Field Density Investigation of Asphalt Mixtures in Minnesota

Abstract

In a current research effort, University of Minnesota and Minnesota Department of Transportation have been working on designing asphalt mixtures that can be constructed at 5% air voids, similar to the Superpave 5 mix design. High field density of asphalt mixtures is desired because it increases the durability and extends the service life of asphalt pavements. The paper investigates the current situation of field densities in Minnesota, to better understand how much improvement is needed from the current field density level to the desired level, and to identify possible changes to the current mix design to improve field compactability. Field densities and material properties of 15 recently constructed projects in Minnesota are investigated. First, a statistical analysis is performed to study the probability distribution of field densities. Then, a two-way analysis of variance is conducted to check if the nominal maximum aggregate size and traffic levels have any significant effect on field densities. A correlation analysis is then conducted to identify significant correlations between the compactability of mixtures and their material properties. The results show that the field density data approximately obey normal distribution, with an average field density of 93.4% of theoretical maximum specific gravity; there are significant differences in field density between mixtures with different traffic levels; compactability of mixtures is significantly correlated with fine aggregate angularity and fine aggregate gradation of the mixtures.

Relating Ndesign to Field Compaction: A Case Study in Minnesota

“…It is important to note that the observed differences in compactability between different N design levels are most likely a result of the differences in the mesoscopic material properties, such as effective binder content, aggregate gradation, angularity, and so forth. The same data were used in a different study ( 21 ) to investigate correlations between the compactability and material properties. Significant correlations were identified between the compactability of the mixture and the fine aggregate angularity and the fine aggregate gradation characterized using the Bailey method.…”

Developing Representative Test Specimen Conditions for Rutting Mechanical Test Methods of Airfield Pavements.pdf

“…This was nearly expected based on the bimodal distribution of the original data for joint cores in Figure 6, delineating two different peaks in the respective histogram. It is worth noting that previous distribution of field density data has been reported in the literature with left-skewed and leptokurtic (i.e., kurtosis > 3) properties, rather than normal distribution (19).…”