Repeated Triaxial Testing During Mix Design for Performance Characterization

The advancement of the Superpave gyratory compactor (SGC) has led to a recognized need for a simple test that preferably can be performed on SGC samples during mix design that would rank performance potential of the mixtures if used in a pavement. Although it has proved difficult to find one test that can rate mixture potential for rutting and fatigue cracking and modulus, a limited study was conducted on Illinois mixtures that provides evidence that a simple test performed during mix design has the potential to predict a diverse set of performance characteristics. The results are presented for 10 Illinois dense-graded mixtures of surface and binder (9.5 and 12.5 mm) gradations that were tested in an asphalt pavement analyzer (APA) and subjected to flexural beam fatigue, unconfined repeated load permanent deformation, and diametral resilient modulus testing. The mixtures were further subjected to a rapid triaxial test procedure using SGC compacted samples, as taken from the SGC machine, and tested at 50°C in a triaxial stress reversal mode. The triaxial testing provides data that predicts resilient modulus, APA rutting results, fatigue coefficients, and permanent deformation characteristics of accumulated strain at tertiary failure, loads to tertiary failure, and the exponent to the standard logarithmic permanent deformation curve. The excellent correlations obtained from this study provide direct evidence that this test protocol may provide a structural evaluation procedure to supplement the volumetric mix design process and warrants further study.