The Bituminous Mixtures Laboratory (BML) specializes in the research of asphalt pavement mixtures. This laboratory supports the Federal Highway Administration's (FHWA’s) efforts to develop, evaluate, and improve materials, mixture design technology, and performance-based tests for asphalt paving mixtures. The laboratory's activities are aimed at extending the life and improving the performance of asphalt pavement, reducing vehicle wear and tear, and shortening construction delays.
The BML conducts research in areas related to asphaltic materials for highway applications including aggregates, bituminous mixtures, and recycled/reclaimed materials such as reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), and ground tire rubber (GTR). The laboratory includes equipment for generation and characterization of laboratory-produced mixes simulating hot mix asphalt (HMA) and warm mix asphalt (WMA) mixture production and to simulate long-term pavement performance. The laboratory is also equipped to characterize field-core specimens through a variety of innovative testing procedures.
Recent Accomplishments and Contributions
American Association of State Highway and Transportation Officials (AASHTO) Standards
- Improvement and update of AASHTO TP 107 “Determining the Damage Characteristic Curve and Analysis Parameters Using the Asphalt Mixture Performance Tester (AMPT) Cyclic Fatigue Test” (2017).
- Improvement and update of AASHTO TP 378 “Determining the Dynamic Modulus and Flow Number for Asphalt Mixtures Using the Asphalt Mixture Performance Tester (AMPT)” (use of small size specimen part) (2016).
- Currently assisting in development of AASHTO testing standard to characterize the fatigue and stiffness properties of asphalt mixture with small-scale specimen.
Contributions to Forensic Studies
- National Transportation Safety Board (NTSB) TX Field Cores Volumetric Testing (NTSB, 2016).
- Forensic Evaluation of Low Skid Resistance Ultrathin Bonded Wearing Course (Eastern Federal Lands Highway [FLH] Division, 2014).
- Fatigue Properties Characterization of the LTPP SPS 9 Full Depth Asphalt Pavement (FHWA LTPP Program, 2012).
See the Publications page for recent papers and articles.
Recent Research Projects
- Effect of the Asphalt Binder Replacement on the Performance of Asphalt Pavement Containing High RAP and RAS.
A general concern regarding high RAP/RAS mixtures is the possibility of not having enough binder available to properly coat the aggregates. The objective of this study is to examine the effect of added virgin binder on the laboratory performance of high-RAP asphalt mixtures.
- Effect of Inplace Density on the Long-term Performance of Asphalt Pavement.
This ongoing study investigates asphalt-concrete compaction and its impact on performance of pavements built with and without geosynthetic base reinforcement.
- Performance-Based Asphalt Concrete Mixture-Design Framework and Application to Performance-Related Specifications.
This research is to develop a performance-based mix-design framework that can provide guidance on adjusting asphalt materials and designs to achieve required performance targets based on mechanistically predicted performance results that support performance-related specifications for achieving longer life.
- In Situ Performance Characterization with Reduced Scale Dynamic Modulus, Cyclic Direct Tension Fatigue, and Monotonic Direct Tension Tests.
This research aimed to develop fast, simple, and accurate performance tests on the AMPT to quantify cracking resistance of asphalt pavement layers when lift thickness does not allow the full-size geometry to be obtained from construction. Three performance tests—dynamic modulus, cyclic direct tension fatigue, and monotonic direct tension tests—were performed on the small-scale specimens fabricated from the accelerated loading facility (ALF) field cores. The laboratory testing results were compared to the field ALF cracking performance to validate the testing method.
- Using Small-Scale Specimens for AMPT Dynamic Modulus and Fatigue Tests.
This study investigated the feasibility of performing dynamic modulus and fatigue-performance tests using reduced-scale specimens in an AMPT. Performance tests were carried out on small-scale specimens in the AMPT for 10 asphalt mixtures with various nominal maximum aggregate sizes and included both laboratory-prepared and field-cored specimens. The objective of this study was to evaluate AMPT specimen size and geometry effects on dynamic modulus and fatigue to implement the option of small-sample testing to evaluate engineering properties of constructed pavements. This research shows that the small-scale approach is very promising, as it allows the field-compacted fatigue and stiffness characteristics of pavements to be assessed. The applications of this research are field validation of cracking tests, performance-based quality assurance, and forensic investigations.
- Performance Characterization of Asphalt Mixture Containing Re-refined Engine Oil Bottom (REOB) Residue.
This study evaluated a well-controlled group of asphalt binders of the same performance grade (PG) made with a wide range of REOB contents: 0, 2.5, 6, and 15 percent. The most practical indicator of the possible presence of a considerable quantity of REOB with measurable changes to the rheological and performance characteristics was the difference between the bending beam rheometer (BBR) m-value temperature grade and the BBR S stiffness temperature grade, ΔTC. When a binder exhibited a large ΔTC, it was associated with larger differences in performance losses depending on the binder tests, and to a lesser extent the mixture test. The ΔTC-performance disruption was made worse by oxidative aging by means of double pressure aging vessel (PAV) conditioning as well as holding the binder at extended low temperatures before testing. The impact of REOB on moisture damage resistance showed higher moisture sensitivity with increasing REOB content, but did not interfere with liquid antistrip additives. Mixture cracking tests results were mixed. Low-temperature relaxation, strength, and fracture measured with Thermal Stress Restrained Specimen Test (TSRST) showed the fracture strength had slight increases or decreases with 2.5 and 6 percent REOB and could be interpreted as unaffected. Aging also improved the average strength of these mixes. However, the strength of the highest 15 percent REOB mix was measurably decreased and made worse by aging. The impact of REOB on intermediate temperature fatigue-cracking performance depended on the aging condition and whether stress-control or strain-control performance was considered.
- Full-Scale and Laboratory Performance Testing for Asphalt Pavement with High RAP and WMA.
This research project aimed to quantify cracking resistance of high RAP/RAS mixtures that use lower temperature production with WMA and to investigate limitations and provide recommendations for combining the two technologies. Ten test lanes were built in 2013 at the ALF. RAP contents provided up to 40 percent recycled binder ratio (RBR) in both HMA and WMA reduced-temperature production. RAS has been incorporated to provide 20 percent RBR in HMA. The objective of the experiment was to establish realistic boundaries for high-RAP and RAS mixtures employing WMA technologies based on percent-binder replacement and binder-grade changes. A longer-term objective is to evaluate the impact of field aging on material properties of the mixtures and to populate nationally developed aging models.
The laboratory is equipped to perform mixture designs and test asphalt mixtures for density, moisture susceptibility, dynamic modulus, and to capture various modes of distress. Extraction and recovery of binders and aggregates from asphalt mixtures can be performed to enable examination of the components. Aggregates can be tested for properties such as gradation, specific gravity, abrasion resistance, shape, form, and texture. Recovered binders, on the other hand, can be tested in the Binder Laboratory and in the Chemistry Laboratory.
Some of the basic and specialized laboratory services include, but are not limited to:
- Mixture design and material-characterization testing.
- Evaluation of inservice asphalt-pavement performance.
- Implementation of new technology.
- Forensic analysis.
- Technical assistance.
- Research advice.
A detailed list can be found on the lab’s equipment page.
The publications page provides citations for all reports and papers from the lab.