Effect of Shape Parameters and Gradation on Laboratory-Measured Permeability of Aggregate Bases

The current study was undertaken to evaluate the effect of aggregate shape parameters (i.e., angularity, sphericity, form, and texture) and gradation on the permeability of commonly used aggregate bases in Oklahoma. Aggregates used in this study were collected from three different quarries. For each aggregate type, upper and lower limits of three different gradations, modified AASHTO #57, Oklahoma Aggregate Association (OKAA) Type M, and Oklahoma DOT (ODOT) Type A, were selected. Permeability of 18 different combinations of aggregate types and gradations (three aggregate types×three gradations×two gradation limits) were tested using a falling-head permeability approach. For a selected gradation, the lower limit exhibited higher permeability values than the upper limit. Also, permeability was found to increase with an increase in effective diameter and void ratio. An increased coefficient of uniformity and fine content resulted in lower permeability, as expected. Furthermore, the shape parameters of different aggregate types were measured using an aggregate imaging system (AIMS). The coefficient of permeability was found to increase with reduced gradient angularity and increased sphericity. The texture index was found to have minimal impact on the coefficient of permeability. A regression model was developed using aggregate shape and gradation parameters to estimate permeability of aggregate bases.