The American Concrete Institute (ACI, www.concrete.org), online learning (ACI University) offers a series of free online education presentations to engineers, educators, researchers, contractors, students, and others in the construction industry and built environment. One of the many online presentations reviews the Effect of Frozen Rebar on Surrounding Concrete During Cold Weather Placement, published by Ronald L. Kozikowski, Materials and Construction Engineer at North Starr Concrete Consulting, located in Dover, New Hampshire.
ACI free online education presentations and web sessions are recorded at ACI Conventions and other concrete industry events, addressing a broad spectrum of concrete-related topics, including sustainability, emerging materials, design, and construction practices. Past ACI free online education presentations and web sessions are either archived on the ACI website or incorporated into the ACI Online Continuing Education (CEU) Program, depending on the content of the education presentation or web session.
Further, the ACI web session the Effect of Frozen Rebar on Surrounding Concrete During Cold Weather Placement addresses monitoring for cold weather concreting in low temperatures, 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
First, Ronald L. Kozikowski explains the large thermal mass of concrete, at about 95% – 99% by volume, contrasted with the small thermal mass and high conductivity of steel. As a part of the heat balance calculations in cold weather and low temperatures, the combined warm concrete and cold steel only lower the final equilibrium temperature by about 1ºF – 3ºF. However, the heat balance calculations fail to show the kinetics — the rate at which the concrete undergoes heat transfer and equilibrium in the field during real-world conditions.
Second, the speaker highlights the two main criteria for cold weather concreting and cold surfaces, as published in ACI 306.1-90: Standard Specification for Cold Weather Concreting (Reapproved 2002) and other ACI 306 cold weather concreting standards:
- Preparation of surfaces in contact with fresh concrete, and;
- Identifying and heating massive metallic embedments.
Third, ACI 306R-88 indicates that “the placement of concrete around massive metallic embedments that are at temperatures below the freezing point of the water in concrete may result in local freezing of the concrete at the interface.” The Mandatory Requirement Checklist in ACI 306.1-90 Standard Specifications for Cold Weather Concreting requires the construction specifier to identify massive metallic embedments, stating that the massive embedments “…must be at a temperature above freezing prior to placement of concrete…”
Fourth, the web session reviews numerous ACI cold surface recommendations, and notes how strategies for cold surfaces differ between ACI documents, specifications and guidelines. ACI 306.1-90 Standard Specification for Cold Weather Concreting 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.
(Source: The 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)
More in the next blog about the Effect of Frozen Rebar on Surrounding Concrete During Cold Weather Placement, cold weather concreting, and weather planning, Weather Controls™ and weather risk management in the construction industry and built environment…