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Frequently Asked Questions
Cement & Concrete
Technology Home > FAQs > Mass Concrete
 Q:We
will be placing a 4 foot thick concrete floor in a cooling tower.
Can you tell us how much additional curing time will be required
due to the thickness?
A: Recommendations for actual curing
time for mass concrete applications vary from 7 to 21 days (or more)
depending on the reinforcement used, the cement and pozzolan or
slag content in the concrete mixture, and the physical dimensions
of the structure (dams, locks, etc.). The recommendation for heavily
reinforced structures is typically 7 days; for concrete mass structures
with portland cement as the sole cementitious material the curing
period is typically 14 days; and for portland-pozzolan mixtures,
21 days or more, depending upon the design strength development.
Common recommendations for mass concrete applications also include
limiting the maximum internal temperature to 70°C (160°F),
and the thermal gradient from the interior to the exterior of the
concrete section to 20°C (36°F) (higher limits are possible
with low coefficient of thermal expansion aggregates).
More information:
Design and Control
of Concrete Mixtures
ACI Committee 207, Mass Concrete, ACI 207.1R-96, ACI Committee
207 Report, American
Concrete Institute, Farmington Hills, Michigan, 1996, 42 pages.
Gajda, J; Kaufman, A; and Sumodjo, F., “Precooling
Mass Concrete,” Concrete Construction, August
2005
Gajda, J, “Great
Thickness Requires Great Lengths,” Roads and Bridges,
January 2005
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