Cavitation resistance of epoxy plastic concretes

Abstract

Operating experience with flow structt~es of high-head hydrocomplexes indicates that, in regions which are especially susceptible to cavitation, concrete is subjected to intensive disintegration as a result of the cavitational erosion. The cavitation resistance of the concrete may be raised by using high quality filiers and special techniques in preparing and placing the mix,* and in addition, by the requisite protection of the surfaces.At present, expensive metal linings are used for protecting the concrete in such regions, even in temporary structures. Attempts to use gunite, natural stone materiais, wood and resin for these purposes were unsuccessful [1]. Repair of damaged surfaces with portland cement concrete and mortar are time-consuming. Moreover, disintegration sets in again, as it is impossible to achieve a strong bonding of old concrete with new.An analysis of studies of the theory of cavitation permits one to forrnulate the essential properties of a material for protective linings resistant to the action of cavitation. Such a materialmust possess exceptional homogeneity, high elasticity, high density and good dielectric properties. It is practically impossible to select a natural construction material which simultaneousIy satisfies all the requirements set forth.Recently, both abroad and in the USSR, particular consideration is being given to investigating the cavitation resistance of polymer materiais [2-4] whose properties are controlled over an extremely broad range. Plastic concretes were used for repaiz of flow structures of Priest Rapids and Rocky Reach dams, and their successful operation over a period of 4 years permitted the metallic lining installed as a cavitation-resistant protective covering on the submerged spillway of Milford Dam to he replaced by epoxy plastic concrete [5][6][7].In the NIS Gidroproekt (All-Union Planning and Research Institute for Hydraulic Engineering) division of polymer materials, investigations], were made of the use of domestic synthetic resins for preparing cavitation-resistant plastic concretes [8,9]. Specimens were tested for the effect of the cavitation trail arising in a two-dimensional flow behind a cylinder, in both rotary and flow-through testing units and in a cavitation tube [10,11,12]. In the flow-through testing unit the velocity of flow was 33, in the rotary 28, and in the cavitation tube 26.4 m/sec. The corresponding cylinder diameters were 20, 15, and 24 mm. The specimens, on an anchored duraluminum base 10 mm thick measured 35• 70 • 150 mm. Tests were conducted with a degree of hardening of not less than 85% [13].The resistance of plastic concretes to cavitation erosion was evaluated according to loss of weight or volume of the specimens with time, during the action of cavitation, up to that moment when the specific erosion reached a steady magnitude.For selection of the basic cementing agent, tests were conducted on sand plaster concretes with a base of various synthetic resins (Table I). From Fig. I it is seen that plastic concretes with epoxy res...

Cavitation destruction of concrete and protective facings under natural conditions

“…Polymer coatings, mainly on an epoxy base, for protection of concrete against various actions, including cavitation, have recently been used in the construction and repair of hydraulic structures in our country (Charvak hydroelectric station) [17] and abroad (Milford, Priest Rapids, Rocky Ridge dams in the USA, and others). However, reliable and comparatively long experience has not been accumulated in the use of these coatings.…”