In his opening speech, V. V. StoI'nikov, Doctor of Technical Sciences, chairman of the coordination commission for hydraulic concrete, stated that the construction of hydraulic plants in the northeastern, northern, and eastern parts of the country brings along several new requirements the concrete has to meet. These requirements have been laid down in the new State Standard 4795-68, which was worked out by the B. E. Vedeneev AII-Union Scientific-Research Institute of Hydraulic Engineering. Many new requirements, such as ultimate strength, capacity to absorb water, shrinkage and swelling, etc., have been introduced. Great care is paid to the frost resistance of the concrete, especially at temperatures below --20~ V. V. Stol'nikov pointed to the chief shortcomings in the practice of setting up specifications for materials for hydraulic concrete; the conditions which the concrete has to stand are not examined with due consideration, and it occurs often that only the general directives of standard specifications are used, whereas the particular circumstances under which the structures must exist are not taken into account, nor are the structural peculiarities of the buildings and their construction methods. What is needed is a more comprehensive and creative approach to the design of the composition of the concrete and to its purpose in accordance with the environmental conditions of the concrete used in structures.Fillers for hydraulic concrete must also be considered with great care, and one may not confine oneself to a former approach that had been used in the construction of gravity structures. Today, fiIlers sometimes do not have the required high quality, though the requirements the concrete has to meet have been raised considerably since the power industry has turned to building thin arched dams and dams in seismic regions of the country. V 9 V. StoI'nikov emphasized the importance of testing the materials at construction sites by piling up and testing experimental blocks of sufficient size on an artiUery shooting range.Three main problems were put at the discussion of the conference:1. Experience gathered with concrete materials in the construction of hydraulic structures.2. Experience gathered in drawing up specifications for materials for various types of concrete for hydraulic structures.3. Investigation of and tests with hydraulic concrete and materials for preparing such concrete.

In opening the Conference, Doctor of Technical Sciences V. V. Stol'nikov characterized the problem involved in the design and determination of the compositions of hydraulic concretes in Soviet and foreign engineering practice and described the basic directions of the scientific-technical progress in the technology of construction materials and concrete for hydropower construction. He pointed out that the firmness and durability of concrete, which depend substantially upon the homogeneity of the concrete in the structures, are basic factors in the economy of these structures. A highly important problem relating to the scientific-technical progress in the fields of concrete technology and construction of concrete structures is the ensuring of homogeneity of the concrete. The investigation of the effects of different technological and production factors upon the homogeneity of concrete and the development of effective measures for eliminating the adverse aspects of these factors constitute one of the main research directions. The design and determination (selection) of the compositions of concrete mixes should be carded out by taking into account a certain homogeneity level of the concrete in the structure. It is necessary to develop norms governing the homogeneity of concrete for different types of large hydraulic structures. It is necessary also to establish norms regulating the fulfillment of the design requirements relating to strength and other indices, the allowable coefficients of variation of the strength characteristics for different degrees of mechanization and organization of concreting operations, etc. The speaker emphasized the convenience of establishing in the design a specific control average concrete strength and an allowable coefficient of variation, instead of the so-called "concrete grade.-Estimated values of the -coefficient of variation-of the concrete, the average control strength, and the frequency of fulfillment of the design requirements for concrete should be adopted at the construction sites.Selection of the concrete composition by taking into account the water demand was the subject of a paper presented by Doctors of Technical Sciences Yu. M. Bazhenov and G. I. Gorchakov and Candidates of Technical Sciences L A. Alimov and V. V. Voronin (Moscow Civil Engineering Institute, MISI). These authors recommended taking into account in the selection of the composition of concrete mixes the "aggregate demand, -that is, the part of the water retained by the aggregates, which depends upon their characteristics and the properties of their surfaces. The bases of an experimental method for selecting concrete mixes by using certain proposed coefficients are described in their paper.Candidate of Technical Sciences V. A. Nevskii and Engineer O. A. Lyakh (RISI) presented a justification for use of the summation of damages for analysis of the frost resistance of concrete and the durability of concrete structures according to the climatic and operating conditions. The establishment of requirements for concr...