Corrosion of steel reinforcement and the alkali silica reaction (ASR) are well documented problems. Many reinforced concrete highway structures are deteriorating as a result of corrosion induced by de-icing salts. Cathodic protection (CP) is one of a variety of techniques available for dealing with this. In principle, CP is likely to cause an increase in the alkalinity of the concrete around the cathodically polarised reinforcing steel with the consequential risk that ASR will be induced in concretes containing reactive aggregates. This report describes research aimed at investigating the possibility of a link between CP and ASR. Cathodic protection was applied either potentiostatically or galvanostatically to steel plates embedded in hardened cement paste of variable alkali and chloride content so that the accumulation of alkali round the steel cathodes could be investigated. Mortar and concrete prisms containing reactive calcined flint were used to assess both the alkali concentration below which alkali silica reaction would not occur and the pessimum content of the reactive aggregate. Steel plates were embedded in concrete prisms containing sub-threshold alkali concentrations and a pessimum proportion of reactive aggregate. CP with various levels of polarisation was applied to the steel plates over a period of time during which the specimens were monitored for expansion. Subsequently the alkali concentration gradients at the plates were measured and the concrete examined for petrographic evidence of ASR. The work described in this Digest was carried out under contract by the Aston University for the Bridges Division of the Structures Group at the Transport and Road Research Laboratory (TRRL).

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