Asphalt Binder and Mixtures Laboratory Overview
The Asphalt Binder and Mixtures Laboratory (ABML) conducts research on physical properties of paving materials such as flow, deformation, and fracture. The laboratory's primary mission is to characterize properly the behavior of paving materials such as asphalt binder and fine aggregate mastic containing asphalt binders.
The ABML has been housed at TFHRC since the 1950s. The 2,500 square-foot laboratory is comprised of state-of-the-art asphalt binder and mixture laboratories, is an active domestic and international collaborator, and is world-renowned for its unbiased research findings. The activities of the ABML are focused on research and implementation.
The ABML is equipped to evaluate the strength, stiffness, and ductility of paving materials and emerging test methods. Work conducted in the laboratory provides the basis for developing or advancing material specifications (e.g., the Superpave performance-based binder specifications) that enable improvement of the durability, longevity, quality, and cost-effectiveness of pavements. Research conducted in this laboratory is in collaboration with one or more of the other Infrastructure materials laboratories.
Recent Accomplishments and Contributions
Development of the Double-Edge-Notched-Tension (DENT) Test
Summary: This method uses the essential work of fracture approach and has a long history of applications in the failure characterization of ductile materials such as plastics, certain metals, and composite materials. Nonlinear fracture mechanics studies showed that the essential work of fracture approach can be used to provide a critical strain tolerance/parameter of a wide range of materials. The test can be used for the fatigue performance characterization of asphalt materials as it replicates the mechanics of failure in ductile materials. In the case of extensive ductility, the fracture process is controlled by a continuous flow of energy through the plastic deformation region to the fracture region that progressively reduces the energy release rate in the fracture zone. During the testing, the energy partition between a plastic outer zone and an autonomous inner zone that is responsible for fracture is effectively measured. The ratio of the specific essential work of failure and the yield stress of the material (approximated during the testing from the peak loads of the tested samples), can be considered a material parameter. The strain tolerance was validated as a criterion for fatigue performance using the field performance of pavements at the Turner-Fairbank Highway Research Center (TFHRC), Accelerated Pavement Facility (ALF).
Performance Evaluation of Recycled Engine Oil Bottom (REOB) Modified Asphalt Binders and Mixtures
Summary: Following a growing concern from States departments of transportations (DOTs) and other stakeholders, a comprehensive study of REOB-modified pavement materials was initiated. The efficiency of REOB modification in relation to the performance grade (PG) of various binders was evaluated. Special effort was allocated to produce modified binders having various degrees of REOB modification within the same commercial PG. The materials were evaluated for various parameters: fatigue, rutting, low temperature cracking, etc. The binder testing results were correlated with the mixtures testing results for clarity. The study provided data used in the development of guidelines for the use of the REOB modifier.
The ABML is equipped with state-of-the-art rheology instrumentation and the latest asphalt binder test equipment. The Binder Laboratory is an American Association of State Highway and Transportation Officials (AASHTO)-accredited laboratory.
Some of the basic and specialized laboratory services include, but are not limited to:
- Material testing.
- Forensic analysis.
- Technical assistance.
- Research advice.
- Quality assurance.
- Participation in round robin testing.
- Material and test method evaluations.
The ABML operates an array of specialized instruments: Dynamic Shear Rheometers, Bending Beam Rheometer, Asphalt Binder Cracking Device, Ductility Meter DDA-3, Pressure Aging Vessel, Rolling Thin Film Oven, Rotational Viscometer, Evaporative Recovery of Bituminous Emulsions, Asphalt Binder Quality Control Tester (ABQT). These instruments are maintained and calibrated in accordance with the industry norms and regulations and the AASHTO-sanctioned quality control manual.
Dynamic Shear Rheometers (figure 1) are used for rheological characterization of paving asphalts in the intermediate to high temperatures ranging from 42° F (7° C) to temperatures approaching 212° F (100 °C). The Rotational Viscometer (figure 2) is used to determine the rotational viscosity of asphalt binders at temperatures above 212° F (100° C), such as 240° F (115° C) to 424° F (220° C).
Figure 1. Dynamic Shear Rheometer (DSR).
Figure 2. Rotational Viscometer.
The Rolling Thin Film Oven (figure 3) is used with the Pressure Aging Vessel (figure 4) to simulate construction related and long-term aging of asphalts. Rheological properties of asphalt binders provide some indication of pavement conditions after years of service.
Figure 3. Rolling Thin Film Oven.
Figure 4. Pressure Aging Vessel (PAV).
Fracture Related and Fracture Testing
The Ductility Meter DDA-3 Instrument (figure 5) is being advanced to determine the strain tolerance of binders at intermediate temperatures with the Double Edge Notch Test (DENT). The binder strain tolerance in the ductile state has been found to be a good indicator for fatigue performance. The Bending Beam Rheometer (figure 6) and the Asphalt Binder Cracking Device (ABCD) (figure 7) are used to determine the low-temperature (thermal) cracking temperatures of asphalts. The ABCD is used to determine the low-temperature cracking temperature for asphalt binders. The residue of emulsified asphalts for pavement layer bonding tack coats and pavement preservation treatments can be recovered with updated methodologies and characterized with performance grading instruments.
Figure 5. Ductility Meter (DDA-3).
Figure 6. Bending Beam Rheometer (BBR).
Figure 7. Asphalt Binder Cracking Device (ABCD).
Quality Control Testing
The ABT (figure 8) was developed in partnership with Laser Technology, Inc. (LTI) to be used by transportation agencies and asphalt mix producers in the field to quickly and accurately assure they are getting the right asphalt binders grade specified for highway construction. The ABT device tests samples of asphalt binder using an air jet to deform the sample. The resulting deformation and recovery of the asphalt binder is then measured using a laser deflectometer. Only unaged asphalt binders are required for the ABT. The maximum creep deflection and percent recovery values are determined using the ABT. These two parameters may then be used in Quality Control (QC) of asphalt binders. The QC use is designed to help asphalt-producers, users, and suppliers maintain consistent quality during production and use. Additional data generated from the creep and recovery curve is used in predicting the PG of asphalt binder that is tested. The prediction of PG allows DOTs to rapidly determine compliance to PG during the paving season.
Figure 8. Asphalt Binder Tester (ABT).