AASHTO layer coefficients for cement-stabilized soil bases

Layer coefficients of cement-stabilized soil were determined for use in the American Association of State Highway and Transportation Officials (AASHTO) pavement design method. The soils were an A-3 fine sand and an A-6 silty clay. The silty clay was blended with three different amounts of concrete sand. Cylindrical specimens of three differing cement contents were molded and tested for static compressive chord modulus and unconfined compressive strength. Layer coefficients were determined by using the modulus values with the AASHTO pavement design guide's layer coefficient nomograph; the coefficients ranged from 0.09 to 0.27, depending on soil type, sand content, and cement content. Regression equations based on strength, dry unit weight, and cement content were developed to allow estimation of layer coefficients. Layer coefficients were shown to increase with increasing cement content, dry unit weight, and, for the sand-clay mixtures, sand content.