Effect of aggregate surface texture on performance of asphalt concrete mix

• Main Author: Haidar Ali Mohammad Rashid
• Other Authors: Wong Yiik Diew
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Civil engineering::Construction technology
• Online Access: https://hdl.handle.net/10356/154092
• Institution: Nanyang Technological University

Singapore has one of the fastest-growing economies in the world. Excellent transportation systems and road networks are amongst significant contributors to this huge economic growth. However, with the current global environmental issues, Singapore has chosen to adopt a more sustainable development, and sustainable road pavements are an integral part of this approach as roads occupy 12% of land in Singapore. Steel slag is a by-product of the steel-making process and a source of numerous environmental issues when discarded. A wise approach to deal with this kind of waste is to utilise it in any beneficial process or product. The utilisation of steel slag in road-building applications is present in many parts of the world. In comparison to the utilisation of conventional granite aggregates in Singapore, steel slag offers more advantages. In addition to its comparable strength, steel slag is comparatively more hydrophobic, leading to better adhesion with bitumen. This improved adhesion subsequently improves the moisture resistance of the road pavements constructed with steel slag. Although several studies have considered the performance of steel slag as road paving aggregates, there is still inadequate exploration when determining optimal asphalt concrete mix composition and suitable particle size and surface texture. For example, rough-surfaced aggregates produce high strength mix but at the expense of a higher asphalt binder consumption. On the other hand, smooth-surfaced aggregates offer enhanced workability while also consuming lesser asphalt binder. Given the benefits and drawbacks of the abovementioned examples, one can conclude that the effect of surface texture on the stability of an asphalt concrete mix needs to be established. Therefore, this study evaluates the effects of polished and unpolished steel slags in an asphalt concrete mix used in the road pavements. Two different sets of W3B asphalt concrete wearing courses were subjected to numerous tests to determine the suitability and stability of asphalt concrete mix using polished (treated) and unpolished (raw) steel slag. As it is relied upon regularly in the industry, penetration grade 60/70 (Pen 60/70) binder was used for this project. Before fabrication of the specimens, steel slag was placed into the LA abrasion machine and was subjected to 2,000 revolutions to simulate the wear and tear to the aggregates, after which the specimens were analysed through laboratory tests such as Theoretical Maximum Density, Water Absorption, Marshall test, Moisture Susceptibility test and Indirect Tensile Strength test. These tests were carried out for specimens constructed with unpolished slag as well as specimens of polished steel slag. It was found that smoother surface texture in the aggregates resulted in a drop in performance levels of the asphalt concrete mix. Similar findings were also reported in the works of other researchers working with polished steel slag. Asphalt concrete mix with polished aggregates were found to be more susceptible to water damage as well as to cracking when subjected to cyclic loadings. Despite the tendency of the polished surface to absorb less water, its mechanical properties do not make it a better candidate to be used as aggregates in the road pavements as it would be more prone to moisture damage and cracking.