Evaluation of Crushed Concrete Base Strength

This research project was conducted with two primary objectives, which include: 1) determine whether current Mississippi Department of Transportation (MDOT) requirements for recycled concrete aggregates (RCA) provide adequate materials for a roadway granular pavement layer and 2) determine whether RCA materials provide the same structural value comparable to crushed limestone granular layers. In order to accomplish these objectives, seven RCA materials were obtained from Mississippi suppliers for testing and evaluation. For comparison purposes, three limestone samples were also obtained and subjected to the same testing regimen. These ten materials were subjected to typical laboratory characterization tests in order to evaluate each material. In addition, California Bearing Ratio and resilient modulus testing was conducted in order to compare the strength and stiffness of the various materials. Based upon the results of the research, RCA meeting all applicable current MDOT requirements should be allowed for granular pavement layers. Because RCA materials can have excessive absorption, RCA stockpiles should be maintained in the field at a moisture content representative of a saturated surface dry condition. This should improve the construction and testing in-place RCA granular pavement layers. A protocol was developed to improve the reliability and repeatability of Proctor testing and preparation of strength and stiffness test specimens.