Adamu, Asnake (PhD)Getachew, Bayu2018-07-192023-11-112018-07-192023-11-112013-05http://etd.aau.edu.et/handle/12345678/9328So far, the usual practice in Ethiopia to maintain concrete structures is simply plastering and masking the defects (ugly looking) without considering the structural aspect of the structure. But such activities should not be called maintenance unless the overall condition of the concrete structure is regained through the task accomplished. When the defects or a failure of the concrete structure is a bit exaggerated, demolishing and reconstruction was the best option and was practiced so far. In concrete bridge failures, reconstruction of the structure instead of rehabilitation for every defect or failure is very difficult in terms of money and construction. That is the amount of money involved for reconstruction of bridge is much and very expensive. In addition closing of the road may interrupt traffic flow, which has significant impact on the economy of the country especially when the bridge is on the federal road. So rehabilitation or maintenance of concrete bridges become very crucial and mandatory to stop failure of bridges before reaching their design period and to avoid unnecessary expense to construct a new bridge instead of maintaining and lengthen the service life of the bridge. Proper design and construction does not mean that the bridge will serve about its design life. Because lack of inspection and controlling with minor rehabilitation may make the bridge to fail before serving to its maximum capacity. So monitoring, inspection, and maintenance of every concrete bridge have to be done starting from construction day before failure, which leads to erection or construction of a very expensive new bridge. Unlike the practice we used to do before, concrete bridge rehabilitation techniques, materials and procedures are burning and crucial issue now a day, being many of the bridges are reaching about their design life and need rehabilitation before failure. Considering the urgency of the issue, the universities in particular and the country in general with the respective parties have to think of the problem and participate on provision of possible solutions. Although not satisfactory or to the requirement of the country, Ethiopian Road Authority (ERA) in collaboration with Japan International Cooperation Agency (JICA) has maintained some bridges within the last five to eight years. Concrete bridge maintenance is not an easy task, because regaining the overall condition especially the structural strength of concrete bridge by simple plastering is difficult. So the use of different admixtures (modifying agents), additives (fine mineral powers) and epoxies is mandatory following the procedures and specifications given by the suppliers. At this time there are many suppliers for the construction company involved in maintenance or construction. Considering the importance of concrete bridge rehabilitation on a national base currently, this study has done to address the basic defects, causes of defects, materials for maintenance and possible techniques and procedures of rehabilitation. It has also given some idea about rehabilitation, so that the respective sectors and researchers can have an assignment on the issue for further investigation and work.enEnvironmental EngineeringThesis