Effects of alkali-silica reaction on a hydropower structure after 50 years of ongoing deterioration

The Nalubaale hydropower station was constructed between 1949 and 1954. Deterioration of the powerhouse structure was first noticed in 1964 when hairline cracking in the generator floor started to appear. The cracking progressively continued resulting in degradation of the generator floor, upper gallery and structural frame of the powerhouse. It was not until 1990 that alkali-silica reaction (ASR) in the mass concrete elements was identified to be the root cause of the deterioration. The condition of the powerhouse structure was reassessed in 2015 25 years after the investigations in 1990. The assessment comprised the determination of the concrete properties 50 years after ASR had initiated and a comprehensive evaluation of instrumentation data was undertaken to identify the effects of ASR on the powerhouse structure. This paper presents the findings of the condition assessment and provides an update on the concrete properties after more than 50 years of ongoing ASR. It also provides an assessment of the residual life of the structure and proposes rehabilitation methods to control the effects of ASR