Experimental Assessment of Aggregate Surfacing Materials

Résumé du livre

An extensive suite of geotechnical laboratory tests were conducted to quantify differences in engineering properties of three crushed aggregates commonly used on Montana highway projects. The material types are identified in the Montana Supplemental Specifications as CBC 6A, CBC 5A, and CTS 2A. Results from R value tests and direct shear tests performed on large samples (12 in. by 12 in.) indicates the CBC 6A aggregates generally exhibited the highest strength and stiffness of the three material types. In terms of strength parameters, there was no statistically significant difference between CBC 5A and CTS 2A materials. The CBC 6A and 5A materials exhibited similar average R values, which were both slightly greater than the CTS 2A materials. Overall, the CTS 2A materials generally exhibited the lowest average strength and stiffness. Although this material was the poorest performer when compared to the two CBC materials, it still exhibited relatively high strength and stiffness. Drainage capacity was quantified by conducting multiple saturated constant head permeability tests on 10 inch diameter samples of each material type. The CBC 6A and CTS 2A materials had the highest average permeability values, while the CBC 5A materials had the lowest. Permeability was shown to depend more on the fine fraction void ratio (e sub f) than on aggregate type or maximum particle size. An analytical method of predicting permeability based on e sub f was developed, which will allow Montana Department of Transportation designers to estimate permeability based on gradation and state of compaction. Overall, the CBC 6A materials were generally the best performers in this study. In general, the CBC 5A aggregates exhibited the second highest strength and stiffness, but also had the lowest drainage capacity. The CTS 2A aggregates exhibited the lowest strength and stiffness, but had relatively good drainage capacity. The ability to substitute CTS 2A material for CBC aggregates depends on the relative importance that is assigned to strength, stiffness, and drainage in the pavement design model.