Types of Concrete additives

Concrete additives are usually liquid and are only added in very small amounts whilst mixing the concrete. They have a physico-chemical action and are classified into so-called efficiency groups depending on their effect in freshly mixed or hardened concrete.

1. Concrete deflocculants

These concrete additives depressurise the water, improving workability while at the same time reducing or maintaining the prescribed water-cement ratio.

2. Plasticising admixtures

These concrete additives are advanced deflocculants. They have a particularly strong deflocculant action and enable efficient concrete installation with very soft to liquid consistencies. Plasticising admixtures are usually treated as deflocculants and are added in the transport concrete mixer. Plasticising admixtures based on polycarboxylate ether usually have a high consistency and no longer need to be added at the construction site

3. Air-entraining agents

Concrete with high resistance to frost and thawing salt must have a minimum content of micro air voids (smaller than 0.3 mm) which can be obtained by adding air entraining agents. Ice has a larger volume than water. If the expansion of the frozen water is prevented in the concrete, then the concrete may burst. The additional air voids offer the necessary space for this extension.

4. Water resisting admixtures

These are used to improve the water imperviousness of the concrete. Water resisting admixtures are designed to protect the structure from penetrating substances that may be harmful to water.

5. Setting retarders

These delay the setting time of the concrete, which may be required for several reasons, e.g. hot weather or jointless components with a large mass (e.g. bridge superstructures, strong base plates, concrete for kerb stones). Over-metering can, however, have the opposite effect and turn the setting retarder into a setting accelerator agent!

6. Setting accelerators 

These chemically accelerate the setting of, for example, shotcrete or sealing mortar up to just a few seconds after spraying or placing. An alternative, without the disadvantage of considerable reduction of the 28 day- and final strength is physically-active micro silica dust.