Compaction is of special concern during cold weather paving because as ambient temperatures decrease, HMA cool-down rates increase and the time available for compaction (before cessation temperature is reached) is reduced. Therefore, special care should be exercised when paving in cold weather to ensure the HMA is sufficiently compacted before cessation temperature is reached.
Most State DOTs affected by cold weather have temperature stipulations in the standard specifications that place special restrictions or prohibitions on cold weather paving. Two situations most often linked to inadequate compaction due to low ambient temperatures are:
- Late Season Paving. Late season paving basically can result in paving during cold ambient temperatures. Paving thin lifts or using open-graded mix in cold weather can result in little time available for compaction. Using MultiCool, a 45 mm (1.8 inch) lift of dense-graded HMA delivered to the site at 135°C (275°F) and paved in 7.2°C (45°F) temperatures and a 16 km/hr (10 mph) wind will reach cessation temperature in about 16 minutes. Because of this, many northern tier States establish a “paving season” that significantly limits paving during colder times of year. For example, many northern state paving seasons are only mid-spring to mid-fall.
- Night Paving Operations. Cessation temperature is applicable day or night. Naturally, this can be a problem for night paving even during warmer months because ambient night temperatures are often much lower than daytime temperatures.