Evaluation of Depth of Deterioration of Concrete Structure after Fire Using Stress Wave Method

The aim of the present research is to evaluate the degree of deterioration by means of stress waves. In this study, the stress waves generated by the impact of a steel ball on concrete surface are recorded by a displacement receiver 200 mm away. The received signal is analyzed in the frequency domain. The frequencies of the dominant response in the spectrum are used to evaluate the depth of deterioration for concrete specimens experienced various high temperatures. Two types of specimens were used for investigation. One is small specimen with dimensions 40*40*15 cm. These specimens were heated with the temperatures 300 to 800°C. The other is a large concrete plate with the size 240*130*15 cm. The specimen is heated by fire with the highest temperature 600°C. The principal frequencies obtained from the small specimens were compared to the depth of deterioration evaluated by drilled core. The cores were sliced into thin disks and the depth of the deterioration was evaluated by the dynamic elastic modulus of the disks. The test procedures were also applied to the big plate specimen to obtain the depth of deterioration. The test results show the depth of deterioration can not be evaluated when it is less than 2 cm. A linear relationship can be found between the lowest peak frequency and the depth of deterioration.