© 2017 by Proceq SA
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© 2017 by Proceq SA
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5.8. Compound Measurement – Perpendicular Crack Depth
Select “Compound Measurements”
Select “Crack Depth”
Select parameter setting “b”.
Measure and enter the distance “b”
Transducers in first position – Start
“t1” is measured. Stable reading
indicated by a tick
Transducers in 2nd position - Start
“t2” is measured. Stable reading is
indicated by a tick and result screen
is displayed.
The display shows:
- “t1”
- “t2”
- Crack Depth
Save the result or press start to
repeat the measurement.
5.9. Minimum Dimensions
Minimum dimensions are recommended for accurate test results.
Minimum path length
100 mm for concrete with maximum aggregate size of 20 mm or less.
150 mm for concrete with maximum aggregate size between 20 mm and 40 mm.
Minimum lateral dimensions of the sample
This is dependent on the transmission wavelength and the pulse velocity. The minimum path
length should be equal to or greater than the transmission wavelength, or a severe reduction in
the pulse velocity may be detected. The following table taken from BS 1881: Part 203 shows
the minimum recommended lateral dimensions for the test object.
Tx Frequency kHz
Pulse velocity
3500 m/s
Pulse velocity
4000 m/s
Pulse velocity
4500 m/s
Minimum Lateral Dimensions of Test Object
24
146 mm
167 mm
188 mm
54
65 mm
74 mm
83 mm
150
23 mm
27 mm
30 mm
5.10. Transducer Selection Guide
Generally, lower frequencies allow more depth of penetration. Higher frequencies allow better
resolution in the measurements.
The inhomogeneities in concrete influence the propagation of an ultrasound pulse. This influ-
ence can be significantly reduced by choosing the frequency, f, such that the wave length,
λ
, is
at least twice as large as the aggregate size.
λ
is given by:
λ
= c/f,
where c is the pulse velocity (speed of sound) in concrete. The table below shows typical ag-
gregate sizes and the corresponding maximum recommended frequency, respectively:
c (m/s)
3500
4000
4500
aggregate
size (mm)
8
16
32
8
16
32
8
16
32
fmax (kHz)
219
109
55
250
125
63
281
141
70
i
Note:
The crack depth measurement uses the method described in BS 1881:Part 203.
For good results, the crack must be perpendicular to the surface and free of water
or debris. The crack must be sufficiently wide to prevent the wave from propagating
around it.
Rebars close to the crack will also affect the result. If these conditions are not met, the
crack depth will appear much smaller than it is.
