About the research
For unbound materials, the MEPDG uses the AASHTO soils classification as described in AASHTO M145 or the Unified Soils Classification (USC) definitions as described in ASTM D 2487. Unbound materials are categorized by grain size distribution, liquid limit and plasticity index value. The designer selects the primary unbound material type using one of the classification systems and then provides further input to determine appropriate material properties to be used for design. While it is expected that resilient modulus testing is to be completed for Level 1 designs, many agencies, including the Iowa DOT are not equipped to complete resilient modulus testing. Therefore, for Level 2 designs, correlation equations have been developed with more commonly used testing protocols to estimate the resilient modulus of the unbound materials. However, resilient modulus of the unbound granular and subgrade materials is a required input in any mechanistic-based pavement analysis and design process. With more and more agencies adopting the mechanistic-empirical design concept in their pavement designs, it is anticipated that Iowa DOT may implement the resilient modulus testing protocol considering the benefits that can be derived. The objectives of this research are to design and implement a laboratory study for evaluating the unbound granular materials and subgrade soils commonly used in Iowa using resilient modulus equipment and establishing a database of resilient modulus values.