PSI - Issue 43

Vlastimil Bílek et al. / Procedia Structural Integrity 43 (2023) 107–112 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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All the above-mentioned tendencies were expected and they are in accordance with the knowledge about concrete technology. There is no explanation why water-cured and better hydrated concretes do not have more significantly higher mechanical properties. The values in Tab. 3 show better values for foil-cured specimens. A hint for insight into this problem can be found in the last lines of Tab. 4. The finest threshold, P3, covers the finest pores and some microcracks. A relative increase of porosity (P3-P1)/P1 is higher for the water-cured specimens (except for w/c = 0.30). It means that the finest pores are closed thanks to shrinkage in the case of foil-cured concrete, but they keep their original size in the case of water-cured specimens or some swelling of the finest detected pores. This idea generally corresponds to the conclusions of Acker (2004). This indication is not very reliable, but it can be one of the parameters which affect the values of mechanical properties. 4. Conclusions Concretes with various water-cement ratios under two different conditions of curing were prepared and tested for fracture mechanical properties together with CT. The following conclusions can be drawn: • Some unexpected results were obtained concerning the higher properties – strengths and fracture toughness – for concrete specimens cured without a source of curing water. • The compressive strength of foil-cured and relatively dry specimens might be explained by non compressible water in pores. • The explanation of lower bending strengths and lower fracture toughness is more complicated. There were not detected any significant increases in cracks in the concrete without water curing. • CT shows some indication. There is a slightly higher increase of the finest detected porosity in water cured specimens, which can be affected by the swelling of the C-S-H gel and non-affected size of pores, while pores in the foil-enveloped specimens are closed thanks to shrinkage. Acknowledgements This outcome has been achieved with the financial support of the Czech Science Foundation project No. 21-08772S - Influence of Self-Healing Effects on Structural Fatigue Life Extension of Structures Made of High-Performance Concrete (InShe). The 5 th author would also like to acknowledge the financial support from the mobility project No. 8J22AT008 – Mechanical Fracture Quantification of the Role of Hemp Fibres on Self-Healing Processes in Selected Composites (KvaRK) References Acker, P., 2004, Swelling, shrinkage and creep: a mechanical approach to cement hydration, Materials and Structure/Concrete Civil and Engineering, Vol. 37, 237 – 243 Aïtcin, P. -C., 2011. Binders for Durable and Sustainable Concrete, (528 pp) Spoon Press. Aïtcin , P.-C., 2014. The problems with high strength and low w/c ratio concretes, Cement Wapno Beton, 19/81, nr 2 , 127 – 137, Aïtcin, P. -C., Mindess, S, 2011. Sustainability of Concrete, Spoon Press, 328. Bilek, V., 1999. Possibility of explanation of interesting development of mechanical characteristics of concrete, 8th International EXPERTCENTRUM Conference held by the RILEM Technical Committee 160-MLN, Bratislava, Slovakia, 213 – 218. Karihaloo, B.L., .Nallathambi, P., 1989, An improved effective crack model for determination of fracture toughness of concrete, Cem.Concr.Res., Vol.19, 603 – 610 Karihaloo, B.L., 1995, Fracture Mechanics and Structural Concrete. Pearson Education Limited. Kurdowski, W., 2014, Cement and Concrete Chemistry, Springer, 700. Mahmoodi, S., Sadeghian, P., 2019, Self-Healing Concrete: A Review of Recent Research Developments and Existing Research Gaps, 7th International Conference on Engineering Mechanics and Materials, CSCE Annual Conference Laval, QC, Canada, MA11-1 – MA11-10 Qureshi, T., Al-Tabbaa, A., 2020, Self-Healing Concrete and Cementitious Materials Talaiekhozan, A., Keyvanfar, A., Shafaghat, A., Andalib, R., Majid, A. M. Z., Fulazaki, M.A., Zin, R.M., Lee, C.T., Hussin, M.W., Hamzah, N.,Marwar, N.F., Haidar, H.I., 2014. A Review of Self -Healing Concrete Research Development, Journal of Environmental Treatment Techniques, 2(1), 1 – 11.