Cavitation resistance of concrete

Abstract

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...