Road and Transportation Engineering

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Browsing Road and Transportation Engineering by Author "Abubeker, Worake (PhD)"

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    Experimental Investigation on Rutting Criteria of Asphalt Mix Using Refusal Density and Wheel Tracking Tests
    (Addis Ababa University, 2022-02) Taye, Demeke; Abubeker, Worake (PhD)
    Ethiopian Road Authority (ERA) has administered around 156 road projects in the years from 2017 to 2021. From those road projects, 94.87% of road projects has being constructed using the Marshal mix design procedure in the preparation of asphalt mixes. ERA manual recommends that the air void after refusal density test is used as a requirement for rutting resistance of the asphalt mixes for roads subjected to heavy traffic. In this study, twelve mixes were prepared with 19 mm and 12.5 mm nominal maximum aggregate size (NMAS) and using bitumen grades of 60/70 and 80/100 penetration grade. The mixes are commonly used for asphalt surfacing in most road projects. Mix designs were performed using the Marshall mix design procedure based on the Asphalt Institute and ERA manual guidelines. Following to the determination of optimum binder content of the mixes, the refusal density tests were conducted by applying further compaction effort using the Marshall hammer. The mixes were then subjected to the wheel tracking tests. The wheel tracking tests were conducted with 20,000 wheel passes and test temperatures of 46C and 50C for mixes with 80/100 and 60/70 bitumen penetration grade, respectively. Texas Hamburg Wheel test requirement was used to evaluate the mixes performance to rutting. The test result indicated that most of the mixes did not fulfil the air void criteria after secondary compaction. From those mixes, more than 50% of the asphalt mixes does not fulfil the performance test requirements (after the wheel tracking test). Therefore, it is found that the percent refusal density (PRD) test may not be a reliable method to indicate the rutting resistance of the asphalt mixes. Thus, other performance tests are recommended to design asphalt mixes for roads subjected to high traffic.