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.