Browsing by Author "Mesfin, Gebretsadik"

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    Blending of Volcanic Cinder and Natural Gravel for Sub-Base Road Construction, a Case Study of Gelan Asphalt Project, Addis Ababa, Ethiopia
    (Addis Ababa University, 2015-06-06) Mesfin, Gebretsadik; Hailemariam, Tirufat (PhD)
    Pavement design is aimed for achieving a pavement structure which is economical, comfortable and yet safe to travel by motorist; and which minimizes development of pavement distress features during the design life of the pavement. However, inappropriate selection of road materials for construction may cause early pavement failure. Low quality or out-of-specification materials are usually available from local sources. If there is appropriate treatment of the materials or/and structural design, the optimum use of local materials can be permitted, the construction can be accelerated and significant monetary benefits can be realized.Acccordingly in this study it was attempted to define the requirement related to blending of some volcanic cinder gravel from south east of Addis Ababa for Gelan Asphalt road project. The performance of mechanically blended volcanic cinder with natural gravel was evaluated in meeting Ethiopian Road Authority (ERA) manual specification. The cinder gravel was blended with some trial proportions of 1:1, 2:1 and 3:2 weathered natural gravel by mass and different test including grain size distribution, Attereber limit, California Bearing ratio Linear shrinkage, Loss Angeles Abrasion and perographic analysis has been conducted. Results showed that blending of 50% of natural gravel with 50% volcanic cinder, and 67% natural gravel with 33% of volcanic cinder has no plasticity characteristic and its plastic product is zero. However blending of 60% of weathered natural gravel with 40% of volcanic cinder improves its index properties and readily can be used for sub-base road construction as far as it satisfies ERA sub-base materials requirements.
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    Extent of Adhesion Losses in The Wheel- Rail Contact Under Contaminated Conditions
    (Addis Ababa University, 2014-12) Mesfin, Gebretsadik; Daniel, Tilahun (PhD)
    Railway vehicles require a certain level of adhesion between wheel and rail to operate efficiently, reliably, and economically. Different levels of adhesion are needed depending on the vehicle running conditions. In the wheel tread–railhead contact, the dominant problem is low adhesion, as low adhesion on the railhead negatively affects railway operation: on one hand, the vehicle will lose traction resulting in delay when driving on low-adhesion tracks; on the other hand, low adhesion during deceleration will extend the braking distance, which is a safety issue. This thesis examines the influence of several contaminants, i.e., water, mud, leaves, oil and grease, on the adhesion in the wheel tread–railhead contact. This study will also improve our knowledge of the low-adhesion mechanism and of how various contaminants influence adhesion. In this thesis, the adhesion conditions were assessed using a twin disc test machine. Thus the research methodology used was a laboratory test; the aim of which was to study the extent of adhesion coefficients over a range of slip values with and without contaminants. Thus the outcomes from lab test were the coefficients of adhesions of each contaminant within 0 to 10% slip values so as to sort out which of them are the worst to cause loss of adhesion. With this regard oil and grease have been found to create less adhesion than leaves unlike the researches made abroad so far.