Refining AIMS

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
texture.

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
layers.

The commercial AIMS, shown in this conceptualized rendering, will be an integrated hardware/software system.

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
product technology.

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
those tests.

“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
product.

A future look

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.

AIMS characterizes aggregate shape properties, which influence pavement performance.

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,”
he says.