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The standard method of evaluating the quality of concrete
in buildings or structures is to test specimens case
simultaneously for compressive, flexural and tensile
strengths. The main disadvantages are that results are
not obtained immediately; that concrete in specimens
may differ from that in the actual structure as a result
of different curing and compaction conditions; and that
strength properties of a concrete specimen depend on
its size and shape, and off course on the testing methodology.
Although there can be no direct measurement of the strength
properties of structural concrete for the simple reason
that strength determination involves destructive stresses,
several non-destructive methods of assessment have been
developed. These depend on the fact that certain physical
properties of concrete can be related to strength and
can be measured by non-destructive methods. Such properties
include hardness, resistance to penetration by projectiles,
rebound capacity and ability to transmit ultrasonic
pulses. These non-destructive methods may be categorized
as penetration tests, rebound tests, pullout techniques,
dynamic tests, maturity concept. It is the purpose of
this Digest to describe these methods briefly, outlining
their advantages and disadvantages.
Compressive strength with velocity
A correlation between the compressive strength of concrete
and the velocity of sound propagation has been established.
The relationship is presently an empirical one with
all test data having to be related to pre-established
standards. The method is, however, applicable to both
field and laboratory concrete when sufficient knowledge
concerning the mix design is available.
Impact of metric conversion
The reinforcing-steel industry announced plans to fully
convert to soft metric rebar production. How will the
change affect nonmetric reinforced-concrete construction
projects? Federally funded construction projects now
required to be designed in metric units and built with
metric materials. The reinforcing-steel industry is
committed to supporting metrication and, earlier this
year, a number of rebar mills announced that they are
beginning to phase in the production of soft metric
bars. During this transition period, the mills will
reduce and eventually eliminate their output of inch-pound
bars. But what impact will the switch to soft metric
rebar have on private-sector construction products that
donâ€™t have to be built using metric units?
Modern Steel Reinforcement Bar
This method uses two coils. The first coil is connected
to a power supply which feeds it a low frequency i.e.
(102Hz) AC signals. The second coil feeds directly into
When a rebar is introduced to the coilsâ€™ electromagnetic
field, a higher voltage is induced in the other coil.
The amount of voltage change is direct function of the
magnetic characteristics, location and size of the metallic
object. By combining two sensing coils in a balanced
configuration. The precise position of the object can
Testing of Concrete and Morter
This paper presents the results obtained from tests
conducted with a new pin penetration nondestructive
apparatus to determine the compressive strength of hardened
concrete and mortar at early age. The concrete tests
were carried out on 3 x 6 in. (75 x 150 mm) cylinders
and on 18 x 24 x 4 in. (460 x 610 x 100 mm) slab while
the mortar tests were performed on an equal size slab
and on 2 in. (50 mm) cubes. The concrete mixes were
made with Type I cement, lime and sand. It was found
that the pin penetration tester can be used successfully
to determine the compressive strength of concrete and
mortar at early age from 10 hours up to 28 days.
Testing of Floor Slabs
The most common test result at present in use for the
control of concrete quality in building and civil engineering
projects is the cube crushing strength, and the debate
on the correlation possible between the recorded value
of such a standard test on a small sample and the true
value of the concrete in the corresponding structure
is endless and often acrimonious. The industry recognize
the need for a quick, simple and accurate assessment
of the quality of concrete members at the earliest possible
opportunity after casting, and the relationship of non-destructive
testing to specifications has been previously discussed.
Building Materials Article - Permeability
More than one thousand years after the Romans erected
concrete structures, scientists are still trying to
define and measure permeability, the key to good durability.
In an Immediate Past Chairmanâ€™s address presented
before the Road and Building Materials Group (not the
construction Materials Group) John Figg describes the
theoretical basis of permeability studies, the equipment
and methodologies involved, and reviews the results
of recent work in the field.
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