- freely available
Materials 2019, 12(21), 3507; https://doi.org/10.3390/ma12213507
2. Materials and Equipment
- Correction of antenna sizes and positions;
- Background removal with automatic foreground/background detection to mask uniform structures such as the surface and possible stratifications;
- Automatic gaining to compensate the damping of the radar waves in the base material;
- Time-zero estimation (automatic recognition of the surface position);
- Temperature compensation to allow immediate and accurate measurements directly after start-up.
3. Test Results and Analysis
4. Fibre Spacing Determination and Discussion
- for positive integer numbers n:
- for other positive numbers z:
- The method based on the electromagnetic induction technique can be applied to estimate the approximate volume of steel fibre in a hardened SFRC element and the uniformity of fibre spacing. However, the method requires calibration to obtain good quality of results in deeper layers due to the “shadow” cast by the fibre present in the top layers. The method can be applied to detect steel fibre up to the 120 mm thickness of the tested element.
- The method based on the radar technique is suitable for instant detection of the areas with a clearly spaced fibre volume (too low or too high local fibre concentration). Theoretically, the method can be applied to detect steel fibre presence up to the 200 mm thickness of the tested element, yet only fibre present in upper layers is correctly detected. The testing equipment based on the radar technique used for fibre detection is able to recognize fibre concentration fields but not a single fibre.
- Both methods together can detect fibre concentration in SFRC volume but cannot detect a single fibre.
Conflicts of Interest
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