A simple and quick way of locating steel reinforcement has become important on the construction site. The reasons for locating steel include:

  • A quality control check to determine if reinforcement was installed;
  • To avoid hitting reinforcement when removing a core or drilling a hole;
  • When doing a rebound hammer test. This test requires that you be at least 1 inch from any reinforcement;
  • When determining relative humidity in concrete slabs using in situ probes. Although avoiding the reinforcement is not stated in the test method, installing the in situ probe in or directly against the reinforcement will result in erroneous values.

There are many metal locators available to the contractor, with costs varying from $30 to several thousand dollars. The ease of using the metal locator also varies; some are relatively easy to use while others require extensive training to interpret the results.

In most cases, the contractor will only occasionally use the metal locator. Unlike forensic engineers that need detailed information about the reinforcement, the contractor usually needs equipment that is easy to use and will answer basic questions, such as was the reinforcement installed or how can I avoid the reinforcement if coring or drilling a hole into the concrete?

Zircon, the manufacturer of two inexpensive metal locators, asked me to evaluate its equipment to determine if it was easy to use and whether it meets most of the needs of the contractor. While I was recently in Ethiopia to start an ACI chapter, I found that the concrete construction industry there was rapidly developing, and I discovered that the industry there is interested in improving its technology.

So I proposed to Zircon that we evaluate the equipment at universities in Ethiopia with college students. The reasons for this would be:

1. The students will be the next generation of engineers and project managers. This would introduce the concept and idea of non-destructive testing and give them some first-hand experiences in doing it.
2. The students have learned English as a second language. This would provide a good evaluation of the instructions. If the students can follow the written instructions and the provided DVD, and then use the equipment correctly, then the instructions would be considered adequate.
3. Most students have little or no field experiences and are unfamiliar in using construction equipment. This will emphasize to them the need to learn the correct procedures of using the equipment before using it on the construction site.

During the laboratory exercise, we told the students our company had just bought these metal locators and they were responsible to learn how to use them. They had the instructions and the DVD that came with the metal locators. Thus, the students had to learn the procedures on their own.

Before the laboratory, we had prepared some test beams with various sizes of reinforcement which were off center so that the students could get four readings of cover (depth of reinforcement) on each beam. Due to limited time, each group was given one of the metal locators to evaluate. The following is a summary of the students’ evaluation.

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