Abstract
Properties such as durability and moisture resistance of asphalt concrete significantly improve pavement service life. When siliceous aggregate is used, then preventing moisture damage and stripping become distinctly required. Typically, stripping could be prevented by either using antistripping agents or by modifying the binders. The anti-stripping agent achieve its purpose by changing the aggregates' affinity for water through changing the zeta potential (promote bitumen adsorption due to negative surface charge). On the other hand, modifications of binders promote interface bonding between aggregate particles and bitumen. However, the process of applying anti-stripping agents or adhesion promoters is typically costly and, in some cases, may negatively impact other performance characteristics of pavement. Accordingly, this paper examines the merit of applying natural bitumen (gilsonite) instead of typically used anti-stripping chemicals in order to both promote resistance to moisture damage and reduce construction cost in asphalt. In addition to being quite low-cost, Gilsonite has a chemical composition nearly similar to that of petroleum based asphalt which makes it very compatible with asphalt binder.
Highlights
Moisture-induced damage is one of the main distresses of flexible pavement
There are many similarities between functional groups of gilsonite powder and neat bitumen. This result conforms to the gilsonite formation hypothesis which states that gilsonite is a natural bitumen-based material (Ameri et al, 2011)
It can be stated that an increase in gilsonite content increases Indirect Tensile Strength (ITS) values generally, there is no straight-line relationship between values
Summary
Moisture-induced damage is one of the main distresses of flexible pavement. The main mechanism of this distress is due to de-bonding of bitumen and aggregates caused by the presence of water. Since natural bitumen (gilsonite) has a significant amount of polar components, including asphaltene and resins (Nader et al, 2014), this study examined its effectiveness relative to commonly used additives (such as lime) to improve bitumen-aggregate adhesion strength, when exposed to water. The results of research conducted by Kök et al (2011) have shown that increasing the gilsonite content improves resistance to rutting They concluded that application of gilsonite has an effect on hightemperature performance of bitumen similar to that of polymers such as Styrene-Butadiene-Styrene (SBS). Huang et al (2005) used gilsonite as an intermediate layer to reduce stress concentration This way, asphalt concrete acts as a threelayered composite mixture in which coarse aggregates are coated with a thin film of stiff gilsonite before being mixed with the bitumen. Optimum bitumen content for an unmodified mixture was determined according to the Superpave mix design, assuming a design high air temperature of 39-40°C
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