| Stone Matrix Asphalt (SMA) mixtures were developed in Europe where they have proven to be very resistant to rutting, cracking, and polishing. SMA mixtures are characterized by a stone-on-stone aggregate structure filled with a rich binder-filler mastic. Implementation of SMA in the United States began in 1991. The traditional method of design for SMA mixtures has utilized the Marshall procedure, but recipe formulations of component percentages and restrictive material guidelines persist. A better design method was needed that could provide an engineering basis for the selection and optimization of materials.; In this research study, SMA mixtures from several field projects and experimental mixtures containing typical Florida materials were tested in accordance with several well-known techniques used to evaluate conventional asphalt mixtures. These tests included: (1) compaction and shear strength testing with the Gyratory Testing Machine; (2) a rutting test using the Georgia Loaded Wheel Tester; (3) a rutting test using a confined repeated-load procedure; (4) resilient modulus tests at low, moderate, and high temperatures; (5) the indirect tensile strength and strain test; (6) wet/dry moisture damage tests, and (7) a low-temperature diametral-creep compliance test.; Each of the rutting tests do indicate that the SMA mixtures are generally very resistant to permanent deformation. However, the procedure used to evaluate fatigue cracking indicated that many SMA mixtures were less resistant to fatigue than standard dense-graded mixtures. The validity of this assessment is uncertain. Tests on the mixtures and the aggregates show that some of the softer Florida limestones tend to be more prone to degradation which may lead to moisture damage and increase the potential for ravelling or loss of skid resistance. A preliminary assessment of the impact that SMA may have on the paving and aggregate supply industries indicates that due to limited application of this technology to heavy-traffic-type roadways the effect will be very minor. |
