The Washington State Department of Transportation (Washington State DOT) examined temperature differentials in hot-mix asphalt paving over four construction seasons. From those studies it was found that low-density areas can be caused by temperature differentials in the mat. The study summarized is based on an examination of 17 projects during the 2000 Washington State DOT paving season to determine density differentials in the mat with a "density profile." A density profile is a series of density readings taken in a longitudinal direction over a 15-m (50-ft) section through a low-temperature area. From this collection of density readings, the density range (the difference between the maximum and the minimum readings) and the density drop (the difference between the average and the minimum readings) are determined. The density range and drop are used to determine if low-temperature areas result in inadequate compaction. The criteria set forth by the Washington State DOT included temperature differentials greater than or equal to 14 deg C (25 deg F), a maximum density range of 96 kg/cu m (6.0 lb/cu ft), and a maximum density drop of 48 kg/cu m (3.0 lb/cu ft). Evaluation of the density profiles showed that when the temperature differential exceeded 14 deg C (25 deg F), 89% of the density profiles failed to meet the density criteria, but only 19% failed to meet the density criteria when the temperature differential was less than 14 deg C (25 deg F). It was found that pavements that experienced large temperature differentials during placement produced substantial density differentials.
Abstract