Development of a Simplified Design Procedure for Determining Layer Thickness in Long-Life Pavements

This study is a part of the research for developing the technologies of long-life pavements having a design life of more than 40 years. The objective of this study was to develop a simplified design procedure for determining the layer thickness needed for long-life pavements. High modulus asphalt binder for the intermediate layer was introduced and applied in this procedure. To develop the models for predicting the critical pavement responses, a synthetic database was established through use of a finite element program with various combinations of layer thickness and modulus. The synthetic database includes structural and material information, surface deflection, and critical pavement responses. From the developed synthetic database, this paper suggests the minimum layer thickness and modulus value—based on the concept of limited strain level—for long-life pavements. This study also determined experimentally the fatigue endurance limit of asphalt mixtures used in this study. A long-life pavement should have an intermediate layer with a thickness greater than 175 mm (6.89 in.), and an asphalt mix with a modulus greater than 3.5 GPa (507 ksi) should be used. Measured strain values from the accelerated pavement testing and field test sections have been used to validate the proposed design procedure. The validation study has shown that the use of a high modulus asphalt mix is capable of reducing the tensile strain at the bottom of the asphalt concrete layer and layer thickness significantly. The validation study has also shown that the proposed procedure can predict the measured strain values from the test sections within an acceptable level.