Alkali - Silica Reactions in Concrete Dams - Alkali Leaching in the Votna Dam
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Alkali - silica reaction (ASR) is a common durability problem for concrete. There are three conditions that need to be fulfilled for the reaction to occur: sufficient moisture, alkali reactive aggregates and high alkali content in the concrete. The reaction can lead to alkali-silica gel formation, which can expand when absorbing water. This expansion can lead to a volume increase of the concrete. Consequently the concrete may crack and forces due to constrained expansion may develop. This study focuses on Votna 1 dam, constructed in 1966 1968. The dam is a double curved arch dam connected to a slab dam, which is situated in the south western part of Norway 950 m above sea level. The structure was diagnosed with ASR in 1987 1988. The research question addressed in this thesis is how deep leaching affects the alkali content in in-situ concrete. To the authors knowledge there is currently no data available on this.The extent of leaching is investigated by measuring the alkali metal profiles in concrete cores using the cold water extraction method. Concrete cores were retrieved from a selection of locations with different exposure conditions at the slab dam. The extraction method allowed measuring alkali metal leaching in the cores taken from the dam. For submerged and partially submerged exposure, leaching appeared to reduce the alkali content in outer 10 cm of dam. The concrete exposed to rain and the concrete sheltered inside the dam exhibited no clear leaching profiles, but variations in the alkali content starting from 5 cm and going towards the surface were observed. The reason for these variations is still unknown.