Performance evaluation of asphalt concrete pavements in Ethiopia, the application of HDM-4 road deterioration sub-model
Many road performance models have been developed and used as important inputs for design and evaluation of pavements especially in the Post-AASHO Road Test era. The Highway Development and Management model (HDM-4), a computer model originally developed by the World Bank, is particularly useful because it integrates pavement performance models to the initial construction, maintenance and road user cost models thereby enabling economic and financial evaluation of a project or alternative projects. This research focused on a level two calibration of the road deterioration sub-model of HDM-4, specifically the models of asphalt concrete (AC) on granular base pavements to the conditions in Ethiopia, taking Addis-Modjo-Awasa Road as a case study. To meet the objectives of the study, a thorough evaluation of historical data of the road was conducted and suitable calibration pavement sections identified. A methodology for field data collection was crafted. The field data collection includes measurement of pavement deflection using a Benkelman Beam and the measurement of pavement conditions of roughness, rutting and cracking using automated survey vehicle. The calibration process includes prediction of pavement deterioration taking the calibration factor as unity and scaling to match the observed level of deterioration. The procedure of calibration is based on the provisions of the HDM-4 calibration manual prepared by Bennett and Paterson in the year 2000. The results showed that the calibration factors are well within the typical values of factors included in the calibration manual of HDM-4 (Paterson and Bennett 2000) indicating that the road deterioration models are generally applicable to the asphalt concrete pavements to the Ethiopian conditions. The prediction of cracking initiation and progression and the collected data generally show wider dispersion, resulting in higher calibration factors especially for cracking initiation. The predictions of rutting and roughness progression are more stable, and the calibration factors are close to unity. The study also showed that local condition of material quality, workmanship and the environmental effects of drainage affect deterioration rates more than traffic loading.