The American Concrete Institute (ACI, www.concrete.org) web session entitled the Effect of Frozen Rebar on Surrounding Concrete During Cold Weather Placement addresses monitoring for cold rebar and cold weather concreting, as part of the ACI 306 Cold Weather Session in March 2014 in Reno, Nevada. The mission of ACI Technical Committee 300 Design and Construction, 306 – Cold Weather Concreting is to “develop and report information on cold weather concreting.” Active documents of ACI Technical Committee 306 – Cold Weather Concreting include:
- ACI 306.1-90: Standard Specification for Cold Weather Concreting (Reapproved 2002)
- ACI 305RS-10/306RS-10 Guía para la Colocación de Concreto en Clima Caliente y Clima Frío
- ACI 306R-16: Guide to Cold Weather Concreting
The web session reviews numerous ACI cold surface recommendations, and notes how strategies for cold surfaces differ between ACI documents. ACI 306.1-90 Standard Specification for Cold Weather Concreting (Reapproved 2002) recommends to use warm concrete to heat forms and steel, and then to maintain the required concrete temperature through the protection period. However, ACI 301-10 Specifications for Structural Concrete instructs to heat forms and steel to a minimum temperature of 35ºF.
Further, the American Concrete Institute ACI 306R-10 Guide to Cold Weather Concreting outlines the following five objectives of cold weather concreting practices:
- Prevent damage to concrete due to freezing at early ages;
- Ensure that the concrete develops the required strength for safe removal of forms;
- Maintain curing conditions that foster normal strength development;
- Limit rapid temperature changes, and;
- Provide protection consistent with the intended serviceability of the structure.
ACI 306R-10 Guide to Cold Weather Concreting best practice recommends all surfaces to be above the freezing temperature of water. However, ACI 306R-10 warns to limit the surface temperature to no more than 10°F greater than or 15°F less than that of the concrete to avoid inconsistent setting, rapid moisture loss, and plastic shrinkage cracking. ACI 306R-10 Table 5.1, Temperature of Concrete includes recommended concrete temperatures by the air temperature range and by the minimum dimensions of the concrete section size.
(Source: American Concrete Institute (ACI, www.concrete.org) Effect of Frozen Rebar on Surrounding Concrete During Cold Weather Placement, Ronald L. Kozikowski, North Starr Concrete Consulting)
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