducer or the high slump-retention PCE?

Stiff at the start means raise the standard reducer. Rapid slump loss after 30 minutes means raise the high slump-retention PCE.

Why does my PCE dose keep changing?

Because the cement, the clay in the sand, and the temperature all consume PCE. The dose must cover what they consume.

Can I combine several admixtures?

Yes. Most real mixes combine several. Just test the combination first.