AP04_1.vp 1 Introduction Mechanical properties of concrete are changing in the course of its ageing. Ageing of concrete is accelerated by cli- matic conditions, mechanical stress, aggressive liquid, etc. This article deals with a question of irradiation influence, which arises, for example, as a consequence of uranium 238U and 235U fission reaction in the nuclear reactor. It concerns neutrons and gamma irradiation acting on concrete construc- tions and accelerating their surface and internal changes. The concrete in these facilities plays not only the structural role, but also the role of shielding material that has to absorb the aforementioned types of irradiation and prevents their pene- tration. Of the irradiation spectrum we will observe only influ- ence of gamma irradiation. The gamma irradiation is being absorbed at the passage through concrete, what can induce water radiolysis �1� in the material and consequently chemical reactions leading to changes of the concrete phase composi- tion �2� and thus the hydration degree decrease. We can ex- pect that this hydration degree decrease becomes evident by the decrease of the concrete strength. This hypothesis is being proved in this article. 2 Concrete composition Samples determined for testing were made according to the formulation, which is stated in Table 1 �3�. This form- ulation was used at construction of the containment of the nuclear power plant Temelín. Composition of cement CEM I 42,5 R Mokrá is listed in [3]. Concrete beams, on which consequently the experiment took place, were made of this mixture. Volume mass of concrete 28 days old was 2358 kg × m�3. 3 Method of irradiation Irradiation was carried out in the company Bioster a.s. Veverská Bítýška, where 60Co is used as a gamma irradiation source. The activity of source 60Co at the beginning of ex- periment was A � 462 kCi (1.73×1016 Bq) and at the end of experiment was 449 kCi (1.68×1016 Bq). These values were necessary for calculating of total radiation dose rate which was 0.935 kGy × h �1. Concrete beams at dimensions 0.4×0.1×0.1 m after 90 days from concreting were used for the experiment. Each beam had gamma irradiation do- simeters fixed on it. Beams were irradiated for 90 days with a dosing input of approx. 0.25 kGy × h�1, i.e. the maximum dose was 0.5 MGy for the whole period of irradiation. The dif- ference between radiation dose rates is caused due to items, © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 57 Czech Technical University in Prague Acta Polytechnica Vol. 44 No. 1/2004 Influence of � Irradiation on Concrete Strength V. Sopko, K. Trtík, F. Vodák Aging of concrete due to gamma irradiation. Strength of concrete are in a good correspondency with already known results. Keywords: concrete, gamma irradiation, strength. Component Mass Cement 499 kg [42,5R] Water 215 kg Plasticizer (Ligoplast SF) 2.8 kg Aggregates: 0 –4 mm 705 kg 8 –16 mm 450 kg 16 –32 mm 527 kg Table 1: Composition of 1 m3 of concrete 0.7 0.8 0.9 1 1.1 1.2 1.3 0 100 200 300 400 500 600 Dose [kGy] Te n si le st re n g h t ra tio Fig. 1: Dependence of tensile strength ratio on dose 0.7 0.8 0.9 1.0 1.1 0 100 200 300 400 500 600 Dose [kGy] C o m p re ss iv e st re n g h t ra tio Fig. 2: Dependence of compressive tensile strength ratio on dose which were placed between source of radiation and irradiated samples. Classical rectifying diodes calibrated by means of standard dosimeters were used as dosimeters �4�, which error is about twenty per cent. Standard dosimeters are limited for higher doses of the gamma irradiation, therefore, the dosim- eters, which we used, were calibrated for lower doses and con- sequently extrapolated for high irradiation doses. 4 Method of strength measurement At first, the flexural strength test (three – point support- ing) was applied to concrete samples. After this destructive test the compressive strength test was used on the first frag- ment (in accordance with ČSN 73 13 18) and the tensile strength test on the second fragment of splitting (in accor- dance with ČSN 73 13 17). Conclusion Measured values of concrete strength (Fig. 1, 2) are ac- cording to current measurments obtained by various experi- mentators viz [5]. Acknowledgments This work was supported by MŠMT ČR (Contract No. J 04-098-2100000 20). References [1] Assessment and management of ageing of major nuclear power plant components important to safety: Concrete containment buildings (Pachner J.); IAEA – TECDOC – 1025, IAEA- Vienna 1998, ISSN1001-4289. [2] Bouniol P., Aspart A.: “Disappearance of oxygen in con- crete under irradiation: the role of peroxides in radiolysis.” Concrete and Cement Research, Vol. 28 (1998), No. 11, p. 1669–1681. [3] Vodák F. et al: Trvanlivost a stárnutí betonových konstrukcí jaderných elektráren. FSV ČVUT, 2002. [4] Prouza Z., Obraz O., Sopko B., Spurný F., Škubal A.,Kits J., Látal F.: “Dosimetric Parameters of a New Czechoslo- vak Neutron Si Diod.” Radiation Protection Dosimetry, Vol. 28 (1989), No. 4, p. 277–281. [5] Kaplan M. F.: Concrete Radiation Shielding (Nuclear Phys- ics, Concrete Properties, Design and Construction), Longman Scientific & Technical, England, 1989. Ing. Vít Sopko phone: +420 224 354 435 e-mail: sopko@fsv.cvut.cz Department of Physics Doc. Ing. Karel Trtík, CSc. phone: +420 224 354 626 e-mail: trtik@fsv.cvut.cz Department of Concrete Structures and Bridges Prof. František Vodák, DrSc. phone:+420 224 353 886 e-mail: vodak@fsv.cvut.cz Department of Physics Czech Technical University in Prague Faculty of Civil Engineering Thákurova 7 166 29, Praha 6, Czech Republic 58 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 44 No. 1/2004 Czech Technical University in Prague