1. Impact-Echo
A Non-destructive Testing Technique

2. Agenda
• Introduction to Impact Echo
• Theory
• Instrumentation
• Purpose
• Operation
• Interpretation
• Strengths/Weaknesses
• Commercial Products
• References

3. Introduction
• Non-destructive test
• Looks for flaws/imperfections in the material
• Can estimate thickness to within 3%
• Primarily used for concrete & masonry
• Approx. 25 years old
o Developed from ultrasonic pulse echo (1940’s)
• Similar idea to chain dragging

4. Theory – Stress (Sound or pressure) waves
Figure 1: A mechanical impact creates stress waves through a material. These
(reflected)waves can be measured to gage depth of a discontinuity. Certain
waves will dominate based on the location of the discontinuity. Wave velocities
must be known to determine depth of flaw.

5. Instrumentation
• Steel ball (4-15mm) impacts  Source: http://ciks.cbt.nist.gov/~carino/ie_Fig2.GIF
(2-10 m/s) the concrete,
creating stress waves
(<80kHz & λ=5cm-6m).
o Transmitter  Pulse echo
o Can be spring loaded
o Start from large impactor
small
• Transducer measures
surface displacements
o Placed adjacent to impactor
o Measures primarily P-waves
o Piezoelectric

6. Purpose
• Plain, reinforced and
post-tensioned concrete
• Can be used to sense:
– Cracks
– Delamination
– Voids
– Honeycombing
– Debonding

7. Operation
• Impact produces stress
waves in the material;
reflected waves from voids
are detected by the
transducer
• These reflected waves set up
a resonance condition
having a distinctive
frequency
• Waveform is transformed
into spectra (FFT)
• Should have an idea of what
to look for
o Size of flaw
• Operate parallel to regular
occurring grooves

8. Interpretation
Peaks are associated with a certain “characteristic frequency”, specifying
a distance to the discontinuity.

9. Strengths and Weaknesses
• Only need access to one surface • Data can be difficult to interpret;
especially on thick plates or on
layered materials (overlays, soil)
o Layered- needs special attention
• Internal flaws can be detected
• Small voids can be missed
o limited by size of wavelength
• Can determine depth of the
internal flaws • Complicated geometries poses
difficulties
• Easily repeatable • Flaws beneath sensed flaw must be
evaluated from the opposite side
• Can construct a map of • Flaw detection length constraints:
discontinuities o Lmin = d/4, L>d/3
• Requires adequate frequency
resolution

10. Equipment
Basic Test Set Up Portable Impact Echo
(PIES) Test Set Up

11. Transducers
Cylindrical Transducer Pistol Grip Transducer Dual-Head Transducer

12. Use of Each Transducer
• Cylindrical – For testing in narrow and
confined spaces
• Pistol Grip – is easier to use and well suited to
flat surfaces.
• Dual Head – Used for independent
measurements of wave speed which can be
used to determine depth and thickness

13. ASTM C 1383 Procedures
Figure 5: Two-step procedure for measuring plate thickness:
Procedure A is used to determine the P-wave speed and Procedure
B is used to determine the thickness frequency.

14. Suppliers and Costs
• Impact Echo Instruments www.impact-echo.com
– System “A” - $12,500
– System “B” - $11,500
– System “C” - $9,500
• Olson Instruments www.olsoninstruments.com
– IE 1 - $5,000
– IE 2 - $10,000
– IE T - $13,000
• Qualitest USA www.WorldofTest.com
– PIES System - $16,995
*does not include prize of laptop computer*

15. Test Standards
• ASTM Standard C1383-98a for measuring the
p-wave speed and thickness of concrete plates
using the impact echo method
• ACI 228.2R-98 Nondestructive Test Methods
for Evaluation of Concrete Structures