Mastering Cold Weather Concreting: Practical Tips and Techniques

Cold weather concreting might sound tricky, but with the right guidance and strategies, you can ensure a successful construction process even when the temperatures drop. Let’s explore some practical tips and techniques to master the art of concreting in cold weather.

Understanding Cold Weather Concreting

In construction, cold weather concreting involves placing, finishing, curing, and protecting concrete when the outdoor temperature averages below 4.4°C (40°F) for more than three consecutive days. To avoid potential issues, it’s crucial to maintain the fresh concrete temperature at 12.7°C (55°F) or higher throughout the process.

Temperature Impact on Set Time

The setting time of concrete significantly varies with temperature. At a comfortable 21°C (70°F), concrete sets in approximately six hours. However, as the temperature drops to 4.4°C (40°F), the set time extends to over 14 hours. If freezing occurs during the process, it may lead to a 50 percent loss in strength, increased permeability, and reduced weather resistance.

Strategies for Successful Cold Weather Concreting

1. Preparations

Before cold weather sets in, meticulous planning is essential:

• Plan ahead, anticipating cold weather conditions.
• Ensure all necessary equipment, including heaters, insulation materials, and enclosures, are ready on-site before starting the concreting process.
• Consider air-entraining concrete for structures exposed to freezing and thawing cycles.
• Keep detailed records of job conditions, recording weather and surface temperatures at least twice daily.

2. Concrete Pouring

During concrete pouring, adhere to these strategies:

• Avoid pouring concrete around large embedments unless the temperature is above freezing.
• Maintain fresh concrete based on Table 1 (see below) for durability, considering the use of high-early strength concrete.
• Refrain from using “antifreeze” compounds to lower the freezing point of concrete.
• Be cautious with calcium chloride or chloride-containing admixtures under specific conditions.

Table 1: Minimum Concrete Temperature Immediately After Pouring and during the Protection Period

3. Concrete Protection

Ensure effective concrete protection with these strategies:

• Use windbreaks, enclosures, supplementary heat, or adjusted concrete mixtures to combat ambient temperature effects.
• Adhere to minimum concrete temperature requirements during the protection period (refer to Table 1).
• Measure concrete temperature at the surface of the element.
• Safeguard concrete against freezing for a minimum of 3 days, or longer if structural strength is crucial.
• Protect concrete surfaces against freezing within the first 24 hours after placing during potential freezing temperatures.
• Remove protections if the concrete surface temperature is within -6.6°C (20°F) of the surrounding temperature.
• Exercise caution in protecting cylinders for strength tests.

4. Concrete Curing

Follow these guidelines for effective concrete curing:

• Cure concrete to prevent moisture loss.
• If heated enclosures are used, provide extra moisture through sprinkling or steam.
• Ventilate fuel-burning heaters to avoid thermal cracking during cooling.
• Leave forms in place when possible.
• Reshore until concrete reaches the required design strength.
• If curing below 15.5°C (60°F), consider water reducers or retarders.
• Avoid exposing concrete placed in late fall or winter to deicing salts or vehicle-dripped salts.

Mastering cold weather concreting is a step-by-step process that involves careful planning, precise execution, and continuous monitoring. By following these practical tips and techniques, you can ensure the success of your construction project even in chilly weather conditions.