With innovative and high-performance asphalt mixes such as EME2 and warm-mix asphalt being applied on WA roads, the possibility that these new technologies may not sufficiently bond with adjacent layers is a concern. For a pavement to perform optimally, adjacent pavement layers need to be fully bonded together, otherwise the full structural capacity will not be realised. WARRIP is developing a standard test method that will assess the bond strength between two asphalt layers (new and existing) using the Leutner shear test apparatus. This new test method will be used to investigate the effects of temperature, surface texture and tack coats on bond strength. Developing a standard Main Roads test method is the first step to establishing bond strength limits for pavements in WA and nationally.
Effective bonding of successive layers in full-depth asphalt (FDA) pavements is critical for managing traffic-induced stresses and achieving the expected service life. Main Roads Western Australia (Main Roads) is concerned that adequate bonding between asphalt layers may not be consistently achieved in WA. In the absence of a standard bond strength test, specification and minimum criteria, the aim of this project is to assist Main Roads in the adoption of a reliable method to quantify the bond strength achieved between asphalt layers.
Sufficient bonding between pavement layers is fundamental for achieving good pavement performance. Most
pavement design and evaluation techniques assume that successive pavement layers are fully bonded together, with no displacement between them. However, anecdotal evidence suggests full bond is not always achieved. Theoretical evaluation and research have shown that poor interlayer bonding affects stress/strain distributions within a pavement structure. This reduces the capability of the pavement to support traffic and environmental loadings. West, Zhang and Moore (2005) indicated that a reduction in interface bonding of only 10% could result in a decrease in fatigue life of 50%.
- Literature review of current Australian practice
- Review of Australian and International standard test methods
- Australian Practice – none of the Australian state road agencies currently adopt a test method for assessing the bond strength between asphalt layers. However, most indirectly address the issue through the specification of tack coat application rates.
- Existing Destructive Asphalt Bond Strength Tests – three main types with numerous derivatives including:
- Existing Non-Destructive Asphalt Bond Strength Tests:
- Impulse methods
- Vibration methods
- Sonic/ultrasonic seismic methods
- Thermal methods
WHAT HAVE WE LEARNED?
- Destructive methods are typically used for quality control and for ranking tack coat materials and application rates
- Non-destructive methods are commonly employed for forensic investigation of long lengths of pavement where delamination is suspected. These methods can provide an indication of both the extent and severity of delamination in FDA pavements
- The Leutner shear tester has been recommended for further investigation
- Assessment of standard methods utilising the Leutner shear tester
- Benchmarking the performance of typical FDA pavements in WA
How do results from laboratory tests correlate with field performance?