The Strength of Bituminous Mixtures and Their Behavior under Repeated Loads, Part 2

Abstract

At the previous year's meeting of the Highway Research Board, the authors presented two fundamental, mathematical relationships for sheet-asphalt mixtures tested in the unconfined state. The first expression related the strength of these mixtures to the temperature and the rate of deformation. The second expression related the number of repetitions of applied stress necessary to cause failure as defined by some suitable criterion, the temperature and the rate of deformation. Since that time the investigation has been continued to include the evaluation of strength and deformation characteristics of a sheet-asphalt mixture subjected to repeated loads and with varying degrees of lateral support. The information from this study was used to further verify the above mentioned relationships. The inclusion of lateral support as a variable made this study more realistic from the standpoint of actual field performance in bituminous pavement where some degree of confinement is known to exist. Lateral support was obtained by use of the triaxial cell. To establish the fact that the relationship among strength, temperature, and rate of defoliation was valid for bituminous-aggregated mixtures other than sheet asphalt, specimens were formed from a bituminous concrete mixture with a maximum aggregate size of 1/2 inch. This comparison was limited to relationships determined from tests performed in the unconfined state. Finally, since it is known that a severe condition of loading for a flexible pavement or bituminous mixture is a stationary load, a test was Included to evaluate the sheet-asphalt mixture under this condition. Variables of temperature and applied stress were included, and the testing was limited to the sheet-asphalt mixture tested in the unconfined state.