Penetration or Windsor probe test ~ there are various
interpretations of this test. It is a measure of the penetration of a
steel alloy rod, fired by a predetermined amount of energy into
concrete. In principle, the depth of penetration is inversely
proportional to the concrete compressive strength. Several
recordings are necessary to obtain a fair assessment and some can
be discarded particularly where the probe cannot penetrate some
dense aggregates. The advantage over the rebound hammer is
provision of test results at a greater depth (up to 50 mm).
Pull out test ~ this is not entirely non destructive as there will be
some surface damage, albeit easily repaired. A number of circular
bars of steel with enlarged ends are cast into the concrete as
work proceeds. This requires careful planning and location of bars
with corresponding voids provided in the formwork. At the
appropriate time, the bar and a piece of concrete are pulled out
by tension jack. Although the concrete fails in tension and shear,
the pull out force can be correlated to the compressive strength
of the concrete.
Ref: BS 1881†207: Testing concrete. Recommendations for the
assessment of concrete strength by near-to-surface tests.
Materials Testing---Concrete