The Profometer test is a widely used non-destructive testing technique designed to quickly and accurately detect the location, size, and concrete cover of steel reinforcements embedded within concrete structures. The test employs a small, portable instrument called a Profometer or rebar locator, which is lightweight (weighing less than two kilograms), battery-operated, and easy to handle without the need for electrical connections.
Purpose of the Profometer Test
The primary objectives of the Profometer test include assessing the precise location of steel bars within concrete, measuring the diameter of the reinforcement bars, and evaluating the thickness of the concrete cover protecting the steel. This information is vital for structural evaluation, maintenance, and repair works.
Principle of the Test
The Profometer operates on the principle that steel reinforcement embedded in concrete disturbs the electromagnetic field emitted by the device. By measuring changes in this field, the instrument can detect the presence, position, and size of the steel bars beneath the concrete surface.
Calibration of Profometer Equipment
For accurate and reliable results, calibration of the Profometer is essential before starting any testing and once again after completion. Calibration is performed using a provided test block with known reinforcement sizes and cover thicknesses. The operator measures these known values at various locations with the Profometer and compares the recorded readings to the standard values printed on the block to verify accuracy.
Profometer Test Instrument and Accessories
The Profometer comes with a set of probes designed for specific measurements: a path measuring device and spot probes for locating bars, a diameter probe for measuring bar thickness, and a depth probe for evaluating concrete cover. These probes connect to the main instrument by cables, and the device is equipped with onboard memory and integrated software to process measurements and generate statistical reports.
Test Preparations
Before conducting the test, a thorough assessment of the structure is necessary. Adequate safety arrangements, such as staging, ladders, or suspended platforms, should be provided to access all test areas. The concrete surface is marked with chalk lines into panels of equal size to ensure systematic scanning.
Profometer Test Procedures
- Determining Steel Bar Location:
The path measuring device and spot probes are moved across the concrete surface, connected to the Profometer, to scan for the steel bars. When a bar is detected, its location is displayed on the instrument’s screen and marked on the concrete surface for reference. - Measuring Bar Diameter:
After locating the bar, the diameter probe is placed parallel to the bar axis. The instrument records four measurements, and the average is calculated to determine the bar diameter accurately. - Determining Concrete Cover:
The depth probe is placed directly above the detected reinforcement. Upon nearing the steel, the device emits an audio beep and visual signal, recording the concrete cover thickness in memory.
Precautions
Several factors can influence the accuracy of the Profometer readings. The arrangement and congestion of reinforcement, variations in iron content within cement, and the presence of aggregates with magnetic properties can affect measurements. Metal ties used for reinforcement binding can also disturb the electromagnetic field, requiring careful interpretation of results.
Advantages and Limitations
The Profometer test offers many benefits: it is entirely non-destructive, fast, and provides reasonably accurate results when reinforcement is not overly congested. The lightweight, handheld instrument allows one person to conduct the test without assistance.
However, there are some limitations. Closely spaced or bundled rebars and the presence of binding wires can reduce measurement accuracy. Additionally, the use of special cement types containing high alumina or pigments may cause the concrete cover thickness to be underestimated. For rebars spaced more than 32 mm apart, recalibration of the instrument may be necessary.
Applications of Profometer Test
The Profometer test is valuable in various scenarios, including:
- Evaluation of Concrete Structure Strength:
In older structures where original construction drawings are unavailable, the Profometer helps identify the number, size, and condition of reinforcement bars, aiding in strength assessment and structural upgrades. - Corrosion Analysis:
It assists in evaluating the condition of reinforcement to detect corrosion without damaging the concrete. - Quality Control and Assurance:
The technique is employed during new construction to verify reinforcement placement and concrete cover conformity. - Preliminary Investigation Before Drilling or Coring:
Locating rebars is crucial to prevent damage during drilling, cutting, or coring operations and is often a prerequisite for other non-destructive tests.
The Profometer test is an essential tool in modern construction and maintenance, providing critical insights into concrete structures while preserving their integrity. Its ease of use, speed, and non-destructive nature make it a preferred choice for engineers and inspectors worldwide.