APPENDIX A: NONDESTRUCTIVE PAVEMENT TESTING DEVICES
GENERAL INFORMATION
mounted in a towable trailer, an impulse load is
applied to the pavement system through a buffer
Historically, pavement deflection data have
system and steel plate, and complete operation of
been collected by a variety of equipment that falls
the device and testing sequence is controlled by a
into four categories: 1) static beam deflection
computer housed in the towing vehicle. The pri-
equipment, 2) automated beam deflection equip-
mary difference is the addition of a segmented
ment, 3) steady-state dynamic deflection equip-
steel plate to more evenly distribute the load on
ment, and 4) impulse deflection equipment (Smith
uneven surfaces. Also, deflection is measured by
and Lytton 1984).
seismic displacement transducers that are differ-
The following sections provide a brief and sim-
ential transformers, and the applied impulse load
plistic description of the only two categories still
is longer than that of a Dynatest.
used by responding state DOTs, impulse deflec-
tion equipment and steady-state dynamic deflec-
tion equipment. Although written several years
STEADY-STATE DYNAMIC
ago, Report No. FHWA/RD83-097 (Smith and
DEFLECTION EQUIPMENT
Lytton 1984) provides a comprehensive overview
of all four categories of NDT equipment and is
Steady-state dynamic deflection equipment in-
highly recommended for detailed descriptions.
cludes any pavement testing device that applies a
dynamic force to produce a sinusoidal vibration
in the pavement system. A static load is placed on
IMPULSE DEFLECTION DEVICES
the pavement surface, then a steady-state sinusoi-
dal vibration is induced with a dynamic-force gen-
Impulse deflection equipment includes any test-
erator. The magnitude of peak-to-peak force is
ing device that applies an impulse load to the
generally increased during testing. (The static load
pavement surface. This is accomplished by lifting
must also be adjusted accordingly to prevent the
and dropping a mass from an adjustable height
device from bouncing off the pavement surface.)
onto a buffer system that transmits the force
through a loading plate to the pavement surface.
Dynaflect
The impulse load and resulting pavement re-
Chronologically preceding FWDs, the Dynaflect
sponse closely approximate a moving wheel load
is also trailer mounted and can be towed by any
and associated pavement deflection. FWDs are
standard vehicle. The Dynaflect was one of the
impulse deflection devices.
first types of steady-state dynamic deflection de-
vices on the market.
Dynatest falling weight deflectometer
A static load is applied to the pavement sur-
As was discussed in the main text, Dynatest
face, then a sinusoidal vibration is applied through
FWDs are by far the NDT device most commonly
an unbalanced fly wheel system. Velocity trans-
used by state DOTs. Dynatest pavement testing
ducers measure pavement deflection. Testing fre-
equipment is mounted on a trailer, and can be
quency and pavement response (deflections) are
towed by a van, truck, or automobile. Drop heights
measured simultaneously. Before the introduc-
are varied to yield a desired load range. Pave-
tion of FWDs, the Dynaflect was used for overlay
ment response is measured by (generally) seven
design more than any other automated pavement
velocity transducers located at desired distances
testing device.
from the center of the load plate. The complete
operation, including raising and lowering the load
Road Rater
plate and sensors, raising and dropping the mass,
Road Raters can be trailer mounted or incorpo-
recording deflections, and signaling the operator
rated within a vehicle such that towing is unnec-
when the system can be moved to the next site, is
essary. Load magnitudes vary for different models.
computer controlled.
A load is applied to the pavement through a
steel loading plate. The dynamic force is applied
KUAB falling weight deflectometer
by a steel mass accelerated by a servo-controlled
Conceptually, the KUAB is very similar to the
hydraulic actuator, and deflections are measured
Dynatest FWD: pavement testing equipment is
using four (or more) velocity transducers.
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