- Author
- Carino, N. J.
- Title
- Performance of Electromagnetic Covermeters for Nondestructive Assessment of Steel Reinforcement.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
- NISTIR 4988, December 1992, 131 p.
- Distribution
- Available from National Technical Information Service
- Keywords
- covermeter | building technology | concretes | eddy current | electromagnetic device | magnetic reluctance | nondestructive testing | reinforcing bars
- Abstract
- Covermeters are electromagnetic devices for locating steel reinforcing bars in concrete structures. An experimental study was carried out to compare the basic characteristics of two types of commercial covermeters (magnetic reluctance and eddy current). Experiments were carried out using single bars and multiple bars with various configurations. One group of single-bar tests studied the relationships between meter reading and cover thickness. Empirical equations were fitted to the data, and the values of the equation parameters were found to be relatively insensitive to the bar size. The other group of single-bar tests examined the relationship between meter reading and horizontal distance between the meter probe and the bar axis (offset). Data were fitted with a bell shaped, quadratic exponential function. The parameter characterizing the decay of the meter reading with offset was found to depend on the cover in a well-defined manner. This parameter was used to characterize the differences in the influence zones of the probes. Tests with multiple, parallel bars were conducted to determine the critical spacings below which the location of the individual bars could not be discerned and below which the meter amplitude exceeded the single-bar value. A simple summation model was used to predict the response based on the individual-bar response. Criteria were proposed to estimate these critical spacings based upon the single-bar responses. Other tests showed that the meters cannot discern a bar located directly below another bar. The ability of the meters to locate the ends of bars was also investigated, and the eddy-current meter appeared superior for this purpose. The final series of tests examined the ability of the meters to measure the length of a lap splice, and the meter based upon magnetic reluctance appeared superior for this purpose. Recommendations for developing a standard test method and for improvements in meter performance are provided.