Rehabilitation of cracked concrete dams.

摘要

This thesis addresses the rehabilitation of cracked construction joints in concrete dam which are located in severe climatic conditions. In order to measure the strength of joints between concrete materials and repaired concrete structures, when subjected to severe thermal conditions, a large scale experimental program has been implemented. This program is intended to evaluate the strength of weak concrete interfaces at different temperatures. Interfaces are weaker than the base material because of the residual strain accumulation usually caused by the differential curing histories of the two adjacent concrete layers. In addition to uniaxial specimens and wedge splitting specimens, wedge specimens cast in two stages were prepared and tested in this research program. After the splitting test, the specimens were repaired and by gluing the two halves together using different repair materials. The set-up used in the experiment includes a cold chamber where the temperature may reach –50°C. The chamber has circular holes at the top and bottom ends to allow steel extension pipes to transmit the load. The tests are carried under crack opening displacement control at a rate of 0.05 μm/sec. The fracture parameters are extracted for low temperature as well as room temperature. In general, with repair materials under dry conditions and low temperature have a brittle behavior. Also, higher energy release rates are consistently observed at low temperature. Furthermore, specimens are found to be weaker when repaired under wet surface conditions. Finally, the effect of thermal residual stress state in the interfaces between successive lifts of concrete on the fracture parameters is also addressed as part of this research to identify the source of joint weakness. Based on the experimental test results, recommendations are proposed to fix a dam failure. The dam in question is the Long Spruce Generation Station on the Nelson River in Northern Manitoba.