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Repair of concrete in highway bridges: a practical guide

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This practical guide covers all aspects of concrete bridge repair in sufficent depth to implement a best value option. It is designed and written for readers who are new to the field and wish to become familiar with the process involved in a bridge repair starting with inspection through carrying out remedial workd and monitoring the repair. Deciding the course of action for a particular structure includes several key stages at which alternative options should be considered. This is done through an easy to follow flow chart. This is followed by non-concrete repair options (such as surface treatments, cathodic protection, chloride extraction and realkalisation) and concrete repair options (such as patch repair with mortar, concrete, flowable concrete, sparyed concrete)

Secondary Doc. 01/08/02 Transport Research Laboratory Add icon
Repair of concrete in highway bridges: a practical guide

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This practical guide covers all aspects of concrete bridge repair in sufficent depth to implement a best value option. It is designed and written for readers who are new to the field and wish to become familiar with the process involved in a bridge repair starting with inspection through carrying out remedial workd and monitoring the repair. Deciding the course of action for a particular structure includes several key stages at which alternative options should be considered. This is done through an easy to follow flow chart. This is followed by non-concrete repair options (such as surface treatments, cathodic protection, chloride extraction and realkalisation) and concrete repair options (such as patch repair with mortar, concrete, flowable concrete, sparyed concrete)

Secondary Doc. 01/08/02 Transport Research Laboratory Add icon
Corrosion protection of external tendons in post-tensioned concrete bridges

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A number of lengths of stressed post-tensioning strand, unstressed wires from post-tensioning strand and steel coupons, were exposed in the box sections of two externally post-tensioned concrete bridges. Samples were also exposed outside the structures. The temperature and humidity both inside the box sections, adjacent to the stressed samples, and outside the structures were also monitored. Time-of-wetness probes were positioned along the length of one of the structures. The objective was to determine the corrosivity inside the box sections and thus the degree of corrosion protection required by externally post-tensioned tendons. Results over five years indicate that although the corrosivity within a concrete box section is much lower than outside, bare tendons are not an option and some form of corrosion protection is required.

Research 01/01/02 Transport Research Laboratory 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 284 An assessment of repair and strengthening techniques for brick and stone masonry arch bridges

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TRRL is undertaking research to examine the various repair and strengthening techniques applicable to masonry arch road bridges to enable the Scottish Office and the Department of Transport to improve on the advice given on the assessment of highway bridges and structures for load carrying capacity in Technical Memorandum SB3/84 and Advice Note BA 16/84 respectively. The report studies a variety of techniques, provides cost comparisons and discusses the associated advantages and disadvantages. It describes effectiveness in terms of observed defects. The information was provided by Country and Regional Councils throughout England, Scotland and Wales and by other relevant authorities in the form of case histories returned in response to a postal enquiry. A total of 180 examples were supplied from which a shortlist of 50 case histories was studied and details are included in the associated dossier. These bridges were inspected during the study and defects recorded in terms of an arbitrary severity rating system. These notes, together with substantial comments and opinions of the contributing authorities form the basis of the report. The cost assessment attempts to relate simple combinations of bridge dimensions to reported overall costs. Factors affecting cost are discussed. For the sake of comparison repair and strengthening techniques have been grouped as relating to the arch ring, the foundations and the spandrel walls, although most remedial works involve consideration of all three.

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
TRL LR 980 Conditions within ducts in post-tensioned prestressed concrete bridges

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an investigation was made of the grouting of twelve post-tensioned prestressed concrete bridges built between 1958 and 1977. ten of these structures were examined in situ and the other two had been demolished. voids were found in ten of the bridges including the most recently built structure. they were often continuous along the accessible length of a duct although they were not evenly distributed but tended to be concentrated at high points. local voids were found at anchorages in one of the demolished bridges in what were otherwise fully grouted ducts. the grout was usually dry and its quality ranged from soft and 'crumbly' to hard. exposed wires were observed in six of the bridges. they were usually covered with a thin film of cement paste indicating that grout had initially flowed through the duct at full, or nearly full bore. the cement film was intermingled with surface rust on some of the wires but, with the exception of one strand in a virtually empty duct, there was no evidence of pitting or loss of sectional area. the application of a low air pressure to the ducts showed that they were not completely sealed from the atmosphere. the grout should continue to protect the tendons provided it does not carbonate and chloride ions are excluded.

Research 01/01/81 Transport Research Laboratory Add icon
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