U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


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Bituminous Mixtures Laboratory

 

Laboratory Purpose: The Bituminous Mixtures Laboratory specializes in the research of asphalt pavement mixtures. This laboratory supports Federal Highway Administration'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 weather 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 measured engineering properties and 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 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, abrasion resistance, and  shape, form and texture. Binders, on the other hand, can be tested and characterized according to standard or Superpave procedures in the Binder Rheology Laboratory.

The Bituminous Mixtures Laboratory is constantly evaluating new equipment and innovative test procedures used for pavement performance prediction for the following distresses:

  1. Rutting. Longitudinal surface depressions running along a pavement's wheel paths. These depressions may be due to deformations in an asphalt pavement layer, an underlying layer, or in multiple layers. Tests used in the Bituminous Mixtures Laboratory evaluate the susceptibility of asphalt mixtures to resist accumulated plastic deformations deform under controlled loads.
  2. Fatigue Cracking. Jagged cracks in an asphalt pavement layer that eventually interconnect to form a pattern often referred to as "alligator cracking." These cracks are caused by repeated traffic loads flexing the asphalt pavement layer.
  3. Thermal Cracking. Transverse and longitudinal cracks caused by the contraction and buildup of stresses in an asphalt pavement layer with decreasing temperature. Most of these cracks are uniformly spaced. (Transverse and longitudinal cracks may be caused by other mechanisms as well.) Cracking may result from temperature cycling or from a single temperature drop, also known as low temperature cracking.

 

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 Gyratory Compactor (SGC)

Asphalt Mixture Performance Tester (AMPT) - The AMPT is a testing machine specifically designed to measure asphalt mixture engineering properties. It is a compact servo-hydraulic testing machine that was developed through work completed under National Cooperative Highway Research Program (NCHRP) Projects 9-19, Superpave Support and Performance Models Management, and 9-29, Simple Performance Tester for Superpave Mix Design. With the AMPT, a mixture’s rutting resistance can be quickly evaluated using the flow number test. The AMPT also greatly simplifies the development of dynamic modulus master curves needed for pavement structural design using the AASHTOWare® Pavement ME Design (formerly DARWin-ME™) Pavement Design and Analysis Software. In addition to the flow number and the dynamic modulus tests, which have been standardized, work is currently underway to develop and standardize a direct tension fatigue test for the AMPT that can be used to evaluate the resistance of a mixture to fatigue and top down cracking.

Asphalt Mixture Performance Tester (AMPT)

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 Shear Tester (SST)

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.

Laboratoire Central des Ponts et Chaussees (LCPC) Pavement Rutting Tester

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.

Hamburg Wheel-Tracking Device

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.

Linear Kneading Compactor

LCPC Thermoregulated Mixer - Can mix up to 80 kg of asphalt paving mixture in a single batch at temperatures up to 240 °C.

LCPC Thermoregulated Mixer

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)

Temperature Stress Restrained Specimen Test (TSRST)

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.

MTS(r) Servo-Hydraulic Testing System

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.

 

 

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
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