Bond strength of underwater repair concretes under hydrostatic pressure

Complex investigation of the influence of hydrostatic pressure on the bond strength of underwater concretes (UWC) to the concrete substrate was carried out. A new-developed apparatus made possible to cast the repair concrete under water on the previously prepared concrete substrate and use hydrostatic pressure 0.5 MPa. This pressure corresponds with placing of the repair concrete at the depth of 50 m. The bond strength of the repair layers of the concrete to horizontal and vertical surfaces was investigated; this was possible by using the specially formed concrete substrates. The bond strength was determined using pull-off methods according to the European Standard EN 1542. Favourable effect of the pressure on the bond strength of underwater repair concretes was observed for the horizontal substrates. In the case of vertical substrates (a vertical wall model), however, decrease of the bond strength of UWC was observed in the layers near the water surface. The most effective method of the surface treatment during the placement of the underwater repair concrete under hydrostatic pressure appeared to be sand-blasting.