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
viable.

“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.”

Boosting pavement performance

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.

Pine Instrument Co.’s prototype aggregate imaging system automates the process of measuring aggregate characteristics.

“AIMS allows the comparison of aggregates with
a scientifically based system,” Meininger says. “It measures
aggregates in a non-biased way.”