Patching and coating

The rest of this section will discuss the options of patching and coating, realkalization and inhibitor application for carbonation repairs. 

Patching and coating is used for repairing carbonation and chloride induced corrosion damage. They are generally more successful for carbonation as was shown in a recent study by Seneviratne (2000) and Sergi (2000). 

If realkalization is as effective as claimed then the choice between realkalization and patching and coating is a question of convenience and cost, together with a realistic appraisal of the effectiveness of anticarbonation coatings. 

They are used extensively to react with epoxy or phenoHc resins, yielding adhesives that are useful in casting and laminating, in stmctural work, for patching and sealing compounds, and for protective coatings. The amount used in epoxy appHcations far exceeds the use with phenoHc resins. 

Chlorinated rubber floor paints are probably the most common of the lower-cost floor paints on the market. They produce tough and chemically resistant coatings, but their adhesion to concrete is not always good. They tend to wear off in patches and cannot be considered as a durable floor treatment except under light traffic conditions. However, re-coating is a simple job and floors can easily be repainted over weekend shutdowns, for example. Similar paints based on other resins such as acrylics, vinyls and styrene butadiene are also used. 

In the course of long-term storage, crude oils may be contaminated by oxidized or hardened oils that eventually coat the tank walls as a patch and provide uneven quality deterioration. This can be prevented by periodic cleaning of the tanks. 

Chapters 6 and 7 are then concerned with repair and rehabilitation options, first the conventional physical intervention of concrete repair, patching, overlaying and coatings. The electrochemical techniques of cathodic protection, chloride extraction and realkalization are dealt with in Chapter 7. 

Figure 6.6 (a) Roof structures before treatment showing obtrusive anticarbonation coatings and exposed reinforcement due to chloride and carbonation-induced corrosion, (b) Roof structures after repair and coating where the visual effect of patch repairs are minimized by application of Keim Concretal Lazure coating. 

If a combination of patching and sealing is required for a carbonated structure, the patch repairs must remove all carbonated concrete around the steel. In some cases this will only require exposure of the front face but in more extreme conditions it may need concrete removal behind the steel to restore the passive alkaline environment. Much has been published about anticarbonation coatings and their effectiveness but it is not easy to find independent information about specific products. Careful comparison of product information may be required. This may include the requirement for independent testing. The principle of anticarbonation coatings are that they are porous enough to let water vapour move in and out of the concrete but... 

Due to the problems with prestressing steel, realkalization would probably not be used as the alternative of patch repairing and coating would provide more cost effective solutions. In any case, it would be unusual for carbonation to take place in prestressed structures due to the high cement contents and high cover in such elements. If carbonation had reached prestressing steel in such structures there would probably be concerns about the strength of the concrete. 

The need to plasma-treat the PDMS surface just before use may be a disadvantage of the planar electrode. This would add a plasma system to the required equipment for patch clamp experiments. However, the planar electrodes do not require use of the high-quality optical microscope and micromanipulators currently required for patch clamp recording. In addition, conventional patch pipettes commonly require several processing steps before use including heat polishing and coating. 

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