EXPLORATORY INVESTIGATION TO DEFINE STRUCTURAL PROPERTIES OF GRANULAR BASE MATERIALS USING GYRATORY TEST PROCEDURES

The Gyratory Testing Machine (GTM) has been used to develop testing procedures for the simulation of field compaction for subgrade soils and asphalt mixtures. A GTM asphalt mix design procedure was slightly modified for the compaction and testing of granular base course materials. Three different base course aggregates were selected on the basis of carbonate content to determine whether cementation would increase their strength and structural properties. Test samples were prepared with and without one percent lime at moisture contents near optimum. The lime was intended to accelerate any potential strength gain. Other tests including triaxial shear and resilient modulus were also performed after 14 days of curing in an effort to identify differences in properties. The results of this limited testing program indicated that Gyratory Shear (GS) strength remained unchanged during densification except for one lime-treated aggregate which exhibited a large increase during densification. Relationships between GTM and triaxial resilient moduli (MR) were established but the effect of cementation was not observed. A relationship between GS and MR at the sum of principal stresses (theta) equal to 138 kPa was developed and used to formulate a GS prediction of the AASHTO base layer coefficient. Although preliminary, these results indicate that shear strength as measured in the GTM can be used to obtain structural properties of granular base course materials. The key advantage of this test procedure is the relatively short testing time required to obtain strength properties. Consequently, density-moisture content effects could be determined without the complexity of triaxial resilient modulus tests. (a) For the covering entry of this conference, please see ITRD abstract no. E202467.