The physical behavior of asphalt concrete is related to the volumetric characteristics of the mixture. A significant challenge facing asphalt pavement engineers is predicting the future density and air voids of asphalt paving mixtures after construction and during service. How rapidly changes in density and voids occur during service can be related to the ability of the pavement to withstand forces imposed from vehicles and the environment. Densification of asphalt concrete after construction and during trafficking varies between mixtures and is related to the method of laboratory compaction, design criteria, and construction technique. This study describes a procedure for quantifying compactibility of mixtures and suggests a procedure for considering densification rate as a criteria for describing optimum asphalt mixtures.
The so-called refusal density of six types of asphalt concrete mixtures was evaluated in this study as function of vibratory hammer compaction. Three aggregate gradings ranging from 1–1/2 inch to 3/8 inch (37.5 to 9.5 mm) maximum aggregate size were compacted in the laboratory using three models of portable vibratory compactors administered by two operators. The resulting factorial experiment was analyzed to determine effect on volumetric properties due to hammer, aggregate grading, asphalt content and operator.
Vibratory compaction was compared with Marshall, kneading, and gyratory compaction procedures to determine differences between each method and for each grading with respect to density and voids characteristics. A new procedure is outlined for using the vibratory compaction technique for development of a new asphalt concrete design method and for adapting the technique for determining the sensitivity of asphalt concrete mixtures to further densification under traffic.
Results of the study indicate that all three vibratory hammers evaluated compacted asphalt concrete to higher levels of density than achievable by conventional Marshall, Hveem or gyratory methods and therefore, should be capable of producing mixtures with higher density than could be obtained after trafficking. The implication of this efficiency during laboratory compaction is a design tool that could provide information regarding the potential for mixtures to reach a plastic condition in service as related to void content.