Condition assessment of a thin walled monolithic concrete structure
  S. Christi, K. Sivasubramanian, K. N. Lakshmikandhan, V. Venkatesan and P. Sivakumar
  Presently, many structures in the country are very old and it becomes increasingly significant to develop techniques for condition assessment of these concrete structures. Impact-echo is an advanced NDT method being popularly used for the evaluation of elements with thickness greater than 100mm. The present work focuses on extending the applicability of impact-echo method for the evaluation of thin structural elements. Towards this, a model test structure is cast with thin wall elements, beams, columns and pedestals. The evaluation of the present condition of these structures is carried out using the non-destructive testing methods. The work was inspired from a field problem wherein the insufficient compaction of the concrete had led to water leakage in a cooling tower built with thin wall elements. The present work aims to apply the impact echo method for the identification of defects in the thin walls of the structure. The identification of the good and the bad concrete region is carried out using the thresholding technique. A detailed investigation is carried out to assess this threshold frequency. The air-coupled impact-echo is a method being applied for identifying shallow depth defects. This method has been used to validate the results from the impact-echo method. The results indicate that the impact-echo method can be confidently used in the field for evaluation of thinner elements.