Overview
In 1999 the research project FA12/94 "Methods to determine the adhesion between pavement layers" has been accomplished. It was found that the shear test according to Leutner was a suitable method to characterise interlayer and in-layer shear properties of asphalt pavements. For pavements with asphalt concrete and SMA wearing courses a value of 21kN was proposed as a requirement immediately after construction. However, since it was not within the scope of that project, the study could not provide information on long-term adhesion properties. The new project is intended to fill that gap by re-evaluating the still existing sections after 10 years of operation.
Goal of the project is the quantitative determination of the development of interlayer adhesion in asphalt pavements during service in order to establish a relationship between test results immediately after construction (contract values) and the adhesion properties during operation (after exposure of the road to traffic and climate). The investigation deals with the properties between and within the wheel tracks.
The examination of the layered composite is carried out as early as the research FA 12/94 using the Shearing test Leutner. Based on changes in the FA 12/94 investigation and the testing of the Swiss standard SN 640 961 while a test temperature is chosen from 25 ° C.
Examines each 5 from the wheel track (trafficked area) and 5 from marginal areas (non-moving energy range) are tested and averaged extracted cores.
Funding
Results
In the framework of this project all remaining sections from FA 12/94 were investigated again, after 10 or more years of trafficking in order to predict the long term performance of the adhesion properties.
After 9 to 13 years of trafficking a minor (min. 7%) or major (45%) improvement of the adhesion shear force between surface and base course could be observed compared to the situation directly after construction.
From 14 investigated sections, only 2 sections showed a decrease in the average shear force between 4.5% and 32%. While it was found that one of these two sections showed severe rutting and an increased shear force outside the wheel path compared to the original value, the other section did not reveal any surface distresses.
In most cases no significant difference between the shear values in and outside the wheel path could be determined. Often the difference was negligible. For the section with SMA surface courses in some cases the value was greater outside, in others inside the wheel path.
Only for the sections with asphalt concrete surface courses was the increase of the adhesion properties in the wheel path by 17% to 39% clearly bigger than outside where the increase was only 5% to 10%.
In cases were the surface course shows problems such as rutting or cracking or was much more distressed in the wheel path compared to outside the wheel path, the average shear forces and/or the shear forces in the wheel path after trafficking were definitely smaller than the shear forces directly after construction.