A superplasticizer is an admixture based on a polycarboxylate ether (PCE) that increases workability of concrete and decreases water requirement without excessive loss of workability. Typical dosage of liquid superplasticizers is from 1 to 3 liters per cubic meter of concrete.
High early strength development and low porosity are advantageous characteristics of superplasticizer concrete. These advantages are particularly useful for prestressed beams and units that require overnight heat-curing.
Higher than normal workability of flowing concrete containing a superplasticizer is maintained for about 30 to 60 minutes, after which time the concrete must be placed before it loses its workability. This requires care, especially if the concrete is to be transported by ready-mixed trucks which have long journey times to the job site.
Swelling & Segregation
The amount of segregation and bleeding in air-entrained flowing or high-strength concrete containing a superplasticizer depends on the type of superplasticizer used, dosage, initial slump value and other factors such as humidity, temperature, and the presence of other admixtures. It is essential to follow strict procedures in order to avoid segregation and bleeding.
Studies on concrete containing SMF-, SNF and MLS-type superplasticizers show that these concretes are as durable as control concrete. This is despite a higher air-void spacing factor and a lower water:cement ratio.
Viscosity Modifying Admixtures
In addition to water-reducers, superplasticizers are also accompanied by viscosity modifying admixtures, which help to obtain concrete with higher tolerance to slight changes in the water content. They are mainly high molecular weight polymers, such as modified polysaccharides, welan or xanthan gums and synthetic copolymers.