Manuale di Istruzione
Instruction Manual
21/05/2012 58-E4800 Rev. 4 EN
The slope of the best straight line drawn through the points (tan) shall be measured and
recorded as the mean pulse velocity along the chosen line on the concrete surface. Where
the points measured and recorded in this way indicate a discontinuity, it is likely that a
surface crack or surface layer of inferior quality is present and a velocity measured in
such an instance in unreliable.
3.3.3 Evaluation of homogeneity and uniformity of concrete
Drawing a grid on the concrete member and measuring the transit time in the grid points
it is possible to evaluate the concrete homogeneity. It is important to make use of
diagrams to clearly represent the test results and to demonstrate the mean quality of the
concrete.
3.3.4 Presence of cracks, voids, deteriorated regions
When an ultrasonic pulse travelling through concrete meets a concrete-air interface there
is a negligible transmission of energy across this interface (due to diffraction and
reflection) so that the transit time is necessarily longer than in similar concrete with no
defects. It is possible to make use of this effect locating defects, voids, deteriorated
regions and cracks.
If the length of the defect is very small it is impossible to make significant evaluation
(e.g. it is impossible to reveal voids with length smaller than the head diameter).
3.3.5 Correlation of pulse velocity and strength
It should be realised that the important physical properties of materials which influence
pulse velocity are the elastic modulus and the density. In concrete these properties are
related to the type of aggregate, its proportion [in the mix] and its physical properties and
the physical properties of the cement paste, which relate. mainly, to the original
water/cement ratio [of the mix] and the maturity of the concrete.
On the other hand, the strength of concrete is more related to W/C ratio than to aggregate
type and proportions of aggregate and paste Thus correlations between the pulse velocity
and strength of concrete are physically indirect and have to be established for the specific
concrete mix. For an unknown concrete; the estimation of strength, on the basis of pulse
velocity alone, is not reliable.
3.3.6 Estimation of time for formwork striking and prestressing
If some small doors are preset in the concrete moulds, it is possible to control the process
of hardening in the concrete structure.
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