Cement accelerator

A cement accelerator is an admixture for the use in concrete, mortar, rendering or screeds. The addition of an accelerator speeds the setting time and thus cure time starts earlier.[1] This allows concrete to be placed in winter with reduced risk of frost damage.[2] Concrete is damaged if it does not reach a strength of 500 pounds per square inch (3.4 MPa) before freezing.[3]:19

Typical chemicals used for acceleration today are calcium nitrate (Ca(NO3)2) and sodium nitrate (NaNO3). Calcium chloride (CaCl2) is the most efficient and least expensive accelerator[4] and was formerly very popular but is corrosive to reinforcement bars so its use is not recommended[5] and in many countries is actually prohibited. Thiocyanate compounds can also corrode reinforcing but are safe at recommended dosage levels.[6] Sodium compounds might compromise the long term compressive strength[7] if used with alkali-reactive aggregates.[3]:6

References

  1. ↑ Justnes, H. (2000): Accelerator Blends for Portland Cement. Proceedings of Cement and Concrete Technology in the 2000s, September 6–10, 2000, Istanbul, Turkey, Vol. 1, pp. 433-442
  2. ↑ ACI 306R-88: Cold Weather Concreting. "Archived copy" (PDF). Archived from the original (PDF) on 2011-07-25. Retrieved 2011-03-05.
  3. 1 2 Korhonen, Charles J.; Cortez, Edel R.; Durning, Timothy A. (1997), "Antifreeze Admixtures for Concrete", Special Report 97-26, Cold Regions Research and Engineering Laboratory, ISBN 9781428913158
  4. ↑ "ASCC Position Statement #31" (PDF). Concrete International. Vol. 32 no. 02. American Concrete Institute. February 1, 2010. p. 55.
  5. ↑ CEMENT ADMIXTURES ASSOCIATION: Admixture Sheet – ATS 4: Accelerating admixtures, "Archived copy" (PDF). Archived from the original (PDF) on 2011-09-03. Retrieved 2011-03-05.
  6. ↑ Nmai, Charles; Corbo, Jack (November 1, 1989). "Sodium Thiocyanate and Corrosion of Steel in Concrete and Mortar". Concrete International. Vol. 11 no. 11. pp. 59–67.
  7. ↑ Volset, D.(2010): The Use of Antifreeze Agents. http://www.mapei.com/public/NO/linedocument/the_use_of_anti-freeze_agents.pdf


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