DETERMINATION OF DYNAMIC MODULI AND PERMANENT DEFORMATION OF MARYLAND ASPHALT MIXTURES USING AMPT
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Full implementation of the mechanistic-empirical pavement design guide (MEPDG) in Maryland requires Level 1 (measured) material properties to characterize asphalt mixtures commonly used in the state. Specifically, these proprieties are the dynamic modulus (DM) and the repeated load permanent deformation (RLPD) properties. To achieve this goal, 28 asphalt mixtures were collected from construction sites/asphalt plants and tested in the Maryland State Highway Administration Office of Materials Technology Asphalt Technology Division laboratory. The DM and RLPD testing was performed on all 28 asphalt mixtures following the AASHTO PP 60, AASHTO PP 61 and AASHTO TP 79 protocols. In addition to the 28 asphalt mixtures from Maryland, DM and RLPD data for 18 asphalt mixtures tested in NCHRP Project 9-30A were also included in parts of this study. In addition to developing a catalog of typical Level 1 material properties for common Maryland asphalt mixtures, this study produced several other important results and findings. These include: (1) The L-1 inputs (measured E* and G* and recalibrated coefficients of rut model, K1, K2, K3) consistently give lesser predicted distresses than L-3 inputs (predicted E* values, default G* values, and default coefficients of rut model) in MEPDG software. (2) The average percentage differences for each predicted distress at all levels of traffic are highest for L-1 versus L-3 inputs and lowest for L-1 versus L-1A (measured E* and G* data and default coefficients of rut model) inputs. (3) The recalibration of Witczak E* model removes the bias toward underprediction in the original Witczak model. The distresses predicted using L-3 (CWM-Calibrated Witczak Model based on Maryland mixes) inputs are closest to the distresses predicted using the measured L-1 inputs. (4) The total number of samples required for complete characterization of one asphalt mixtures as per AASHTO PP 61 and AASHTO TP 79 can be reduced from 12 to 3. The reduction in total specimen preparation (from 60 to 15 hours) and testing time (from 30 to 10 hours) represents substantial economies in structural characterization of asphalt mixtures and motivates state agencies to perform DM and RLPD testing on routine basis to develop performance based specification.