Corrosion Protection of Cables in a Concrete Structure

Abstract

Steel reinforcing cables in concrete are protected against corrosion by injecting a carrier fluid and corrosion inhibitors into interstitial spaces between the wires of the cable at a first location along the cable and causing the fluid to pass through the interstitial spaces between the wires of the cable to a second location along the cable. The cable comprises an array of wires confined together and intimately surrounded by a covering material which is engaged with a periphery of the cable so that there are insufficient interconnected spaces between the cable and the covering material to allow passage of fluid longitudinally along the cable outside the cable itself. The method can be used with pre-stressed concrete, with post-tensioned bonded cables and with extruded un-bonded mono-strand cables.

Claims

1. A method for use with a steel reinforcing cable embedded in a member comprising concrete; wherein the cable comprises an array of wires extending along the concrete for providing reinforcement thereto; wherein the wires are wound in a helix so as to hold them as a confined twisted array with each wire butting against its neighbors and held in contact with its neighbors by loads therebetween generated by the tension on the confined twisted array; wherein the cable is intimately surrounded by a covering material which is engaged with a periphery of the cable so that there are insufficient interconnected spaces between the cable and the covering material to allow passage of fluid along the cable between the cable and the covering material; the method comprising: inserting a fluid into interstitial spaces between the wires of the cable at the first location along the cable; and causing the fluid to pass through the interstitial spaces between the wires of the cable to a second location along the cable; wherein the fluid comprises a liquid which expels moisture from the interstitial spaces between the wires of the cable.

2. The method according to claim 1 wherein the fluid is selected to reduce corrosion of the steel wires of the cable.

3. The method according to claim 1 wherein the fluid comprises corrosion inhibiting material.

4. The method according to claim 3 wherein the corrosion inhibiting material is selected from the group consisting of: Amines Amino alcohol; Amino carboxylate; Calcium sulfonate; Organofunctional silane, silane, siloxane or silicone Grease amine Oil amine Amine salts with nitrous or chromic acids, Amine salts with carbonic acid, carbamic acid, acetic acid, substituted benzoic acids and organic esters of nitrous acid, phthallic acid or carbonic acid, Primary, secondary and tertiary aliphatic amines, Cycloaliphatic and aromatic amines, Polymethylene amines, Mixtures of nitrites, urea, hexamethylene tetramine and ethanolamines, and Nitrobenzene and 1-Nitronaphthalene.

5. The method according to claim 3 wherein the corrosion inhibiting material comprises Calcium sulfonate or Organofunctional silane.

6. The method according to claim 1 wherein the fluid impregnates a region of the covering material surrounding the cable and wherein the fluid interacts with the covering material to change its properties within the impregnated region.

7. The method according to claim 6 wherein the fluid interacts with the covering material to reduce permeability of the impregnated region.

8. The method according to claim 6 wherein the fluid interacts with the covering material to increase the electrical resistivity of the impregnated region.

9. The method according to claim 6 wherein the fluid comprises generates a hydrophobic zone around the cable.

10. The method according to claim 1 wherein the fluid forms a protective film on exposed portions of the wires.

11. The method according to claim 1 wherein the fluid comprises a liquid selected from the group consisting of: Silane, Siloxane, silicone, Oil, Organic solvent, Calcium sulfonate, and Polymer resin.

12. The method according to claim 1 wherein the fluid comprises a liquid selected from the group consisting of: Water, Water containing dissolved salts, Water containing suspended particles.

13. A method for use with a steel reinforcing cable embedded in a member comprising concrete; wherein the cable comprises an array of wires extending along the concrete for providing reinforcement thereto; wherein the wires are wound in a helix so as to hold them as a confined twisted array with each wire butting against its neighbors and held in contact with its neighbors by loads therebetween generated by the tension on the confined twisted array; wherein the cable is intimately surrounded by a covering material which is engaged with a periphery of the cable so that there are insufficient interconnected spaces between the cable and the covering material to allow passage of fluid along the cable between the cable and the covering material; the method comprising: inserting a fluid into interstitial spaces between the wires of the cable at the first location along the cable; and causing the fluid to pass through the interstitial spaces between the wires of the cable to a second location along the cable; wherein the fluid impregnates a region of the covering material surrounding the cable and wherein the fluid interacts with the covering material to change its properties within the impregnated region.

14. The method according to claim 13 wherein the fluid interacts with the covering material to reduce permeability of the impregnated region.

15. The method according to claim 13 wherein the fluid interacts with the covering material to increase the electrical resistivity of the impregnated region.

16. The method according to claim 13 wherein the fluid comprises generates a hydrophobic zone around the cable.

17. A method for use with a steel reinforcing cable embedded in a member comprising concrete; wherein the cable comprises an array of wires extending along the concrete for providing reinforcement thereto; wherein the wires are wound in a helix so as to hold them as a confined twisted array with each wire butting against its neighbors and held in contact with its neighbors by loads therebetween generated by the tension on the confined twisted array; wherein the cable is intimately surrounded by a covering material which is engaged with a periphery of the cable so that there are insufficient interconnected spaces between the cable and the covering material to allow passage of fluid along the cable between the cable and the covering material; the method comprising: inserting a fluid into interstitial spaces between the wires of the cable at the first location along the cable; and causing the fluid to pass through the interstitial spaces between the wires of the cable to a second location along the cable; wherein the fluid comprises a gas and effects a drying action on the wires of the cable to expel moisture from the interstitial spaces between the wires.

18. Method according to claim 17 wherein the application of a gas is continued to effect the drying of the covering material adjacent to the cable.

19. The method according to claim 17 wherein the gas and the moisture are collected at the second location for analysis of a moisture content thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] FIG. 1 is a vertical cross-sectional view transversely through a concrete member at an injection site for a fluid into the interstices of a reinforcing pre-stressed cable in a method according to the present invention.

[0100] FIG. 2 is a vertical cross-sectional view longitudinally through a concrete member at a bonded post-tensioned reinforcing cable showing fluid injection into ends of the cable in a method according to the present invention.

[0101] FIG. 3 is a cross-sectional view through the cable and surrounding sleeve of the concrete member of FIG. 2.

[0102] FIG. 4 is a cross-sectional view through an un-bonded post-tensioned cable with surrounding plastic sleeves showing the interstices of the cable containing the injected fluid.

DETAILED DESCRIPTION

[0103] In FIG. 1 is shown a pre-stressed steel reinforcing cable 10 embedded in a concrete member 11. The cable 10 comprises an array of wires 12 confined together and under tension. Typically the wires are wound around a helix at a shallow angle so as to hold them as a confined array with each wire butting against its neighbours and held in contact with its neighbours by the loads therebetween generated by the tension on the helical array. Thus each wire has its surface in direct contact with its neighbour along its length as indicated at 13.

[0104] In the pre-stressed system shown in FIG. 1, the cable is intimately surrounded by the concrete itself by casting of the concrete while the cable is in place in the form so that the concrete is engaged with a periphery of the cable at the peripheral surface of the outermost wires. Thus the concrete in the casting process butts intimately with all of the peripheral surfaces of the wires and prevents the formation of any spaces around the cable to allow passage of fluid longitudinally along the cable in spaces between the cable and the covering material. Thus there are in effect no interstitial spaces and certainly no interconnected interstitial spaces between the cable and the covering material itself.

[0105] However the wires themselves remain separate and leave interstitial spaces 15 between each wire and its neighbours. The method of the present invention therefore comprises inserting a fluid 16 into the interstitial spaces 15 between the wires of the cable.

[0106] The fluid is injected or inserted at a first location along the cable and the fluid is caused to pass through the interstitial spaces between the wires of the cable to a second location along the cable. The location in FIG. 1 is at a position along the length of the cable so that a hole 17 is drilled to intersect the cable from a surface 18 of the concrete member to the cable so that one side face of the cable is exposed in the hole. A tube 19 is inserted into the hole and held in place by an adhesive or by a suitable coupling 20 which holds the tube in place to resist the pressure in the fluid tending to displace the tube. Alternatively, the hole may be excavated and may extend around the periphery of the cable at the location of the excavation. Many different mounting arrangements can be used and one example only is shown where a flange 21 is fastened to the surface 18 by screws 22.

[0107] The fluid 16 is provided by a pressurized container 23 which is attached to the tube. The container can be of any arrangement depending on the pressure to be applied. In one example the pressure is of the order of 50 to 100 psi which requires only a plastic container with a hand pump for generating the pressure. In other cases a pressure pump, pressure pot, piston pump, gear pump, hydraulic cylinder or compressor may be used to generate the required fluid pressure to enable the material to flow. Depending on the type of pumping and associated measuring devices, the applied pressure and flow rate can be adjusted and monitored. Intermediate holes can be provided to monitor the movement of the fluid along the length of the cable or to progressively insert the fluid into the cable, section by section to minimize the distance the fluid is required to flow from each injection location. Vacuum may be applied at a position separate from the point of application of the fluid to assist in flow and penetration of the fluid along the length of the cable.

[0108] The fluid 16 at the side face of the cable can penetrate between the wires into the interstices 15 into the interstices of the wires within the cable itself. From those interstices the fluid can pass along the cable to a second location. The second location not shown in FIG. 1 can be at an end of the cable or can be at another intermediate location on the cable. In order to complete protection of a long length of cable, a number of locations along the cable can be selected and fluid injected to pass along the cable to a next location.

[0109] The fluid 16 is selected as defined above so that it includes a carrier as defined and a corrosion inhibitor as defined which provides properties suitable to reduce corrosion of the steel wires of the cable. The corrosion inhibitor may improve the durability of the structure by improving or modifying the properties of the surrounding concrete. The carrier and the corrosion inhibitor may in some cases be the same material. As the corrosion inhibitor has the above properties and is preferably one of the materials defined hereinafter, the corrosion inhibitor is necessarily different from the covering material which, as explained above is the concrete itself, a surrounding grout or grease.

[0110] In FIG. 1 the fluid includes a liquid carrier which may expel moisture or react with moisture from the interstitial spaces 15 between the wires of the cable and impregnate the surrounding concrete to generate a hydrophobic zone 24 around the cable by diffusing or spreading outwardly from the cable into the surrounding concrete. The fluid may also act to coat the wires and form a protective film on the surface of the wires. The interior wire surfaces may be largely or fully coated. The exterior wire surfaces in direct contact with the surrounding concrete and may receive only a partial protective film coating. The use of a fluid which acts to coat the wires and form a protective film is particularly beneficial to provide corrosion protection to steel wire surfaces which are exposed to air bubbles, voids or pockets in the surrounding concrete, grout or filler material at certain points along the length of the cable. The fluid can reach these bubbles, voids or pockets via the interstitial spaces even though they are not interconnected through the covering material.

[0111] Thus the injection of the carrier liquid such as oil, amine, amino alcohol, calcium sulfonate, silane, siloxane, silicone, organic solvent or other polymer causes the liquid to diffuse or migrate outwardly to impregnate into a surrounding volume of concrete or mortar surrounding the cable to form a generally cylindrical impregnated zone around the cable. Depending on the material used it may be difficult for moisture to penetrate. The fluid may be free of water. The fluid can be selected so that it interacts with the covering material to change the properties of the covering material within the impregnated region. Thus for example, the fluid interacts with the covering material to reduce permeability of the impregnated region. Thus for example, the fluid interacts with the covering material to increase the electrical resistivity of the impregnated region. Thus for example, the fluid forms a protective film on exposed portions of the wires. Thus for example, the impregnated zone around the cable includes a corrosion inhibiting material. Thus for example, the impregnated zone around the cable has an increased electrical resistance. Thus for example, the impregnated zone around the cable has a reduced permeability.

[0112] In FIGS. 2 and 3, the method is used with a post-tensioned system in which the cable 30 formed by wires 30A with interstices 30B is contained within a tubular container 31 extending along the concrete member 32 between the ends 34, 35. The wires of the cable are intimately surrounded by a filler material or grout 33 inserted into the tubular container 31 after tensioning of the cable 30 within the tubular container so that the filler material 33 is bonded intimately to the wires of the cable 30. In many cases multiple cables are present inside a singular tubular container (duct) wherein the filler material surrounds each of the cables. The duct assembly containing multiple cables is often referred to as a tendon or multi-strand assembly.

[0113] Again, the method comprising inserting a fluid into interstitial spaces 30B between the wires of the cable at a first location at the end 35 along the cable and causing the fluid to pass through the interstitial spaces between the wires of the cable to a second location at the end 34 along the cable.

[0114] In FIGS. 2 and 3, the fluid comprises a gas from a pressurized supply 36 arranged to effect a drying action on the wires of the cable to expel moisture from the interstitial spaces between the wires. In this case the gas may be used in a testing procedure to drive moisture from the interstitial spaces between the wires, which is then collected at the end 34 (or an alternate location) at a sample extractor 37 at an outlet 40 for analysis of a moisture content. In this way an initial testing procedure can be provided which detects the presence of any moisture and then goes onto a remediation process if moisture is detected.

[0115] A vacuum pump 38 can be provided connected to the outlet 40 to assist in drawing the gas more effectively along the path. A valve 39 controls the connection of the outlet 40 to the sample collector 37 or to the vacuum 38.

[0116] Similar to the previous example illustrated in FIG. 1, liquid can be injected into the interstices and can provide benefits similar to the example previously described.

[0117] In FIG. 4 the cable 40 comprises an array of wires 41 confined together to form an elongate cable with interstices 42 where the cable 40 is contained within an extruded plastic sleeve 43 extruded onto the cable. There is provided an un-bonded filler material, typically grease 44, between the cable 40 and the sleeve 43 arranged to allow sliding of the cable within the sleeve during tensioning.

[0118] The intimate engagement of the extruded jacket or sleeve 43 and the penetration of the inside surface of the sleeve into the exterior interstices of the wires around the cable causes the grease 44 to be contained or compressed onto the exterior surfaces around the wires 41 of the cable both around the outside of the wires and into the interstices between the wires so that there are no paths around the wires within the sleeve.

[0119] As explained and shown previously the fluid is injected into interstitial spaces 42 between the wires of the cable 41 at a first location along the cable and the fluid passes through the interstitial spaces between the wires of the cable to a second location along the cable.