What is Cover meter testing?
The objective of cover meter testing is to locate and determine the depth or size of reinforcing bars. Some equipment allows bar diameter to be estimated if previous calibration is performed.
Cover meter surveys are principally used to confirm cover distance of reinforcement from the concrete surface to ensure durability.
Results are also often used to assist with other testing methods (e.g., sampling, carbonation depth, total and free chloride content, half-cell potential measurements) to determine the exact position of reinforcement.
How does Cover meter testing work?
A cover meter survey is based on ferromagnetic induction principles and can be used to detect the location, size and depth of reinforcement in a concrete element.
The equipment induces “eddy-currents” to flow around the circumference of the bar, producing a magnetic field.
The head of the device picks up the magnetic signal and pulse techniques separate this signal from that transmitted (thus no signal is produced in the absence of a metallic material).
A distinct maximum in induced current is observed when the long axis of the probe and reinforcement are aligned and when the probe is directly above the reinforcement. The strength of the signal can be calibrated to the size of the bar and the depth below the surface. If one of these parameters is known, the other can be deduced.
What is Cover meter testing used for?
Deterioration process | Defects | Control of repairs |
All | This technique is useful to evaluate construction | All |
How do I carry out Cover meter testing?
Cover meter testing is simple, quick and easy to carry out. Several standards documents such as BS 1881-204 have been developed which prescribe the basic test methodology that must be used as follows:
Clean the surface to remove debris and ensure clear access for the device. This may involve brushing or wiping the area.
Follow the manufacturer’s instructions to calibrate, often involving setting the device against known conditions or using calibration blocks supplied with the meter.
Divide the area into grid sections and methodically scan each section to ensure full coverage.
Use the meter's indications (audio or visual cues) to pinpoint the location of reinforcement bars.
Once rebar is located, the meter can provide the concrete cover depth based on electromagnetic signal strength.
Compile measurements to assess compliance with specifications or to identify areas needing further investigation or repair.
What equipment and expertise are required for Cover meter testing?
A cover meter is a specialized non-destructive test device employing pulse-induction technology to detect metallic objects within the concrete. Calibration blocks are essential for ensuring the device's accuracy before each use. Additionally, sophisticated software is useful for data logging, analysis, and visualization, enabling engineers to interpret the results effectively and make informed decisions.
Among the most popular devices in the field are the Proceq Profoscope and Profometers known for their precision; the Elcometer 331 Model TH, recognized for its comprehensive detection capabilities; and the Hilti Ferroscan PS300, which offers detailed imaging of the reinforcement layout.
These devices are complemented by software such as Hilti PROFIS Ferroscan Map, or ElcoMaster from Elcpometer. Each are designed to work seamlessly with their respective hardware, offering extensive analysis and reporting functionalities. Some systems such as the Proceq PM8000 combine the two in an all-in-one data collection, analysis and presentation tool.
What are the advantages of Cover meter testing?
Leaves no marks on concrete surface, allowing for repeated use over time for monitoring purposes.
Quick and efficient test which provides immediate results and rapid assessment.
Easy to use and generally requires less technical expertise compared to other testing methods, making it accessible for a wide range of users.
Precise measurements of concrete cover depth over reinforcement bars.
Cover meters are handheld and easily portable, facilitating on-site assessments without the need for bulky equipment.
Beyond measuring cover depth, some advanced models estimate rebar diameter, further aiding structural analysis.
In most cases requires no surface preparation.
What are the disadvantages Cover meter testing?
Performance can be affected by environmental conditions, such as extreme temperatures or moisture content in the concrete.
Effectiveness decreases as the depth of concrete cover increases, limiting its use for deep embedded rebars. Intended depth of usage is only 0-185mm.
Nearby metals can cause interference and create false positives.
Cover meters require regular calibration to maintain accuracy, which can be overlooked or improperly executed.
Unable to detect non-metallic reinforcement such FRP rebars.
How accurate is Cover meter testing?
Cover meters, sophisticated tools used for non-destructive evaluation of reinforced concrete, offer a high degree of accuracy in locating rebars and measuring the thickness of the concrete cover.
Specifically, these devices can achieve a depth measurement accuracy of ± 2% or 3 mm for concrete covers up to 150 mm, irrespective of the reinforcing bar's size. This precision ensures compliance with construction standards and structural integrity assessments.
Additionally, cover meters estimate the diameter of reinforcing bars with an accuracy of ± 10%, a crucial parameter for structural analysis and rehabilitation projects. This technical proficiency underscores the instrument's value in diagnosing and maintaining the health of concrete structures, combining empirical data with advanced signal processing to inform engineering decisions and interventions.
What are the limits of Cover meter testing?
Cover meter testing is effective for locating rebars and measuring concrete cover in structures with accessible, metallic reinforcement. However, its effectiveness diminishes for deeply embedded (>185mm) rebars or in highly congested areas due to its limited spatial resolution and susceptibility to surface conditions. Surface coating can also affect results.
Its spatial resolution limits accurate measurement of closely spaced rebars, particularly in congested reinforcement areas. Surface conditions, such as conductive coatings or corrosion, can also impact the test's accuracy, necessitating minimal but specific surface preparation.
Cover meters are unable to detect non-metallic reinforcements such as FRP BARS or provide a comprehensive structural health analysis, necessitating additional testing methods for in-depth evaluations. This method is best used as part of a broader diagnostic strategy to ensure all critical aspects of structural integrity are assessed.
Ancillary information
Maturity of test: > 10 years
Qualification & interpretation : Inspector
Service disruption: No
Preliminary works: No
Time consumption Low (< one hour)
Cost Low
Access to element 1 face