Flexural properties of chemically stabilised subgrade in designing semi-rigid pavements

Abstract

Although flexural fatigue cracking of chemically-stabilised subgrade (CSS) layers is a major distress in semi-rigid pavements, the fatigue model of the CSS layer in the Mechanistic-Empirical Pavement Design Guide (M-EPDG) has not been calibrated. Design of semi-rigid pavements with regard to flexural fatigue life of the CSS layer was conducted using the M-EPDG method. Cylindrical and beam specimens of a lean clay, mixed with different types (cement kiln dust (CKD) and lime) and amounts of additives were prepared in the laboratory. Resilient modulus, modulus of rupture (MoR), flexural modulus and four-point flexural fatigue (FPFF) beam tests were conducted. Also, finite element (FE) models of different pavement sections having different thicknesses of hot mix asphalt (HMA) and different materials and thicknesses of CSS layer under traffic load were developed. The minimum required thickness of the HMA layer to avoid fatigue failure in the CSS layer was determined for different sections using the laboratory test results and the FE analyses. Finally, the effect of considering the flexural properties and fatigue life of the CSS layer on the designed HMA layer thickness was evaluated. The results showed that for the CSS materials with relatively low laboratory fatigue lives, the fatigue cracking of the CSS layer contained the most critical distress to be considered in designing the pavement structure. It was also found that by substituting the CSS resilient modulus with the properly-determined flexural modulus in the mechanistic-empirical design procedure, the designed HMA thickness, and, consequently, the construction cost could decrease significantly.