Experience in constructing the Bratsk and Mamakan hydroelectric power stations [1,2] has shown that in dams constructed= in regions of rigorous climate some of the concrete freezes under certain conditions. All known works [3,4, 5] devoted to the deformative character of frozen concrete were limited to laboratory tests, which for a number of reasons are conditional In this article we will examine the effect of negative temperature on strains of massive concrete based on data of field investigations* of the Bratsk hydroelectric power station dam.About 1000 remote-controlled gauges for measuring the strains of the concrete were embedded in the structure for observations; 170 instruments were enclosed in so-called "shrinkage cones" [6] situated in 41 blocks of the structure and which permitted measuring free volume changes; 120 of the instruments were periodically subjected to the effect of negative temperature.T

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Hydraulic construction in regions of Eastern Siberia and the North :has brought up new problems regarding the change of the physical and mechanical properties of concrete during its freezing. This problem is extremely timely, since as early as during the construction period the concrete of a structure is subjected to negative temperatures, which have an effect on its thermal-stress state. During the operating period the temperature determines the magnitude of deflections and opening of horizontal joints on the downstream face and thereby influences the behavior of the structure.The standards presently in effect (SNIP II-A 10-62) do not take into account the change of the physical and mechanical properties of concrete at negative temperatures. In particular, the recommended coefficient of linear expansion 1 • 10 "s dee -I, cannot be extended to concrete exposed to negative-temperature effects.All presently known investigations were carried out on specimens made of mortar of a simulated composition of concrete, whereby the rate of freezing exceeded by 1-2 orders the real rate of temperature changes in hydraulic structures.As investigations [1, 2] showed, nonobservance of one of the conditions characteristic for the temperature and moisture regime of massive concrete (absence of moisture exchange with the external environment, presence of large aggregate fractions, low rate of freezing) makes the resvlts of laboratory and full-scale investigations incomparable.During recent years the B. E. Vedeneev All-Union Scientific-t~Jesearch Institute of Hydraulic Engineering has been analyzing the data of full-scale investigations of temperature deformations in the dams of the Bratsk and Ust'-llimsk hydroelectric stations with simultaneous laboratory tests, the technique of which is sufficiently close to the conditions existing in massive concrete.The results of the fu11-scale and laboratory investigations proved to be completely identical [3,4]. The average minimum temperature at a distance of 0.5 m from the downstream face of the Bratsk dam (the mixing water is retained at this depth in the concrete) was from -15 to -18"C, having dropped during the severe winter of 1967-68 to -80"C. The minimum temperature of the specimens ranged from --36 to --40"C.The composition of the experimental blocks and laboratory specimens covered all grades of concrete placed in the construction of the Bratsk and Ust'-Ilimsk stations, cement manufactured by the Krasnoyarsk, Irkutsk, and Aehinsk plants (slag-Portland, sand, and pozzolana cements), and various aggregates. Therefore, the results obtained can be extended to any concrete used in hydraulic construction. The only restriction is the petrography of the aggregate, since the concretes of the Bratsk, Ust'-llimsk, and I

Comprehensive full-scale investigations of the Bratsk and Krasnoyarsk hydroelectric station dams produced extensive experimental data on the behavior of high darns under rigorous climatic conditions and in particular, revealed the role of temperature as a most important factor governing stress and strain in dams.