Issue 40

S. K. Kourkoulis et alii, Frattura ed Integrità Strutturale, 40 (2017) 74-84; DOI: 10.3221/IGF-ESIS.40.07 83 equal to about 40% of its value before the sudden jump. This discontinuity can be again considered as a clear indicator that the specimen enters its critical stage and macroscopic fracture is impending. Another interesting conclusion drawn from Fig.13b is that the pre-failure indicators provided by the AE technique are in very good agreement with similar ones obtained by another sensing technique known as Pressure Stimulated Currents (PSC) [16-20]. Indeed it is seen from Fig.13b that just before the “jump” of the graph of the cumulative hits/s the PSC recorded by a pair of electric contacts starts increasing gradually. The same signal (PSC) exhibits a very steep “jump” just before the macroscopic fracture of the specimens. Considering the data of these two protocols it can be concluded that a combined use of the AE and PSC techniques may be proven valuable in the direction of further enlightening the internal damage process of specimens made of building materials as well as in the direction of providing safe pre-failure indicators. R EFERENCES [1] Korres, M., Toganides, N., Zambas, C., Skoulikidis, Th., Study for the restoration of the Parthenon, Vol.2a, Athens: Ministry of Culture, Committee for the Preservation of the Acropolis Monuments (in Greek), (1989). [2] Kourkoulis, S.K., Marinelli A., Dakanali, I., Α combined experimental and numerical study of the pull-out mechanism of threaded titanium bars embedded in marble, ECCOMAS Congress 2016-VII European Congress on Computational Methods in Applied Sciences and Engineering, M. Papadrakakis, V. Papadopoulos, G. Stefanou, V. Plevris (eds.), Crete Island, Greece, 5-10 June 2016. [3] Dakanali, I., Stavrakas, I., Triantis, D., Kourkoulis, S.K., Pull-out of threaded reinforcing bars from marble blocks, Procedia Structural Integrity, 2 (2016) 2865-2872. [4] PETRES ALFAS M. & D. SARRIS S.A.: http://petresalfas.com [5] Ninis, L., Kourkoulis, S. K., Sakellariou A., Evaluation Criteria for building stones in the restoration of the Epidaurean Asklepieion, Proceedings of the Interdisciplinary Workshop “The building stone in monuments”, Athens, November 2001, IGME Publishing, Eds. M. Varti-Mataranga and Y. Katsikis, , (2002) 235-248 (in Greek). [6] Kehayas, K., Comparison of results of conventional triaxial- and multilevel triaxial-tests on marly limestone, Diploma Thesis, Technical University of Crete, Supervisor Z. Agioutantis, Chania, Crete, 2012 (in Greek). [7] Kaklis, K., Agioutantis, Z., Vafidis, A., Mavrigiannakis, S., Kouvela, M., Feggos, G., Characterization of bioclastic limestone of Alfas-Rethymon by laboratory and in-situ tests, 1st National Conference for building materials and ele- ments, Athens, 21-23 May 2008, Technical Chamber of Greece (in Greek). [8] Aggelakopoulou, E., Design and evaluation of restoration mortars for the Acropolis monuments, The Acropolis Restoration News, 13 (2013) 13-17. [9] http://www.aalborgwhite.com Aalborg white cement paste [10] Grosse, C.U., Ohtsu, M., Acoustic Emission testing, Basics for research - Applications in Civil Engineering, Springer- Verlag Berlin Heidelberg, (2008). [11] Fowler, T.J., Blessing, J.A, Strauser, F.E. Intensity analysis, Proceedings of the 4 th International Symposium on Acou- stic Emission From Composite Materials AECM-4, Seattle (1992), American Society for Nondestructive Testing, Columbia (1992) 237-246. [12] Ohno K., Ohtsu, M., Crack classification in concrete based on acoustic emission. Construction and Building Materials, 24(12) (2010) 2339-2346. [13] AE and Related Nondestructive Evaluation (NDE) Techniques in the fracture mechanics of concrete, Woodhead Publishing Series in Civil and Structural Engineering, editor Masayasu Ohtsu, 57 (2015). [14] Aggelis, D., Shiotani, T., Momoki, S., Hirama, A., Acoustic emission and ultrasound for damage characterization of concrete elements, ACI Materials. J. 106 (6) (2009) 509-514. [15] Kourkoulis, S.K., Dakanali, I., Petropoulou, V., Acoustic emission versus pressure stimulated currents in uniaxially compressed natural building stones, Accepted for presentation at the 14 th International Conference on Fracture (ICF 14), Rhodes Island, Greece, June 18-23, 2016. [16] Stavrakas, Ι., Triantis, D., Agioutantis, Z., Maurigiannakis, S., Saltas, V., Vallianatos, F., Pressure Stimulated Currents in rocks and their correlations with mechanical properties, Natural Hazards and Earth System Sciences, 4 (2004) 563-567. [17] Vallianatos, F., Tzanis, A., Electric current generation associated with the deformation rate of a solid: Preseismic and coseismic signals, Physics and Chemistry of the Earth, 23 (9-10) (1998) 933-939. [18] Vallianatos, F., Triantis, D., Tzanis, A., Anastasiadis, C., Stavrakas, I., Electric earthquake precursors: From laboratory results to field observations, Physics &Chemistry of the Earth, 29 (2004) 339-351.