For More Information

Stephen Sebesta
Research Scientist
Flexible Pavements – 304B CE/TTI
Texas A&M Transportation Institute
The Texas A&M University System
3135 TAMU
College Station, TX 77843-3135
Ph. (979) 458-0194 Ext. 80194
s-sebesta@tti.tamu.edu

Lab worker inspecting an asphalt sample core.State-of-the-art laboratories and an extensive array of equipment support TTI’s materials and pavements research. The Materials Laboratory has American Association of State Highway and transportation Officials (AASHTO) Materials Reference Laboratory (AMRL) accreditation and contains an extensive Strategic HIghway Research Program (SHRP) binder and mixture laboratory. Researchers also utilize the Wisenbaker Engineering Research Center (WERC), which contains a large structural test laboratory, several machine/electronic shops, and general purpose labs.

Below are more detailed descriptions of specific facilities.

Equipment

Asphalt Binder and Chemistry Laboratory

Four well-equipped laboratories (approximately 6,000 square feet), known as the Asphalt Binder and Chemistry Laboratory, are devoted exclusively to asphalt chemistry research in the Department of Chemical Engineering. Researchers at the center test properties of asphalt binders, evaluate the change in oxygen content of asphalt after aging, and compute surface tension and contract angle data for fluid-fluid and fluid-solid systems, among other analytical tests. The center is well known for its lab-scale asphalt refinery. Called ROSE (Residual Oil Supercritical Extractor), the refinery is unique in that it enables researchers to make custom research batches of asphalt and test their properties. The department also has a surface characterization laboratory and an analytical laboratory. Equipment and instrumentation in these labs are state of the art and extensive as needed to accommodate a variety of projects.

Asphalt Mixture Testing Laboratory

The TTI Asphalt Mixture Testing Laboratory has a full range of equipment needed for sample preparation and evaluation. The lab has standard capabilities for assessing asphalt mixture characteristics (such as stability and skid resistance) and asphalt cement properties (including viscosity, softening point, and flash point). TTI also has the capabilities for performing the SHRP binder specification tests: bending beam rheometer, dynamic shear rheometer, and Brookfield viscosity. Complete molding and test equipment for Hveem and Marshall testing are available. In addition, a computer-controlled ductility machine enables ductility to be assessed as a function of either rate or force.

The laboratory contains a versatile combination of asphalt compaction devices: three gyrating molding machines, hydraulic and electric-hydraulic kneading compactors, and a European rolling wheel compactor. The latter instrument produces test cores with uniform densities throughout, so deformation behavior is highly realistic. The variety of compaction methods available to TTI researchers enables the generation of asphalt samples that conform to the range of standards of specifications found in the field.

Asphalt Pavement Analyzer

The asphalt pavement analyzer evaluates fatique cracking and rutting susceptibility of asphalt concrete specimens or pavement samples.

Dynamic Shear Rheometer and Bending Beam Tester

In testing asphalt binders, the dynamic shear rheometer and bending beam tester give researchers a master curve of the complete rheological behavior of the binder from plant to pavement.

FISONS Element Analyzer

FISONS measures the percentage of carbon, hydrogen, nitrogen, sulphur, and oxygen in asphalt test samples.

Overlay Tester

Unique to TTI, the overlay tester is used to measure stress and strain for fracture mechanics research and to test new asphalt mixes at very controlled temperatures.

Pressure Aging Vessel

This instrument forces oxygen into asphalt samples at pressures of 300 pounds per square inch (PSI) and high heat to simulate the asphalt aging that would occur in the field over a number of years.

Concrete Laboratory

A fully equipped concrete laboratory tests and evaluates aggregates, cements, and fresh and hardened concrete. It contains three compression testing machines, with maximum capacities ranging from 120,000 to 250,000 pounds.

A cylinder compressometer enables the determination of Poisson’s ratio and modulus of elasticity for concrete compressive cylinders. This information establishes creep curves for high-strength concrete. Multi-position strain gauges and test frames assess concrete creep and shrinkage. The laboratory has a full range of standard equipment to evaluate properties of separate concrete ingredients or batch concrete mixes.

Pavement Non-Destructive Testing Equipment

Pavement Non-Destructive Testing Equipment is a nondestructive geophysical method that “sees” underground and produces a record of subsurface features—without drilling, probing, digging, or coring. Since 1988, researchers at TTI have been developing, testing, and implementing ground-penetrating radar (GPR) technology for TxDOT to use in its road repair and maintenance activities.

Pavement Non-Destructive Testing Equipment operates by transmitting pulses of high-frequency radio waves (electromagnetic energy) into the ground through a transducer or antenna. The transmitted energy is reflected from various buried objects or distinct contrasts between different earth materials. The antenna captures the reflected waves and stores them for subsequent analysis. TTI-developed software (COLORMAP) then converts these signals into information meaningful to engineers. Pavement Non-Destructive Testing Equipment can monitor changes in layer thickness of pavements and detect areas of either trapped moisture or air voids beneath the roadways.

On a national level, the American Association of State Highway and Transportation Officials is beginning efforts to implement use of Pavement Non-Destructive Testing Equipment across the country. Currently, TTI is continuing research and development of Pavement Non-Destructive Testing Equipment use on the state’s highways. Researchers have delivered training courses in numerous TxDOT districts, as well as created analysis software and interactive CD-ROM and web-based training tools for TxDOT personnel. TTI is working with Texas A&M University’s Department of Electrical Engineering to develop and implement more specialized antennas that can provide detail at varying depths. With three Pavement Non-Destructive Testing Equipment systems operating and active, TxDOT and TTI plan to continue supporting the research and working to add more units to the current stock.

Pavement Profiler Evaluation Facility

Located at the Texas A&M Riverside Campus, TTI‘s Pavement Profiler Evaluation Facility was set up to aid in the evaluation, support and implementation of profiling products, technology and initiatives. Initially constructed in 1999, the facility has a 2000-ft long dense-graded hot-mix asphalt (HMA) test track on which inertial profiler certifications are conducted to support state implementation of ride specifications and pavement management activities. With funding from the Federal Highway Administration (FHWA), the Texas Department of Transportation (TxDOT), and the Texas A&M Transportation Institute, two additional test tracks were built in 2013 that added continuously reinforced concrete pavement (CRCP) and open-graded HMA sections on which inertial profiler evaluations may be conducted. In 2015, the Texas A&M Transportation Institute added another section with a stone-matrix asphalt (SMA) surface. Over the years, the facility has been used to test inertial profilers from U.S. state departments of transportation, FHWA, profile equipment manufacturers, and international consulting firms.

Profile Measurement Equipment

Digital surveying equipment and the SurPRO reference profiler are used to maintain reference profiles on the certification test tracks. In addition TTI owns a portable inertial profile measurement system with line lasers for ride quality verifications and profile measurements on research projects.

Soils and Aggregates Laboratory

The Soils and Aggregates Laboratory is equipped with standard as well as advanced soil testing equipment. The following is a sample of the tests that can be performed in the Soils and Aggregates Laboratory and associated laboratories at Texas A&M University.

  • Atterberg limits
  • grain size—sieve analysis
  • grain size—hydrometer analysis
  • laboratory vane shear strength
  • consolidation tests (load step)
  • hydraulic conductivity test
  • triaxial test
  • direct shear test
  • soil suction test
  • cation exchange capacity
  • sodium adsorption ratio
  • pH
  • electrical conductivity
  • pressure plate apparatus
  • special triaxial test for unsaturated soils
  • resonant column test
  • cyclic triaxial test
  • rod shear test

The following is a sample of the tests that can be performed in the field with the in situ testing equipment in the Geotechnical and Geoenvironmental Program at Texas A&M University.

  • drilling rig (Geology Department)
  • standard penetration test
  • Shelby tube sampling
  • cone penetrometer test
  • pressuremeter test (TEXAM, OYO, and PENCELL)
  • self-boring pressuremeter test (TEXAM)
  • borehole shear test
  • crosshole test
  • load cells (100 tons T/C, 400 tons C, 1000 tons C)
  • settlement probe
  • WAK test
  • LATWAK test
  • instrumented hammer test
  • geophone recording

HM-4000 Erosion Function Apparatus (EFA)

In 1991, Jean-Louis Briaud, program manager of the Geotechnical and Geoenvironmental Program at TTI and professor of civil engineering at Texas A&M University, began work on the design of a new device. He hoped to measure the erodibility of soils and rocks, a phenomenon referred to as scour, which occurs due to the erosion of soil around bridge foundations by the action of flowing water. Shortly thereafter, Briaud was joined by Hamn-Ching Chen, a professor of civil engineering at Texas A&M. The purpose of the research, originally sponsored by the Texas Department of Transportation (TxDOT), was to help prevent bridge failures due to the effects of scour.

Predicting the effects of scour is important because out of the 1,000 bridge failures in the United States over the last 30 years, 60 percent were due to scour. Currently, 25,000 bridges in the U.S. are scour critical, meaning their foundations could fail due to erosion.

After a decade of developmental research by the Scour Research Team at TTI, the HM-4000 Erosion Function Apparatus (EFA) is now being manufactured by the Humboldt Manufacturing Company and patented through TTI and the Texas A&M Technology Licencing Office. The EFA is designed to be used in conjunction with the scour rate in cohesive soils (SRICOS) method of scour prediction, a site specific method (also developed at TTI) that involves collecting soil samples and testing them in the EFA.