United States Department of Transportation
i
Adhesion testing procedure for hot-poured crack sealants.
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2008-11-01
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[PDF-1.36 MB]
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Abstract:Crack sealing is a common pavement maintenance treatment because it extends pavement service life significantly.
However, crack sealant often fails prematurely due to a loss of adhesion. Because current test methods are mostly
empirical and only provide a qualitative measure of bond strength, they cannot predict sealant adhesive failure accurately.
Hence, there is an urgent need for test methods based on bituminous sealant rheology that can better predict sealant field
performance. This study introduces three laboratory tests aimed to assess the bond property of hot-poured crack sealant to
pavement crack walls. The three tests are designed to serve the respective needs of producers, engineers, and
researchers. The first test implements the principle of surface energy to measure the thermodynamic work of adhesion,
which is the energy spent in separating the two materials at the interface. The work of adhesion is reported as a measure of
material compatibility at an interface. The second test is a direct adhesion test, a mechanical test which is designed to
closely resemble both the installation process and the crack expansion due to thermal loading. This test uses the Direct
Tensile Test (DTT) machine. The principle of the test is to apply a tensile force to detach the sealant from its aggregate
counterpart. The maximum load, Pmax, and the energy to separation, E, are calculated and reported to indicate interface
bonding. The third test implements the principles of fracture mechanics in a pressurized circular blister test. The apparatus
is specifically designed to conduct the test for bituminous crack sealant, asphalt binder, or other bitumen-based materials.
In this test, a fluid is injected at a constant rate at the interface between the substrate (aggregate or a standard material)
and the adhesive (crack sealant) to create a blister. The fluid pressure and blister height are measured as functions of time;
the data is used to calculate Interfacial Fracture Energy (IFE), which is a fundamental property that can be used to predict
adhesion. The stable interface debonding process makes this test attractive. This test may also provide a means to quantify
other factors, such as the moisture susceptibility of a bond. In addition, the elastic modulus of the sealant and its residual
stresses can be determined analytically. While the direct adhesion test is proposed as part of a newly developed
performance-based guideline for the selection of hot-poured crack sealant, the blister test can be used to estimate the
optimum annealing time and installation temperature.
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