| Measuring Thickness Of Concrete Essay, Research Paper
Measuring Thickness of Concrete
Measuring Thickness of Concrete Elements Using Drilled Concrete Cores
When doing construction one of the major concerns is that the work
being done complies with the design specifications. In this ASTM
test, C 174M-97, the thickness of a concrete pavement, slab, or
structural element is determined by measuring the length of a core
drilled from a concrete structure. This allows the contractor,
as well as the owner, to see that the concrete is being poured to
meet the requirements. (ASTM, C 174M-97, 1)
In order to complete this experiment a particular tool will
be needed. It is a 3-point calipering device that will measure
the length of axial elements of the core. This apparatus must
conform to certain requirements. It needs to be designed so
that the specimens will be held with its axis in a vertical
position by three symmetrically placed studs or posts of
hardened steel bearing against the lower end. The end of the
studs that bear against the surface of the specimen need to be
rounded to a radius of not less than 6 mm and not more than
13 mm. The apparatus needs to allow for the measuring of
specimens of different nominal lengths over a range of at
least 100 to 250 mm. It needs to be made in order to make
a measurement at the center of the upper end of the specimen
and at eight additional points spaced at equal intervals
along the circumference of a circle. The device that makes
contact with the end surface of the specimen needs to be
rounded to a radius of 3 mm. Finally the instrument for
measuring needs to be stable and sufficiently rigid to
maintain its shape and alignment without a distortion or
deflection of more than 0.25 mm during all normal measuring
operations. Before any measurements are made, though, the
apparatus needs to be calibrated with suitable gages so
that errors caused by mechanical imperfections in the
apparatus are known. (ASTM, C 174M-97, 1)
The measuring apparatus is not the only thing that needs to
meet certain requirements. The specimen needs to be drilled with
the axis normal to the surface of the structure, and the ends
should be free from all conditions not typical of the surface
of the structure. Any sample that shows any defects during
the drilling cannot be used. If there are any particles bonded
to the surface of the concrete they need to be hammered or
chiseled in order to remove the particle. Once again, if the
concrete is damaged during the chiseling then the sample will
not be used. (ASTM, C 174M-97, 1)
The procedure for this test is simple. The first thing
is to place the specimen in the apparatus with the upper surface
bearing against the hardened-steel supports. The central
measuring position needs to be directly over the midpoint of the
upper end of the specimen. After the positioning is complete
you make nine measurements of the length on each specimen, one
at the central position and one each at eight additional
positions spaced at equal intervals along the circumference of
the circle of measurements. You read the measurements to the
nearest 1.0 mm. If the surface of the specimen is not
representative of the general plane of the core end because
of a small projection or depression, the specimen shall be
rotated slightly about its axis and a complete set of nine
measurements made with the specimen in the new position.
The average of the nine measurements will be reported as the
length of the concrete core. (ASTM, C 174M-97, 1)
If done correctly the information above should give the
tester the correct measurement of any concrete slab,
pavement, or structural element. Two things need to be
reemphasized, though, in order for the test to come out
accurate and credible. The first is that the instrument
needs to meet all of the requirements that were listed,
and it needs to be used correctly. Second, no sample can
be damaged in any way. If all of these criteria are met
then you will have an accurate and credible test every time.
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