Correlation between Shape of Aggregate and Mechanical Properties of Asphalt Concrete Digital Image Processing Approach

The importance of the shape of aggregate particles on their mechanical behavior of bituminous materials is well recognized. In asphalt concrete, the shape of aggregate particles affects the durability, workability, shear resistance, tensile strength, stiffness, fatigue response, and optimum binder content of the mixture. In recent years, DIP techniques are widely used to analyze the shape indexes of aggregate. In this study, the shape characteristics such as aspect ratio, elongation, flatness, form factor, roundness, shape factor, and sphericity were determined by DIP technique. The coarse aggregate was proportioned into three size fractions, namely, 19 to 12.5 mm, 12.5 to 9.5 mm, and 9.5 to 4.75 mm. Coarse Aggregate sizes of 19 to 12.5 mm and 12.5 to 9.5 mm were selected by hand as three categories of flat, elongated, and spherical. In addition, a control mixture containing all of aggregate shapes was prepared. ImageJ Java program was used as the image analysis program. This program measures a lot of geometrical values such as area, perimeter, length and angle. Asphalt concrete specimens were fabricated in accordance with ASTM D 1559. Marshall stability and flow values were determined and volumetric properties of all Marshall specimens were calculated. The test results indicated that there is a good correlation between some shape indexes of aggregate and asphalt concrete properties. The DIP was shown to be a useful tool for quantifying the morphological characteristics of coarse aggregates. Therefore, DIP technique proposed in this study may be used instead of some mechanical asphalt concrete tests which are cumbersome and time consuming. However, further studies may lead to use the DIP technique in aggregate quality assurance and quality control procedures and stability and flow values for HMA concrete can be predicted using DIP. It should also be pointed out that further studies on the image analysis system are needed to make more useful and practical method for DIP.