June 1, 2008
A Federal Highway Administration (FHWA) grant will help move a prototype system
that analyzes the properties of aggregates used in pavement closer to market,
making specification of paving materials that enhance roadway durability and
skid-resistance more reliable.
FHWA awarded $200,000 to Pine Instrument Co. of
Grove City, Pa., to refine and test its aggregate imaging system,
which combines hardware that captures digital images of aggregate
samples and software that analyzes characteristics — such as shape
and texture — that affect pavement quality.
The grant was one of five awarded under the
agency’s Technology Partnerships Program, which encourages industry
to develop technologies now at the prototype stage in partnership
with transportation agencies. The goal is to test promising
innovations designed to improve highway quality and safety or reduce
congestion in real-world settings and help make them commercially
“Through the Technology Partnerships Program,
we’re working to accelerate private sector engagement in addressing
the challenges of building and maintaining the nation’s highway
system,” says FHWA Associate Administrator King W. Gee. “Industry
innovation is essential to meeting the demands of roadway users for
quality and safety.”
Research has shown that the characteristics of
aggregates used in hot-mix asphalt, hydraulic cement concrete, and
unbound aggregate pavement layers influence the structural integrity
and durability of pavement systems. These also affect the skid
resistance of pavement surfaces.
Key aggregate characteristics include shape,
such as round, elliptical or flat; angularity, the sharpness of the
corners of the aggregate particles; and texture, the smoothness or
roughness of the particle surfaces. Accurate characterization of
these properties — which vary with the type and source of aggregates
and processing techniques — can improve specifications for projects
and ultimately boost pavement performance and driver safety.
Manual methods now used to measure these
characteristics can be time consuming and subjective, according to
Richard Meininger, FHWA research highway engineer. That can lead to
inconsistencies in measurement, quality assurance and mix design.
The number of flat and elongated particles, for
example, characterizes coarse aggregate shape. The angularity of
gravel is determined by counting the number of particles with one or
two crushed faces. Fine aggregate angularity is assessed by
measuring the void percentage of an aggregate sample as it flows
through a funnel.
A “National Cooperative Highway Research
Program” study, described in “Test Methods for Characterizing
Aggregate Shape, Texture and Angularity (NCHRP Report
555),”evaluated emerging test methods for measuring aggregate
characteristics. The analysis looked at factors such as accuracy,
cost, ease of use, and readiness for implementation.
The study recommended Pine Instrument’s
aggregate imaging system, or AIMS, for its ability to characterize
both fine and coarse aggregates and its ease of use in central and
field laboratories. The AIMS research prototype was developed in
collaboration with NCHRP’s IDEA (Innovations Deserving Exploratory
Analysis) program and FHWA.
“AIMS allows the comparison of aggregates with
a scientifically based system,” Meininger says. “It measures
aggregates in a non-biased way.”
Researchers tested an AIMS prototype at the
Texas Department of Transportation and FHWA’s mobile asphalt
materials testing laboratory. The mobile lab demonstrated how AIMS
can be used to classify aggregate stockpiles for form, angularity
and texture and its potential to replace aggregate consensus
property test procedures for Superpave asphalt mix design with an
automated, repeatable method that provides similar data, says
Matthew Corrigan, mobile lab project manager.
The mobile lab has an ongoing project to
collect AIMS data on a variety of aggregate sources used in asphalt
pavements throughout the United States, Corrigan explains. Future
plans call for linking AIMS aggregate data with asphalt pavement
performance in the field and recommending which aggregate properties
are the best indicators for long-life asphalt pavements.
The AIMS system works by capturing digital
images of the particles in an aggregate sample, analyzing the
sample, and providing a graphical output of characteristics. The
system’s software uses a series of analysis algorithms that
objectively quantify aggregate properties on both the macro scale,
such as shape and angularity, and the micro scale, such as surface
The system uses computer digital images to
measure the shape and angularity of individual particles from their
silhouette outline and focal depth, and the texture of coarse
aggregates from the gray-scale images of aggregate surfaces. The
system’s software allows characterization of the distribution of
shape and angularity for correlation with performance in pavement
With the help of FHWA’s grant, Pine Instrument
is now turning the prototype into a user-friendly, industry-ready
product. In phase one of the project, the company is converting the
collection of components that make up the research prototype to an
integrated hardware system. It also is enhancing the analysis
software to make results easier for AIMS users to interpret.
The combined hardware/software system will
undergo a standard ruggedness study at Texas A&M University, a
partner in the project, to determine how a variety of variables
impact results, said Roger Pyle, Pine Instrument’s director of
The project’s second phase will involve tests
at university, commercial and highway agency laboratories to
establish the repeatability and reproducibility of AIMS results in a
multi-laboratory environment. Texas A&M will analyze the data from
“It’s important to have an understanding of how
reproducible the output from the system is,” Pyle says. “We want to
determine how closely the results will match when one aggregate
supplier evaluates a product with one AIMS system and another lab
uses a different system.”
The planned outcome is an industry tool capable
of accurately and rapidly measuring aggregate shape characteristics.
Such a tool would offer an automated method of qualifying aggregate
shape properties and surface texture to meet specifications, ensure
good pavement performance and enhance roadway safety. The ultimate
goal of this whole process is to develop a commercially available
In addition to AIMS, research is under way on
other methods for measuring aggregate characteristics. One uses
X-ray tomography, an imaging method widely used for medical
applications, to obtain detailed, three-dimensional information on
aggregates. Both the National Institute of Standards and
Technology’s Virtual Cement and Concrete Testing Laboratory and
FHWA’s Turner-Fairbank Highway Research Center are conducting
studies using this method.
Another method uses high-resolution laser
detection and ranging (LADAR) technology to provide
three-dimensional measurements of aggregates from which quantitative
characteristics can be calculated. LADAR consists of a photon
source, a photon detection system, a timing circuit, and optics for
the source and receiver. An NCHRP project is developing a LADAR
system capable of precisely measuring aggregate characteristics such
as shape, volume, angularity, and surface texture.
Eventually, research efforts to better
characterize aggregate properties may lead to more precise
specifications for aggregate use on highway construction projects
and better quality control tools for aggregate producers. “Once we
have good aggregate measures that people can have confidence in, we
can come up with more classes of materials and be more specific
about what’s needed for a particular application,” Meininger says.
Better measurement techniques may also increase
the use of local aggregates on construction projects. Aggregates for
U.S. projects are now transported from as far away as Canada and
Mexico, which increases costs and has environmental consequences.
“If local materials can be better characterized in shape, texture
and angularity and qualified in terms of durability, they can be
used instead,” Meininger says.
Improving aggregate measurement and
characterization techniques is just part of the equation, though.
More research is also needed on how aggregate shape characteristics
relate to pavement performance, Meininger notes. “Once we have a
better understanding of that, we can develop better specifications,”
The Technology Partnerships awards are the
first grants FHWA has ever provided directly to general industry.
Other companies received grants to refine and test an asphalt
binder-cracking device, an intelligent asphalt compaction analyzer,
an all-weather pavement marking system for work zones and an
automated pavement marker placement system.
FHWA is considering a second Technology
Partnerships Request for Applications in June 2008. For more
information on the Technology Partnerships Program or on
participating in tests of the technologies, contact Julie Zirlin,
Technology Partnerships Program Manager, at 202-366-9105 or
To view presentations and videos on how the
technologies work and to sign up for e-mail notification of the
projects’ progress, visit
For more information on Pine Instrument’s
aggregate imaging system, contact Dave Savage at 724-458-6391 or
For more information on FHWA’s mobile asphalt
materials testing laboratory, visit
contact Matthew Corrigan at
(Source: Federal Highway Administration)
Photo Credit: Pine