Determining the existing condition with devices among non-destructive testing methods in reinforced concrete structures is an objective engineering step that transforms physical reality into mathematical data. Although they are generally mentioned together in the industry, crack detection is performed with ultrasonic sound waves, while reinforcement detection is performed with electromagnetic waves.

The field application stages of these procedures are as follows, respectively:

1. Stages of Crack and Void Detection with Ultrasonic Pulse Velocity

This method serves to accurately calculate the depth of surface cracks and invisible voids inside by measuring the transmission time of high-frequency sound waves sent into the concrete.

• Surface Preparation: The concrete surface to be measured is cleared of roughness, dust, and paint. A special conductive gel or grease is applied to the surface to ensure no air gap remains between the device probes (receiver and transmitter) and the concrete surface, allowing the waves to be transmitted clearly.

• Device Calibration: The ultrasonic testing device is tested on its own standard calibration bar to perform a reference zeroing and verify reading accuracy.

• Determination of the Measurement Method: The measurement configuration is selected according to the condition and accessibility of the element.

• Reading and Data Collection: The probes are pressed against the surface, and the propagation time of the sound waves in the concrete (in microseconds) is read from the screen. If there is a crack, segregation, or void inside, the waves will have to travel around this obstacle, thus extending the transit time and decreasing the velocity.

• Analysis and Calculation: The reference sound velocity obtained from sound, crack-free concrete is compared with the sound velocity in the damaged or suspicious area using formulas in accordance with standards (e.g., TS EN 12504-4). In this way, the millimetric depth of the crack or the size of the internal void is objectively determined.

2. Stages of Reinforcement Detection (Electromagnetic / GPR)

It is the process of non-destructively detecting the location, diameter, and concrete cover thickness of the steel reinforcement inside the concrete.

• Surface Inspection and Planning: The surface of the load-bearing element (column, beam, shear wall) to be scanned is determined. If there are external metal elements on the surface (nails, flush-mounted plumbing pipes, etc.) that could mislead the magnetic field or radar waves, they are taken into consideration or isolated.

• Scanning in a Grid System: The device is moved slowly on its wheels over the concrete surface. The scanning is performed first on the horizontal, then on the vertical axis to scan the entire area. When the device passes exactly over a steel reinforcement, the signal peaks and gives an audio/visual warning.

• Diameter and Cover Reading: The device locks when it finds the exact center of the reinforcement. The distance of the reinforcement at that point to the surface (concrete cover) and the estimated diameter of the reinforcement are read on the screen and recorded.

• On-site Marking: The locations of the detected longitudinal reinforcements and stirrups are drawn exactly on the concrete surface with chalk or a marker pen. This process ensures that the reinforcement spacing is clearly visible while preparing the as-built survey.

• Data Recording and Physical Verification (Chipping): The data read by the device (quantity, diameter, and spacing of reinforcements) are recorded for reporting. However, since the devices are not 100% infallible, in accordance with the regulations, the concrete is broken at certain points (by chipping/cover removal) to physically reach the reinforcement, and the accuracy of the diameter and cover values given by the device is definitively confirmed by measuring with a caliper.