Behavior of Asphalt Concrete Mixtures in Triaxial Compression

Abstract 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 method in asphaltic mixtures is less well known and seldom practiced. This paper describes the use of the triaxial compression test for asphaltic mixtures for determining their engineering properties such as the friction angle φ, the cohesion, c, and the elastic compression modulus, E. Effects of test temperatures, strain rate, and confining pressures on the compressive behavior of asphalt concrete were studied. The results showed that the friction angle is primarily a function of aggregate 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 temperature and strain rate changes. The confining pressures have no influence on c and φ, but have significant influence on the compression modulus. 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 these materials under controlled environmental conditions. Using these properties, 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 able to describe the stress-strain behavior of the triaxial specimen to failure, predicting both the failure strain and the failure stress fairly accurately. Comparison of analysis with measured lateral deformation at failure also show good agreement. Thus it seems that a simple idealized 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, loaded in compression to failure.