A study of the effect of aggregate characteristics on the behavior of asphaltic mixtures both under static and dynamic loading conditions

Abstract

It has become increasingly evident in recent years that the design of asphalt paving mixtures for use in modern highway and airfield construction should include some fundamental consideration of the dynamic loading conditions to which the pavements are subjected in actual practice. Generally, the pavements fail either by excessive permanent deformations or by fatigue cracking. The properties of materials used in the pavements have an important bearing on the pavement behavior. Hence, this study was undertaken to evaluate the effect of aggregate characteristics on the behavior of asphaltic mixtures, using both static and repetitive load triaxial tests, with particular reference to their resistance to permanent deformation. Three types of coarse aggregates were used in the study, a rounded smooth textured natural gravel; a crushed angular limestone; and a synthetic lightweight aggregate. Each of these coarse aggregates was combined with suitable fine aggregates to obtain a grading satisfying the Asphalt Institute Type IV(a) specification. The same type of asphalt was used for all the three mixtures. The optimum asphalt content for each mixture was determined using the Marshall mix design procedure. The specimens for the triaxial tests were made at the respective optimum asphalt contents using a gyratory compactor developed at the Texas Transportation Institute for large diameter specimens. The equipment used for the repetitive load triaxial tests was also the one developed at the Texas Transportation Institute. All the repetitive load tests were conducted at a constant lateral pressure of 20 psi and at 90F. Three levels of repeated axial stresses were used. Two specimens were tested for each mix at each repeated stress level. The total, rebound and permanent deformations were noted at particular intervals of load repetitions. The testing of a specimen was either continued up to 300,000 stress repetitions (7 days) or until the specimen reached ten percent permanent strain whichever was earlier. ...