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Superplasticizers (SPs), also known as high range water reducers, are additives used in making high strength
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most ...
.
Plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticiz ...
s are chemical compounds that enable the production of
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most ...
with approximately 15% less water content. Superplasticizers allow reduction in water content by 30% or more. These additives are employed at the level of a few weight percent. Plasticizers and superplasticizers retard the curing of concrete. Generally, superplasticizer can be classified into such types:purified lignosulfonates, carboxylate synthetic polymers, sulfonated synthetic polymers and synthetic polymers with mixed functionality cementitious materials. SPs are used where well-dispersed particle suspension is required to improve the flow characteristics (
rheology Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an appli ...
) of suspensions such as in concrete applications. Their addition to concrete or mortar allows the reduction of the water to cement ratio without negatively affecting the workability of the mixture, and enables the production of
self-consolidating concrete Self-consolidating concrete or self-compacting concrete (SCC)selfconsolidatingconcrete.org
National Ready ...
and high performance concrete. They greatly improve the performance of the hardening fresh paste. The strength of concrete increases when the water to cement ratio decreases. The addition of SP in the
truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame constructi ...
during transit is a fairly modern development within the industry. Admixtures added in transit through automated slump management systems, such as Verifi, allow concrete producers to maintain slump until discharge without reducing concrete quality.


Mechanism

Traditional plasticizers are lignosulphonates as their sodium salt. ''Super''plasticizers are synthetic polymers. Compounds used as superplasticizers include sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate and
polycarboxylate Polycarboxylates are linear polymers with a high molecular mass (Mr ≤ 100 000) and with many carboxylate groups. They are polymers of acrylic acid or copolymers of acrylic acid and maleic acid. The polymer is used as the sodium salt (see: sodium ...
ethers. Cross-linked melamine- or naphthalene-sulfonates, referred to as PMS (polymelamine sulfonate) and PNS (polynaphthalene sulfonate), respectively, are illustrative. They are prepared by crosslinking of the sulfonated monomers using formaldehyde or by sulfonating the corresponding crosslinked polymer. The polymers that serve as plasticizers exhibit surfactant properties. They are often ionomers. They function as
dispersant A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their set ...
s to minimize particle segregation (gravel, coarse and fine sands). The negatively charged polymer backbone adsorbs on the positively charged colloidal particles. However, engineers do not fully understand their working mechanisms, resulting, in certain cases, cement-superplasticizer incompatibilities.Ramachandran, V.S. (1995
Concrete Admixtures Handbook – Properties, Science, and Technology
2nd Edition, William Andrew Publishing, p. 121


See also

*
Particle aggregation Particle agglomeration refers to formation of assemblages in a suspension and represents a mechanism leading to the functional destabilization of colloidal systems. During this process, particles dispersed in the liquid phase stick to each other, ...
(inverse process of) * Peptization *
Plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticiz ...
*
Rheology Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an appli ...
*
Surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, fo ...
*
Suspension (chemistry) In chemistry, a suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye, usually must be larger than one micrometer, and will eventually ...


References

{{reflist Cement Concrete Chemistry Colloidal chemistry Heterogeneous chemical mixtures Concrete admixtures