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Cathodic Protection

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Title Document type Published Publisher
Management of Highway Structures Complementary Guidance

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Management of Highway Structures: A Code of Practice was published in September 2005. Since then Government Policy in respect to highway and structures management has developed and evolved in a number of areas, including the introduction of new statutory duties on highways authorities. There have also been developments/advances with regard to recognised good practice. To assist users of the Code, the Roads Liaison Group has prepared this complementary guidance which takes account of these changes and developments. Where appropriate, the complementary guidance provides details of where to find up-to-date information that can assist with the implementation of the good practice set out in the Code. Users of the Code should treat this complementary guidance as up-to-date and having the same status as the Code. Where paragraphs have been amended, they supersede the ones in the Code.

Primary Doc. 27/05/11 UK Roads Liaison Group Add icon
TRL PR 62 The effects of cathodic protection on alkali-silica reaction in reinforced concrete: stage 2

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Steel plates were centrally embedded in concrete prisms made from a potentially reactive siliceous aggregate but with an alkali content just below the threshold level required to induce significant expansion due to alkali-silica reaction (ASR). The aggregate contained 10% of calcined flint (a proportion close to the 'pessimum value' for that material) and the alkali content of the concrete was 2.5kg/cu m (expressed in terms of Na2O equivalent). The steel plates were subjected to cathodic protection applied either potentiostatically (steel potential held at -700mV versus saturated calomel electrode) or galvanostatically (cathodic current density maintained at 20mA/sq m) for periods extending to approximately three and a half years. Strain measurements showed that significant expansion and cracking of the concrete around the steel cathodes occurred in four out of the six prisms in which potentiostatic polarisation (-700mV, SCE scale) was applied. These effects were confined to the material in the vicinity of the cathodes, with ASR products and an accumulation of alkali metal ions being found by petrography and chemical analysis in a region extending to about 15mm from the steel plates. Very little expansion and ASR were detected for the prisms in which constant current cathodic polarisation (20mA/sq m) was applied, even after times when the total charge passed was equivalent to that for the potentiostatically controlled specimens. The inference of this is that, for the type of concrete studies, the fact that constant potential polarisation necessitated the application of high cathodic current densities (>100mA/sq m) during the early stages had a considerable effect in promoting alkali enhancement and ASR around the steel. The results of the present investigations, which constitute the second stage of a two-part programme of research, are related to the earlier findings reported in TRL Contractor Report No 310 (see IRRD 847792). Practical implications for the application of cathodic protection and related electrochemical rehabilitation techniques to concrete structures containing ASR-susceptible aggregates are discussed. (A)

Research 01/01/94 Transport Research Laboratory Add icon
TRL CR 10 The effects of cathodic protection on alkali-silica reaction in reinforced concrete

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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).

Research 01/01/92 Transport Research Laboratory Add icon
TRL CR 4 Bridge decks: Cathodic protection

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Corrosion of reinforcing steel in concrete, particularly on bridges in the road system in this country, is being reported with increasing frequency. Engineers are seeking methods to prevent corrosion occurring in existing structures already contaminated with chlorides from de-icing salts. Following discussions with the Transport and Road Research Laboratory late in 1982, Spencer and Partners were commissioned by the Department of Transport to report on the feasibility of Cathodic Protection for bridge decks. Spencers were to prepare a critical review of the published literature, state and consider the primary design factors relating to the technique and its applicability to bridge decks, provide an outline design with cost estimates and make recommendations. This report presents this information.

Research 01/01/84 Transport Research Laboratory Add icon
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