Is the concrete structure strong and solid? How do you know it?
Just like any adventure, there are a few bumps that can mess with your test results. For instance, the concrete isn’t just concrete—it’s got additives, coatings, or other materials that interfere with your tools. The key to finding and making sure your concrete structures are strong and solid is finding the steel reinforcement layer.
In this article, let’s see the main factors you might run into during the detection process and how they can affect your accuracy:
Factors Impacting the Detection of Steel Reinforcement Layer
Below are the main factors that affect during detection and their potential impact on test results.
Poor Choice of Testing Components
One common issue in on-site testing is the wrong choice of the number of components to be tested. Instead of following the proper standards, the number of components is often decided based on the building’s size. This is where the selected components fail to meet the required specifications.
For example, in smaller work units, only one or two components may be tested. Whereas the standard requires at least 2% of the total number of components, with a minimum of 5. Additionally, some units fail to allocate at least 50% of the tested components to overhanging structures, resulting in inaccurate outcomes.
Inconsistent Flatness of Tested Components
Have you noted the top surfaces of overhanging balconies and indoor floors? They can significantly impact the accuracy of the detection, especially if these tested components have no even surfaces. For instance, if the surface of a balcony is not properly smoothed out and not made even before testing, there might be fluctuations, leading to large variations in values that could make the results unreliable and invalid.
When testing an indoor floor that has visible cracks and uneven patches could affect the readings and lead to inaccurate conclusions about the protective layer’s depth.
Non-Standardized Operation of Detection Instruments
When you use the detection instruments improperly, it can cause major errors. For instance, if the scanning speed is too fast or too slow, the instrument’s sensor might fail to align properly with the reinforcement bars. This misplacement results in significant differences in data, leading to an inaccurate measurement of the protective layer thickness.
Other factors include:
- If the instrument isn’t calibrated correctly, the readings can be off, even if the scanning is done at the right speed. This can lead to false conclusions about the reinforcement layer.
- Uneven pressure or angle while scanning can cause the instrument to shift, leading to inaccurate readings.
- If the sensor isn’t positioned directly over the rebar, it might pick up incorrect signals, skewing the data.
Lack of Pre-Scanning for Hoop Bars
Hoop bars if not considered before testing can interfere with measurement results. For hoop bars with a spacing of less than 120mm, pre-scanning should be performed, and the actual hoop spacing value should be entered into the instrument system settings. Failure to do so can affect measurement accuracy.
For example, if the hoop bars are too close together and their spacing isn’t adjusted in the system, the instrument might read the reinforcement layer as thicker than it actually is. Another example would be testing a slab where the hoop bars are densely packed but not accounted for, resulting in inaccurate readings of the steel reinforcement layer thickness.
Delay in Detecting Frame Structure Beams
This is another factor that affects the detection of the protective layer of steel reinforcement. In frame structures, beam members should be tested before the masonry of the bottom infill wall. But if it gets delayed, this can result in not being able to detect certain areas. And it leaves only exposed members available for testing. This compromises the representativeness of the detection process.
Improper Selection of Testing Locations
A lack of thorough understanding of reinforcement placements can lead to improper selection of testing locations. For example, when testing beam members in frame structures, failure to avoid beam-column nodes and other heavily reinforced areas may result in a higher detected reinforcement count than actually exists, leading to misjudgments or invalid data.
Incorrect Analysis of Reinforcement Placement in Intersecting Beams
When dealing with intersecting beams, it is crucial to correctly differentiate between the top and bottom reinforcements of different beams. Inaccurate analysis can lead to inconsistency, where the protective steel reinforcement layer thickness appears excessive compared to actual conditions.
Additional points to consider:
- Failing to correctly identify which layer of reinforcement belongs to which beam can lead to incorrect measurements of the protective layer, affecting the overall structural assessment.
- If sensors are not positioned accurately at the intersection of the beams, they might pick up reinforcement from both beams, leading to misleading data and overestimation of the protective layer thickness.
- In some cases, reinforcement bars overlap at beam intersections. If this overlap isn’t considered, the protective layer thickness might be inaccurately calculated, showing more coverage than exists in reality.
Failure to Reassess in Marginal Pass Rate Cases
When pass rates fall within the 80-90% range, additional sampling and reassessment should be conducted in accordance with relevant standards. However, this step is often neglected. Furthermore, when test results indicate non-compliance, no corrective measures are implemented, ultimately nullifying the purpose of on-site testing of steel reinforcement layer.
Conclusion
To maintain structural safety and compliance with engineering standards, the accuracy of detection in steel reinforcement layer is essential. Following the proper criteria, preparing the testing surface, and following standardized instrument operations improve the reliability of detection data of the protective layer of steel reinforcement.
Langry offers advanced Non-Destructive Testing (NDT) tools designed to detect and assess the protective layer of steel reinforcement. Langry’s NDT solutions can accurately measure concrete cover thickness, locate reinforcement bars, and identify potential issues such as voids, cracks, or corrosion risks.
Contact Langry today to safeguard your structures with our advanced NDT tools.
