G/Egziabher, EfremAbebaw, Eskedil2018-06-182023-11-112018-06-182023-11-112014-07http://etd.aau.edu.et/handle/12345678/1172Absence of sound natural road construction materials, within the vicinity of the project compound, makes road construction in that area very expensive. The best alternative in those areas, where there is scarcity of suitable construction materials, is upgrading the locally available materials so that they can be used for the proposed construction. Soil stabilization by adding additives is one of the oldest methods of upgrading substandard materials. In the south western part of Ethiopia, in Gambella region, rock and natural gravel, which are the necessary ingredients for construction of pavement structural components, are very scarce. The vast flat land of the region is covered by black clay soil which is underlain by sand deposits within 0.5m – 3m depth. The focus of this study is to stabilize the natural sand, found underneath the black clay soil, with bitumen and cement so that it can be used for road base construction. Additives like, sulfur and cement were added to the sand-bitumen mixture to increase the Marshall stability of the mix. The sand-bitumen mixtures were designed according to Marshall method of mix design and the respective properties were assessed based on the Marshall mix design criteria. The sand-cement mixtures were, on the other hand, designed according to the Joint US Army and Air Force methods and the mixture quality was evaluated based on the specifications, developed by the same agencies. It was found out that the natural sand underneath the black clay soil can be used for roadbase construction by stabilizing it either with bitumen or ordinary portland cement. In bitumen stabilization 15-20 percent sulfur has to be added so that the mix gain sufficient stability. The sand stabilized with 10% ordinary portland cement fulfilled all of the requirements set for base course materials. Economically, cement treated natural sand is the most feasible alternative as compared to the crushed stone base course and bituminous (sand-sulfur-bitumen) base course. Key words: sand-bitumen, sand-sulfur-bitumen, stabilization, sand-bitumen roadbase, cement stabilization, cement treated sand.enSand-Bitume; Sand-Sulfur-Bitumen; Stabilization; Sand-Bitumen Roadbase, Cement Stabilization; Cement Treated SandThesis