STRUCTURAL COEFFICIENTS OF BITUMINOUS CONCRETE AND AGGREGATE CEMENT BASE MATERIALS BY THE LIMITING CRITERIA APPROACH

The structural coefficients of bituminous concrete and aggregate cement base course materials were evaluated using the limiting criteria approach. The limiting criteria were developed by relating the pavement performance to the response of the bituminous concrete and aggregate cement pavements at the Pennsylvania Transportation Research Facility. The pavement response was analyzed using the BISAR computer program. The limiting criteria established were maximum surface deflection, maximum tensile strain at the bottom of the base course, and the maximum compressive strain at the top of the subgrade. Using the BISAR computer program, various combinations of wearing, base, and subbase layer thicknesses which satisfied the limiting criteria were determined. These layer thicknesses provided a basis for computation of the structural coefficients. The analysis assumed the commonly-used wearing course structural coefficient of 0.44 and calculated the required structural number for a pavement life of one million EAL from the equation developed in the AASHO Road Test. The results of this study indicated that the structural coefficients of the base course materials varied with the layer thicknesses of the wearing and base courses. /FHWA/