With the proposed move to a national Mechanistic Empirical Pavement Design Guide (MEPDG) the Portland Cement Association (PCA) initiated this study to review the proposed models for Soil-Cement (S-C) base and Cement Modified Soils (CMS). To provide a smooth transition to the new design procedures researchers evaluated the laboratory procedures needed to provide the input material properties for resilient modulus (MR) and modulus of rupture (Mr). In addition, software tools were developed to introduce the concepts of mechanistic design to pavement designers.
Researchers found that the traditional laboratory resilient modulus test is extremely difficult to run on S-C samples. The induced strains are very low, and the sample preparation and finishing have a major impact on repeatability. A new test including measurement of the seismic velocity appears to provide much more potential. A good correlation was obtained between both tests. The use of unconfined compressive strength to estimate both resilient modulus and modulus of rupture also appears reasonable. Recommendations are provided in this report. A summary was also made of tools for measuring resilient modulus in the field. The use of the Falling Weight Deflectometer (FWD), Portable Seismic Pavement Analyzer, and lightweight FWD are described. From FWD data, the resilient modulus values obtained in the field are substantially less than those measured in the laboratory.
To evaluate the proposed MEPDG model for S-C bases, an attempt was made to calibrate the model with accelerated pavement test data collected by the PCA in the 1970’s. Calibration factors were developed for the proposed model. In addition, a model based on the PCA recommendations was also calibrated. Both calibrated models were built into two software packages developed in this study. These packages are intended as training tools for introducing the concept of handling the S-C or CMS layer in mechanistic-empirical design systems.