Effects of Aggregate and Mixture Properties on the Rutting Performance of HMA Wearing Course

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Addis Ababa University


It is known that the availability of a road network of an appropriate level of service and quality is vital in facilitating the overall economic development of a country. In this regard, Ethiopia, a country which is on the fast- track of rapid economic development, obviously requires a road network which is able to cater for the vast traffic/transport demand. In recent years, the quality of many of the major trunk roads in the country has been compromised, as the roads have experienced deterioration, which has given rise to the need for periodic maintenance and rehabilitation. One of the major types of distresses observed on major sections of the trunk roads is permanent deformation in the form of rutting. Performance of roads with regards to ride-ability and roughness is known to have a considerable cost implication to the road users in terms of operational cost, in addition to affecting their safety and comfort . Permanent deformation, in this regard has a detrimental effect. Rutting in paved roads can be attributed to various factors such as the pavement structure, quality of individual constituent pavement materials, magnitude and regime of loading, environmental factors, such as moisture temperature, and others. Despite the fact that HMA mix design has evolved from the conventional empirical mix design approaches (Marshall and Hveem), to the state-of-the-art and more advanced Superpave procedures, due to the lack of technological advancement, the customary Marshall mix design and testing method, bearing the effects of its empiricism, is what is currently being utilized to design ' better' performing HMA mixtures. This research focuses on assessing the effects of aggregate and mixtures properties on the rutting performance of HMA wearing (surface) course mixtures, by attempting to establish correlations between the independent variables (HMA aggregate and mixture properties) and the dependent variable (rut depth), still adopting the fairly simple and readily available Marshall mix design and testing procedure . To meet the objectives of the study, various tests were conducted on HMA core samples, obtained from a pertinently rutted trunk road segment, selected for the case study -Gohatsion-Dejen Road Segment. Statistical correlation analysis coupled with subjective evaluation was then adopted to assess the effects of the various aggregate and volumetric parameters on the rutting performance of HMA mixtures. The results of the study revealed that mixes with higher air void content (in-place and recompacted), lower voids filled with asphalt( in-place and re-compacted), lower Marshall flow value and higher coarse aggregate angularity generally perform better with regards to rutting. It was also found that 0.45 Power Gradation plots give an important indication on the effect of aggregate gradations on the rutting performance of mixtures, and that mixes with aggregate gradations, which plot on the coarser side of the maximum density line, generally perform better with regards to rutting. On the other hand, the inadequacy of the mere 75 blow Marshall Effects of Aggregate and Mixture Properties on the Rutting Performance of HMA Wearing course ( A case study on the Gohatsion - Dejen Road Segment) AAU By Abraham Efraem v August, 2014 Compaction approach to simulate traffic loading in excess of one million ESA's, for representing the current levels of high traffic loadings was also underlined. Moreover, it was noted that the legal load limit of the country, which is 10 tonnes axle loading, is being exceeded, which would prove to have a considerable effect on the rutting performance of mixtures. Finally, suggestions were made on how to design HMA mixtures with better rutting resistance, still adopting the customary Marshall mix design procedure, coupled with the refusal density approach, and the 0.45 Power Gradation Chart. Key words: Rutting, HMA, Re-compacted, Stability, Flow, Angularity, Voids, Va, VMA, VFA, stripping Marshall Mix Design,



Rutting; HMA; Re-compacted; Stability; Flow; Angularity; Voids; Va; VMA; VFA; stripping Marshall Mix Design; 0.45 Power Gradation Plot; Marshall Compaction; Refusal Density; Axle loading