The first cases of cavitation erosion of concrete of hydraulic structures were noted at the end of the 1930's (Bonneville Dam, USA), but reports about this appeared much later in the literature [1. 2].Cavitation erosion of concrete of hydraulic structures after 1-2 years service has been described and partially analyzed in domestic literature. Such destruction has been noted at the V. I. Lenin Volga [3][4][5], Bukhtarma [6], and Bratsk hydroelectric stations [7], and Suphung station in the Chinese People's Republic [8].In 1963 a field inspection was made of the condition of the concrete in the lower pool of the dam of the V. I. Lenin Volga hydroelectric station.* Unlike previous years, besides the energy dispersion baffles an investigation was the made of condition of the concrete of the spillway face, piers, bottom of the stilling pool, and first subsidiary dam of the third section, which was dewatered for repair for the first time after 7 years of service.The concrete dam is divided by two massive abutment piers reaching to the first subsidiary dam, into three sections (the sections are numbered from the left bank to the right). The stilling device consists of two rows of energy dissipation baffles in the form of truncated pyramids located on the bottom of the stilling pool in staggered order and two subsidiary dams. Twelve deflecting baffles are located in each extreme section to eliminate convergence of the current near the bank abutments.The presence of destruction on such elements as the side faces of the baffles and bottom of the stilling pool in the wake of the piers precluded the assumption that destruction was caused by the impact of floating bodies or the dynamic action of the water flow. An analysis of the possible causes of destruction led to the conclusion that erosion in the examined cases was the result of cavitation. It was found in the inspection that the concrete of the energy dissipation baffles and the deflecting baffles had experienced maximum cavitation destruction. Out of 82 dissipating and deflecting baffles 57 were eroded to a depth of 10-60 cm. Destruction occurred mainly on the dissipation baffles looated in the middle of the span (Fig. 1). One deflecting baffle and 13 dissipation baffles of the first row were severely erorded. For some, up to 60% of the side surfaces were eroded and the exposed 25-cm-diam. reinforcement was deformed (Fig. 2). The presence of a large quantitity of gravel protruding from the concrete was characteristic for the cavitation zone on the inside faces (Fig. 3). This fact, and the results of laboratory tests [9] proved the assumption that cavitation erosion of concrete begins in the "binder-aggregate" contact zone and consists in destruction of the hardened binder, weakening of the bond of sand grains in the conglomerate, and washing out of the mortar component and then of the coarse aggregate particles.Destruction of the upper and front faces of the deflecting baffles and dissipation baffles of the first row was quite insignificant (Figs. 1, 2, and 4). The di...

the construction site of the Inguri hydroelectric project and was devoted to the topic "Acceleration of methods of quality control of hydrotechnical concrete." The conference was attended by more than 70 representatives of 37 planning, research, and construction organizations and of institutes of higher learning of the country, 25 reports were presented. The opening address of Doctor of Technical Sciences Prof. V. V. Stol'nikov was devoted to a review of current accelerated methods of concrete quality control and to the task of the conference.The increased level of demands placed on the concrete of dams and the diversity of concrete characteristics which require daily control were pointed out. Many standard characteristics (maximum tension, impermeability, shrinkage, swelling) have been introduced for the first time into the new State Standard GOST 4795-67. The most important requirements imposed on newly proposed accelerated methods of control should be: a) simplicity and flexibility of the methods of accelerated determinations; b) possibility of statistical analysis of the results; c) reliability of the determinations themselves and reproducibility of the obtained results.

Core tests can give the most reliable information when studying concrete of structures.Rotary core drilling with type ST-1 hard-alloy bits were used in Soviet practice until recently for boring out cores. Owing to the presence in concrete of components having a different strength and the rapid wear of hard-alloy cutters during drilling, cores with a wavy and partially damaged surface are extracted. Testing of such specimens gives underestimated inindices of the properties of concrete characterized by a large scatter, whereupon the underestimation and scatter are higher, the smaller the diameter of the core. Hard-alloy bits have a low wear resistance and rarely provide a sufficiently large core recovery. All aforementioned shortcomings can be eliminated to a considerable extent by using diamond drill bits (Fig. i) [1], the results and experience of using which are given below.

The problem of the cavitation resistance of concrete is one of the principal problem~ in modern hydraulic engineering. This is explained by the lack of knowledge about the problem. The author of article [i] indicates the need to correct the existing recommendations on constructing elements of structures subjected to cavitation during service.In the article considerable attention was devoted to the selection of the type of coarse aggregate for concrete. The effect of the grain shape of aggregate on its cohesion with hardened cement is well known. Disturbance of cohesion along the contact "coarse aggregate graln-mortar component of concrete" was confirmed experimentally under cavitation conditions [3], which permits proposing cavitation tests as a method of determining the adhesion and cohesion of binders. The aforementlo~ed data and the results of investigating the cavitation resistance of concrete as a function of sand grain shape [4], despite the absence, as the author validly notes, of sufficient and accurate data on the effect of gravel or broken stone on the cavitation resistance of concrete, can indicate a slightly higher resistance of concrete with broken stone. Nevertheless the categoric requirement of the existing recommendations of the use of only broken stone in such cases cannot be considered correct, since first, the use of broken stone instead of gravel does not give a substantial increase of cavitation resistance [5]; second, with the same technology of placement the use of concrete with stone in place of gravel involves an increase of the already high consumption of cement, which is determined by the stringent requirements imposed on concrete in the case of the potential danger of cavitation damage. The increase of heat liberation of concrete associated with this and the possibility of its thermal cracking are fraught with still more unfavorable consequences, including from the viewpoint of cavitation erosion dmm-ge of the concrete; third the absence of broken stone owing to the ubiquitous remoteness of objects under construction from existing crushing and gradient plants often does not permit meeting the standard requirements, and the demand for broken stone for preparing comparatively small volume of special concrete cannot serve as sufficient ground for creating a technological llne for producing broken stone.In such cases it is expedient to use gravel of smaller size which is generally available to builders. The effectiveness of this measure was proved experimentally [6], and then verified during the construction and operation of the concrete flumes of the deep escapes of the Toktogul hydrostatlon. For preparing concrete of different parts of the flumes gravel with a maximum size of i0 or 25 mmwas used instead of the recommended but wanting broken stone with a maximum size of 40 mm.The problems raised in the article concerning the relation between the cavitation resistance of concrete and its mechanism of damage, strength, frost resistance, and homogeneity should be considered important. We no...

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