Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
  • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
  • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
  • C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
  • C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F2201/00—Type of materials to be protected by cathodic protection
  • C23F2201/02—Concrete, e.g. reinforced

Definitions

• the invention relates to corrosion protection of steel reinforcement in concrete and in particular to a method of applying such corrosion protection and an associated corrosion protected structure.
• a concrete environment normally provides protection against corrosion for steel reinforcement. If the environment changes so that protection is lost, corrosion tends to arise at the surface of the steel reinforcement and the corrosion products occupy a larger volume than the original materials. Eventually this leads to delamination or spelling (i.e. falling away) of the surface concrete. In some circumstances, the risk of falling concrete or of delamination cannot be tolerated. Another possible problem is that without remedial measures the corrosion can lead to reduction of steel cross section and associated loss of strength. Even in situations where the initial effects of damage can be tolerated, repair costs to make good the structure can be very high.
• One established procedure for protection against corrosion is to pre-coat the steel with a physical barrier, normally of an organic material.
• the established commercial product of this kind is a steel bar or rod coated with epoxy resin by fusion bonding.
• the product is known as fusion bonded epoxy coated rebar or FBECR.
• discontinuities are a potential location for initiation and propagation of corrosion. Once corrosion has commenced at such a discontinuity, the presence of the coating adjacent to the discontinuity can be a disadvantage because in some circumstances it leads to concentration of the corrosion process at the discontinuity.
• Cathodic protection of steel reinforcement in concrete is known as a completely separate form of corrosion protection.
• corrosion of the steel reinforcement is prevented by making it the cathode of an electrolytic cell.
• Cathodic protection can be provided by an impressed current or by means of a sacrificial anode of a metal such as zinc or aluminium connected electrically to the steel reinforcement.
• Cathodic protection can be very effective but may require frequent replacement or maintenance (in terms of the life of a concrete structure) of the anode.
• An objective of the invention is to provide an improved and economical means of corrosion protection of steel reinforcement in concrete.
• a method of protecting steel reinforcement embedded in concrete against corrosion includes the steps of coating the steel with a physical barrier subject to discontinuities and applying cathodic corrosion protection to the steel to provide corrosion protection at the discontinuities.
• the invention also extends to a reinforced concrete structure incorporating corrosion protection provided by the above specified method.
• the invention is based on the discovery that with a coated bar subject only to inadvertent discontinuities, a very small degree of cathodic protection, which is automatically concentrated at the discontinuities, provides very effective protection against the original occurrence of any significant level of corrosion.
• bars 10 The structure shown in the drawing incorporates steel reinforcement constituted primarily by bars 10, 1 1 and 12. Bars 1 1 and 12 are interconnected by cross members such as 13 and 14 and connected to the bars. Also, at the right hand end of the drawing, it can be seen that bars 1 1 and 12 are in fact constituted by a single bar which has been bent at 15 and 16 to form in effect the two bars 1 1 and 12. Bar 10 is shown as not being in physical contact with bars 1 1 and 12 or any other bars.
• the bars have been coated with an epoxy resin by fusion bonding the resin to the surface of the bar.
• Cross members 13 and 14 are connected to bars 1 1 and 12 in such a way as to provide electrical continuity.
• the steel structure is embedded in concrete 17 in a conventional manner.
• a sacrificial anode 18 is embedded in the concrete.
• the anode is installed before the concrete is poured round the steel reinforcement. Aluminium anodes are particularly suitable but zinc anodes could be used.
• the anode 18 is electrically connected through lead 19 to bar 12. Because bar 12 has electrical continuity with bar 1 1 and bars 13 and 14, only a single connection is needed for these bars.
• the capsule may for example be constituted by expanded foam material contained within a cotton fabric outer skin and treated with a conduction enhancing product such as sodium sulphate in solution.
• a conduction enhancing product such as sodium sulphate in solution.
• An alternative encapsulation material is a gypsum-bentonite mixture, again treated with sodium sulphate.
• Other forms of anode encapsulant may be employed.
• an electrolytic cell is created by the anode, the steel reinforcement as the cathode and the concrete as the electrolyte.
• Current flow from the anode through the concrete to the steel reinforcement is concentrated at the reinforcement in the areas of discontinuities.
• the insulating epoxy coating prevents significant current flow. Because current flow into the steel is over only a very restricted proportion of the surface area of the steel, total current flow is low and the sacrificial consumption of the anode is correspondingly slow. It is for this reason that an embedded sacrificial anode is an effective long term possibility for protection of coated bar.
• the encapsulation is such as to allow current flow from the anode itself into the concrete and also to accommodate corrosion products generated at the anode.
• Protection by means of a sacrificial anode has the advantage that it is self -regulating and avoids the known problems of over-protection, in particular embrittlement associated with hydrogen evolution. This is predicted to provide a long and effective maintenance free life for the structure.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Prevention Of Electric Corrosion (AREA)

Applications Claiming Priority (3)

Publications (1)

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Country Status (4)

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• 1994
  • 1994-06-28 GB GB9412979A patent/GB9412979D0/en active Pending
• 1995
  • 1995-06-22 WO PCT/GB1995/001468 patent/WO1996000805A1/en not_active Application Discontinuation
  • 1995-06-22 EP EP95922642A patent/EP0767844A1/de not_active Withdrawn
  • 1995-06-22 AU AU27469/95A patent/AU2746995A/en not_active Abandoned

Non-Patent Citations (1)

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