Laboratory Purpose: The Bituminous Mixtures Laboratory specializes in the research of asphalt pavement mixtures. This laboratory supports 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 tear-and wear, and shortening construction delays.
Laboratory Capabilities: The Bituminous Mixtures Laboratory advanced technology allows researchers to anticipate potential long-term pavement damage and to optimize asphalt mixtures for specific applications. Accelerated testers, for example, may simulate the distress caused by many years of exposure to traffic and adverse weather conditions within a matter of hours by applying combined load, temperature, and humidity factors on asphalt pavement mixtures. Consequently, mixtures with few or no signs of damage can be selected for reliable, long-term highway use. Fundamental mechanical testers, on the other hand, allow pavement technologists to optimize the components of asphalt mixtures based on performance prediction models. These testers measure fundamental properties such as strength and stress-strain behavior, which can be used in performance prediction models to define the behavior of asphalt pavements under various loads, traffic speeds, and weather conditions.
The laboratory has the capability of performing mixture designs and testing asphalt mixtures for density, moisture susceptibility, and resilient modulus. Extraction and recovery of asphalt binders and aggregates may be performed on the mixtures. Aggregates can be tested for properties such as gradation, specific gravity, and sulfate soundness. Binders, on the other hand, can be tested and characterized according to standard or Superpave procedures.
The Bituminous Mixtures Laboratory is constantly evaluating new equipment and innovative test procedures used for pavement performance prediction. Definitions of pavement distress include the following:
Laboratory Services: The Bituminous Mixtures Laboratory is used to assist FHWA field offices, State highway agencies, and the pavement community in general in the design of asphalt mixtures, evaluation of in-service asphalt pavement performance and implementation of new technology.
Equipment: The Bituminous Mixtures Laboratory contains the following equipment.
SUPERPAVE Gyratory Compactor (SGC) - Simulates the kneading action of rollers used to compact asphalt concrete pavements by applying a vertical load to an asphalt mixture while gyrating a mold tilted at a specified angle. SGC is the new equipment used in volumetric pavement design. Specimens produced by this compactor can be used in the Superpave SST and IDT. (AASHTO T312)
SUPERPAVE Shear Tester (SST) - Used to evaluate permanent deformation (rutting) and fatigue cracking susceptibilities in asphalt mixtures. It provides vertical and horizontal loads to a cylindrical specimen in various confining conditions and at different temperatures. The data is used in models that predict pavement performance. (AASHTO TP7)
SUPERPAVE Indirect Tensile Test (IDT) - Evaluates the thermal cracking susceptibility of asphalt mixtures. It loads a cylindrical asphalt concrete specimen through its diametrical axis, and the resulting deformations are used to determine the viscoelastic material properties used in models that predict pavement performance. (AASHTO TP9)
Laboratoire Central des Ponts et Chaussees (LCPC) Pavement Rutting Tester - Measures the rutting susceptibility of asphalt paving mixtures using a reciprocating, pneumatic rubber tire. Slabs of asphalt concrete can be tested at temperatures ranging from 30° C to 70 °C. Rutting susceptibility is based on pass/fail criteria. This machine is used in France to evaluate mixtures that either have no performance history or will be subjected to heavy traffic.
Hamburg Wheel-Tracking Device - Measures the rutting and moisture susceptibility of an asphalt paving mixture by rolling a steel wheel across the surface of an asphalt concrete slab that is immersed in hot water (generally held at 50 °C.) Susceptibilities to rutting and moisture are based on pass/fail criteria.
Linear Kneading Compactor - Used to compact asphalt paving mixtures into slabs needed for various mixture testing devices. The mixture is placed in a mold and loaded through a series of vertically aligned steel plates that compress the asphalt mixture into a flat slab of predetermined thickness and density.
LCPC Plate Compactor - Uses a reciprocating rubber tire to compact asphalt paving mixtures. It is primarily used to fabricate slabs needed for the LCPC Pavement Rutting Tester.
LCPC Thermoregulated Mixer - Can mix up to 80 kg of asphalt paving mixture in a single batch at temperatures up to 240 °C.
Temperature Stress Restrained Specimen Test (TSRST) - Evaluates the low temperature cracking susceptibility of asphalt paving mixtures. The device cools down a beam specimen while restraining it from contracting. As the temperature drops, thermal stresses build up until the specimen fractures. (AASHTO TP10)
Georgia Loaded-Wheel Tester - Measures the rutting susceptibility of asphalt paving mixtures by rolling a steel wheel across a pressurized hose positioned on top of a beam specimen at 40.6 °C. Rutting susceptibility is based on pass/fail criteria.
Laboratoire Central des Ponts et Chaussees (LCPC) Gyratory Shear Compacting Press - Used to preevaluate mixtures for resistance to permanent deformation and to evaluate the workability of an asphalt mixture.
Army Corps of Engineers Gyratory Testing Machine (GTM) - It is a combined compactor and plane strain shear testing machine for soils, unbound aggregates, and asphalt paving mixtures. It applies a stress equal to that applied by a truck tire on the pavement while monitoring the shear strain of the material. The data is used for mixture design and evaluation of rutting susceptibility. (ASTM D 3387)
California Kneading Compactor - Used to fabricate asphalt concrete specimens of various sizes and shapes, including beams for flexural fatigue cracking tests. It simulates the kneading action of pavement rollers by using a steel kneading foot to compact only one portion of the mixture at a time. (ASTM D 1561)
Marshall Mixture Design Equipment - Consists of a Marshall hammer compactor and a Marshall flow and stability testing machine. It has been widely used for more than 40 years to design asphalt mixtures. The procedure is currently being phased out by Superpave. (AASHTO T245)
MTS(r) Servo-Hydraulic Testing System - Performs strength, creep, stress relaxation, and repeated load tests at controlled temperatures. Relationships between mixture properties and pavement distresses can be determined based on the test results. This all-purpose testing system has been fitted recently with a high- pressure triaxial cell that can simulate a pavement's changing stresses as a wheel moves over it.
CS 7600(r) Beam Fatigue Fixture - Used to predict fatigue cracking due to flexure. The MTS(r) is used to apply the loads and acquire the data. (AASHTO TP8)
Laser Particle Size Analyzer - Determines the gradation of materials, such as fine aggregates, that range in size from 0.0001 to 2.0 mm. Material densities are determined using a helium pycnometer.
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Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101-2296
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