Influence of Coarse Aggregate Shape Factors on Bituminous Mixtures

The research represents a laboratory study of the factors effecting the aggregate shape in HMA. The shape of the aggregates particles is not only the factor of aggregate characteristics which effect on the HMA. Other specifications such as aggregate surface texture and aggregate gradation may also effect the HMA. The aggregate shapes are considered for the study of research was cubical, disk and blade shapes. Two aggregate surface textures used in the mix which are smooth and rough particles. The aggregate gradations that are used in the mixtures were high, medium and low gradation. Shape of the aggregate was determined by two methods. The first method was the surface measurement of coarse aggregate, while the second method was particle shape index. Marshal tests and indirect tensile test were performed to investigate the different in behaviors of different samples with different specifications considered in this study taking into account that the control mix contains crushed gravel, rough aggregate particles with disk shape, medium gradation of the aggregate and 4% of limestone powder content as mineral filler. The results showed in that using of cubical aggregate shape increased each of bulk density, Marshall Stiffness, Marshall Stability, Marshall Quotient, Stiffness Modulus and Indirect Tensile Strength of the mix than the disk and blade shapes while decreased each of flow and air voids. The results also showed that medium gradation of aggregate had good results than the other gradations. By using the rough particles the values of the ITS and stiffness modulus were higher than that using smooth particles.