What does ACI recommend regarding monitoring the temperature of concrete during cold weather?

The recommended best practice for monitoring the temperature of concrete during cold weather is to check it not less than twice in a 24-hour period. This frequency is important because it allows for the assessment of temperature variations that can affect the curing and strength development of the concrete. In cold weather conditions, the hydration process of concrete can be significantly slowed down, which could result in incomplete curing if temperatures drop too low.

Regular monitoring ensures that proper precautions can be taken, such as the use of insulation, heating blankets, or other protective measures to maintain adequate temperatures. This approach minimizes the risk of cold weather concrete problems, such as freezing which can lead to a loss of strength and durability.

While monitoring every hour or daily without exception might seem prudent, these options could be excessive depending on specific project requirements and local weather conditions. The guideline to check at least twice within a 24-hour period strikes a balance between vigilance and practicality.