Drainage and Mechanical Behavior of Highway Base Materials

The mechanical and drainage properties of graded aggregate base (GAB) materials used in mechanistic pavement design are the level one inputs. Several highway agencies need an evaluation of the stiffness and drainage characteristics of GAB stone delivered at highly variable gradations to construction sites. To fulfill the current need, the mechanical and drainage properties of seven GAB materials with varying petrography and physical properties were evaluated in the laboratory and field. The resilient modulus and hydraulic conductivity test results obtained in the laboratory were compared with the field measurements. The summary resilient moduli at optimum moisture content (OMC) were generally lower than those at OMC-2%; however, permanent deformations increased with the addition of moisture content. The correlation between the mean laboratory and field stiffness/modulus values was fair to acceptable (R2=0.65 to 0.94), and additional measurements may yield a stronger correlation. An increase in base thickness from 6 to 60cm resulted in a 1.7 to 2.4 times decrease in drainage time depending on the analytical method used. The material cost decreased 1.6 times with a change in the drainage quality from poor to excellent or time-to-drain from 10 to 0.08days. Similarly, a 2.4 times decrease in cost was noticeable with a layer coefficient increase from 0.08 to 0.14. The resilient modulus, permanent deformation, and hydraulic conductivity of GAB materials should be evaluated to design a highway base with adequate stiffness and drainage performance.