PSI - Issue 52

Rakesh Katam et al. / Procedia Structural Integrity 52 (2024) 72–88 Rakesh Katam/ Structural Integrity Procedia 00 (2019) 000 – 000

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The UPV techniques can be used to assess the homogeneity of the concrete (Salim Al-Numan (2015)), the existence of cracks, voids, and other faults, as well as potential changes in the structure of the concrete over time. The ultrasonic pulse is produced by an acoustic transducer and when a transducer produces a pulse, it is subjected to numerous reflections along the edges of the various elements in the concrete. A complex system of stress waves is created by the interaction of longitudinal, shear, and surface waves. The receiving transducer picks up the beginning of the longitudinal waves, which are the fastest to arrive. It is a useful technique for testing structural concrete since only the pulses' elastic properties, which are almost fully independent of the material's properties, affect their velocity. The essential principle of assessing the quality of concrete is that higher velocities can be reached when the concrete's density, homogeneity, and uniformity are good. Lower velocities are attained with poor quality. The pulse strength is dampened and it travels around the discontinuity, lengthening the path and producing lower velocities, if there is a crack, void, or other flaws in the concrete that prevent the pulses from being transmitted. The UPV values for the structural elements range from 0.8 m/s to 5.8 m/s, as shown in Table 4. The higher the UPV number, the higher the concrete's quality. Column A1 (indirect) is categorized as having good concrete quality and has the highest UPV value of 4.2 m/s. However, the tangible quality of elements A3 (direct), b1 (indirect), b2 (indirect), b3, b5, and b6 (indirect) has been challenged due to their UPV values, which range from 0.8 m/s to 3.0 m/s. This suggests that there might be flaws or deterioration in certain components.

Table 4. Ultrasonic Pulse Velocity (UPV) for different structural elements. Element no. UPV (m/s)

Concrete quality

A1 (indirect) A3 (direct) B1 (indirect) b1 (indirect) b2 (indirect) b3 (indirect) b5 (indirect) b6 (indirect)

4.2 0.8 5.8 2.2 1.8 3.0 2.2 2.2

Good

Doubtful Excellent Doubtful Doubtful Doubtful Doubtful Doubtful

After combining RH and UPV, the results provide a conflicting picture of the state of the elements since in RH the surface on the beams appears to be in good condition, however, in UPV the results are uncertain. This demonstrates that while the concrete within is poor, it is good on the outside. this might be a result of beam repairs, as was mentioned earlier. Assuming the structural degradation over 30 years, the present compressive strength of concrete might have reduced by 20% to 50% can be observed from the results. To have more understanding of concrete carbonation test is carried out. The dust is collected on a non-absorbent, chemically inert sheet of metal or tile after being slowly drilled into a small hole that is between 5 and 10 mm deep. On the dust and inside the drilled hole, phenolphthalein is sprayed sparingly. The depth of carbonation is the lowest depth at which the color shifts (pink/purple). By spraying phenolphthalein and noting the color change, the Concrete Carbonation test was carried out at the site location on the damaged areas of the columns. A significant depth of carbonation was revealed by the carbonation test. Rapid carbonation of the low-quality concrete caused the reinforcement to get de-passivated and the concrete to deteriorate as a result. Table 5 displays the outcomes that were obtained.

Table 5. Carbonation test for different structural elements. Element no. Observation

Results

A3 B3

Color less Color less

Carbonated Carbonated