ملخص
Abstract The most common early damage factors that influence the flexible pavement is rutting damage, also known as permanent deformation. this results from the accumulation of small deformations that are not retrieved and occurs every time the wheel passes, as a result of heavy wheel loads. There are two types of rutting. The first type occurs as a result of the high repetition of stresses on subgrade, sub base and base layers under the existing asphalt layer. The second type of rutting occurs as a result of designed asphalt mixes that do not have the sufficient shear strength to withstand repeated heavy loads. The phenomenon of rutting increases on roads with heavy traffic and heavy wheel loads, especially in warmer temperatures. This study is an attempt to contribute to the design of asphalt mixtures of higher resistance to shear through the introduction of a test which measures the shear strength of asphalt mixtures, designed by the Marshall method. This will allow us to determine the optimum asphalt content, which gives greater resistance to shear, and meet the rest of the Marshall test requirements. Also this method can be used to study the effect of different asphalt mixture compositions and properties of asphalt concrete components to produce asphalt mixtures with high resistant to rutting. This study attempts to contribute to the development of shear and bending tests for asphalt mixtures and includes development and manufacturing of equipment and devices used for this purpose. Numerous tests on asphalt mixtures have been conducted, using different types of aggregate, different grading and binder materials to determine the best mixture with high resistance to shear, stability and good performance. Furthermore, this study includes development and manufacturing of a device to measure the double shear and bending test, the development and manufacturing of cylindrical mold to prepare the cylindrical samples for dual direct shear and bending test and development of a method to compact cylindrical samples by making several attempts to compact samples using a cylindrical Marshall equipment. This creates a method capable of producing homogeneous samples similar in density to Marshall samples. Volumetric analysis, stability, flow, shear and bending tests have been performed on bituminous mixture samples. This study concluded that, the maximum values of shear stresses and maximum bending tests of the asphalt mixtures at a temperature of 60 ° C achieved, when Asphalt content very close to the optimum asphalt content for each mixture. Shear stresses and maximum bending of the asphalt mixtures, increase in value when tested at 25 ° C, compared to the same when tested at a temperature of 60 ° C. The study concluded that Marshall properties and the shear and bending tests results for both samples are close to a large extent, this due to the aggregates and bitumen used in asphalt mixes coming from a single source and gradations of the aggregate being too close. Percentage of bitumen content at the maximum values of stability, shear and bending at the same temperature are close to the optimum bitumen content. The value of the maximum shear and bending stresses increases by decreasing temperature. As this study did not include investigation into the effect of different types of aggregate and its grading on shear and bending properties, as the materials used have almost the same properties, it is recommended that a comprehensive study using the developed equipment should be performed to give more knowledge and understanding. The inclusion of different types of aggregate and different binders in bituminous mixtures and investigation into temperatures is recommended.