What is a superplasticizer?
A superplasticizer is an admixture for concrete and mortar that greatly reduces the mixing water needed, or makes the mix far more fluid at the same water content. The European standard EN 934-2 calls it a high-range water-reducing admixture: at equal workability it must save at least 12 percent water. An ordinary plasticizer only needs to reach 5 percent.
It works by keeping the cement particles apart. Older superplasticizers based on melamine or naphthalene sulfonate act mainly through electrical repulsion. Modern products based on polycarboxylate ethers (PCE) also have long side chains that hold the particles apart physically. This allows much greater water savings.
Without superplasticizers, self-compacting concrete (SCC), high-strength concrete and many modern precast elements could not be made.
In practice
- Low water-cement ratio. Less water gives denser, stronger and more durable concrete with less shrinkage. That is the main reason to use one.
- Flowing concrete. With congested reinforcement, slender walls and pumped concrete it helps the mix reach everywhere without segregating.
- Dose to the data sheet. The amount is given as a percentage of cement weight and varies by product. Measure accurately; never guess.
- Watch the working time. With many products the effect fades within some tens of minutes. Plan the pour so concrete is placed straight after delivery.
- Do not mix freely. Admixtures and cement types can interact. Stick to combinations approved by the supplier.
Common mistake: adding water on site because the concrete looks “stiff”. That cancels the benefit of the superplasticizer. Overdosing is also wrong: the coarse aggregate can settle and the concrete can bleed.
Related terms
- Plasticizer
- Admixture
- High-strength concrete
- Bleeding
- Silica fume
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