PSI - Issue 13

Libor Topolář et al. / Procedia Structural Integrity 13 (2018) 1177 – 1182 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1182

6

4. Conclusions

This paper describes an experiment on thermally degraded concrete beams during a three-point bending test. The samples had a central notch and the AE activity was monitored during the tests. Three mixtures were tested and differed in the used aggregate grain size. When considering the flexural strength values, the mixture B had the best results due to the used coarse aggregate grain size, but when relative values are considered, the decrease in all the mixtures is very similar. The only difference is evident when firing to 1200 °C when sintering occurs and the coarse the AE signal duration is indicative of the degree of compactness of the monitored structure, which allows easier passage of the acoustic waves originating from the AE source; the mixture C is the best in this regard  the AE signal energy is indicative of the strength of the inner bonds of the samples, a better internal structure causes higher release of the AE energy; the decrease of this parameter indicates greater damage to the inner bonds, this decrease was the smallest for the mixture C. It can therefore be said that the different types of damage in the degraded material create different AE signals. These differences are connected to the degree of damage of the structure (Farnam et al. (2015)). The results of the experiments can be used to determine the properties of thermally degraded materials as well as the specific properties of the forming microcracks. Acknowledgements This paper has been worked out under the project GAČR No.16 -02261S supported by Czech Science Foundation and the project No. LO1408 "AdMaS UP - Advanced Materials, Structures and Technologies", supported by Ministry of Education, Youth and Sports under the „National Sustainability Programme I" . Ativitavas, N., 2002. Acoustic emission signature analysis of failure mechanisms in fiber reinforced plastic structures (Doctoral dissertation). Bodnárová, L., Zach, J., Hroudová, J., Válek, J., 2013. Methods for Determination of the Quality of Concretes with Respect to their High Temperature Behaviour. Procedia Engineering 65, 260-265. Collepardi, M., 2010. The New Concrete. Grafiche Tintoretto, Italy, pp. 436. Farnam, Y., Geiker, M. R., Bentz, D., Weiss, J., 2015. Acoustic emission waveform characterization of crack origin and mode in fractured and ASR damaged concrete. Cement and Concrete Composites 60, 135-145. Grosse, C. U., Ohtsu, M. (Eds.)., 2008. Acoustic emission testing. Springer Science & Business Media. Hager, I., 2013. Behaviour of cement concrete at high temperature. Bulletin of the Polish Academy of Sciences: Technical Sciences 61(1), 145-154. Kreidl, M., Šmíd, R., 2006. Technical diagnostic. BEN – technical literature, Czech Republic, pp. 406. [in Czech] Landis, E. N., Baillon, L., 2002. Experiments to relate acoustic emission energy to fracture energy of concrete. Journal of engineering mechanics 128(6), 698-702. Nair, A., Cai, C. S., 2010. Acoustic emission monitoring of bridges: Review and case studies. Engineering structures 32(6), 1704-1714. Pazdera, L., Topolar, L., Mikulasek, K., Smutny, J., Seelmann, H., 2017. Non-Linear Characteristics of Temperature Degraded Concrete at High Temperature. Procedia engineering 190, 100-105. Topolář, L., Kucharczyková, B., Kocáb, D., Pazdera, L., 2017a. The Acoustic Emission Parameters Obtained during Three-point Bending Test on Thermal-stressed Concrete Specimens. Procedia engineering 190, 111-117. Topolář, L., Dvořák, R., Pazdera, L. , 2017b. The Assessment of High-Temperature Degraded Concrete Specimens of Different Mixtures by Acoustic Emission Method during Three-Point Bending Test and Pulse Velocity Method in Comparison with Destructive Tests. In Materials Science Forum (Vol. 908, pp. 88-93). Trans Tech Publications. Zhao, J., Zheng, J. J., Peng, G. F., van Breugel, K., 2014. A meso-level investigation into the explosive spalling mechanism of high-performance concrete under fire exposure. Cement and Concrete Research 65, 64-75. References aggregate causes a decrease in the relative flexural strength values. From the point of the AE signal parameters, it can be stated that: 