BEHAVIOR OF ASPHALT CONCRETE MIXTURES IN TRIAXIAL COMPRESSION

The triaxial compression test is one of the most common standard tests for determining the stress-strain behavior and strength parameters of soils under drained and undrained conditions. The use of the test met hod in asphaltic mixtures is less well known and seldom practiced. Thi s paper describes the use of the triaxial compression test for asphalt ic mixtures for determining their engineering properties such as the f riction angle phi, the cohesion, c, and the elastic compression modulu s, E. Effects of test temperatures, strain rate, and confining pressur es on the compressive behavior of asphalt concrete were studied. The r esults showed that the friction angle is primarily a function of aggre gate friction and interlocking, being independent of test temperature and strain rate. The cohesion, on the other hand, is largely dependent on the binder and fines mixture being sensitive to both test temperat ure and strain rate changes. The confining pressures have no influence on c and phi, but have significant influence on the compression modul us, E. The tests can be conducted at controlled temperatures, constant strain-rate, and confining pressures so as to allow the determination of the basic engineering stress-strain and strength properties of the se materials under controlled environmental conditions. Using these pr operties, a constitutive plasticity model based on the Drucker-Prager yield condition can then be applied in an axisymmetric finite element model to describe the mechanical behavior of the asphaltic material in triaxial compression. Analysis shows that the plasticity model is abl e to describe the stress-strain behavior of the triaxial specimen to f ailure, predicting both the failure strain and the failure stress fair ly accurately. Comparison of analysis with measured lateral deformatio n at failure also show good agreement. Thus it seems that a simple ide alized elastic-perfectly-plastic constitutive model, whose parameters can be determined from a triaxial compression test at constant strain- rate, is adequate to describe the behavior of asphaltic mixtures, load ed in compression to failure.