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Reinforcement Corrosion in Concrete

When corrosion of reinforcement in concrete first becomes apparent as isolated concrete cracks or spalls it is often an indication that environmental contaminants are more generally reaching the reinforcement.

 

If left cracking and spalling can become wide spread within a couple of years. It is important that apparent cracks and spalls are repaired and some form of protection applied to all concrete. Very often it will be too late to apply barrier coatings as the contaminants will have already penetrated the concrete. ‘Break out and patch’ is a commonly used repair method but it is often too expensive to be undertaken over all areas of contamination, and where it is it can be disturbing and create structural issues.

 

It has long been recognised that cathodic protection is the ideal repair method in that it can stop reinforcement corrosion without the need for breakout of contaminated concrete.

 

Impressed current CP is suited to major structures where the owner can afford the relatively high design, installation and maintenance cost and the deterioration must be halted over a long design life, e.g. 50 years. Sacrificial Anode CP is less expensive and requires less design and maintenance. It can be installed economically on small structures by relatively inexperienced installers but the anodes generally need to be replaced at 15-20 year intervals.

 

There are various impressed current and galvanic anode types available. All have their place and it is the suppliers responsibility to advise which anode type is most suited to a specific application.

 

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Pipe, Tank and Steelwork Corrosion

 

Hot Dipped Galvanising (HDG) is recognised as one of the most reliable corrosion protection systems available. Unfortunately once it starts to break down it cannot be re-instated - until now. Zinc Tape can be applied to the steel surface and provides better corrosion protection than the original HDG.

 

Zinc Tape for steel corrosion control

Corrosion protection for pipes.

CP for the Resource, Engineering and Transport Industries

Zinc Tape consists of a layer of pure zinc (99,99% of the chemical mass is zinc) with a nominal thickness of 0,080 mm. This tape is supplied with a 0.025 mm thick adhesive, which can resist continuous operating temperature of 80° C and which reacts under electro-conductive pressure.

The adhesive layer is covered by a silicon paper, which protects the band from getting damaged or polluted until the tape is applied.

Zinc Tape is a versatile and easily applied corrosion control coating system that protects structures in the same way as hot dipped galvanising (HDG) . However Zinc Tape can be applied on site to pipes, tanks, poles, piles, girders, frames and other steel items. This ability to provide the equivalent or better corrosion protection than HDG insitu is unique and has made Zinc Tape a major corrosion protection system in Europe. Specialist equipment makes its application rapid and consistent.

No primer is required as the essence of Zinc Tape is to achieve electrical continuity and adhesion between the Zinc Tape and substrate through the specially formulated electro-conductive adhesive. Hence all that is required is that the surface of the steel is prepared and the tape applied. It is not essential to prepare the surface to SA 2.5 and hence blasting is not necessarily required. In many cases preparation by wire brush is more cost effective.

Features of Zinc Tape are:

  • passive protection
  • active protection
  • homogeneous and isotropic structure
  • environmentally friendly
  • requires no superior surface preparation
  • allows for its application at any time during the life-span of the structure
  • enables any existing coating to be repaired or reconditioned
  • easily applied onto single pieces
  • can be subsequently painted
  • can be applied in multiple layers, when an extra-thick coating is required
  • ensures a much longer life-span than that of hot-dip galvanizing

Zinc Tape has been used for over 30 years in Europe (now from Metalnastri but also by its predecessor acquired by Metalnastri) and has been approved for use by many companies.

Zinc TapeTM is designed to cover the surface of iron, steel, aluminium and light metals in order to protect them from corrosion.

The conductive adhesive creates a couple between the surface that needs to be protected and the Zinc Tape so that the Zinc provides galvanic protection as well as protective barrier.

Applications

Zinc Tape is suited to virtually any application where a less noble metal or allow than zinc is exposed to corrosion. Elements on which Zinc Tape have been applied include:

  • Above ground pipe
  • Storage tanks
  • Piles protection
  • Posts
  • Chassis members
  • Galvanised metal roofs, sheds and fences

Like HDG there are many exposures where Zinc TapeTM does nt require coating but in some severe exposures coating may be rquired. Coatings suitable for HDG are also suited to Zinc TapeTM.

Standards

Zinc Tape complies with Italian Standard UNI 10781 2005 “EN-Laminar zinc coating for atmospheric exposure - Zinc pressure sensitive adhesive tape requirements and coating application and testing methods”.

Apart from manufacturing tolerances the standard specifies the following properties for the Zinc Tape:

  • 99.95% zinc min
  • thickness 0.075-0.1mm
  • tensile strength 110n/mm2 min
  • cupping Index 5mmmin
  • 0.1% max adhesive transfer
  • tape peel strength
  • electrical resistance
  • resistance to salt spray
  • surface preparation to ISO 8501-1 requirements

Zinc Tape - Over coating

Follow the hyperlink to find out more about over coatings which can be applied to Zinc Tape.

Technical Data

Zinc Tape has a 0.08mm thick layer of 99.99% pure zinc backed by a 0.025mm layer of conductive adhesive. Conductance is achieved by the inclusion of zinc powder within the adhesive as well as the nature of the adhesive itself. A protective film on the back of the adhesive is removed as the Zinc Tape is applied.

50m rolls of tapes are available in 10, 15, 20, 25, 30, 35, 40, 50, 70, 80, 90, 100,150,200 and 300mm width. In Australia 20,70, 100,120, 150 and 300mm widths are stocked.

Zinc Tape can be used at continuous temperatures of 80°C.

Meta Wrappers are available in 3 sizes to cover any pipe diameters in the range 65-750mm.

Advantages

  • Lower level of surfaces preparation required relative to other surface treatments
  • No Primer required
  • Guarantees a double protection (barrier and galvanic) compared to other on site treatments
  • Provides a remarkable saving in application time
  • Can give a much longer life than hot-dip galvanizing or other zinc coatings of the same mean thickness by providing additional layers at weak points
  • Can be applied in multiple layers. Apply additional strip wherever high levels of protection are required (e.g. welds, corrosion spots)
  • Used to protect damaged HDG
  • Can be over painted
  • Minimal maintenance required during the tapes life
  • Often easily applied in areas of difficult access
  • Can be applied in hot-work restricted areas
  • Economical on long life structure
  • Environmentally friendly

Zinc Tape for the Transport Industry

Zinc Tape with self-adhesive conductive backing is applied to the surface of cars, trucks, buses, armoured vehicles, planes and boats, during manufacturer for corrosion protection in the same way that galvanising does.

Zinc Tape can be applied in strips to critical areas to prevent corrosion to chassis and bodies or between different metals such as alloys and steel or under bolts and hinges. Special washers are also available (see Zinc Tape Washers for Bolts and Hinges).

Applications

To cut production costs and improve vehicle efficiency car bodies are made ever lighter and more rigid by the use of alloys. Where different alloys are electrically connected (e.g. steel: aluminium and steel: light alloy) it can cause a galvanic couple and hence corrosion. Zinc Tape with conductive adhesive is used by some of the worlds leading automotive manufacturers to prevent such corrosion.

Tapes are also used in recessed areas where moisture might collect (e.g. window rebates) or where crevice corrosion can occur (e.g. hinges and bolts).

Zinc Tape for Washers, Bolts and Hinges

The Zinc Tape Washers are made from the same material as the Zinc Tape and are made in accordance with the same standard. However the washers are pre-cut and can be simply peeled from the backing sheet and applied to the nobler element.

Examples of areas where galvanic or crevice erosion occurs:

 protection-hinges-washers-bolts corrosion-hinges-bolts-prevention

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