What are the main causes of degradation in concrete dams, and how are these issues diagnosed?

The main causes of degradation in concrete dams include alkali-aggregate reaction (AAR), freeze-thaw cycles, chemical attack, erosion, and structural overloading. Alkali-aggregate reaction occurs when certain reactive minerals in the aggregate react with the alkaline cement paste, causing expansion and cracking of the concrete. Freeze-thaw cycles cause damage as water penetrates the concrete, freezes, and expands, creating internal stresses that lead to cracking and spalling (surface flaking). Chemical attack can occur from exposure to acidic water, sulfates, or other aggressive chemicals, which can dissolve or weaken the concrete. Erosion is caused by the abrasive action of water flowing over the concrete surface, particularly at spillways or near the base of the dam. Structural overloading can occur due to unforeseen events like earthquakes, floods exceeding design capacity, or unexpected foundation settlements, which can cause cracking and deformation. These degradation issues are diagnosed using a combination of visual inspections, non-destructive testing, and laboratory analysis. Visual inspections involve a thorough examination of the dam's surface to identify cracks, spalling, discoloration, or other signs of distress. Non-destructive testing methods include ultrasonic testing, ground-penetrating radar, and impact-echo testing to assess the internal condition of the concrete without causing damage. Core samples may be extracted and sent to a laboratory for petrographic analysis to identify AAR or other chemical reactions, and for compressive strength testing to assess the concrete's structural integrity. Monitoring instrumentation, such as strain gauges and joint meters, can be used to detect movement and deformation of the dam. Leakage surveys can also determine areas where water is penetrating the concrete and causing damage. Regular monitoring and assessment are essential to detect degradation early and implement timely repairs to ensure the dam's safety and long-term performance.