Super plasticizer (SP) & VMA (viscosity modifying agent)

Super plasticizer (SP)

High-range water reducer, also known as super plasticizer, has made a breakthrough in concrete industry. It is an essential material component that must be used to produce SCC. The HRWRs improve the flowing ability of SCC by their liquefying and dispersing actions. They reduce the yield stress and plastic viscosity of concrete by their liquefying action and thus provide a good flowing ability in SCC. In addition, the HRWRs deflocculated the cement particles and free the trapped water by their dispersing action, and hence enhance the flowing ability of SCC. In dispersing action, the inter-particle friction and thus the flow resistance are also decreased, and therefore the flowing ability of concrete is improved.

High-range water reducers can either increase the strength by lowering the quantity of mixing water for a given flowing ability, or reduce both cement and water contents to achieve a given strength and flowing ability. They contribute to achieve denser packing and lower porosity in concrete by increasing the flowing ability and improving the hydration through greater dispersion of the cement particles, and thus assist in producing high strength and good durability

VMA (viscosity modifying agent)

Viscosity-modifying admixture is relatively a new addition to the family of admixtures for cement paste, mortar and concrete. The common application of VEA is to produce non-dispersible underwater concrete and SCC. VMA improves the viscosity and cohesion of fresh concrete, and thus reduces the bleeding, surface settlement and aggregate sedimentation resulting in a more stable and uniform fresh concrete. In addition, VMA makes the fresh concrete more robust and less sensitive to the small variations in the conditions and proportions of other constituent materials.

Rixom and Mailvaganam (1999) have categorized the VMAs into five classes based on their physical actions in concrete. The classification is as follows:

Class A: Water-soluble synthetic and natural organic polymers, which increase the viscosity of concrete by increasing the viscosity of mixing water.

Class B: Organic water-soluble flocculants, which increase the viscosity of concrete by enhancing interparticle attraction between cement particles

Class C: Emulsions of various organic materials, which improve the viscosity of concrete by increasing interparticle attraction and supplying additional superfine particles in the cement paste.

Class D: Water-swellable inorganic materials of high surface area that improve the viscosity of concrete by increasing the water-retaining capacity of the concrete.

Class E: Inorganic materials of high surface area that improve the viscosity of concrete by increasing the content of fine particles in concrete, and thereby resulting in greater viscosity.

Most widely used VEAs for concrete are of Class A. The VEAs under this class can be further subdivided into natural, semi-synthetic and synthetic polymers.