Civil Engineering Reference
In-Depth Information
It is desirable to measure pulse velocity to within an accuracy of ±2%
which allows a tolerance in the separate measurements of path length and
transit time of only a little more than ±1%.
When such accuracy of path length measurement is difficult or impossible,
an estimate of the limits of accuracy of the actual measurements should
be recorded with the results so that the reliability of the pulse velocity
measurements can be assessed.
Estimation of strength
Concrete quality is generally assessed by measuring its cube (or cylinder)
crushing strength. It has been found that there is no simple correlation
between cube strength and pulse velocity but the correlation is affected by:
a type of aggregate,
b aggregate/cement ratio,
c age of concrete size and grading of aggregate,
d curing conditions.
In practice, if pulse velocity results are to be expressed as equivalent cube
strengths, it is preferable to calibrate the particular concrete used by making
a series of test specimens with materials and mix proportions the same as
the specified concrete but with a range of strengths. The pulse velocity is
measured for each specimen which is then tested to failure by crushing.
Figure 1.23
illustrates a typical UPV/Strength relationship.
The range of strength may be obtained either by varying the age of the
concrete at test or by introducing a range of water/cement ratios. In practice,
on real contracts, tests on cubes prior to compression testing will enable a
calibration curve to be obtained.
If strength monitoring with time is to be carried out, the calibration curve
is best obtained by varying the age but a check on quality at a particular age
would require the correlation to be obtained by varying the water/cement
ratio.
For more information on the use of ultrasound in the examination of
concrete, see Bungey et al., 2006 and the Pundit Reference Manual available
from Proceq Ltd.
1.4.4 Chemical tests
Chemical analysis of concrete can provide extremely useful information
regarding the cause or causes of failure of concrete. The tests most frequently
carried out are listed below:
