CAVITATION RESISTANCE OF CONCRETE

9 1980 Plenum Publishing Corporation
CAVITATZON
&ESZSTANCE OF CONCRETE
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'r~t lime,h FiE. i. Increase of the depth of focl of cavltatlon damage during operation of the structure. On the basis of the aforesaid, we propose to cell the phenomenon, whose name is given in the title of the article by Doctor of Technical Sciences, Prof. V. M. Moskvin, "cavitationerosion damage," meaning in the given case by "erosion damage" the result of the hydrodynamic action of the stream (in addition to purely cavltatlon), which, as a rule, continues to damage concrete that was started under the effect of cavitation. We apply this term to materials on which stream cavitation acts. As for the relation between cavitation resistance and strength, it has been shown experimentally [5, 11] that the relation between them has a complex character, which for a group of homogeneous materials is simplified. In the latter case it will be sufficient to characterize the resistance of a material, for example, concrete, by its strength. It is quite validly noted in the article that "frost resistance has a considerable effect on the cavitation resistance of concrete." We note that both frost and cavitation act on concrete selectively: they primarily damage those parts of the surface where obvious or concealed defects are concentrated (where a more mobile mix was placed, where the mix was compacted insufficiently or the concrete was frozen, etc.). The only difference is that under the effect of frost the concrete of such parts is not damaged so catastrophically quickly as in the case of cavltatlon-eroslon action. The aforementioned defects are mainly a consequence of vlolatlon of concreting technology. Therefore the author's conclusion concerning the mandatory taking of the most effective steps to increase the frost resistance of concrete should be supplemented by instructions on especial,ly careful observance of concreting technology in the case of the potential danger of cavitation, observance of high workmanshlp of performing concreting works, and careful construction control. It is impossible not to agree with Prof. V. M. Moskin's opinion that the use of polymers is an indisputably promising direction in controlling cavltatlon-eroslon damage of concrete. Of course not all "focl of possible cavitation can be eliminated" by using polymer materials in the form of protective facings and coatings, which, apparently the author of the article has in mind. Purthermore, an analysis of the data of experimental and on-site investigations [7, 8] showed that protective facings and coating (even sufficiently thick ones) are, as a rule, torn from the surface of the concrete with its subsequent intense damage. Impregnation with monomer with its subsequent polymerization should be considered another method of using polymeric materials for protecting concrete from cavitation. The effectivenss of this method is confirmed by the results of tests to determine the comparative cavitation resistance, characterized by the depth of ~-,~ge at a steam velocity of 37 m/set, of ordinary concrete, fibrous concrete, and ordlnsry concrete and fibrous concrete impregnated with methyl methacrylate (respectlvely, curves 1, 2, 3, and 4 in Fig. 1 [2]). It is very important that with a test time of 200 h erosion of the impregnated fibrous concrete ceased after only I0 h. This circumstance and the specific character of the zone of damage (grooves with steeps walls) compared to the traditional bowl-shaped focl on other specimens indicate the effectiveness of impregnating fine-grained concretes with monomer (the maxlmum size of the asgregate of the ordinary concrete was 38 ~n and of fibrous concrete 19 mm) and need to provide hlgh-qualit7 impregnation (erosion apparently occurred where the concrete was impregnated worse). Curve 5 in Pig. 1 characterizes deepening of the zone of
CAVITATION RESISTANCE OF CONCRETE Yu. P. Inozemtsev UDC 691.327:620.193
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