Concrete specifications often require the concrete contractor to submit a cold weather concreting plan. A good plan ties the submittal to cold weather requirements in the specification and can help you to avoid having unnecessary requirements imposed on you. Plan details are the key. Including inadequate detail can result in rejection of the plan, but including too much detail can sometimes reduce your cold weather options. The plan should simply describe the means and methods you intend to use in meeting the specification requirements. Submitting the plan and having it approved by the engineer of record provides a written record of your intentions, which can settle a lot of arguments before they start. The only caveat: Don't put anything in the plan that you aren't prepared to do.
ACI 306.1-90, "Standard Specification for Cold Weather Concreting," is a good starting point for preparing the plan. Section 1.5.1 of this document states the following:
"If required, submit detailed procedures for the production, transportation, placement, protection, curing, and temperature monitoring of concrete during cold weather. In the submittal, include procedures to be implemented upon abrupt changes in weather conditions or equipment failures. Do not begin cold weather concreting until these procedures have been reviewed and accepted."
Introduce your plan with the following statement: This Cold Weather Concreting Plan is submitted as required by the Project Specifications and conforms to the requirements established in ACI 306.1-90, "Standard Specification for Cold Weather Concreting," available at www.concrete.org. It's a good idea to also define cold weather so there are no arguments about when the plan must be followed. ACI 306.1-90 defines cold weather as follows:
"A period when for more than three successive days the average daily outdoor temperature drops below 40 F. The average daily temperature is the average of the highest and lowest temperature during the period from midnight to midnight. When temperatures above 50 F occur during more than half of any 24 hr duration, the period shall no longer be regarded as cold weather."
Discuss the details of cold weather concrete production with your concrete supplier. Some suppliers have a written plan that you can use, but you may want to read the plan, then use only some sections from it in your plan. Describe the means to be used for meeting requirements for the minimum and maximum concrete placement temperatures shown in the table below. These may include heated mixing water or aggregates or both.
The commonly specified duration of protection period for concrete exposed to freezing is three days, but this can be reduced to two days if the rate of early strength gain is increased by one or more of the following:
- Adding an accelerating admixture
- Using Type III cement, or
- Increasing cement content by 100 pounds per cubic yard
Any combination of these methods is acceptable, so discuss the most economical method(s) with your concrete supplier. If specifications allow the use of calcium chloride as an accelerator, selecting this option is usually the most economical and efficient way to accelerate both setting time and early strength gain. If only nonchloride accelerators are allowed, changing cement content or type may be more economical. Describe the method(s) to be used in your plan.
Transportation and placement
Generally, concrete can be produced at a high enough temperature at the plant so no special methods are needed to insulate the concrete truck drum. If the concrete will be placed by crane and bucket, pumping, or conveyor very low air temperatures may necessitate steps to ensure that the placement temperature doesn't drop below the allowable minimum. Scheduling deliveries that reduce truck waiting time is the least expensive way of achieving this goal. In the plan, tie the temperature measurements to the action to be taken if the placement temperature falls below the specified minimum.