NL1040804B1

NL1040804B1 - Cathodic protection system for reinforced concrete expansion joint applications.

Info

Publication number: NL1040804B1
Application number: NL1040804A
Authority: NL
Inventors: Ing Roberto Giorgini Ir
Original assignee: Corrpre Eng B V
Priority date: 2014-05-16
Filing date: 2014-05-16
Publication date: 2016-03-02

Abstract

The invention comprises an anode assembly for a cathodic protection system for reinforced concrete structures with expansion joints using a flexible ionic conductive adhesive, sealant or caulk which functions as a flexible salt bridge, applied within the joints bridging adjacent concrete slabs or parts of the reinforced concrete structure and an impressed current or sacrificial anode assembly to overcome the movement and vibrations of the expansion joints which can be found in any concrete structure. The anode assembly may be placed within the flexible ionic conductive adhesive, sealant or caulk, but may be also placed within the expansion joint directly on the surface of the concrete without the use of ionic conductive adhesive, sealant or caulk. The anode assembly for impressed current cathodic protection can be of any electrode material like noble or valve metals (metals from a group including but not limited to tungsten, tantalum, niobium and zirconium) coated with one or more noble metals or coated with mixed-metal-oxides (MMO) in any form or shape, such as tape, mesh, wire, grid, tube or strip. The anode material for sacrificial cathodic protection can be of any electrode material like alkali metals (metals from a group including but not limited to zinc, aluminium and magnesium or any metal which is more electronegative than steel in concrete) in any form or shape, such as tape, mesh, wire, net, grid, tube, strip or rolled sheet, sandwiched, embedded or covered by any electrolytic material containing metal activating agents, humectants, mortars or grouts.

Description

CATHODIC PROTECTION SYSTEM FOR REINFORCED CONCRETE EXPANSION JOINT APPLICATIONS

TECHNICAL FIELD

This invention relates to cathodic protection of reinforcing steel in concrete expansion joint application. More specifically, to anode assemblies for cathodic protection of reinforcing steel in concrete expansion joints and the like.

BACKGROUND OF THE INVENTION

Cathodic protection (CP) of reinforcing steel has been applied to reinforced concrete structures with corrosion damage for over 25 years. World wide experience shows that CP prevents further damage in a reliable and economical way for a long time. CP is particularly suited in cases where chloride contamination has caused reinforcement corrosion. Applications started on bridge decks suffering from corrosion due to deicing salt penetration resulting in severe damage to the concrete. Since the 1970’s, CP has been applied to buildings, marine structures, tunnels and bridge decks and substructures in the US, Europe and elsewhere in the world.

The normal condition of steel reinforcement in concrete is passivity. This is a state with an almost negligible corrosion rate, caused by a thin oxide film (passive layer) on the steel surface, which is stabilised by the high pH in concrete (approximately 13). This passivation layer may be lost by two mechanisms: either carbon dioxide ingress, which reduces the pH to a level of approx. 9 (carbonation), causing a more or less uniform loss of passivation, or the presence of chloride ions, which locally break down the passive film starting pitting corrosion. Chloride may be either cast in or may penetrate from the environment.

The type of corrosion that occurs in reinforced concrete is an electrochemical phenomenon, in which the potential of the reinforcing steel and the exchange of electrical current between the steel and liquid, the electrolyte, present in the pores of the concrete play important roles. In the passive state, the potential of the steel is relatively positive, due to chemical reaction between oxygen and the steel surface. When passivation is lost, iron passes into solution in the form of ferrous ions, leaving excess electrons in the steel, which makes the potential of these spots more negative; this reaction is termed ‘anodic’. Potential differences between anodic sites and the remaining, passive, surface of the steel, i.e. the cathodic areas, cause currents to flow in the concrete pore liquid, accelerating the steel dissolution reaction. The corrosion products are more voluminous than the original steel. The net effect is expansion, causing tensile stresses in the surrounding concrete. After relatively small amounts of steel have been transformed into corrosion products, the concrete cover cracks and spalling or delamination occurs. Cracking and spalling in themselves can be unacceptable, but they also have to be taken as a warning sign of further decay: when left to corrode, the steel bar diameter may decrease below structurally acceptable values. Concrete repair may be necessary and the corrosion protection must be reinstated, for example by cathodic protection.

Principles of cathodic protection of steel reinforcement in concrete Cathodic protection of reinforcing bars in concrete is based on changing the potential of the steel to more negative values, reducing potential differences between anodic and cathodic sites and hence reducing the corrosion current to negligible values. The change of potential is called polarisation. In practice, this can be achieved in two ways, either by means of sacrificial anodes or by means of impressed current.

Cathodic protection (CP) systems are the most effective systems for preventing or controlling corrosion of steel in reinforced concrete. This is realised with impressed current cathodic protection (ICCP) by mounting an electrode, the anode, on the concrete surface or embedded in the concrete, connecting it with the positive terminal of a DC (direct current) power source while connecting the negative terminal to the reinforcement steel cage. And is realised with sacrificial anodes (GACP) by mounting the anode, on the concrete surface or embedded in the concrete, connecting it directly to the reinforcement steel cage.

Through the steel reinforcement cage, electrons flow to the steel/concrete interface, increasing the cathodic reactions, which produce hydroxide ions from oxygen and water. On the other hand water molecules migrate through the concrete to the anode where they are oxidised to oxygen gas, hydrogen-ions and electrons. The basic electrochemical reactions at the anode of an impressed current cathodic protection system in reinforced concrete are:

and

(hypochlorous and hydrochloric acid) if chloride is present.

And the basic electrochemical reactions at the anode of a sacrificial cathodic protection system in reinforced concrete are:

( "Me" is an alkali metal used as a sacrificial anode)

The electrons flow from the anode to the reinforcing steel, which closes the electrical circuit. As a result of this current circulation, cathodic reactions are favoured and anodic reactions at the steel are suppressed. Relatively moderate current densities are able to restore passivity of the reinforcing steel and have various beneficial chemical effects.

Anode materials

The heart of any impressed current cathodic protection system is the anode or electrode material, which can be found on the market in various types, forms and shapes. Depending on the application the anodes of ICCP systems include materials such as graphite, platinised titanium or noble metals or valve metals coated with mixed metal oxide (MMO). Mixed metal oxide coated anodes usually comprise two types of metal oxides. The first one may consist of for example platinum oxide, which conducts electricity and catalyzes certain reactions such as the production of chlorine gas. The other metal oxide is typically titanium dioxide. Titanium dioxide does not conduct electricity and does not catalyze reactions and acts as a cost-effective corrosion protection layer for the anode base material, often titanium.

Common anode materials for ICCP systems for reinforced concrete structures include: • noble metal or valve metal coated with noble metal or coated with mixed metal oxides (MMO) in the form of wire mesh, wire, strip, tape or tubes shaped to fit the surface of the structure and subsequently covered with a cementitious overlay, e.g. spray or shotcrete; • or wires, strips, mesh, tubes placed in holes or slots and backfilled with cementitious grouts; • conductive and electro-active coatings covering the concrete surface.

These types of anodes for impressed current cathodic protection systems need a DC power source that supplies them with the required current.

Sacrificial anodes include materials such as : • zinc, aluminium, magnesium or any type of metal which is more electronegative than steel in concrete, • with or without being embedded or coated with a mortar, • with or without being embedded or coated by an activating material, • of which the mortar may contain or exists of alkaline or acid material, • of which the activating material may be based on coatings, pastes, hydrogels or adhesives containing activating agents or humectants or any combination thereof.

SUMMARY OF THE INVENTION

The invention comprises an anode assembly for a cathodic protection system for reinforced concrete structures with expansion joints using a flexible ionic conductive adhesive, sealant or caulk which fimetions as a flexible salt bridge, applied within the joints bridging adjacent concrete slabs or parts of the reinforced concrete structure and an impressed current or sacrificial anode assembly to overcome the movement and vibrations of the expansion joints which can be found in any concrete structure. The anode assembly may be placed within the flexible ionic conductive adhesive, sealant or caulk, but may be also placed within the expansion joint directly on the surface of the concrete without the use of ionic conductive adhesive, sealant or caulk.

The anode assembly for impressed current cathodic protection can be of any electrode material like noble metals or valve metals (metals from a group including but not limited to tungsten, tantalum, niobium and zirconium) coated with one or more noble metals or coated with mixed-metal-oxides (MMO) in any form or shape, such as tape, mesh, wire, net, grid, tube or strip.

The anode material for sacrificial cathodic protection can be of any electrode material like alkali metals (metals from a group including but not limited to zinc, aluminium and magnesium or any metal which is more electronegative than steel in concrete) in any form or shape, such as tape, mesh, wire, net, grid, tube, strip or rolled sheet, sandwiched, embedded or covered by any electrolytic material containing metal activating agents, humectants, mortars or grouts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows a reinforced concrete structure with an expansion joint. FIG. 2 shows a schematic cross section of an expansion joint between 2 reinforced concrete slabs with a flexible ionic conductive caulk, sealant, paste or adhesive with a sacrificial anode. FIG. 3 shows a schematic cross section of an expansion joint between 2 reinforced concrete slabs with a flexible ionic conductive caulk, sealant, paste or adhesive with an impressed current electrode and power source. FIG. 4 shows a schematic cross section of an expansion joint between 2 reinforced concrete slabs with a flexible ionic conductive caulk, sealant, paste or adhesive with a sacrificial or impressed current anode covered by a regular expansion joint sealant. FIG. 5 shows a schematic cross section of an expansion joint between 2 reinforced concrete slabs with a surface applied sacrificial anode without being covered by a regular expansion joint sealant, but an ionic conductive adhesive being used between the anode and the concrete surface of the expansion joint.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises an improved anode assembly and method for the application of cathodic protection to reinforcing steel in concrete specifically for expansion joints. The anode assembly comprises sacrificial electrode material or impressed current electrode material, placed in an ionic conductive caulk, sealant, paste or adhesive with high elasticity, durability and maintainig its flexible consistency.

The highly flexible and elastic ionic conductive material is used to overcome (a) the expansion and contraction motions caused by temperature changes, and to overcome (b) the shortening and creep caused by prestressing and deflections caused by load, traffic movements.

For extra durability, wear or weatherproofing the installed anode assembly together with the flexible ionic conductive material can be covered by a regular expansion joint sealant for example a polyurethane or silicone based sealant or any other kind of sealant or weather protection. FIG. 1 schematically shows a typical concrete construction with the expansion joint 2 laying between the two concrete slabs 1 and 3. The concrete slabs 1 and 3 are typically not connected and need therefore to be supported by a concrete beam or colomn 4. In this way the concrete slabs 1 and 3 can freely move due to expansion or contraction. FIG. 2 shows an enlarged schematic cross section of the expansion joint 1 with a flexible ionic conductive caulk, sealant, paste or adhesive 3 and the sacrificial anode assembly 4 placed in this ionic conductive material. The sacrificial anode assemby 4 is directly connected to the steel reinforcement 2 in both adjacent concrete slabs with a current conductor 5. The current conductor can be made of any electricity conducting material and need to be connected on to the steel reinforcement in a state of the art durable manner. FIG. 3 shows an enlarged schematic cross section of the expansion joint 1 with a flexible ionic conductive caulk, sealant, paste or adhesive 3 and the impressed current anode assembly 4 placed in this ionic conductive material. The anode assemby 4 is connected to a DC power source 7 by an anode feeder cable or wire 6 on the positive terminal of the powersource 7 and a cable or wire 5 which is connected on the negative terminal of the power source and the steel reinforcement 2 which is common art with these techniques. FIG. 4 shows an enlarged schematic cross section of the expansion joint 1 with a flexible ionic conductive caulk, sealant, paste or adhesive 3 and the sacrificial anode assembly 4 placed in this ionic conductive material 3 but directly connected to the steel reinforcement 2 in both adjacent concrete slabs with a current conductor 5. The sacrificial anode assembly 4 placed in the ionic conductive material 3 is covered for extra protection and durability by a regular expansion joint sealant such as but limited to polyurethane based or silicone based sealants as common art with these techniques. FIG. 5 shows an enlarged schematic cross section of the expansion joint 1 with a flexible ionic conductive caulk, sealant, paste or adhesive 3 placed between the sacrificial anode 4 and concrete surface. In this case there is no need for additional ionic conductive caulk paste or adhesive to fill up the space within the expansion joint. The sacrificial anode assembly 4 placed against the ionic conductive material 3 is covered for extra protection and durability by a waterproof sealant 5 such as but not limited to polyurethane based, silicone based, or visco-elastic polymers based sealants as common art with these techniques.

The schematic examples of anode assemblies shown in the drawings are all shown without terminals for the electrical connections of the anode assemblies. This is done solely for the clarity of the drawings and shall not be limiting.

The advantages of the anode assembly according to the invention compared to existing cathodic protection anodes or anode systems for reinforced concrete, can be summarized as follows: • By embedding the electrode material in a flexible ionic conductive caulk, sealant, paste or adhesive within the expansion joints, the expansion and contraction motions, the shortening, creep and deflections caused by temperature changes, prestressing, load, and traffic movements can be compensated for. • Application of the anode assembly within the expansion joints according to the invention is much easier and faster than the applications of anodes or anode systems according to the prior art by application of the anode assembly within the concrete through cavities, slots, or holes.

All examples given in this descriptive section and in the drawings are intended to be non-limiting, and are provided in order to help in conveying the scope of the invention.

Claims

Conclusions:

An anode assembly for cathodic protection of reinforced concrete on the basis of applied current or sacrificial anodes, characterized in that the anode assembly is arranged in the expansion joints or joints of a reinforced concrete structure using the space of the expansion joint or jointing.

An anode assembly according to claim 1, wherein the anode material is embedded or applied in an electrolytic paste, sealant or glue layer, characterized in that the elasticity of the electrolyte is maintained.

Electrolytic paste, sealant or adhesive layer according to claim 2, which is arranged in the dilatation joint or junction, characterized in that the movements caused by the expansion, shrinking, creeping and vibrations of the concrete structure can be absorbed.

The paste, kit or adhesive layer according to claim 2, characterized in that the ion has conductive and electrically conductive properties.

The paste, kit or adhesive layer according to claim 2, characterized in that the pH comprises greater than 3.

The paste, kit or glue layer according to claim 2, characterized in that the specific resistance comprises less than 500 ohm.m.

An anode assembly according to claim 1, characterized in that the electrode comprises a metal.

An anode material according to claim 6, characterized in that it comprises metal, zinc, aluminum or magnesium.

An anode material according to claim 6, characterized in that the metal consists of an alloy whose natural potential is more electronegative than steel.

An anode assembly according to claim 6, characterized in that the material comprises a mortar.

An anode assembly according to claim 9, characterized in that the material comprises a mortar with a pH greater than 3.

12. Anode assembly as claimed in claim 2, characterized in that the material comprises additives, such as, but not limited to, halogens and salts.

An anode assembly according to claim 2, characterized in that the material comprises moisture-binding additives.

An anode assembly according to claim 1, characterized in that the electrode is electrically coupled to an electrical supply, battery or accumulator.

An anode assembly according to claim 13, characterized in that the electrical supply is coupled to an alternative energy supply such as, but not limited to, solar panels or wind turbines.

Anode assembly according to claim 1, characterized in that the anode assembly is sealed watertight with a kit, tape or coating, such as, but not limited to, silicones, polyurethanes, bitumen or visco-elastic polymers.

An anode assembly according to claim 1, characterized in that the entire dilation joint or junction, in which the anode assembly is located, with a kit, tape or coating, such as, but not limited to, silicones, polyurethanes, bitumen or visco-elastic polymers, is sealed watertight.