Resumen de Effect on Dynamic Modulus Measurement Protocol on Predicted Pavement Performance
B. SHANE UNDERWOOD, MORTEZA ASHOURI, Y. RICHARD KIM
Different standard protocols, AASHTO TP 62 and AASHTO TP 79 used in combination with AASHTO PP 61, exist for the measurement of the dynamic modulus of asphalt concrete. These two protocols are available to meet the needs of both research and practicing pavement engineers respectively, and differ slightly in several key details. For example, the TP 79/PP 61 protocol does not include measurements at temperatures below 5C, whereas the TP 62 protocol requires measurement of the dynamic modulus at -10C. Since the dynamic modulus has become the primary material property input for performing pavement analysis with asphalt concrete, there is concern about potential influences that the choice of test protocol may have on performance predictions, pavement design, and ultimately the actual performance of a pavement structure. This paper presents the results from an analytical study to compare the dynamic modulus values generated by these two protocols. The purpose of this analysis is three-fold: 1) to examine the experimental and analytical procedure suggested in AASHTO TP 79/PP 61 for accuracy and bias; 2) to examine the potential effects of any errors as they relate to routine pavement analysis; and 3) to examine the potential effects of these errors on advanced material model predictions. The differences in the two protocols are first discussed and then the moduli predicted or measured by the two protocols at different temperatures are compared. A database of 17 different mixtures and 48 different individual specimens is used for this purpose. Next, the effects of these differences are assessed in terms of rutting, fatigue cracking, and roughness performance predictions using the NCHRP 1- 37A Mechanistic-Empirical Pavement Design Guide. Following this analysis, the viscoelastic continuum damage model is characterized and then utilized with data from both protocols to make material level thermal cracking predictions and structural level fatigue cracking predictions. It is found that the TP 79/PP 61 protocol does not predict the modulus values at the extreme cold, and to a lesser extent the extreme warm temperatures very well. However, for _____________________________________________________ 1Research Scientist, North Carolina State University, Raleigh, NC 2Graduate Research Assistant, North Carolina State University, Raleigh, NC 3Professor, North Carolina State University, Raleigh, NC The oral presentation was made by Dr. Underwood.
