Evaluation of current Louisiana flexible pavement structures using PMS data and new mechanistic-empirical pavement design guide.
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2012-04-01
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Edition:Final report; July 2009-June2011.
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Abstract:The new Mechanistic-Empirical Pavement Design Guide (MEPDG) developed under the National Cooperative Highway Research Program (NCHRP) Project 1-37A represents a major change as compared to the 1993 AASHTO Pavement Design Guide. The MEPDG provides a rational pavement design framework based on mechanistic-empirical principles to characterize the impacts of traffic, climate, and material properties on the pavement performance. Before replacing the 1993 Pavement Design Guide (and its accompanying DARWin 3.1 design software) currently used by Louisiana Department of Transportation and Development (LADOTD), the nationally calibrated MEPDG distress prediction models need to be further validated and calibrated against the local conditions in Louisiana. The objectives of this study were to use the MEPDG design software (version 1.1) to evaluate the performance of typical Louisiana flexible pavement types, materials, and structures as compared with the pavement performance data from the pavement management system (PMS) and identify the areas for further local calibration of the MEPDG in Louisiana. In this study, a total of 40 asphalt concrete (AC) pavement projects were strategically selected throughout Louisiana with different design traffic and subgrade properties. The selected projects included five typical Louisiana flexible pavement structure types: AC over AC base, AC over rubblized Portland cement concrete (RPCC) base, AC over crushed stone, AC over soil cement base, and AC over stone interlayer pavements. The original pavement structural design information as well as network-level PMS data for the selected projects were retrieved from multiple LADOTD data sources, including the Louisiana pavement management system (LA-PMS) and other project tracking databases. Based on the sensitivity analyses and available pavement design information, a set of Louisiana-condition-based design inputs (i.e., materials, climate, and traffic inputs) for the MEPDG flexible pavement design was developed, and the results were stored in a database named LAMEPDG along with the pavement performance data retrieved from the LA-PMS for all the projects evaluated in this study. The comparison results between the MEPDG-predicted and the LA-PMS-measured distresses indicated that the MEPDG rutting model tended to over-predict the total rutting for AC over RPCC base, AC over crushed stone, and AC over soil cement base pavements in Louisiana. However, it seemed to be adequate for those AC over AC base pavements selected. Meanwhile, the MEPDG load-related fatigue cracking models were found to be adequate for Louisiana's AC over AC base, AC over RPCC base, and AC over crushed stone pavements. However, for AC over soil cement base pavements in Louisiana, the MEPDG-predicted fatigue cracking was considerably less than the wheel-path cracking reported in the LA-PMS. Further statistical analyses generally indicated that the MEPDG prediction errors for both the rutting and the load-related fatigue cracking models could be significantly influenced by different design factors, such as pavement type, traffic volume, subgrade modulus, and project location. Finally, based on the available data, a preliminary local calibration of the MEPDG rutting model was conducted for the selected AC over RPCC base and AC over soil cement base pavements, respectively. A set of local calibration factors was proposed for different pavement materials. On the other hand, further local calibration of the MEPDG fatigue cracking models was recommended before using the MEPDG for the AC over soil cement based pavement design in Louisiana.
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