Effects of aggregates' shape properties on the packing structure of porous asphalt mixture (PAM) by utilising designed aggregates

• Main Author: Yoong, Daryl Wen Kiat
• Other Authors: Wong Yiik Diew
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/138129
• Institution: Nanyang Technological University

In natural aggregates, the particle shape is dependent on the nature of the rock and crushing process which affect the properties of PAM. However, due to the lack of variation in the shape properties in the natural aggregates, the relationship between the packing structure of PAM and specific shape properties is not well established. Therefore, the project aims to study the relationship between the packing structure of PAM and aggregate shape properties (sphericity) by introducing artificially-designed metal aggregates of various shapes such as sphere, cube and cylinder. As a preliminary study, five aggregate gradations (Gradation A, B, C, D and E) with different specifications were analysed to identify the recommended PAM gradation. The selected gradation was used for the incorporation of artificially-designed metal aggregates. The gradations were analysed through experimental tests on Marshall Stability, Dynamic Creep, Indirect Tensile Stress and Water Permeability. The gradations were ranked according to their performance in each respective test to identify the recommended PAM gradation. After implementing a point system method, Gradation C was selected as the recommended PAM gradation to be used in the main study. In the main study, artificially-designed metal aggregates were introduced into the PAM to evaluate the relationship between aggregate shape properties (sphericity) and the packing structure of PAM. The three shapes evaluated were the sphere, cube and cylinder. The PAM specimens were evaluated based on the four experimental tests used in the preliminary study. The results from the main study showed that cube outperformed sphere and cylinder in all the experimental tests. It was also shown that a lower sphericity value is correlated to better performance in the experimental tests. Lower sphericity value implies that the shape resembles less that of a sphere and has more edges on the surface of the particle. This promotes better interlocking between aggregates which leads to a more compact packing structure in the PAM. Hence, it can be concluded that resilient modulus and stability properties of the PAM are improved when aggregates of lower sphericity value are used.