Evaluation of Poisson’s Ratio for Use in the Mechanistic Empirical Pavement Design Guide (MEPDG)

The pavement design industry is moving towards the use of mechanistic principles in designing flexible pavements. To determine the resultant strains in the pavement system using these principles, two material properties are required: 1) modulus and 2) Poisson’s ratio. In flexible pavement design, the required modulus can be determined either in the laboratory or in the field. In the lab, the dynamic modulus and resilient modulus tests are used to determine the modulus values of asphalt and unbound materials, respectively. In the field, the Falling Weight Deflectometer (FWD) is commonly used to determine the modulus of the various materials. However, the value of the Poisson’s Ratio is usually assumed. This research project encompassed the evaluation of whether or not the Poisson’s Ratio can be measured using the same test procedures commonly used to obtain the modulus values for flexible pavement design (i.e., dynamic modulus test for asphalt and resilient modulus test for unbound materials). The research project also evaluated the sensitivity of pavement performance and the FWD backcalculation procedure when varying the magnitude of the Poisson’s Ratio parameter. The results showed that the Poisson’s Ratio can readily be measured during the dynamic modulus (AASHTO TP62) test procedure using a radial Linear Variable Differential Transducer (LVDT) measuring system. Tests conducted on a number of asphalt mixtures also showed that there is a relationship between modulus and Poisson’s Ratio (as modulus decreases, Poisson’s Ratio increases). However, some discrepancies were found between the measured and predicted values when using the Poisson’s Ratio prediction equation provided in the Mechanistic Empirical Pavement Design Guide (MEPDG) software, especially when higher PG asphalt binder grades were used. The results also showed that the Poisson’s Ratio should not be measured during the resilient modulus (M sub R) test for unbound materials. This is mainly due to the fact that the M sub R test does not typically test the material in its natural linear elastic state, which is where the Poisson’s Ratio concept is valid. Sensitivity analysis work with the FWD backcalculation and using the MEPDG illustrated how the predicted pavement response is affected by the selected Poisson’s Ratio value.