Summary of Cold Weather Concreting Procedures

This procedure may be used as the basis for the acceptance or rejection of any concrete element of infrastructure which is to be maintained by the City, and summarizes the ACI Standard Specification for Cold Weather Concreting (306.1-90).

Cold Weather Defined:

The provisions that follow apply to Cold Weather, which is defined as a period of three consecutive days where the average temperature is below 40 degrees F, and not above 50 degrees F for more than half of any one of those three days. A “Cold Weather” situation exists solely based upon previous temperatures, and not upon forecasted temperatures. Concrete protection as outlined is only necessary (with the exception of the paragraph entitled “Protection Against Freezing”) when previous temperatures have created a “Cold Weather” situation. The City will maintain a list of daily temperatures, and will determine when “Cold Weather” exists.

Protection Against Freezing:

For the first 24 hours following placement, concrete should not be allowed to freeze. This can be checked using a high-low thermometer under the insulating blanket, or where the concrete is uncovered, by checking air temperatures for the 24-hour period. Where concrete has frozen in the first 24 hours, it shall be rejected.

Protection During Cold Weather:

If “Cold Weather” conditions exist, concrete temperatures must be maintained at 55 degrees for three days (two days if an approved accelerator is used, the cement content is increased by 100 lbs per CY, or Type III Portland Cement is used).

Protection Deficiency:

If the temperature requirements during the three days are not met, the concrete must continue to be protected until twice the deficiency in degree days is made up. For example, if the average temperature for the three days was maintained at 50 degrees (5 degrees below the requirement), the concrete would need to be maintained at 65 degrees (twice the deficiency) for an additional three days, or at 55 degrees for an additional 6 days. In practice, if the contractor is unable to maintain 55 degrees F, he may also be unable to provide the increased protection requirement, three days after placement, without the use of heat generating equipment. Failure to provide the additional protection required, after first failing to provide the three days at 55 degrees F, shall be grounds for rejecting the concrete.

Subgrade:

Concrete shall not be placed on frozen subgrade.

Backfilling Requirements:

This procedure does not address the strength of the concrete necessary for backfilling or form removal. Generally, concrete should reach 75% of its design strength prior to backfilling. This strength can be determined through the use of field-cured cylinders. Concrete must have 5 days where the average daily temperature is above 50 degrees F prior to backfilling unless field-cured cylinders are taken. These days do not need to be consecutive.

In practice, this policy gives the contractor a guarantee that concrete that is placed in the winter, but which is not “cold weather” as defined in Note 1, will not be rejected for lack of protection so long as it is protected from freezing for 24 hours.

Summary of Cold Weather Concreting Procedures

Michael S. Ross

2000-11-22

Joe Archer

City of Overland Park