Covermeters are widely used for the non-destructive testing of concrete structures to determine if reinforcement bars are adequately covered with concrete and to determine the location of safe spots for drilling for strengthening or repair work. Recent developments in Covermeter design has seen the addition of data-logging as a key feature for portable Covermeters with software supporting the analysis of data sets generated on the sites of concrete structures. Covermeters have also made use of intelligent sensor technology to allow a range of interchangeable sensors to be used with a single Covermeter including borehole sensors for finding pre-stressing or post-tensioning tendons deep within the reinforcement structure, sensors for the detection and measurement of stainless steel reinforcement and Half-Cell for the assessment of corrosion conditions. This paper describes the use and capabilities of such a Covermeter. The analysis, interpretation and presentation of the data will be discussed.
A Covermeter is a basic tool for the non-destructive testing of both old and new concrete structures. The location, orientation and sizing of reinforcement bars and the determination of the depth of concrete cover provide essential information about the structure for acceptance, for maintenance and for planning modifications to structures. The use of Covermeters and the requirements of their accuracy for use are described in BS 1881 Part 204¹. Reinforcement bars can be detected using a pulsed electromagnetic field generated by a coil. Secondary search coils detect the resulting eddy currents induced in the bars and the location, orientation, depth (cover) and diameter of the bars can be determined from this return signal. Recent developments in the design of Covermeters have added new features including the ability to log data in memory and to then analyse this information by means of a software package. In addition Half-Cell measurements to determine the potential for corrosion in the reinforcement bar can be undertaken using the same software package. This allows both the cover and the Half-Cell potential to be assessed simultaneously. This paper describes the use and capabilities of a Covermeter with Half-Cell capability and discusses the analysis, interpretation and presentation of the data.
The detection and measurement methodology of the Covermeter described by John Alldred² is the basis of the latest design of pulsed electromagnetic induction Covermeters. This latest Covermeter design has new features for linear and grid data logging and is compatible with data management software. In addition, this Covermeter design is capable of operating with a Half-Cell sensor to assess the potential for active corrosion at the points where the concrete cover has been determined. Figure 1 shows an example of a Covermeter with a search head connected. For the comprehensive survey of a concrete structure, a number of sensor head options exist to deal with the difficulties that arise when there are multiple layers of rebars or tendon ducts located below the first level of rebar or when the rebars are congested or covered by a thick layer of concrete. In addition to the standard search head there is a narrow pitch search head, a deep cover search head and a borehole probe available as User choice options.
