Soft water attack on concrete tunnel linings in the Ingula pumped storage hydro-power scheme: Assessment of concrete resistance and protection

The resistance of the concrete tunnel linings at the Ingula Pumped Storage Scheme (IPSS) to soft water attack was investigated. Concrete disc specimens obtained from cores taken from selected locations of the tunnel lining were exposed to a simulated soft water attack testing regime in a site laboratory using the actual (soft) water to which the tunnel linings will be exposed when in service. The assessment was carried out for around four months. The aggressivity of the soft water was quantified using Basson Indices. The results showed that the water is readily aggressive and will lead to corrosion of the concrete tunnel lining. The experimental work showed the average surface rate loss of the linings to be approximately 1.1 mm/a, which, if sustained in the concrete linings, would amount to an average loss of about 10 mm in a 10-year period. This will result in increased surface roughness and hence higher head losses due to increased friction coefficients. It was recommended that a protective epoxy coating be applied on the tunnel lining to limit the reduction in power generation efficiencies.