Quality of grouted construction joints at the Krasnoyarsk dam

Abstract

1. Control drilling and hydraulic testing of holes intersecting grouted joints permits evaluating the quality of the grouting on the basis of an analysis of the opening characteristics and degree of filling of the hole with cement stone, the state of the concrete surfaces, and the characteristics of the cement stone in the joint. 2. Three characteristic types of concrete surfaces in joints were established from an analysis of the cores. From the viewpoint of formation of cement stone in the joint and of bond with the concrete, a smooth surface without cement laitance is highly desirable. In order to obtain such a surface it is necessary to sue smooth surface plastic forms, to form the surfaces of the keys as gently as possible, to reduce the roughness of the first-stage concrete (especially at horizontal interfaces between blocks), and to remove the hardened cement laitance. 3. As a result of the core analyses, three cement stone groups were established which differ in their physicomechanical characteristics. For the grouting techniques followed under the given bonding conditions in the joints, basically high-strength cement stone is formed. However, even within the limits of a single outline there are zones of medium- and low-strength cement stone. The core analysis revealed the presence in some locations of cement stone corresponding to the second-stage grouting with a layer thickness of up to 1.0 mm. 4. Hydraulic testing of the control holes revealed that the perviousness of the joints decreased sharply after grouting; however, it is, as a rule, impossible to obtain complete watertightness of the outline for the given grouting techniques (with open air removal). 5. In order to obtain high-strength cement stone in the joint and to improve its bond with the concrete it is necessary to apply the grout with a maximum joint opening, which should be forced wider by increasing the grouting pressure, or by closing partially the air-removing conduits, whereby the cement stone is compressed in the joint by the forces caused by the elastic aftereffect of the deformed dam pillars.