| The purpose of this study was to develop an approach to study the fracture or adherenceenergy of asphalt using an Atomic Force Microscope (AFM) with respect to sample filmthickness and loading rate. The focus of the study was based on pull-off experimentsperformed within a micro-grid of asphalt phase in order to determine micromechanicalproperties such as adhesion. The materials used in this study included asphalt AAA, AAD andAAM from the Materials Reference Library (MRL) of the Strategic Highway ResearchProgram (SHRP), chosen due to variations in crude source, chemical composition andelemental analysis for each asphalt type. Data analysis and information collected during thisstudy met expectations.A new FD-AFM test was used to study the work of adhesion and adherence energy ofasphalt as a function of film thickness and pull-off rate. Different samples of various filmthicknesses were prepared, and then tested with FD-AFM. Data were recorded and analyzedby regression analysis to derive adherence energy, which is a function of reversible work ofadhesion and dissipated (plastic flow) energy.For AAA the average work of adhesion for all three film thicknesses was measured to be65±3mJ/m2. For AAD the average work of adhesion for all three film thicknesses wasmeasured to be71±3mJ/m2. For AAM the average work of adhesion for all three filmthicknesses was measured to be89±2mJ/m2.AAA exhibited lowest work of adhesion but high plastic (dissipation) energy as afunction of rate. AAD and AAM had higher work of adhesion values but lower plastic(dissipation) energy as function of rate. AAD and AAM also showed less dependence of filmthickness on changing adherence energy as compared to AAA. It was also observed thatasphalts with higher work of adhesion values were also higher in viscosity. It was speculated that AAA may be a better fracture resistant asphalt compared to AAD and AAMbased on the assumption that it had higher plastic (dissipation) energy. |
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