Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Chemical vs. Physical Acceleration of Cement Hydration: CaCl2 vs. Limestone Powder



Dale P. Bentz, Franco Zunino, Didier Lootens


Cold weather concreting often requires the use of chemical accelerators to speed up the hydration reactions of the cement, so that setting and early-age strength development will occur in a timely manner. While calcium chloride (dihydrate – CaCl2∙2H2O) is the most commonly used chemical accelerator, recent research using fine limestone powders has indicated their high proficiency for physically accelerating early-age hydration and reducing setting times. This paper presents a comparative study of the efficiency of these two approaches in accelerating hydration (as assessed via isothermal calorimetry), reducing setting times (Vicat needle), and increasing early-age mortar cube strength (1 d and 7 d). Both the CaCl2 and the fine limestone powder are used to replace a portion of the finest sand in the mortar mixtures, while keeping both the water-to-cement ratio and volume fractions of water and cement constant. Studies are conducted at 73.4 °F (23°C) and 50 °F (10 °C), so that activation energies can be computed for the hydration and setting processes. Because the mechanisms of acceleration of the CaCl2 and limestone powder are different, a hybrid mixture with 1 % CaCl2 and 20 % limestone powder (by mass of cement) is also investigated. Both technologies are found to be viable options for reducing setting times and increasing early-age strengths, and it is hoped that concrete producers and contractors will consider the addition of fine limestone powder to their toolbox of techniques for regulating performance in cold weather and other concreting conditions where acceleration may be needed.
Concrete International


Acceleration, calcium chloride, cement hydration, early-age strength, limestone powder, setting time.


Bentz, D. , Zunino, F. and Lootens, D. (2016), Chemical vs. Physical Acceleration of Cement Hydration: CaCl2 vs. Limestone Powder, Concrete International, [online], (Accessed July 15, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created November 1, 2016, Updated October 12, 2017