Evaluation of Aggregate Gradation on Increasing Safety of Pavement Surfaces

With an increase in traffic volume and speed of vehicles on highways، the number of accidents has also increased. Reduced pavement friction between a vehicle’s tire and the pavement surface in wet weather conditions is the primary contributing factor in many accidents، and wet pavement friction is considerably affected by the range، which is based on the microtexture and macrotexture of the surface. microtexture and macrotexture are functions of the aggregate gradation type، and therefore one way to increase the skid resistance is use the best gradation features. This research is based on two stages. In stage I، twenty five asphalt core samples from a site in Iran were selected، and the microtexture، macro texture، asphalt content and gradation were measured for each. The British Pendulum Test (BPT) was used to quantify the microtexture، and a sand patch test (modified for laboratory use) was used to measure the macrotexture in terms of texture depth. In stage II of the study، four gradations in the range from the previous stage were selected and optimum asphalt contents determined. The microtexture and macrotexture of the four gradations were measured for the optimum asphalt contents. Results showed that the S-shape gradation proved to be most effective for improvement of the skid resistance and it can use in design process of asphalt.