Superplasticizers are a type of linear polymer chemical additive used in cement and concrete manufacturing as high range water reducers. This simply means that superplasticizers reduce the amount of water necessary to make cement and concrete products workable. The result is the creation of a free-flowing wet concrete mixture and a stronger finished product. In addition, the reduced water content also requires less cement mix, thus lowering costs.
Chemically speaking, superplasticizers come in four main chemical groups, all of which include sulfonic acid as a component of the polymer: polycarboxylate derivatives, sulfonated melamine-formaldehyde condensates (SMF), sulfonated napthalene-formaldehyde condensates (SNF), and modified lignosulfonates (MLS). As a linear polymer, the superplasticizer creates dispersion between the cement particles and the water content of the mix by neutralizing the ionic charge of the cement particles. When this happens, the particles of cement and the water are separated, making the cement flow more freely with less water content.
The addition of a superplasticizer to a cement or concrete mix creates slightly slower set-up, or drying, times. When coupled with the raised slump value of the superplasticizer-enhanced concrete products, it is understandable how these two characteristics could be beneficial to the concrete and cement industry. Adding superplasticizers to the mixer at the cement production plant allows cement to stay workable for a longer period of time, reducing the amount of water that must be hauled to a work site. In addition, the ability of the superplasticizers to create free-flowing cement and concrete mixtures that are essentially self-leveling make delivery of these products more efficient.
Despite the obvious advantages of superplasticizers, there are a few drawbacks to these products. For optimal performance and to avoid slump loss, superplasticizers should be added at a job site, immediately before delivery of concrete. Unfortunately, this involves the added expense of special equipment, a reduced amount of control over the uniform addition of superplasticizers, and it often results in the addition of extra water to the mix. Adding the superplasticizers at the concrete and cement manufacturing plant reduces these risks and the wear on the truck mixer. Doing so can, however, result in slump loss prior to reaching the customer's job site.
