WO2009067783A1

WO2009067783A1 - A cap for corrosion protection of reinforced steel bar in concrete

Info

Publication number: WO2009067783A1
Application number: PCT/CA2008/001893
Authority: WO
Inventors: Philip S. Lambertucci
Original assignee: Corbec Corporation
Priority date: 2007-11-27
Filing date: 2008-10-27
Publication date: 2009-06-04

Abstract

The present invention concerns a cap affixed to the end of a reinforcing steel bar (rebar) used in reinforced concrete. The cap protects the steel rebar from corrosion from electrolytes, such a water and saline solution. The invention also concerns a cap/rebar combination and a method of protecting steel rebar from corrosion in reinforced concrete. The cap comprises a rebar contacting surface at a base of a bore defined within the cap, and a retainer on an internal wall surface, the surface circumscribing the rebar contacting surface, the retainer fixedly attaching the cap on the steel rebar. The cap comprises at least one of zinc, aluminum and magnesium, and the steel rebar contacts the rebar contacting surface tightly to produce a barrier against the electrolyte and to establish a galvanic current, to cathodically protect the rebar in the presence of the electrolyte from corrosion.

Description

A CAP FOR CORROSION PROTECTION OF REINFORCED STEEL BAR IN CONCRETE

TECHNICAL FIELD

The present invention concerns a cap affixed to the end of a reinforcing steel bar (rebar) for protecting the steel rebar from corrosion, as well as, the cap/rebar combination. The present invention further describes a method of protecting steel rebar from corrosion in reinforced concrete .

BACKGROUND OF THE INVENTION

The penetration of moisture into concrete, often accompanied by other corrosive products, such as road salt causes corrosion of bare steel reinforcing bars in concrete. The water/road salt combination produces an electrolyte which is particularly corrosive to unprotected steel. Steel rebar is found in concrete structures to improve concrete's tensile strength. Reinforced concrete is used in structures such as elevated highways, access ramps, bridges and viaducts, where the water and road salt often combine, to produce an electrolyte that has only short distance to travel through the concrete to reach the rebar. Typically, any rebar within 3 feet of a surface, where corrosive products may be present, will likely be exposed to corrosion and may compromise structural integrity of the concrete at worst, or at least require continuous and costly maintenance . Various solutions have been proposed to protect the reinforced steel or rebar in concrete. One such solution is Hot Dip Galvanizing, which is a zinc coating metallurgically bonded to clean steel. In Hot Dip galvanizing the rebar is immersed in a bath of molten zinc. This method has been used to effectively combat corrosion of reinforcing steel in concrete. Zinc coating offers both a cathodic and barrier protection by fully enveloping the steel in a zinc cover.

As a general practice, galvanizing is done on stock lengths of reinforcing steel of 40 feet. These completely coated bars are used where continuous lengths are required by design.

The galvanizing of varied sizes of bars in varying quantities, is substantially more costly than the galvanizing of fixed quantities of stock length bars. In addition, increased costs are further incurred by the re-handling and re-bundling of multiple smaller sized bundles. Consequently, a construction project requiring cathodically protected reinforced steel is subjected to both increased cost, longer schedules and frequent production delays .

The construction project would benefit from both reduced galvanizing and handling costs if the practice of cutting the end of the reinforcing steel bars after galvanizing were adopted. The practice of protecting the cut ends of the rebar, must completely ensure the corrosion protection of the cut end of the reinforcing steel. Various methods have been proposed to protect steel members in various applications. U.S. Patent 5,263,292 relates to a post-tensioned anchor assembly having an anchor and a steel tendon affixed within the anchor. The tendon is protected by a cap that covers the end of the tendon. This cap is made of an anodic material such as zinc or magnesium. The cap provides corrosion protection by sealing the terminal end of the steel tendon within the anchor assembly. The cap has a generally cylindrical outer surface and a closed cylindrical inner surface. The inner surface of the cap allows the cap to be threadably affixed in electrical contact with the end of the tendon.

U.S. Patent 5,469,679 teaches a protective sealing cover made of flexible material for easy application over an exposed end of cut reinforcing bar. The 5,469,679 Patent attempts to resolve the problem of rebar corrosion due to the cutting end of rebar without the use of galvanic protection. The cover of U.S. Patent 5,469,679. contains a water impermeable sealant which surrounds the end of the cut bar for protection against corrosive agents.

Clearly, it is preferable not to have bare steel rebar or galvanized steel with bare ends in concrete, and particularly in concrete that will be between 2 and 4 feet from a boundary wall exposed to water and road salts, that produce corrosive electrolytes. Thus to avoid corrosion less than stock length requirements are cut to size by the fabricator prior to shipment to the galvanizer. This procedure ensures that all the bars are completely coated with zinc. A purpose of this invention is to permit the cutting of stock lengths reinforcing steel and while fully protecting the cut ends from corrosion. The practice is particularly- well suited to galvanized steel rebar, and may also be used on bare rebar to improve corrosion resistance also.

SUMMARY OF THE INVENTION

In one aspect of the present invention there is provided a cap for protecting a steel rebar from corrosion by an electrolyte in a reinforced concrete, the cap comprising: a rebar contacting surface at a base of a bore defined within the cap, and a retainer on an internal wall surface, the internal wall surface circumscribing the rebar contacting surface, the retainer for fixedly attaching the cap on the steel rebar, wherein the cap comprises a material selected from the group consisting of zinc, aluminum and magnesium, and the steel rebar contacts the rebar contacting surface producing a barrier against the electrolyte and establishing a galvanic current in the presence of the electrolyte between the steel rebar and the material to cathodically protect the steel rebar from corrosion.

In another aspect of the present invention there is provided a steel rebar cathodically protected from corrosion by an electrolyte for reinforced concrete, the rebar comprising: a steel rebar member, the member including at least one end and a cap fixedly attached to the at least one end, each cap comprising: a rebar contacting surface at a base of a bore defined within the cap, and a retainer on an internal wall surface circumscribing the rebar contacting surface, the retainer for fixedly attaching the cap on the steel rebar, wherein the cap comprises a material selected from the group consisting of zinc, aluminum and magnesium, and the steel rebar contacting the rebar contacting surface producing a barrier against the electrolyte and establishing a galvanic current in the presence of the electrolyte between the steel rebar and the material to cathodically protect the steel rebar from corrosion.

In yet another aspect of the present invention there is provided a method of protecting steel rebar for reinforced concrete from corrosion comprising: identifying an end of the steel rebar to be protected; providing an cap for protecting a steel rebar from corrosion by an electrolyte in a reinforced concrete, the cap comprising: a rebar contacting surface at a base of a bore defined within the cap, and a retainer on an internal wall surface, the internal wall surface circumscribing the rebar contacting surface, the retainer for fixedly attaching the cap on the steel rebar, wherein the cap comprises a material selected from the group consisting of zinc, aluminum and magnesium, and the steel rebar contacts the rebar contacting surface producing a barrier against the electrolyte and establishing a galvanic current in the presence of the electrolyte between the steel rebar and the material to cathodically protect the steel rebar from corrosion, the cap for frictionally attaching onto the end of the rebar, and attaching the cap to the end to produce a cap/rebar system such that the end and the rebar contacting surface are in contact . BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

Fig. 1. is a perspective view of an anode cap in accordance with a preferred embodiment of the present invention;

Fig. 2 (a) is a front elevation view of the anode cap of Fig. 1;

Fig. 2 (b) is a side elevation view of the anode cap of Fig. 1;

Fig. 2 (c) is a sectional view of Fig. 2 (a) taken along cross-section line A-A;

Fig. 3 is a side elevation view of a steel reinforcing bar fitted with the cap of Fig.l;

Fig. 4 (a) is a side elevation view partially sectioned of a reinforcing steel bar (PRIOR ART) ;

Fig. 4 (b) is the cross section A-A of the reinforcing steel bar of Fig. 4 (a) (PRIOR ART) ;

Fig 5 (a) is a photograph of a reinforced steel bar immersed in a saline solution; and

Fig. 5 (b) is a photograph of the reinforced steel bar immersed in a saline solution as in Fig. 5 (a) and including a cap according to Fig. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A cap 10 according to one embodiment of the present invention is illustrated in Fig. 1. The cap 10 includes: an outer wall 20 and defines an inner bore 14. Within the bore 14 there is an inner wall 24 which circumscribes an internal surface, defined as the rebar contacting surface 28. The cap 10 has a top 12. The inner surface 24 includes a retainer, which may take many forms. In a preferred embodiment the retainer defines least one rib indentation 32 on the outer wall 20, and produces at least one rib 30 (Fig. 2 (b) ) which projects from the internal wall 24 into the bore 14, and in such a way to contact side wall of the rebar 2, and in a manner that the cap 10 is affixed permanently or fixedly attached onto the end 4 of the rebar 2.

The retainer, typically includes more than one rib 30, and commonly includes four ribs 30. These ribs 30 in a preferred embodiment are in two pairs diametrically opposed to each other, a clearer representation of the rib indentation 32 and the projection which the means by which the cap 10 is retained on the rebar is defined a depth 35 of the ribs 30 in the direction towards the center of the bore 14 is found in Fig. 2 (b) and 2(c) .

There are various methods by which the ribs 30 can be made. The cap 10 may be cast or molded and then pinched to produce the rib projections 30 within the bore 14. Clearly, when pinched the outer wall 20 will include indentations on the outer surface, while a purely molded cap may have a completely non- indented, or smooth outer surface. Fig. 2 illustrates a side view of the cap according to one embodiment of the present invention. In this embodiment a rib height 34 and a rib length 36 is defined. Although, the rib height 34 and rib length 36 dimension have been represented on the rib indentation 32, they are substantially that of the rib 30. Therefore, various forms of ribs 30 may be used to mechanically retain the end of a steel reinforcing bar. In a preferred embodiment the rib 30 may be formed in such a manner that it includes an edge permitting the rib to pass over rebar while hindering removal of the cap .

The bore 14 is dimensioned to allow passage of a reinforced steel bar or rebar member such that an end 4 of the rebar may securely contact the rebar contacting surface 28, and such that a tight engagement between the rebar and the rib 30 is maintained, and a barrier to the electrolyte is produced.

In a preferred embodiment the rebar contacting surface 28 is reasonably flat and capable of contacting the end 4 of a rebar 2 (Fig. 3) and produces a cap/rebar system. The cap 10, is sized appropriately for the diameter 8 (Fig. 4 (b) ) of the rebar on which it will be affixed, and offers both a cathodic and a barrier protection against corrosion, which is equal to that protection offered by a continuously galvanized coating. Barrier protection is provided at the rebar contacting surface 28 due to a compression fit of the end 4 of the rebar 2 on the rebar contacting surface 28. The rebar contacting surface 28 is sufficiently thick and compressible and allows for the variation from flatness of a slightly non-flat end 4, and is thus still capable of forming the barrier protection. The cap 10 is in a preferred embodiment punched and drawn from no.190 zinc alloy in sheet form. The chemical analysis of alloy 190 indicate that it is a zinc alloy, comprising mainly Zn (> 98 wt%) and includes between 0.70 to 0.90 wt% copper, along with varying amounts of titanium, lead, cadmium, iron, aluminum, magnesium, manganese, and nickel at low levels. Although zinc and zinc alloys are a preferred embodiment, other metals and alloys may also be used to produce an anode. Other possible metals that may be used to provide cathodic protection include magnesium and aluminum and alloy combination of the preferred metals.

The caps 10 are manufactured in sizes to suit standard metric and English measure reinforcing bars commonly designated by numbers, i.e. #10 bar or #15 bar.

Fig 3 illustrates a cap 10, installed on a rebar 2 with ribs 30 fit over the reinforcing bar ridge deformations 6 (Fig. 4 (a) ) where the cap 10 is collapsed onto the bar 2 to retain the cap 10 on the rebar 2. Cap or bore depth 38 is established, to assure that the ribbed portion of the cap overrides, the deformation ridge at a end 4 of the rebar 2, this contact between the ridge 6 and the rib 30 helps to ensure that the cap 10 remains fixedly attached to the rebar. The depth 38 is preferably at least 2 times the outer diameter of the rebar, and in a particularly preferred embodiment is at least 1.25 time the outer diameter of the rebar. In another preferred embodiment the rib projection 35 is greater than the deformation ridge height 9. Fig. 4 (a) illustrates a partial cross section of a steel rebar showing the axial cross section and the clearly defined deformation ridges 6. Fig. 4 (b) shows the cross section B-B and the means by which the rebar diameter 8 is measured, as well as a deformation ridge height 9. Table 1 indicates various diameters of common steel rebar. Outer diameter tolerances are roughly + 1/16" for rebar up to #5 [similar to metric #20] , while for rebar sizes from #6 [similar to metric #25] and more the diameter tolerance is + 1/8" . The caps 10 of the present invention must be sized to allow the caps to be affixed onto the rebar given.

TABLE 1 OVERALL REBAR DIAMETER

The preferred method of affixing the cap to the reinforcing bar end is to gently tap the cap 10 onto the rebar 2 with a flat instrument such as a small hammer or the flat back of a linesmans pliers, or crimping device. Alternatively, should the reinforcing bar be at the higher tolerance end of the bar diameter, (smallest acceptable size of that diameter) the cap 10 can be hand installed and crimped onto the bar using linesmans pliers or other crimping device. Both methods of attaching the cap 10, produce a secure fit and offer equal corrosion protection for the rebar. The fitted cap/rebar system is ready to be used in an fluid or semi-fluid cement mix. Typically, the cap/rebar system comprises a plurality of cap/rebar meshed together. The cap/rebar system is typically placed in the appropriate location and the pumpable cement mix is pumped to immerse the cap/rebar system with the pumpable cement mixture, which is then allowed to solidify to concrete. Thus the cap/rebar system is contacted with the fluid cement mixture, typically the mixture is pumped into a mold in which the cap/rebar system is placed thus surrounding the cap/rebar system. Various other operations such as removing entrained air may also be conducted before the cement mix is allowed to harden into concrete.

With factory installation, the caps 10 are affixed immediately after cutting the bar and exposing the bare end 4. Completed bars are then bundled with caps securely affixed and shipped to the project site for installation. In cases where a field cut of a galvanized bar is required, the exposed bare end 4 can immediately be protected from corrosion by the installation of the zinc cap 10. Field inspectors look unfavourably on bare cut ends of galvanized reinforcing bars. In many cases the only acceptable solution is to replace the bar with a fully galvanized one. In a few cases, the reinforcing bar installer may be allowed to coat the bare end of the bar with zinc rich paint. This can be time consuming as the paint is not always on hand, and even when present, the painting of a minimum of two coats must be given sufficient time to dry prior to the pouring of cement over the bars, which can promote questions as to the effectiveness of the repair. The field installation of the zinc cap 10 assures corrosion protection without down time. In a preferred embodiment the caps 10 may be painted a bold color, to be easily visible, possibly red or orange, so that the caps 10 can be easily seen by the field inspector, who could then confirm their installation.

While originally conceived to protect bare (cut or exposed) ends 4 of Hot Dip Galvanized steel reinforcing bars, the caps 10 can also be used to offer cathodic protection from corrosion of bare ends 4 of any coated or uncoated steel reinforcing bars 2.

The caps 10 will serve as a positive corrective measure on bare ended steel reinforcing bars which, by error, may have been installed to close to the edge of a concrete form, allowing insufficient concrete cover over the bar's end. Moisture penetration will quickly corrode the bare bar with resulting premature rust stains leeching through the thin concrete cover and possible structural problems. In the case of bare ended steel rebar 2, cap 10 may be placed at both ends for greater corrosion protection.

The zinc Cap 10 represents an effective, efficient and economical method of assuring corrosion protection of bare ends of coated or uncoated steel reinforcing bars 2 in concrete. Ease of installation both in factory or field applications will ultimately lower project overall costs by the reduction of time and processing and handling costs.

The caps 10 are in a preferred embodiment manufactured from 190 alloy zinc sheet 0.020" thick. Caps 10 are generally cylindrical in shape with only one end open. Cap depth 38 is typically + 3/4". The cylindrical walls 24 of the caps include ribs 30, which are installed in a manner to fit over the reinforcing bar deformations ridges 6. zinc caps 10 can be manufactured in a variety of diameters to suit standard reinforcing bar designations of either English or metric measure.

EXAMPLE

Two pieces of bare (non-galvanized) #3 [#10] rebar were cut into 12" pieces. A saline solution was 5 wt% sea salt (NaCl) in water was prepared. One of the two pieces of bare rebar was fitted at one end with a cap 10 of zinc 190 alloy. The bare and the capped bare pieces of rebar where each immersed in the prepared saline solution and allowed to stand. Fig. 5 (a) illustrates, the bare rebar after 14 days (336 hours) . The rust is clearly visible in the saline next adjacent to the rebar and above the rebar partially obstructing the view of the bare and now rusted rebar. Rust is also clearly visible in the solution next to the rebar which is clearly corroding quite quickly.

Fig. 5 (b) illustrates the condition of the same type of bare rebar as in Fig. 5 (a) but having a cap of the present invention after 14 days (336 hours) . The capped bar rebar is clearly visible has a dark color which indicates that no rust formed after 14 days .

The embodiment ( s ) of the invention described above is (are) intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims .

Claims

CLAIMS :

1. A cap for protecting a steel rebar from corrosion by an electrolyte in a reinforced concrete, the cap comprising: a rebar contacting surface at a base of a bore defined within the cap, and

a retainer on an internal wall surface, the internal wall surface circumscribing the rebar contacting surface, the retainer for fixedly attaching the cap on the steel rebar,

wherein the cap comprises a material selected from the group consisting of zinc, aluminum and magnesium, and the steel rebar contacts the rebar contacting surface producing a barrier against the electrolyte and establishing a galvanic current in the presence of the electrolyte between the steel rebar and the material to cathodically protect the steel rebar from corrosion.

2. The cap according to claim 1, wherein the retainer comprises at least one rib projecting into the bore for fixedly attaching at least one deformation ridge of the steel rebar.

3. The cap according to claim 2, wherein the body has a length that is at least 1.25 times the outer diameter of the steel rebar.

4. The cap according to claim 3, wherein the length is at least 2 times the outer diameter of the steel rebar.

5. A steel rebar cathodically protected from corrosion by an electrolyte for reinforced concrete, the rebar comprising:

a steel rebar member, the member including at least one end and

a cap fixedly attached to the at least one end, each cap comprising:

a rebar contacting surface at a base of a bore defined within the cap, and

a retainer on an internal wall surface circumscribing the rebar contacting surface, the retainer for fixedly attaching the cap on the steel rebar,

wherein the cap comprises a material selected from the group consisting of zinc, aluminum and magnesium, and the steel rebar contacting the rebar contacting surface producing a barrier against the electrolyte and establishing a galvanic current in the presence of the electrolyte between the steel rebar and the material to cathodically protect the steel rebar from corrosion.

6. The steel rebar according to claim 5, wherein the rebar member is galvanized and the at least one end has been cut exposing bare steel .

7. The steel rebar according to claim 5, wherein the rebar member is bare steel .

8. The steel rebar according to claim 5, wherein the retainer comprises at least one rib projecting into the bore for fixedly attaching at least one deformation ridge of the steel rebar.

9. A method of protecting a steel rebar for reinforced concrete from corrosion comprising:

identifying an end of the steel rebar to be protected;

providing an cap for protecting a steel rebar from corrosion by an electrolyte in a reinforced concrete, the cap comprising:

a rebar contacting surface at a base of a bore defined within the cap, and

wherein the cap comprises a material selected from the group consisting of zinc, aluminum and magnesium, and the steel rebar contacts the rebar contacting surface producing a barrier against the electrolyte and establishing a galvanic current in the presence of the electrolyte between the steel rebar and the material to cathodically protect the steel rebar from corrosion, the cap for frictionally attaching onto the end of the rebar, and attaching the cap to the end to produce a cap/rebar system wherein the end and the rebar contacting surface are in contact.

10. The method according to claim 9, wherein the cap is attached to the end with a hammer or crimping device.

11. The method of claim 9, further comprising contacting the cap/rebar system with a fluid cement mix and allowing the mix to harden to become concrete .

12. The method according to claim 9, wherein the retainer comprises at least one rib projecting into the bore for fixedly attaching at least one deformation ridge of the steel rebar.