superplasticizers are linear polymer chemical additives used as high range water reducers for cement and concrete mixing. They make wet concrete mixable with less water and produce a more workable, self-consolidating, and higher strength concrete than concrete without super plasticizers at the same water/cement ratio. They also reduce the risk of segregation, bleeding, and air entrainment problems.
Compared to traditional sulphonated super plasticizers, the new NSF and NSCA have shown a greater efficacy when the dosage is increased and the concrete is mixed for 1 minute after addition of superplasticizer. This is due to the average molecular weight which increases with increasing dosage, and their ability to fluidize the mix at low temperatures where hydration reactions of cement slow down. This enables them to retain their effectiveness at lower temperatures, thus reducing slump loss and enhancing workability.
Another advantage of superplasticizers is that they do not diminish the cement setting. They can be used to supplement fly ash and silica fume in high strength concrete mixes. When a dosage of superplasticizer is added at the beginning, it allows the concrete to achieve a desired slump with a low water/cement ratio while still being easy to place on site and develop early strength.
There are four main types of superplasticizers, all of which contain sulfonic acid as part of the polymer: sulphonated melamine-formaldehyde condensates (SMF), sulphonated napthalene-formaldehyde condensates, lignosulphonates, and modified lignosulphonates. The most commonly used one is MLS, which can be compatible with rammed earth materials. The optimum superplasticizer dosage can be determined using marsh cone test, depending on the type of cement, w/c ratio, and superplasticizer.