In recent years there has been a trend toward operating asphalt plants at lower mixing temperatures. These lower temperatures result primarily from a desire to conserve the energy required to produce the mixtures. The most direct result of lower mixing temperatures is lower temperatures during compaction. The effect of these lower compaction temperatures on performance has not been established, but laboratory studies have led to some questions that need to be addressed. The purpose of this paper is to summarize the results of a field and laboratory study performed at The University of Texas at Austin, Center for Transportation Research, to analyze the effect of lower compaction temperatures on the engineering properties of asphalt concrete mixtures.

Both the field and laboratory studies were conducted as part of an investigation of premature distress of a recycled asphalt concrete overlay. It is significant to note that field observations, as well as laboratory results obtained during construction, indicated that the specified laboratory densities were attained. Even though other factors contributed to the distress, data developed as a part of this study showed that the low compaction temperatures during construction had an adverse effect on the engineering properties of the asphalt concrete and thus contributed significantly to the development of the premature distress.

The field study included examining the construction records to evaluate factors, such as mixing and compaction temperatures, as well as density and Hveem stability of job control laboratory specimens. In addition, a condition survey was performed to determine the nature and extent of the observed distress.

The laboratory study involved preparation of specimens under different combinations of compaction temperature and density observed in the field with subsequent testing to determine Hveem stability, and dry and wet static tensile strengths. The results presented in the paper include a discussion of the interaction between compaction control parameters and the occurrence of distress. Results from these studies indicate that lower mixing and compaction temperatures produce adverse effects on the engineering properties of hot mixed asphalt concrete.