GB2430938A - Backfill - Google Patents
Backfill Download PDFInfo
- Publication number
- GB2430938A GB2430938A GB0600661A GB0600661A GB2430938A GB 2430938 A GB2430938 A GB 2430938A GB 0600661 A GB0600661 A GB 0600661A GB 0600661 A GB0600661 A GB 0600661A GB 2430938 A GB2430938 A GB 2430938A
- Authority
- GB
- United Kingdom
- Prior art keywords
- backfill
- anode
- steel
- concrete
- cavity
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000004567 concrete Substances 0.000 claims abstract description 33
- 229910052751 metal Inorganic materials 0.000 claims abstract description 20
- 239000002184 metal Substances 0.000 claims abstract description 20
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims abstract description 13
- 235000011941 Tilia x europaea Nutrition 0.000 claims abstract description 13
- 239000004571 lime Substances 0.000 claims abstract description 13
- 239000011800 void material Substances 0.000 claims abstract description 10
- 238000000034 method Methods 0.000 claims abstract description 8
- 229910000831 Steel Inorganic materials 0.000 claims description 25
- 239000010959 steel Substances 0.000 claims description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 23
- 239000000463 material Substances 0.000 claims description 11
- 239000002245 particle Substances 0.000 claims description 9
- 239000003792 electrolyte Substances 0.000 claims description 5
- 239000000945 filler Substances 0.000 claims description 5
- 150000003839 salts Chemical class 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- 239000011345 viscous material Substances 0.000 claims description 4
- 239000012530 fluid Substances 0.000 claims description 3
- 150000002500 ions Chemical class 0.000 claims description 3
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims description 2
- 239000000920 calcium hydroxide Substances 0.000 claims description 2
- 229910001861 calcium hydroxide Inorganic materials 0.000 claims description 2
- 239000013078 crystal Substances 0.000 claims description 2
- 230000000717 retained effect Effects 0.000 claims 1
- 239000000725 suspension Substances 0.000 claims 1
- 229920000642 polymer Polymers 0.000 abstract description 4
- 239000004927 clay Substances 0.000 abstract description 3
- 238000013022 venting Methods 0.000 abstract description 3
- 239000000047 product Substances 0.000 description 19
- 239000004568 cement Substances 0.000 description 13
- 238000006243 chemical reaction Methods 0.000 description 8
- 239000011148 porous material Substances 0.000 description 8
- 238000011282 treatment Methods 0.000 description 8
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 6
- 238000004090 dissolution Methods 0.000 description 6
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 239000004570 mortar (masonry) Substances 0.000 description 5
- 239000011701 zinc Substances 0.000 description 5
- 239000004411 aluminium Substances 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 239000011396 hydraulic cement Substances 0.000 description 4
- -1 hydroxyl ions Chemical class 0.000 description 4
- 229910052725 zinc Inorganic materials 0.000 description 4
- 239000000292 calcium oxide Substances 0.000 description 3
- 235000012255 calcium oxide Nutrition 0.000 description 3
- 239000000499 gel Substances 0.000 description 3
- 239000004576 sand Substances 0.000 description 3
- 229910000838 Al alloy Inorganic materials 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- 239000011398 Portland cement Substances 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000018044 dehydration Effects 0.000 description 2
- 238000006297 dehydration reaction Methods 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 101100457461 Caenorhabditis elegans mnm-2 gene Proteins 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 241000168096 Glareolidae Species 0.000 description 1
- 229910000861 Mg alloy Inorganic materials 0.000 description 1
- 229910001294 Reinforcing steel Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 229910001297 Zn alloy Inorganic materials 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000004308 accommodation Effects 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 238000001246 colloidal dispersion Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 150000004677 hydrates Chemical class 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 239000011429 hydraulic mortar Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 239000011431 lime mortar Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000000123 paper Substances 0.000 description 1
- 229920006327 polystyrene foam Polymers 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 239000003340 retarding agent Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000003566 sealing material Substances 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
- C04B28/04—Portland cements
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
- C04B28/10—Lime cements or magnesium oxide cements
-
- 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
- C23F13/04—Controlling or regulating desired parameters
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/20—Resistance against chemical, physical or biological attack
- C04B2111/26—Corrosion of reinforcement resistance
- C04B2111/265—Cathodic protection of reinforced concrete structures
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/90—Electrical properties
- C04B2111/94—Electrically conducting materials
-
- 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
-
- 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
- C23F2213/00—Aspects of inhibiting corrosion of metals by anodic or cathodic protection
- C23F2213/20—Constructional parts or assemblies of the anodic or cathodic protection apparatus
- C23F2213/21—Constructional parts or assemblies of the anodic or cathodic protection apparatus combining at least two types of anodic or cathodic protection
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Ceramic Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Inorganic Chemistry (AREA)
- Structural Engineering (AREA)
- Prevention Of Electric Corrosion (AREA)
Abstract
A method of accommodating the pressure arising from the delivery of a large current density off a sacrificial anode metal [1] located in a cavity [2] in concrete [3] is disclosed. It comprises substantially surrounding the anode with a pliable viscous backfill [4] such as a lime putty or clay and providing a space into which the backfill may move. The space may be provided by venting the backfill to space outside the cavity through an opening [5] or by including a void space within the backfill [6] or a void space within the cavity [7]. The void space in the backfill or cavity may be generated using a weak foamed polymer.
Description
BACKFILL
FIELD
This invention is concerned with the protection of steel in concrete using sacrificial metal anodes and, in particular, the accommodation of voluminous products resulting from the action of a sacrificial metal embedded in a cavity in the concrete.
BACKGROUND
Discrete sacrificial anodes have been embedded in cavities in concrete to protect the reinforcing steel. In the process the anode metal dissolves to form products that often have a greater volume than the metal from which they were derived. As a result, pressure is exerted on the surrounding concrete which can lead to damage of the concrete. A backfill is a material surrounding a sacrificial anode that maintains an electrolytic contact between the electrolyte in the environment and the surface of a sacrificial anode. An anode is an electrode that supports a net oxidation reaction on its surface. The backfill should preferably be capable of accommodating the products of the anodic reaction.
One commercially available sacrificial anode assembly based on WO 94/29496 comprises a zinc anode activated by hydroxyl ions in a weak porous material that surrounds the zinc. The zinc corrodes to form soluble products that precipitate out in the pores of the surrounding material.
Accommodating the voluminous products of sacrificial metal dissolution is addressed directly in WO 03/027356 and WO 2005/035831. In addition to features of the commercially available product based on WO 94/29496, WO 03/027356 describes a void behind the sacrificial metal into which the metal will be displaced as voluminous products of metal dissolution are formed, and the use of fibres in the anode encapsulating mortar or backfill.
WO 2005/035831 describes the use of a layer of reinforcement to restrain the expansive pressure from the voluminous products and compress a porous anode assembly.
PROBLEM TO BE SOLVED
When sacrificial metal dissolution is accelerated using a DC power supply, high volume products will be produced at a rate much greater than that encountered in the more conventional use of sacrificial anodes. As a result an improved method of accommodating this relatively rapid expansion is needed.
SUMMARY OF THE INVENTION
A method of protecting steel in concrete comprises forming a cavity in the concrete, placing a puttylike ionically conductive backfill in the cavity, inserting an anode consisting of a metal less noble than steel into the backfill, providing a space into which the backfill may move when subjected to pressure and passing a current from the anode to the steel in the concrete. The space may be provided by venting the backfill to space outside the cavity or by including void space within the cavity or within the backfill. The backfill is a pliable, viscous material that retains its pliable, viscous properties while a high current density is delivered off the anode. The backfill preferably hardens slowly to form a weak porous material that can accommodate the longer term, lower expansion rates resulting from the reduced rate of forming products at the anode after an initial high current treatment. The conductivity of the backfill primarily arises from one or more dissociated salts within the backfill. Possible backfills comprise a mixture of fine solid particles in water. A preferred backfill will consist at least in part of lime putty and may also contain a weak foamed polymer filler to trap air voids within the backfill. A weak foamed polymer may also be used to trap air within the cavity.
ADVANTAGEOUS EFFECT OF THIS INVENTION
The combination of a puttylike backfill and a space can accommodate the relatively fast generation of high volume product arising from the delivery of a high current density off a sacrificial anode embedded in a cavity in concrete. The delivery of a high current off the anode may only be required for a relatively brief initial period when a space into which the backfill may move may be provided outside the cavity. After this time the putty can harden slowly to form a weak porous material that can accommodate additional expansive product generated at a lower rate within the pore system of the backfill without placing the surrounding concrete at risk. The use of a putty as opposed to a liquid allows the anode to be installed in cavities in sides and soffits of concrete structures as the putty may hold the anode in position in the cavity. The putty also retains electrolyte in the longer term to ensure anode function.
DESCRIPTION OF THE DRAWINGS
Figure 1 shows a discrete sacrificial metal anode embedded in a puttylike backfill in a cavity in concrete together with various spaces to accommodate movement of the backfill.
Figure 2 shows the current density driven off an aluminium anode embedded in a lime putty in concrete using a 12V DC power supply connected between the anode and embedded steel.
Figure 3 shows the galvanic current density off an aluminium anode connected to the steel after completing the impressed current treatment described in Figure 2.
MODE OF THE INVENTION
Brief high current electrochemical treatments have been developed to arrest and prevent steel corrosion in concrete. A brief treatment may involve the delivery of a charge to the steel of the order of 50 to 500 kC/m2 (charge per unit area of steel) in a short period. It is possible to do this in as little as 48 hours using a power supply but it will typically take a longer time.
A sacrificial anode metal may be used in an impressed current mode in the delivery of a high current for a brief initial period. Referring to Figure 1, an anode [1] is located in a cavity [2] in concrete [3]. The anode consists of a metal less noble than steel. The principal anodic reaction is the dissolution of the anode metal. It is preferably selected from aluminium, zinc or magnesium or an alloy of aluminium, zinc or magnesium.
The anode is substantially surrounded by a pliable viscous backfill [4]. The backfill is not rigid and it is also not a runny fluid. The properties of the backfill mean that it can move into adjacent available space when subjected to pressure. The backfill retains is pliable viscous properties while a high rate of production of voluminous products at the anode persists. The rate of production of products at the anode is related to the current delivered off the anode.
High initial impressed current densities are likely to persist for at least 2 to 3 days and will more typically be delivered for one week. High initial current densities may extend to 3 months. Thus the backfill should retain its pliable viscous properties for at least 48 hours and will preferably retain these properties for up to 3 months.
The backfill is ionically conductive to support the metal dissolution reaction on the sacrificial metal anode. The conductivity of the backfill substantially arises from one or more dissociated salts within an electrolyte contained in the backfill. The resulting ions in the electrolyte preferably assist with the dissolution of the sacrificial metal. Examples of such ions include hydroxyl ions, sulphate ions and halide ions.
The backfill may slowly harden in time, but after hardening it will preferably form a weak porous material capable of continuing to accommodate the voluminous products of the anodic reaction that are generated at a slower rate. It is preferable that the compressive strength of the backfill does not exceed 10 N/mm2 and more preferably does not exceed 2 N/mm2.
Examples of the backfill include gels, clays, putty, and heavily retarded cement or fine mortar paste. Cement products harden by reaction with water (hydration). They can therefore harden under water. In this respect they differ from other suggested backfill materials which may only harden when exposed to the air and, in some cases, the pliable viscous properties may partially be restored when the backfill is re-hydrated.
Gels typically contain more than 60% water. As noted in US 6254752, a very high water content is an advantage in temporary electrochemical treatments designed to deliver high currents for a brief period after which the anode system is removed. However dehydration of the gel results in shrinkage that can isolate the anode from the surrounding concrete if the anode is also installed for longer term use. This will be the case when the sacrificial metal remaining after an initial impressed current treatment is connected to the steel to provide sacrificial protection.
Improved dimensional stability may be achieved by reducing the water content. This may be achieved using a dispersion of fine solid particles in water. Clay particles are less than 5 microns in diameter and some clays contain less than 50% water when fully saturated. Silt particles will have diameters of up to 50 microns and sand particles will be larger. The inclusion of larger particles (silt and sand) improves dimensional stability and results in a courser backfill.
Concretes and mortars include substantial quantities of sand and larger aggregate particles as well as relatively little water. When they are based on the use of hydraulic cements like Portland cement, the reaction between the cement and water will typically produce a rigid material in less than 12 hours. This reaction may be retarded by adding a retarding agent that retards the setting reaction of the cement to retain the pliable viscous properties of the concrete or mortar or cement paste mix for a longer period. Cement based mixes harden to produce relatively strong materials but the strength may be reduced and the porosity increased by increasing the water content of the mix A preferred backfill contains lime putty produced by slaking quicklime (CaO) to form a colloidal dispersion of fine calcium hydroxide crystals in water. Matured lime putty has a relatively consistent volume and reacts with carbon dioxide in the air to form a weak porous material consisting mainly of calcium carbonate that has a compressive strength of less than 0.5NImm2. Lime putty may be blended with other materials to improve the properties of the backfill. Lime putty like clay does not set while it is waterlogged and the puttylike characteristics can be partially restored after a short period of dehydration if it is mixed with water.
A space is provided into which the backfill will move when subjected to pressure. The space may be provided outside the cavity through an opening [5] connecting the cavity to the external environment. A wide opening from the external environment to the cavity may be partially filled with a sealing material [8] such as a cement or mortar paste, to inhibit rapid moisture loss from the cavity. At the end of a brief high current treatment when the formation of voluminous products slows down, it is preferable to seal the opening to the external environment and to use other space within the cavity to accommodate the voluminous products.
A space may be provided by including voids within the backfill [6] or voids within the cavity [7]. The void space may be created using a filler material that traps a compressible fluid like air within the putty or within the cavity. An example of a filler material is a weak foamed polymer such as polystyrene foam.
The anode and backfill may be assembled as a separate unit prior to installation in a concrete structure. This may be achieved by forming a porous container or mould with an opening to facilitate placing the backfill and anode in the container. The porous mould or container may be made using a layer of hydraulic cement or mortar formed into an appropriate shape. Excess water in the cement results in the formation of capillary porosity as the cement hydrates. The mould or container may also be formed from a material like cardboard or a porous cloth or even one or more layers of thin absorbent paper impregnated with a hydraulic cement with a high water to cement ratio. The use of a cement that sets to form a porous material such as hydraulic cement results in a rigid container or mould.
The pliable viscous backfill is installed within the container and the anode is inserted into the backfill. The container then forms an outer porous layer of the anode assembly. A conductor connected to the anode protrudes from the container to facilitate making a connection to the anode. The opening to the container may be sealed after the backfill and anode are installed in the container. If an opening venting the backfill to the external environment is left open, it is preferable that the container is a rigid container. If no opening is left, it is preferable that one or more features is present from the list comprising, a portion of the container or seal is easily broken to create an opening when the anode is used, a portion of the container or seal is elastomeric, a compressible void space is present in the container, a compressible void space is present in the backfill These features are needed to accommodate expansion within the anode assembly.
Example
An anode 15mm in diameter and 100mm long comprising a bar of the aluminium alloy known as US Navy specification MIL-A-24779(SH) that was cast around a titanium wire to facilitate the electrical connection to the aluminium was embedded in a lime putty in a 25mm diameter by 130mm deep hole in a concrete block. The basic arrangement is shown in Figure 1. The concrete block measuring 380 by 270 by 220mm was made using graded all-in-one 20mm aggregate and ordinary Portland cement in the ratio 8:1. The water to cement ratio was 0.6 and 4% chloride ion by weight of cement was added to the mix by dissolving sodium chloride in the mix water. A sheet of steel with a surface area of 0.125m2 was included in the concrete block. The lime putty was produced by slaking and maturing quicklime and was sourced from a manufacturer of lime putty and lime mortars. The hole in the concrete block containing the lime putty and the anode was left open to the air. The concrete block was stored in a dry indoor environment and the temperature varied between 10 and 20C.
The anode and the steel were connected to a I2Volt DC power supply for a period of 13 days during which a charge of 65kC was delivered from the anode to the steel. The current density delivered off the anode for the first 11 days is given in Figure 2. For most of this time, the current delivered off the anode was greater than 5000mA/m2. During this period water and corrosion products accumulated at the location of the anode and moved out of the hole containing the anode and the putty onto the surface of the concrete.
At the end of the period of impressed current treatment, the DC supply was removed and the anode was connected to the steel. The galvanic current out of the anode was measured using a 1 ohm resistor as a current sensor in the connection between the anode and the steel. The current density delivered off the anode acting purely in a galvanic mode for the next 40 days is given in Figure 3. For most of this period, the current density delivered off the anode was between 500 and 600 mNm2.
Claims (10)
1. A method of protecting steel in concrete that comprises forming a cavity in the concrete and placing an ionically conductive backfill in the cavity and inserting a compact discrete anode consisting of a metal less noble than steel into the backfill and passing a current from the anode to the steel in the concrete characterised in that the backfill is a pliable viscous material and the pliable viscous properties of the backfill are retained for at least 48 hours after exposure to air and the compressive strength of the backfill does not exceed iON/mm2 within 7 days of exposure to air and the conductivity of the backfill primarily arises from one or more dissociated salts in an electrolyte contained within the backfill and a space is present to accommodate backfill movement when under pressure.
2. A method as claimed in claim 1 where the cavity contains a space to accommodate backfill movement.
3. A method as claimed in any of claims 1 or 2 where an opening connects the backfill to a space outside the cavity.
4. A method as claimed in any of claims 1 to 3 where the compressive strength of the backfill is less than 2 N/mm2.
5. An ionically conductive anode backfill for use in cavities in concrete with a discrete anode less noble than steel that substantially comprises fine solid particles in water characterised in that the fine solid particles are less than 30 micron in diameter and the water content is less than 60% of the weight of the backfill and the conductivity of the backfill primarily arises from one or more dissociated salts in the water contained within the backfill and the backfill is a pliable viscous material that retains its pliable viscous properties for at least 48 hours after exposure to air and the compressive strength of the backfill does not exceed 2 N/mm2 within 7 days of exposure to air and the backfill retains its pliable viscous properties while it remains waterlogged for a minimum of 3 months.
6. An ionically conductive anode backfill for use in cavities in concrete with a discrete anode less noble than steel that consists at least in part of lime putty characterised in that the lime putty is a colloidal suspension of fine calcium hydroxide crystals in water.
7. An ionically conductive anode backfill for use in cavities in concrete with a discrete anode less noble than steel that substantially comprises a pliable, viscous material and a weak filler material characterised in that the conductivity of the backfill primarily arises from one or more dissociated salts in the water contained within the backfill and the backfill retains its pliable viscous properties for at least 48 hours after exposure to air and the compressive strength of the backfill does not exceed 2N/mm2 within 7 days of exposure to air and the weak filler material traps a compressible fluid within the backfill.
8. The production of a separate unit that consists of an anode less noble than steel and a pliable viscous backfill and a porous outer layer comprising forming a porous container and at least in part filling the container with a pliable viscous backfill that retains its pliable viscous properties for at least 48 hours after exposure to air and inserting an anode less noble than steel into the backfill.
9. The production of a unit as claimed in claim 8 where the opening to the porous container is sealed and the unit includes one or more features present from the list comprising a portion of the container or seal is easily broken to create an opening, a portion of the container or seal is elastomeric, a compressible void space is present in the container, a compressible void space is present in the backfill.
10. An anode assembly for protecting steel in concrete substantially as herein described above and illustrated in the accompanying drawings.
Priority Applications (34)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB1105079A GB2478207A (en) | 2005-10-04 | 2006-01-13 | Protection of steel in concrete |
DK06710171.7T DK1861522T3 (en) | 2005-03-16 | 2006-03-14 | Processing process for concrete. |
CA2893678A CA2893678C (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
CA2601516A CA2601516C (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
JP2008501428A JP4806006B2 (en) | 2005-03-16 | 2006-03-14 | Concrete processing method |
EP06710171.7A EP1861522B2 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
CN2006800083421A CN101142341B (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
EP13199244.8A EP2722418B1 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
ES06710171T ES2584833T5 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
US11/908,858 US7909982B2 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
EP17158238.0A EP3190210A1 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
PCT/GB2006/050054 WO2006097770A2 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
AU2006224340A AU2006224340B2 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
DK13199244.8T DK2722418T3 (en) | 2005-03-16 | 2006-03-14 | TREATMENT PROCESS FOR CONCRETE |
CN201210060738.8A CN102618875B (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
KR1020077023349A KR101381053B1 (en) | 2005-03-16 | 2006-03-14 | Treatment process for concrete |
GBGB0605988.5A GB0605988D0 (en) | 2006-01-13 | 2006-03-27 | Backfill |
BRPI0617969-0A BRPI0617969A2 (en) | 2005-10-04 | 2006-10-02 | use of an anode and filler to protect steel in reinforced concrete construction and combination of anode and filler |
CA2624461A CA2624461C (en) | 2005-10-04 | 2006-10-02 | Sacrificial anode and backfill |
DK06779653.2T DK1934385T3 (en) | 2005-10-04 | 2006-10-02 | Offer anode and filling material |
US12/067,632 US8002964B2 (en) | 2005-10-04 | 2006-10-02 | Sacrificial anode and backfill |
EP06779653.2A EP1934385B1 (en) | 2005-10-04 | 2006-10-02 | Sacrificial anode and backfill |
AU2006298558A AU2006298558B2 (en) | 2005-10-04 | 2006-10-02 | Sacrificial anode and backfill |
PCT/GB2006/050310 WO2007039768A2 (en) | 2005-10-04 | 2006-10-02 | Sacrificial anode and backfill |
NO20074790A NO343826B1 (en) | 2005-03-16 | 2007-09-19 | Treatment process for concrete |
HK08104400.8A HK1110100A1 (en) | 2005-03-16 | 2008-04-18 | Treatment process for concrete |
US12/636,411 US8211289B2 (en) | 2005-03-16 | 2009-12-11 | Sacrificial anode and treatment of concrete |
US13/052,670 US8349166B2 (en) | 2005-03-16 | 2011-03-21 | Treatment process for concrete |
US13/213,151 US8337677B2 (en) | 2005-10-04 | 2011-08-19 | Sacrificial anode and backfill |
US13/537,716 US8999137B2 (en) | 2004-10-20 | 2012-06-29 | Sacrificial anode and treatment of concrete |
HK12110534.8A HK1169841A1 (en) | 2005-03-16 | 2012-10-23 | Treatment process for concrete |
US13/723,420 US20130118897A1 (en) | 2005-10-04 | 2012-12-21 | Sacrificial anode and backfill combination |
US13/735,457 US9598778B2 (en) | 2005-03-16 | 2013-01-07 | Treatment process for concrete |
US14/679,142 US20150211128A1 (en) | 2004-10-20 | 2015-04-06 | Sacrificial anode and treatment of concrete |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB0520112A GB2426008B (en) | 2005-03-16 | 2005-10-04 | Treatment process for concrete |
PCT/GB2005/050186 WO2006043113A2 (en) | 2004-10-20 | 2005-10-17 | Improvements related to the protection of reinforcement |
Publications (3)
Publication Number | Publication Date |
---|---|
GB0600661D0 GB0600661D0 (en) | 2006-02-22 |
GB2430938A true GB2430938A (en) | 2007-04-11 |
GB2430938B GB2430938B (en) | 2011-08-31 |
Family
ID=35999486
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB0600661A Expired - Fee Related GB2430938B (en) | 2004-10-20 | 2006-01-13 | Backfill |
Country Status (1)
Country | Link |
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GB (1) | GB2430938B (en) |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH04116184A (en) * | 1990-09-04 | 1992-04-16 | Tobishima Corp | Method for setting anode in reinforced concrete structure electrically corrosion-proof construction |
EP0499437A1 (en) * | 1991-02-12 | 1992-08-19 | Ici Americas Inc. | A method of cathodically protecting a reinforced concrete structure and the structure obtained thereby. |
US5292411A (en) * | 1990-09-07 | 1994-03-08 | Eltech Systems Corporation | Method and apparatus for cathodically protecting reinforced concrete structures |
US20040186221A1 (en) * | 2002-12-23 | 2004-09-23 | Sethuraman Pitchumani | Process for manufacture of proton conductive polymer gel useful as backfill for sacrificial and impressed current anode systems |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1444382A4 (en) * | 2001-09-26 | 2006-03-08 | J E Bennett Consultants Inc | Cathodic protection system |
GB2427618B8 (en) * | 2004-10-20 | 2019-05-01 | E Chem Tech Ltd | Improvements related to the protection of reinforcement |
-
2006
- 2006-01-13 GB GB0600661A patent/GB2430938B/en not_active Expired - Fee Related
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH04116184A (en) * | 1990-09-04 | 1992-04-16 | Tobishima Corp | Method for setting anode in reinforced concrete structure electrically corrosion-proof construction |
US5292411A (en) * | 1990-09-07 | 1994-03-08 | Eltech Systems Corporation | Method and apparatus for cathodically protecting reinforced concrete structures |
EP0499437A1 (en) * | 1991-02-12 | 1992-08-19 | Ici Americas Inc. | A method of cathodically protecting a reinforced concrete structure and the structure obtained thereby. |
US20040186221A1 (en) * | 2002-12-23 | 2004-09-23 | Sethuraman Pitchumani | Process for manufacture of proton conductive polymer gel useful as backfill for sacrificial and impressed current anode systems |
Also Published As
Publication number | Publication date |
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GB2430938B (en) | 2011-08-31 |
GB0600661D0 (en) | 2006-02-22 |
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Owner name: ROBERTS, ADRIAN C Free format text: FORMER APPLICANT(S): CONCRETE PRESERVATION TECHNOLOGIES LTD Owner name: GLASS, GARETH K Free format text: FORMER APPLICANT(S): CONCRETE PRESERVATION TECHNOLOGIES LTD Owner name: DAVISON, NIGEL Free format text: FORMER APPLICANT(S): CONCRETE PRESERVATION TECHNOLOGIES LTD |
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Effective date: 20160113 |