Testing Methods
Dynamic Shear Rheometer -- DSR
The DSR uses parallel plate geometry with 25 mm (neat binder & rtfo residue) or 8 mm (pav residue) diameter, circular plates for SHRP testing. Asphalt binder response to shear is dependent on the rate and time of loading. These specifications ensure that at upper in service temperatures, the AC will provide pavement with the necessary resistance to rutting and shoving. The DSR analysis correlates (approximately) to a tire traveling over pavement at 55 mph under actual service conditions.
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Rolling Thin-Film Oven -- RTFO
The Superpave test schedule employs the RTFO conditioning procedure to simulate the effects experienced by AC during plant mixing. By comparing results obtained for analysis of the un-aged binder with those for the RTFO residue, changes to the AC properties during mixing may be determined
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Bending Beam Rheometer -- BBR
The Superpave testing schedule uses BBR analysis to determine the low temperature performance grade of AC. Small rectangular beams of known dimensions are cast in molds using hot AC and allowed to set for one hour. Prior to de-molding beams excess binder is shaved from molds. Beams are then conditioned at test temperature in the instruments constant temperature bath for one additional hour prior to analysis. The maximum bending stress in the beam is divided by the maximum bending strain to determine the flexural creep stiffness of the AC sample at a given temperature.
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Pressurized Aging Vessel -- PAV
The Superpave program uses the pressurized aging vessel to simulate the effects experienced by in service AC. Twenty hours of PAV conditioning at 2.1 MPa (305 psi) and temperatures ranging from 90 – 110 °C (depending on AC grade) is equivalent to approximately 5 – 7 years of in service aging and oxidation.
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Direct Tension Test
The Direct Tension Test is used to investigate thermal strain due to contraction at low temperatures. Thermal Stress Analysis (TSAR) software uses results of DTT and BBR AC analysis to determine the Critical Cracking Temperature of pavement.
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