Superplasticizer

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Superplasticizers (SPs), also known as high range water reducers, are

additives used for making high-strength concrete or to place self-compacting concrete. Plasticizers are chemical compounds enabling the production of concrete 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 also retard the setting and hardening of concrete.[1]

According to their dispersing functionality and action mode, one distinguishes two classes of superplasticizers:

  1. Ionic interactions (electrostatic repulsion): lignosulfonates (first generation of ancient water reducers), sulfonated synthetic polymers (naphthalene, or melamine, formaldehyde condensates) (second generation), and;
  2. Steric effects: Polycarboxylates-ether (PCE) synthetic polymers bearing lateral chains (third generation).[2]

Superplasticizers are used when well-dispersed

concrete strength and its durability. Superplasticizers greatly improve the fluidity and the rheology of fresh concrete. The concrete strength increases when the water-to-cement ratio decreases because avoiding to add water in excess only for maintaining a better workability of fresh concrete results in a lower porosity of the hardened concrete, and so to a better resistance to compression.[3]

The addition of SP in the truck during transit is a fairly modern development within the industry. Admixtures added in transit through automated slump management system,[4] allow to maintain fresh concrete slump until discharge without reducing concrete quality.

Working mechanism

polyethers are effective superplasticizers.[5]

Traditional plasticizers are

polycarboxylates ethers. Cross-linked melamine- or naphthalene-sulfonates, referred to as PMS (polymelamine sulfonate) and PNS (polynaphthalene sulfonate), respectively, are illustrative. They are prepared by cross-linking of the sulfonated monomers using formaldehyde or by sulfonating the corresponding crosslinked polymer.[1][6]

Idealized structure of naphthalenesulfonate/formaldehyde polymer used as a superplasticizer.
colloidal suspension through steric interactions thanks to its lateral chains. Note: the PCE molecules are adsorbed onto positively-charged cement particles (tricalcium aluminate
(C3A) mineral phase).

The polymers used as plasticizers exhibit

ionomers bearing negatively charged groups (sulfonates, carboxylates, or phosphonates...). They function as dispersants to minimize particles segregation in fresh concrete (separation of the cement slurry and water from the coarse and fine aggregates such as gravels and sand respectively). The negatively charged polymer backbone adsorbs onto the positively charged colloidal particles of unreacted cement, especially onto the tricalcium aluminate
(C3A) mineral phase of cement.

Melaminesulfonate (PMS) and naphthalenesulfonate (PNS) mainly act by

electrostatic interactions with cement particles favoring their electrostatic repulsion while polycarboxylate-ether (PCE) superplasticizers sorb and coat large agglomerates of cement particles, and thanks to their lateral chains, sterically favor the dispersion of large cement agglomerates into smaller ones.[7]

However, as their working mechanisms are not fully understood, cement-superplasticizer incompatibilities can be observed in certain cases.[8]

See also

References

  1. ^
    ISBN 978-0-7277-3611-6.{{cite book}}: CS1 maint: DOI inactive as of January 2024 (link) CS1 maint: multiple names: authors list (link
    )
  2. S2CID 139995838
    .
  3. doi:10.1016/j.cemconres.2008.04.007
    .
  4. ^ "In-transit concrete management system | GCP Applied Technologies".
  5. ^
    ISBN 978-0-85709-028-7
    .
  6. doi:10.1680/adcr.2000.12.4.153
    .
  7. ISSN 0958-9465
    .
  8. ISBN 0-8155-1373-9
    p. 121

Further reading

External links
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