||Keeping Us Safe: Standards for Radiographic Imaging of Concrete
Propose to Refine Detection of Structural Defects
Draft standards for radiographic examination of concrete under
way in Committee E07 on Nondestructive Testing will facilitate crucial non-invasive
inspection of bridges and other structures.
A Subcommittee E07.01 task group drafting these standards represents
research laboratories, state Department of Transportation inspectors,
and the Federal Highway Administration (FHWA). The goal is to
establish a radiographic standard which can be used in inspecting
concrete in buildings, bridges and highways, said Habeeb H. Saleh,
Ph.D., research scientist, NDE Validation Center, FHWA, McLean,
Va., and the task group chair.
In his paper, Radiographic Examination of Concrete, Saleh explained
that radiographers normally use steel radiography standards to
determine the requirements for inspecting concrete. The normal
practice, he related, has been to scale the requirements for
steel by a factor of three since concrete density is approximately
one third of the steel density. In most cases, the goal is to
locate metallic material embedded in concrete, rather than detecting
defects in concrete itself.
Compared with steel, which is homogenous, concrete is a completely
heterogeneous material because concrete has constituents that
differ in density. Additionally, the scattered photons from concrete
can influence the quality of images. These two factors should
be taken into consideration in order to generate radiographic
images with quality high enough to locate minor defects in both
embedded steel and concrete.
As standards for radiographic examination of concrete are non-existent,
new standards being drafted specifically for concrete will provide
an advantage to inspectors of buildings, bridges, and highways.
When people radiograph concrete looking for defects, use of a
concrete standard may improve the quality of results, Saleh averred.
The task group plans to develop:
A set of concrete quality-image indicators;
Acceptable standards for radiographs, and digital images;
A standard calibration curve for exposure time vs. photon energy
for given concrete thickness and source strength; and
A method for photon-scattering correction to enhance digital
Comments or participation in this activity is invited. For further
technical information contact Habeeb Saleh, Ph.D., NDE Validation Center, Federal Highway Administration,
McLean, Va. (phone: 202/493-3123). Committee E07 meets June 24-28
in Norfolk, Va. For meeting or membership details, contact Director
George Luciw, ASTM (phone: 610/832-9710). //
Copyright 2001, ASTM