Abstract
The adhesion bonding between asphalt and aggregate significantly influences field performance and durability of asphalt pavement. Adhesion promoters are typically used to improve asphalt-aggregate bonding and minimize moisture-related pavement damage, such as cracking and raveling. This study evaluated the effectiveness of plant ash byproduct as adhesion promoter to improve asphalt-aggregate adhesion performance. Three commonly used aggregate types (granite, basic rock, and limestone) and two asphalt binder types were used in laboratory testing. A modified stripping test method was developed to evaluate test results with image analysis and measurement of asphalt film thickness. The contact angle test and scanning electron microscopy (SEM) with energy disperse spectroscopy (EDS) were conducted. Test results showed that plant ash lixivium significantly improved asphalt-aggregate adhesion. Among three aggregate types, granite yielded the worst asphalt-aggregate adhesion for both control and treated specimens. The effectiveness of adhesion promotion varied depending on the type of asphalt or aggregate and temperature. The SEM/EDS observations showed that the mesh-like crystalline was formed at the interface between asphalt binder and aggregate in the treated specimen, which was believed to enhance the interfacial bonding and prevent asphalt film peeling off from aggregate.
Highlights
The adhesion strength of asphalt binders is an important parameter for durability of asphalt pavements
Many previous studies have found that the damages of asphalt pavements including cracking, raveling, and permanent deformation are related to the degradation of asphalt-aggregate adhesion strength [4,5,6,7]
The specimens were soaked in the plant ash lixivium for one hour and dried in oven at for two stripping test was conducted on three types of aggregates
Summary
The adhesion strength of asphalt binders is an important parameter for durability of asphalt pavements. To increase asphalt-aggregate adhesion strength and eventually improve the performance and durability of asphalt pavement systems, better understanding of the bonding mechanism and microstructure of asphalt-aggregate interface is needed [8,9]. The exact chemical compositions of plant ash lixivium vary depending on different raw materials (i.e., wheat straw, rice straw, wood straw, and corn cobs) [21,22,23,24]. Plant ash lixivium was proposed to improve the asphalt-aggregate interface adhesion, which is rarely reported in previous literatures. The image analysis was combined with the traditional test in this study to investigate the effectiveness of plant ash treatment on interface bonding. Advanced tests including contact angle test, SEM, and EDS were conducted to evaluate how the plant ash lixivium influence asphalt-aggregate adhesion by directly observing the microstructures of asphalt-aggregate interface zone. The observations can help explain the physicochemical adhesion mechanism of asphalt-aggregate system
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