Concrete Admixture is one ingredient of concrete that is added to the mix before or during mixing to modify concrete properties. Concrete admixture are used to modify the properties of fresh and hardened concrete in order to achieve the desired objectives or purpose of the concrete mixture. It is also used for economic purpose when admixture allows reduction of concrete ingredients proportions or permits saving in construction practices. Concrete admixtures have their history for hundred of years. The latest generation is polycarboxylates or polymer based admixture.
Polycarboxylates or polymer based concrete admixtures are High Range Water Reducing admixture (HRWR) or we can also say “Ultra” High Range Water Reducer. Used at low dosage, polycarboxylates admixtures still can reduce water as much as high dosage of conventional admixtures.Used at higher dosage, polycarboxylates admixtures can produce Self Compacting Concrete SCC (concrete with very high flowability but still with good cohesion). Because of their strong water reduction capacity, they are particularly designed for production of High Strength Concrete. Polycarboxylates HRWR mode of action is based on steric hindrance, this means particle separation due to long polymer molecules.
Polycarboxylates or polymer based admixtures like any newest generation admixtures are expensive products compared to traditional admixtures (Melamine, Naphtalene or lignosulfonates based) but their performances (even at low dosage rate) can allow cement reduction which could make the mix more cost effective. For lower grades of concrete (lower than 40 MPa on cylinder samples), conventional admixtures are still generally the best solution (especially economically). Use of Polycarboxylate admixtures in RMC (ready-mix-concrete) is normally less required than in Precast concrete because of generally lower concrete grades. This admixture type is very suitable for underwater anti-washout concrete.