Concrete Core Test
1.1 scope
available for nondestructive testing of hardened concrete which forms a laboratory specimen or part of a structure, structural component or other type of engineering construction. Some tests cause varying degrees of localized damage or defacement and may therefore be considered partially destructive; these methods are all defined as nondestructive. All the tests can be performed on the concrete as cast and do not require the removal of samples for subsequent analysis or testing. Methods of testing hardened concrete which require sample extraction are either dealt with in other Parts of BS 1881 or elsewhere (1, 2). NOTE 1. Damage caused by the extraction of small-diameter cores may not be significantly greater than that due to some of the nearto- surface methods included here, provided that reinforcement is not cut during extraction. In cases where strength determination is required they may offer similar or better accuracy with fewer calibration problems (3). NOTE 2. The titles of the publications referred to in this standard are listed on the inside back cover.
1.2 Definitions
For the purposes of this Part of BS 1881, the definitions
given in BS 2787 and BS 6100 : Part 6 apply, together
with the following.
1.2.1 non-dertructivr test. A test that does not impair tha
Intended performance of the element or member under
investigation.
1.2.2 location. A region of concrete that is being assessed
and that, for practical purposes, is assumed to be of unlform
q u a l i t y .
1.2.3 near-to-surface test. A test that measures some
property of the concrete near to, but below, the surface.
1.2.4 standard cube strength. The measured compressive
strength of a cube made, cured and tested in accordance
with BS 1881 : Parts 108,111 and 116 respectively.
1.2.5 estimated in situ cube strength. The strength of
concrete at a location in a structural member estimated by
indirect means and expressed as the compressive strength
of specimens of cubic shape.
1.3 Principal considerations
T1.3.1 Advantages of nondestructive testing Nondestructive testing offers significant advantages of speed, cost and lack of damage in comparison with test methods which require the removal of a sample for subsequent examination. These factors will permit more t-ktt’nsive testing and thus enable an investigation to be wider ranging with respect to the concrete structure under ~r~;lrnln;rtlon than would otherwise be possible. The immediate avarlabrltty ot results may also be an impOrtWIt advantage of this type of testing.
O1.3.2 Properties measured
301 Object
The range of properties that can be assessed using nondestructive
techniques is large and includes fundamental
parameters of the concrete such as density and elastic
modulus in addition to strength. Other properties which
can be assessed include concrete surface hardness, surface
absorption and moisture condition as well as reinforcement
location, cover and corrosion risk. The quality of
workmanship and structural integrity may also be checked
by the ability to identify and locate voids, cracking and
delamination.
The required property is not measured directly by a
number of the available methods and precise correlations
are not always easy to achieve. In some instances estimates
of the required property can only be achieved by
comparative means.
3.2 Principle of Test
When the plunger of rebound hammer is pressed against the surface of the concrete, the spring controlled mass rebounds and the extent of such rebound depends upon the surface hardness of concrete. The surface hardness and therefore the rebound is taken to be related to the compressive strength of the concrete. The