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 174 M-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 174 M-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 174 M-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 174 M-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 174 M-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.