The detrimental effects of low compaction temperatures or aggregate segregation have been documented for at least forty years. Lower compaction temperatures are directly related to an increase in air void content, which decreases the strength of the pavement. Even with a perfect mix design, if the mix is not properly compacted in the field, the final product will not last for its intended length of time.
The goals of this study were to determine what kind of problem the Washington State Department of Transportation (WSDOT) experiences with hot-mix paving, whether temperature differentials or aggregate segregation or both, the possible causes of those problems, and what WSDOT can do to fix the problem.
The study found that WSDOT experiences temperature differentials on many projects and to some extent aggregate segregation (typically in longitudinal streaks). The study also found that because many factors are involved with paving operations, no one single piece of equipment or operation will guarantee that temperature differentials will not occur, but that techniques can be utilized to offset the effects of the temperature differentials. The study utilized a density profile procedure that provides a method of determining the effect of the temperature differentials in the finished product. It can locate potential areas of low density, test those areas, and provide results (via a nuclear asphalt content gauge) to determine the extent of the problem.
Density differentials are a primary concern in hot-mix paving. If temperature differentials exist, but the finished pavement has a uniform density of 93% or greater for dense-graded mixes, then the pavement should serve its intended purpose for its intended length of time. The density profile procedure does not guarantee a uniform mat density, but it can be used as a quality control tool to help attain a uniform density. This could be a major step in achieving a higher quality hot-mix product.