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Non-Destructive Field Testing of Concrete
The most common method of non-destructive field testing is through a process called sounding.
Sounding involves striking the concrete surface and interpreting the sound produced. Solid concrete will produce a ringing sound, while concrete that is spalled, delaminated, or contains voids will produce a flat or hollow sound.
Sounding test of concrete is accomplished using a variety of tools. Sounding of small areas and vertical or overhead structural elements is best achieved by using a hammer or steel rod. A steel chain can also be dragged over the surface under evaluation.
This method is best suited for slab surfaces where large areas can be tested in a reasonable amount of time.
Non-destructive evaluations is also conducted using ultrasonic pulse velocity methods.
Two common approach include a pulse velocity meter and an impact echo system. The pulse velocity meter can detect defects such as the depth of cracks and loss of bond. The impact echo system can detect the thickness of a thin concrete section, locate a crack within the concrete, and locate voids or defects such as honeycombing.
Should the approximate size and location of the embedded reinforcing steel be desired, nondestructive testing methods include ground-penetrating radar and magnetic testing using a pachometer.
While both systems result in identifying the size and location of embedded reinforcing, the ground-penetrating radar also provides a three-dimensional representation of the concrete, identifying the different layers of reinforcing.
Destructive Field Testing of Concrete
Destructive testing methods include exploratory openings, corings, and pull-out testing. Exploratory openings can reveal conditions such as depth of cracks, delamination, reinforcing size, and pattern and coating information. Cutting an opening in the area of a previous repair reveals information about the preparation, application, and performance of the repair.
Concrete core cutting determine the conditions similar to exploratory openings but on a limited scale. Core cutting can provide insights into depths of cracks, depths of delamination, and reinforcing sizes. A core can also be sent to a laboratory for petrographic analysis.
Pull-out testing can determine the bond strength between a coating and the concrete substrate or between two cementitious materials.
The application of this test when used for determining coating bond is covered by ASTM D 4541, Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers.
The test method calls for bonding a plug to the surface coating. The area around the plug is then cut away to isolate the bond area. The testing apparatus is set over the plug and attached to the plug.
A force is applied through the testing apparatus until the plug is pulled from the substrate. Review of the plug will reveal the type of failure (i.e., failure in the topping, along the bond line, or in the substrate).
An approximation of the bond strength can be determined through a reading on the apparatus; however, this value is a qualitative answer, since different apparatus types will yield different results.