Asphalt Pavement Technology
Bituminous Mixtures Laboratory (BML)
Equipment | BML Publications
The Bituminous Mixtures Laboratory (BML) specializes in the research of asphalt pavement mixtures. This lab supports FHWA's efforts to develop, evaluate and improve materials, mixture design technology and performance-based tests for asphalt paving mixtures. Like other laboratories at TFHRC, BML's extensive resources and innovative technology are 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. The lab's activities are aimed at extending the life and improving the performance of asphalt pavement, reducing vehicle tear-and wear, and shortening construction delays.
BML's 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.
BML is constantly evaluating new equipment and innovative test procedures used for pavement performance prediction.
Definitions of Pavement Distress
- 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 deform under controlled loads.
- 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.
- 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.
