There is a range of other types of admixtures with specific functions which are not covered by the harmonised EN 934:
Increase the cohesion, entrain air bubbles and retard the setting of mortar for masonry, allowing it to be delivered to a building site by ready-mix in large volumes that can still be used within a working life of typically 24 to 36 hours.
Provide a very rapid set to concrete that is sprayed onto vertical and overhead applications, preventing it from falling off before it has time to set. Mainly used in tunnelling applications for early roof support. Dosage may exceed 5%
These admixtures may work for many years after the concrete has set, increasing the corrosion resistance of reinforcing steel to reduce the risk of rusting that can cause the cover concrete to crack and scale.
Powerful surfactants that allow very large amounts of air to be formed in the concrete, producing a low strength, light weight material, particularly suitable for filling large voids.
Used to reduce pump pressure in long pump lines or where difficult aggregates are being used. Very effective with lightweight aggregates.
Semi-dry or Earth-dry concrete used to make pavers or blocks requires special admixtures to aid full compaction without effecting the properties required for immediate demoulding.
Concrete shrinks, mainly due to loss of excess water. This causes internal stresses that lead to cracking or curling, especially in slabs. These SRA admixtures reduce the shrinkage stress.
These admixtures allow the re-use of water and washings used to clean out ready-mix trucks at the end of a working day. The washings are treated with the admixture and then combined back into the following day’s concrete without any detrimental effects to the concrete quality.
The classification of form/mould release agents is covered by the French MRA Classification by French Concrete Admixture Association SYNAD. More information on this classification is available in French at the SYNAD website.
The German association DBC has also produced guidance on the environmental aspects of mould release agents which is available on our publications page.