KR101381053B1 - Treatment process for concrete - Google Patents

Abstract

Single anode systems used in multiple electrochemical treatments to control steel corrosion in concrete include porous mounting materials comprising sacrificial metal and electrolytes that can support high forced anode current densities with forced current anode connections. . Initially, a power source 5 is used to drive current from the sacrificial metal 1 to the steel 10 to convert oxygen and water 14 to hydroxyl ions 15 on the steel and to convert chloride ions 16. It is attracted to the porous material 2 around the anode to cause the corrosion sites to move from the steel to the anode, restoring the steel passivation and activating the anode. Cathodic protection is then applied. This is preferably cathodic protection applied by disconnecting the power source and connecting the activated sacrificial anode directly to the steel.

Concrete, corrosion, temporary forced current treatment, low current prevention treatment, sacrificial metal.

Description

Treatment process for concrete

The present invention relates to the electrochemical treatment of reinforced concrete to prevent deterioration due to corrosion of steel. More particularly, it relates to a hybrid electrochemical treatment for preventing steel reinforced corrosion and thus preventing the onset of corrosion.

Corrosion of steel is an important issue in reinforced concrete. Both continuous electrochemical treatment and transient electrochemical treatment have been used to counter this problem. These include conducting current from the installed anode system to the steel through the concrete. In all cases, the steel becomes the cathode of the formed electrochemical cell. In forced current electrochemical treatment, the anode is connected to the negative terminal and the steel is connected to the negative terminal of the DC power source. In sacrificial electrochemical treatment, a protective current is provided by corrosion of the sacrificial anode directly connected to the steel.

Continuous or long term electrochemical treatments are aimed at maintaining the treatment in the foreseeable future. Electrochemical treatment periods are generally measured annually. A well-known group of continuous or long term technologies is cathodic protection. This includes forced current cathode protection, sacrificial cathode protection, intermittent cathode protection and cathode protection. In these techniques, long term or permanent anodes apply a small current to the steel reinforcement. Average current densities per unit area of the steel surface are generally in the range of 2 to 20 mA / m ² to counteract existing degradation and 0.2 to 2 mA / m ² to prevent the onset of degradation. The current can be pulsed but the average applied currents are generally within this range. The current can sometimes be modified with modifications based on analysis of working data.

Temporary or short term electrochemical treatments are established for the purpose of stopping the treatment in the foreseeable future. Electrochemical treatment periods are generally measured on a daily, weekly or monthly basis. Temporary treatments designed to prevent reinforcing corrosion include chloride extraction (US 6027633) and re-alkalisation (US 6258236). In these systems, a temporarily installed anode system is used in connection with a transient DC power supply for applying a large current of 1000 mA / m ² per unit area of the steel surface for a short period of time (typically less than three months) for steel reinforcement. do.

Anodes are electrodes that support a net oxidation process. Anodes for concrete structures can be divided into inert anodes or sacrificial anodes. They can also be divided into separate or unseparated anodes, as well as anodes embedded in the porous matrix and anodes attached to the concrete surface to make them accessible. Anode systems comprising an anode and a supporting electrolyte can be divided into transient and long term anode systems. The differences are summarized in the following paragraphs.

Inert anodes withstand anode consumption. They have been used in most electrochemical processes, with the theoretical exception being sacrificial cathodic protection. The main anode reaction is the oxidation of water to produce oxygen gas and acid. Acids attack cement pastes in concrete. As a result, the current density from inert anodes is likely to be limited to less than 200 mA / m ² per unit area of the anode surface. A widely used anode system is a mixed metal oxide (MMO) coated titanium mesh mounted in a cementitious overlay on a concrete surface (US 5421968). Separated porous titanium oxide anodes claimed to apply higher anode current densities of up to 1000 mA / m ² from the anode surface were also used (US 6332971).

Sacrificial anodes are consumed in the process of applying a protective current. The main anode reaction is the dissolution of the sacrificial metal. As a result, the life of the sacrificial anode is limited. Sacrificial anodes have been applied as a mesh with mounted (buried) separation anodes in sacrificial cathode protection system (WO 9429496) and overlay in sacrificial cathode protection (US 5714045). However, at the end of their life, the need to replace the anodes reluctance to use the mounted sacrificial anode systems. Sacrificial anode systems were also attached directly to the concrete surface (US 5650060) and are accessible to facilitate anode replacement. The use of sacrificial anodes in the forced current role is hesitant because the anode is consumed more rapidly in this role. However, surface-applying anodes are easy to replace and systems of this type have generally been used as forced current anodes at anode current densities of less than 25 mA / m ² (US 5292411).

Separation anodes are generally separate small anodes that are mounted in holes in the concrete or installed in locations where a patch repair for the concrete is warranted. A detailed description of the separation anodes is given in US Pat. No. 6,217,742. The mounted separation anodes are strongly attached to the concrete and are less common in attachment failures than non-separation anodes applied to the concrete surface.

Temporary anode systems are usually attached to the concrete surface to apply short-term, high-current, temporary electrochemical treatments and are typically removed after a treatment period of less than three months. The transient anodes are surrounded by an electrolyte material such as saturated cellulose fiber which is easily removed at the end of the treatment process or by a transient electrolyte such as liquid stored in a tank (US 5538619). High drive voltages are typically required with high volume electrolytes to support high current outputs. In contrast, long-term anode systems for applying protective current for many years can be strongly attached to concrete and mounted in holes in the concrete to improve anode attachment.

Forced current cathodic protection is the most proven method of preventing chloride-induced corrosion of steel in concrete. However, a high level of maintenance is required when compared to the inspection or maintenance of other reinforced concrete structures. In addition, forced current cathodic protection systems are localized after all cracked and broken concrete areas have been repaired, and then in some anode systems high start up cathode current densities have deleterious effects resulting from acid and gas production. It only works normally at protection current densities significantly lower than steel corrosion rates. Low current densities eventually prevent corrosion, but corrosion-induced damage continues until the corrosion process is prevented.

Temporary electrochemical treatments quickly inhibit the corrosion process and require no maintenance after the initial treatment. However, substantial levels of chloride remain and there are concerns regarding the durability of such treatments in chloride containing environments. In addition, the treatment period can last for several months and access to the treatment surface is limited during this time.

Sacrificial cathodic protection is not always evaluated as strong in preventing corrosion. However, this is a low maintenance and reliable process that can be used in the preventive role.

The problem addressed by the present invention is the efficient use of strong electrochemical protection treatments against corrosion of steel in concrete to prevent corrosion and to achieve long term durability of the protective effect that requires minimal maintenance and minimal confusion while the system is installed. Is provided.

Analysis of valid data provides strong evidence that electrochemical treatments applied to reinforced concrete retard corrosion by restoring alkalinity at corrosion sites using relatively small amounts of charges. The existing electrochemical is thus separated into two states: short initial high current treatment to prevent rapid corrosion to minimize further damage and subsequent prolonged preventive treatment with maintenance conditions to maintain passivation and ensure durability. Treatments can be improved. A single multi treatment anode is disclosed that can apply both an initial high current short term electrochemical treatment to resist corrosion and subsequent long term, low current treatment to prevent subsequent onset of corrosion. To apply an initial high current treatment, the multi treatment anode can apply a very high current density from the anode surface at low safety DC voltages. In order to achieve a durable long term preventive treatment, a multi treatment anode is used in the cathodic protection role, preferably connected to steel as a sacrificial anode.

Multi-process anodes are based on using sacrificial anode metals to act as transient high forced currents. One observation that has led to the development of multi-treatment anodes is that aluminum alloy sacrificial anode metals are removed from the anode surface at very low safety DC voltages that are not positive enough to cause gas evolution even when the sacrificial anode is mounted in a porous material in a cavity formed in reinforced concrete. Current densities in excess of 10,000 mA / m ² (per unit anode area). This is possible because anode reactions easily occur on sacrificial anode metals compared to anode reactions occurring on inert forced current anodes. Small separation anodes of very high current density can thus be mounted in concrete to limit the confusion caused during short high forced current processing. The short high forced current treatment moves the corrosion sites from the location on the reinforcing steel to the sacrificial anodes because the hydroxides produced in the steel raise the pH and aggressive ions such as chloride and sulfate are pulled from the concrete to the sacrificial anode. The anode can thus be used as an activated sacrificial anode to maintain the passivation of the steel.

Accordingly, according to a first aspect of the present invention, there is provided a method of protecting steel in concrete, including using an anode and a DC power source, and a temporary forced current treatment and a low current prevention treatment, wherein the temporary forced current treatment is A high current treatment using a DC power source to drive a current from the anode to the steel to improve the environment in the steel, and the low current prevention treatment to suppress the onset of steel corrosion after application of the temporary forced current treatment. A method is provided wherein the same anode is used in both treatments and the anode comprises a sacrificial metal member that undergoes sacrificial metal dissolution as its main anode reaction.

Another observation that led to the development of multiple processing techniques was the high charge density of aluminum alloy anodes. Four aluminum alloy anodes, 100 mm long and 15 mm in diameter, have sufficient charge to apply about 500 mA for a week and 1 mA for 50 years in their forced current and sacrificial anode functions. The high charge density of some sacrificial anodes means that long lifetimes can be achieved from small sacrificial anodes mounted in concrete. This alleviates the concern about the cost of replacing the anode mounted in the porous material after the end of its life.

The inclusion of a forced current anode connection detail on the small disconnected sacrificial anode reduces the risk of corroding the connection when the isolated sacrificial anode is used as a forced current anode. Forming a sacrificial anode metal around a forced current anode that can be used for a forced current cathode protection role after the sacrificial metal has been consumed can also be used to increase the life of the treatment.

Anodic reactions occurring on the sacrificial metal occur more readily than anode reactions occurring on the inert anode and require less drive voltage and produce less acid and less gas. This makes short high current electrochemical treatments easier to apply. Applying a high current to the steel cathode of the electrochemical cell quickly prevents the corrosion of the steel and prevents further corrosion damage. Aggressive ions in concrete are attracted to the anode by forced current treatment. Combining these aggressive ions with the sacrificial metal forms a sacrificial anode that is activated without adding other active chemicals to the concrete. Connecting this sacrificial anode directly to steel provides a simple way to apply continuous, preventive treatment to inhibit future corrosion initiation. Corrosion zones are effectively moved from the steel to the anode installed during the initiation treatment. Mounting the anode system in concrete allows the concrete surface to be used during high forced current electrochemical treatment.

The invention is explained in more detail by way of example with reference to the following figures:

1 is a schematic diagram of the use of a positive electrode in a hybrid forced current-sacrificial electrochemical treatment;

2 shows an experimental setup used to determine the anode potential-current relationship;

3 shows a potential-current relationship determined on an aluminum alloy anode and a mixed metal oxide (MMO) coated titanium anode;

4 shows the current density driven from an aluminum alloy anode in an aggressive environment using a DC power source in Example 1;

5 shows galvanic current density applied from an aluminum alloy anode following initial forced current treatment in Example 1;

6 shows the current density driven from 25 aluminum alloy anodes in a mild environment using a DC power source in Example 2; And

FIG. 7 shows galvanic current density applied from 25 aluminum alloy anodes following initial forced current treatment in Example 2. FIG.

Hereinafter, the second current means a current larger in magnitude than the first current, and in the following embodiments, the first current and the second current are referred to as low current and high current, respectively.
Mechanism of Electrochemical Protection

Electrochemical treatments applied to steel in concrete include cathodic protection and prevention, intermittent cathodic protection, chloride extraction and re-alkalisation. The protective effects induced by these treatments are negative driven potential shifts that dissolve the steel to prevent formation (corrosion) of positive iron ions, steel that removes chloride ions from the steel surface and makes the environment less aggressive. Bringing the phase into the passivation phase of the phase, and generating hydroxyl ions on the steel surface to stabilize the formation of the passivation phase on the steel. The general interpretation of reinforced concrete electrochemical treatment is that different treatments rely on different protective effects. In this interpretation, the basis of cathodic protection is the achievement of negative drive potential changes. Re-alkalization of carbonated concrete requires the creation of a reservoir of hydroxide around the steel. Chloride extraction requires the removal of chloride ions from the concrete. Intermittent cathodic protection relies on changing the environment in the steel by removing chlorides or generating hydroxyl ions to prevent steel corrosion during the short period of time that the protective current is interrupted.

Most of the electrochemical treatments used to inhibit the corrosion protection of steel in concrete can neglect the protective effect of the voice potential change by achieving this by inducing open circuit steel passivation by extracting chloride from steel and generating hydroxyl ions Has been discussed. Although this observation is still being debated in the case of cathodic protection (see discussion and answers in the Journal of Materials in Civil Engineering, 13 (5) 396-398, 2001), the contrast and analysis of the following useful evidence is one protective effect: Suggests that it seems to have a dominant effect on the success of all electrochemical treatments applied to steel in environmentally exposed concrete. This dominant protective effect is an increase in pH at the steel / concrete interface.

Environmentally exposed concrete is concrete that is periodically dried so that the cathodic reaction dynamics on the steel (reduction of oxygen) are weakly polarized (to facilitate oxygen reduction). In this environment, steel is generally protected by an antifreeze and the antifreeze failure is mainly caused by chloride contamination or carbonation of the concrete cover. Steel passivation is indicated by a positive open circuit (uninterrupted current) potential. The open circuit potential is the result of the coupling of the potential of the iron electrode with that of the oxygen electrode. Passive steel has an open circuit potential that is directed towards the potential of a more positive oxygen electrode. When the passivation membrane collapses, the open circuit potential further approaches the negative iron electrode. The open circuit potential should not be confused with the driving potential. A positive open circuit potential indicates the presence of an intact passivation film on the steel, and using an external power source to drive the steel potential to a more positive value increases the force that induces iron to dissolve into the positive iron ions, Resulting in corrosion.

In the case of chloride-induced corrosion, local dissolution of iron at defects in the passivation membrane is subsequently followed by the production of iron oxides and hydrogen ions upon reaction with water. The positive charge of the hydrogen ions is balanced by the negative charge of the chloride ions and the local production of hydrochloric acid occurs. This local pH reduction destabilizes the passivation membrane and causes acceleration and propagation of the corrosion process, often referred to as fitting corrosion. Chloride ions do not directly destabilize the iron oxide that forms the passivation film. This is an indirect result of local pH reduction.

Carbonation-induced corrosion is also caused by a decrease in the pH of the concrete resulting from the reaction of carbon dioxide with water and alkalinity generally present in concrete. The production of hydroxides in steel is widely recognized as a protective effect that depends on the application of re-alkalization to carbonated concrete. This is a less intense treatment than chloride extraction and its application to counteract chloride induced corrosion provides several practical advantages. Typical re-alkalization treatments require the application of 600 kC / m ² (168 Ah / m ² ) or 1 A / m ² per week (per steel surface area) to re-alkaline substantial portions of the carbonated concrete cover. This can be compared with a charge density of about 3600 kC / m ² (1000 Ah / m ² ) applied in general chloride extraction treatment.

Evidence that the formation of hydroxide in steel is also a major protective effect of electrochemical treatments applied to chloride contaminated concrete results primarily from the relatively low applied current density and charge densities that lead to open circuit steel passivation in chloride contaminated concrete.

In a laboratory study of intermittent cathodic protection applied to steel in heavily contaminated chlorides exposed to aggressive simulated marine environments (Glass, Hassanein and Buenfeld, Corrosion Science, 43 (6) 1111-1131, 2001), more floating potential Open circuit steel potential change to values became evident after 6 months when an integrated protective current density of 6-40 mA / m ² (per steel surface area) was applied to the steel. This positive potential change indicates that the steel is immobilized. The bottom line is that intermittent specimens showing open circuit steel potentials typical of floating steel remain intact, whereas corrosion in the control specimens and those with less intense treatment resulted in corrosion-induced cracking. Supported by photographs of specimens obtained after 12 months of cathodic protection. Further analysis of this data shows that for specimens with an integrated protection current density of only 6 mA / m ² , steel passivation was induced with a charge of less than 100 kC / m ² (less than 28 Ah / m ² ).

Strong evidence of the relatively small charge densities actually required to prevent chloride-induced corrosion is indicated by the analysis of extensive data obtained in field protection laboratory cathodic protection studies. Cathodic protection design current densities are typically up to 20 mA / m ² and cathodic protection systems generally operate at lower current densities. However, it is common to make quite large potential changes with such relatively small current densities after less than 50 days of cathodic protection. Significantly large potential changes in small applied current densities are possible only in floating or near-floating steel (Glass, Roberts and Davison, Proc. 7th Int. Conf. Concrete in Hot and Aggressive Environments, October 2003, Volume 2, p. 477-492, 2003) Clear evidence of such induced passivities has been made under laboratory conditions (Glass, Roberts and Davison, Corrosion 2004, NACE, Paper No. 04332, 2004). The charge equivalent to a protection current of 10 mA / m ² applied for 50 days is less than 50 kC / m ² . This is the more common charge density needed to induce steel passivation on the recovered concrete structure and is very small compared to the charge (3600 kC / m ² ) applied in the normal chloride extraction process.

The importance of the generation of hydroxyl ions in steel is also supported by the observation that this induction of open circuit steel passivation is achieved using a substantially lower cathodic protection current density compared to localized steel corrosion rates. Average corrosion rates of 0.02 mm steel site loss per year and local corrosion rates of more than 0.1 mm per year are not uncommon in chloride contaminated concrete. This is equated with a corrosion current density of about 20 to 100 mA / m ² . However, the cathode protection design current densities are almost always less than or equal to 20 mA / m ² and the applied current densities are always less than the design current density (BS EN 12696: 2000).

Two other factors reinforce this amazing observation. Firstly, applied protective current is not efficient in directly reducing the rate of corrosion in environmentally exposed concrete. The technical reason for this is that the cathodic reaction kinetics are weakly polarized (which occurs easily) in this environment. Second, current flows preferentially into cathodes that are more positive than the corrosion anodes of natural corrosion cells formed in concrete. It has been found that even in an environment where the geometry and resistance changes are suitable for current distribution for corroded steel, the proper applied current preferentially flows to the floating steel (Glass and Hassanein, Journal of Corrosion Science and Engineering, Volume 4, Paper 7). , 2003).

Under these conditions, it is considered very difficult for the applied current to cause extraction of any chloride from the corrosion anode locations. In order to reverse the direction of the local current in the corrosion position, sufficient current must be applied to drive the potential to a value more negative than the open circuit potential of an isolated corrosion position that is not connected to any floating steel. At moderately applied protective current densities typically used for reinforced concrete cathode protection, the net anode current always leaves locations of high corrosion activity. However, re-alkalization of such sites is still possible because the pH concentration gradient between the surrounding concrete and the corrosion sites provides extra force to transfer hydroxyl ions to the corrosion sites. This combines with the electric field imposed by the cathodic protection system, which weakens the strong electric field maintaining high hydroxyl ion concentration gradients so that the pH rises. As the pH rises, the process of establishing active corrosion sites on the steel is reversed until the point where insoluble iron oxides are the most stable corrosion by-product and the steel passivation film is reformed is reached. The process of re-alkalizing corrosion sites to achieve an open circuit steel passivation may be referred to as pit re-alkalisation.

The analysis shows that the range of charge densities applied to steel reinforcement of concrete to induce open circuit steel passivation may be of a smaller order than previously recognized in US 6322691 as required for stand alone transient electrochemical treatment. Smaller aggressive environments require smaller charges. In recovered concrete structures, charge densities as small as 30 kC / m ² may be sufficient, and charges of 100 kC / m ² have been shown to induce steel passivation in severely chloride-contaminated concrete at simulated marine exposure conditions in the laboratory. , And 600 kC / m ² have been shown to be sufficient not only for corrosion sites, but also for re-alkalization (pit re-alkalization) of a substantial part of the concrete cover in re-alkalization of carbonated concrete.

Improvement of electrochemical process

Numerous factors can be considered when considering how to improve electrochemical treatment techniques for reinforced concrete. These are:

The rate at which the corrosion process is prevented,

-Charge density required to resist corrosion

Durability of the treatment, and

Contains the maintenance conditions of the process.

It has been noted that relatively low charge densities can be used to restore the steel passivation. Temporary electrochemical treatments to prevent corrosion can thus be substantially less intense than the intense transient electrochemical treatments that are often applied. In particular, the duration of the temporary electrochemical treatment can be reduced. Thus, the temporary electrochemical treatment can be applied for less than 3 months, preferably less than 3 weeks. However, the durability of the short term treatment will be questioned except for the immediate reduction of the corrosion rate. Such short initial treatments may be better if supplementary long term corrosion protection treatments are applied.

The improved treatment may thus be a hybrid electrochemical treatment with an initial charge density sufficient to resist corrosion and induce open circuit steel passivation, followed by a low maintenance cathodic protection treatment to prevent any subsequent onset of corrosion. have. It would be advantageous to use the same anode system in strong forced current treatment to prevent corrosion and subsequent low maintenance treatments to maintain steel passivation.

Two examples of such dual stage electrochemical treatments are:

Short drive high current from the sacrificial anode to immobilize the steel, and then directly connect the sacrificial anode to the steel to provide a low sacrificial current cathodic protection treatment, and

A voltage is applied to an inert forced current anode coated with a sacrificial metal member, wherein the sacrificial metal member initially facilitates a high anodic reaction rate associated with a high protective current density to immobilize the steel and When exhausted, the forced current anode includes providing a low forced current cathode protection treatment.

The average current applied during the initial current electrochemical treatment will generally be on the order of magnitude greater than at least the resulting average current applied during the low current protection process. Low current protection treatment generally involves applying an average current of less than 5 mA / m ² and greater than 0.2 mA / m ² to the steel surface.

Processing technology

According to a first aspect of the present invention, there is provided a method for protecting steel in concrete, the method comprising using a positive electrode and a DC power source, including a temporary forced current treatment and a low current prevention treatment, wherein the temporary forced current The treatment is a high current treatment using a DC power source to drive current from the anode to the steel to improve the environment in the steel, and the low current prevention treatment initiates steel corrosion onset after application of the temporary forced current treatment. The same anode is applied for suppression and the same anode is used in both treatments, the anode comprising a sacrificial metal member that undergoes sacrificial metal dissolution as its main anode reaction.

According to a second aspect of the present invention, there is provided an anode for protecting steel in concrete, the anode comprising a sacrificial metal member having a forced current anode connection detail, the anode being a compact discrete anode. anode, the sacrificial metal member is less noble than steel, the forced current anode connection item comprises a conductor having at least one connection point, the conductor being +500 above the potential of the copper / saturated copper sulfate reference potential. maintaining a floating state at a potential more positive than mV, the conductor is substantially surrounded by the sacrificial metal member over a portion of its length to form an electrical connection that conducts electrons between the conductor and the sacrificial metal, The connection point is located far from the sacrificial metal member where the conductor can be easily connected to another conductor. It characterized in that positioned on the portion of the conductor section.

According to a third aspect of the invention, there is provided the use of the anode according to the second aspect of the invention in a method according to the first aspect of the invention.

According to a fourth aspect of the present invention, there is provided the production of an activated sacrificial anode mounted in a chloride contaminated concrete structure, wherein the production of the mounted active sacrificial anode is carried out between the conductor and the sacrificial metal member which is less noble than steel. Providing a path through which electrons move, forming a cavity in the concrete structure, and a portion of the conductor is left exposed to provide a connection point and the sacrificial metal member in a porous material comprising an electrolyte in the cavity. Mounting and providing a path through which electrons flow between the anode terminal of the DC power source and the conductor; driving a high current from the sacrificial metal to attract chloride ions present in concrete to the surface of the sacrificial metal. Enable and disconnect the DC power source from the conductor Li includes a step.

According to a fifth aspect of the present invention, there is provided a method of protecting steel in concrete, the method comprising a temporary high impressed current electrochemical treatment followed by an improved environment in the steel. And a low current preventative treatment for suppressing the onset of steel corrosion, wherein in the temporary forced current treatment, an anode is used, and the same anode is used in the low current prevention treatment, and the anode is used as the main anode reaction. A sacrificial metal member that undergoes sacrificial metal dissolution, wherein the anode is connected to a positive terminal of a DC power source in the transient forced current treatment and the anode is connected to the steel to prevent the steel from the sacrificial metal member in the low current prevention treatment. Providing an electron conduction path to the furnace .

One example of a preferred hybrid electrochemical treatment is shown in FIG. 1. The sacrificial metal member 1 is mounted in a porous material 2 containing an electrolyte in a cavity 3 formed in the concrete 4. The sacrificial metal member is connected to the positive terminal of the DC power source 5 via an electrical conductor 6 and an electrical connection 7. A forced current anode connection detail is used to connect the sacrificial metal member 1 to the electrical conductor 6. This preferably includes forming a sacrificial metal member around a portion of the conductor 8 that remains floating during the forced current processing. The conductor 8 provides a convenient connection point 9 from the sacrificial metal to facilitate the connection to another electrical conductor. The negative terminal of the power source 5 is connected to the steel 10 using an electrical conductor 11 and a connection 12. The electrical connection 13 is not made while the power source is connected to the anode and the steel.

First, a large, short term forced current is driven from the anode assembly 18 into the steel 10 for a short period using the DC power source 5. During the process, oxygen and water 14 are converted to hydroxyl ions 15 on the steel. This neutralizes acidic corrosion sites and aids in the recovery of the protective passivation film on the steel. In addition, aggressive ions such as chloride ions 16 are attracted from the concrete to the porous material 2 around the anode. This short forced current treatment modifies local environments around the mounted steel and around the mounted anode. The changes mean that the local environment in steel supports steel passivation while the environment at the anode maintains sacrificial anode activity. Corrosion locations effectively move from the locations on the steel reinforcement to the sacrificial anode installed. After the forced current process is finished, a long term low power cathode protection process can then be applied using the same anode.

It is preferable to disconnect the power supply 5 from the electrical connections 7 and connect the remaining sacrificial anode metal directly to the steel via the electrical connection 13. Activated separation sacrificial anodes formed by transient forced current treatment are then used for long term sacrificial cathode protection roles to maintain steel passivation. This is desirable because the current output from the sacrificial anodes will, to some extent, tailor higher self sacrificial anode current output to more reliable and more aggressive environments than that of the DC power supply. In addition, observations can be tailored to complimentary end-user requirements for protected structures that are not critical to sacrificial anode system functionality. A simple way of observing work performance uses a non destructive potential mapping technique to determine whether the only regions of bipolar activity are located at the locations where the separate sacrificial anodes are mounted.

The connections 7, 9, 12, 13 and the conductors 6, 8, 11 are all electron conducting connections or conductors providing a path through which electrons move. They are also called electronic connections or electronic conductors. The conductors are generally wires or electrical cables. These conductors and connections are different from ion conductors or ion connections. The electrolyte in the concrete 4 provides an example of an ionic connection between the sacrificial metal member 1 and the steel 10. To achieve sacrificial cathode protection or prevention, both electronic and ionic connections are needed between the sacrificial metal member and the steel.

The DC power source 5 for short high current processing includes a mains powered DC power supply or battery. It is advantageous if the connection between the positive electrode and the positive terminal of the power source is kept as short as possible to minimize the risk of corrosion on this connection.

Preferred anodes include small separate sacrificial metal members with a forced current anode connection breakdown. Small separation anodes may be mounted in cavities formed in reinforced concrete. This improves the bond between the anode and the concrete structure. Examples of such cavities include a maximum diameter of 30 mm that can be cut into a concrete surface and a maximum diameter of 50 mm that can be formed by coring or drilling as well as long chases of depth 50 mm and Holes of length 200 mm. If the cavities are holes formed by drilling, it is desirable to keep the diameter below 30 mm. The number of anodes is generally distributed over the concrete structure to protect the mounted steel.

The forced current anode connection item is used to connect the anode to the positive terminal of a DC power source. All metals connected to the positive terminal of the DC power source are at risk of becoming positive if they come into contact with the electrolyte in the surrounding environment, and thus need to be protected from anode melting if this is not intended. Existing miniature separate sacrificial anodes for reinforced concrete are provided with connection items consisting of non-insulated steel or galvanized steel wire that rely on the sacrificial operation of the anode to protect the connection line. These connections undergo induced anode melting and corrode with the sacrificial metal when the anode is driven like a forced current anode.

The forced current connection item in the small disconnected sacrificial anode is made by forming a sacrificial metal member around a portion of the conductor that provides a connection point and includes a second portion that remains floating when the anode is driven with a positive potential by the power supply. Can be. Floating conductors are those in which when the potential is driven to positive values, no pronounced metal dissolution occurs on them and therefore no visible corrosion-induced degradation. Conductors and sacrificial metal members are generally more noble than the copper / saturated copper sulphate reference electrode and can be +500 mV or even +2000 mV more noble than the copper / saturated copper sulphate reference electrode. During the initial forced current processing it will be driven with a positive potential. Copper and steel do not float in their natural state at these positive potentials when in contact with the electrolyte.

The example of FIG. 1 shows a sacrificial metal member 1 formed around a portion of the conductor 8 with a second portion extending beyond the sacrificial metal providing a connection point 9. To achieve a floating conductor, an inert conductor that is naturally floating with the electrolyte in the anode potentials present in the forced current treatment can be used. Optionally, the conductor may be isolated from the electrolyte in the environment by the presence of an insulating layer on a portion of the conductor that extends beyond the sacrificial metal member to form a junction with the presence of the surrounding sacrificial metal member. Preferred connection items include casting a sacrificial metal member around a portion of the inert titanium wire that provides a connection point on the exposed portion of the titanium wire from the sacrificial metal member for convenient connection of the titanium wire to other electronic conductors. This may be another titanium wire or an insulated electrical cable that facilitates the connection of the anode to the anode terminal of the DC power source.

Inert conductors can derive their corrosion resistance from one or more materials, examples of which include stainless steel, platinum, tantalum, zirconium, including carbon, titanium, nickel-chromium-molybdenum stainless steel alloys (zirconium), niobium, nickel, nickel alloys including hastalloy, monel and inconel. Conductors can be made from these materials and protected with inert coatings of these materials. Titanium is a preferred material because it is readily available and resistant to anode dissolution over a wide range of potentials.

When the inert forced current anode is used as a conductor having a sacrificial metal member formed around the anode, the anode can be used as the inert forced current anode when the sacrificial metal member around the inert anode is consumed. This extends the functional life of the anode system. Examples of inert forced current anodes include metal oxide coated titanium, platinum titanium and niobium platinum. Inert anode conductors are, in theory, surrounded by salts or porous metal oxides resulting from the dissolution of the sacrificial metal. This provides a layer that maintains a pH gradient between the surrounding concrete and the inert anode that limits the acidic attack of the surrounding concrete. It also provides a route through which any gas produced at the anode can escape. These faces allow the inert anode core to be driven at current densities beyond those normally imposed on the use of such anodes when directly in contact with cement mortar or concrete.

Insulating materials can be used to float a conductor, such as steel, to separate the conductor from the electrolyte in the surrounding environment. This prevents corrosion induced degradation of a portion of the conductor that is not protected by the sacrificial metal when the anode is used in the forced current role. In this case, it is preferable to extend the insulator over the surface of the anode metal into which the conductor enters the anode metal or into the anode metal. This is to maintain the separation of the conductor from the electrolyte in the surrounding environment when the sacrificial anode metal is dissolved around the conductor. It is desirable to insulate all cables between the anode and the anode terminal of the DC power source from the electrolyte in the low environment.

The sacrificial metal is preferably less noble (not corroded) than steel. Examples include zinc, aluminum or magnesium or their alloys. Aluminum zinc indium alloys are preferred. Aluminum has a high charge density and therefore a good lifetime volume ratio. Alloying elements promote anode activity, which is further encouraged by the presence of chloride contamination in the surrounding environment.

The main anode reaction that occurs at the sacrificial metal anode is the dissolution of the sacrificial metal. This oxidation reaction is easier than the oxidation reaction of water, which produces a gas and an acid, the main anode reaction occurring at an inert forced current anode. Thus large anode current densities can be applied at low drive voltages from the sacrificial metal members. Dissolution of the sacrificial metal produces a metal salt. The production of gases can be avoided and the only acid produced is the result of secondary hydrolysis of the metal salts. This secondary reaction will be limited. The minimum pH value is determined by the equilibrium between the metal salt, the acid present (determining the pH), and the metal oxide. Problems related to the production of acid and gas, which typically occur at inert forced current anodes, can be avoided by using sacrificial metal elements at the anode. In this way a current density of greater than 200 mA / m ² per unit area of the anode surface, preferably greater than 1000 mA / m ² , can be achieved on the mounted anode without the occurrence of significant degradation of the surrounding concrete.

In the past, the preferred placement of sacrificial anode materials was an accessible and easily replaced concrete surface. However, the loss of adhesion to the concrete substrate and the rapid drying of the concrete surface in the absence of moisture limit the performance from the surface anodes. These problems can be overcome by mounting sacrificial metal anodes in the porous material of the cavity of the concrete. The porous material holds the anode in place and the bubbles also hold the electrolyte and provide space for the product of the anodization. To accommodate the products of anodization, the porous material has 'putty like' properties, including compressive strength of less than 1 N / mm ² , preferably less than 0.5 N / mm ² , and a void space. It is preferable to include).

One feature of using sacrificial metals in forced current mechanics is the ease of overcoming any accidental anode-steel shorts (contact between the anode and the steel, which provides a path for electrons to flow directly from the anode to the steel). This is because the sacrificial metal preferentially erodes at the location of dissimilar metal shorts, creating metal oxides that break the direct short.

One advantage of using a mounted sacrificial metal anode is the high forced current density that can be delivered from the anode. The magnitude of the current determines the anode polarization behavior (anode current output as a function of anode potential) of the aluminum alloy anode mounted on the plaster of the hole in the concrete, and this polarization behavior is mixed metal oxide (MMO) coating in the same environment. Evaluation was made by comparing with that determined on a titanium inert anode.

An aluminum alloy was cast around the MMO coated titanium wire to produce a sacrificial anode having an exposed aluminum surface of 2180 mm ² connected to the length of the exposed titanium wire. The aluminum alloy was US Navy definition MIL-A-24779 (SH). A 1.0 mm ² copper core sheathed cable was connected to the exposed titanium wire. Copper-titanium connections were maintained in a dry environment on concrete.

An inert anode was produced using a short length MMO coated titanium ribbon connected to a 1.0 mm ² copper core sheathed cable. The connection was insulated and the exposed MMO coated titanium surface was 1390 mm ² .

The polarization behavior (potential-current relationship) of aluminum and MMO coated titanium anodes was determined using the experimental setup shown in FIG. 2. Concrete blocks 20, 300 mm long, 140 mm wide and 120 mm deep are dried 20 mm all-in graded aggregate (0 to 20 mm), ordinary Portland cement (OPC) And water were cast using a weight ratio of 8: 2: 0.95, respectively. Sodium chloride was dissolved in water before mixing to contaminate the concrete blocks with 3% (based on the weight ratio of chloride ions to cement) chloride.

While the concrete was still fluid, two holes 21 22 mm in diameter and 90 mm in diameter were floated 200 mm to form a concrete block by pressing a rigid plastic tube into the concrete. A steel rod 22 of diameter 10.5 mm and length 140 mm was placed in the center of the concrete between the two holes. It extends 40mm above the concrete surface. The ends of two flexible Luggin capillaries 23 with an inner diameter of 2 mm were placed in the center of the concrete between each hole and the steel rod. Two additional steel bars 24 were mounted 100 mm apart from the holes 21 to be used as counter electrodes in the test. Sheathed copper core cables were connected to the exposed ends of the steel rods.

After the concrete had hardened, the rigid plastic tubes were removed, the aluminum anode and the MMO coated titanium anode were centered in the individual holes and the remaining space in the holes was filled with a gypsum-based finishing plaster, so that the indentation of the surface on the anode ( indentation). The plaster was left to harden to form a rigid porous material. Filled capillaries 23 with conductive gels prepared by heating a mixture of agar powder, potassium chloride and water in a ratio of 2: 2: 100, respectively, on a weight ratio basis with stirring. The gel filled capillaries extended into small containers 25 containing saturated copper sulfate solution. A piece of brightly polished copper 26 was placed in each container to form two copper / saturated copper sulfate reference electrodes. A copper core cable was connected to the copper of the reference electrode and the connection was insulated.

A potentiostat and a function generator 27 were used to adjust and change the potential of the anode relative to the potential of the reference electrode by passing current from the counter electrodes to the test anode. Separate tests were conducted for each anode. The anode and its nearest copper / saturated copper sulfate reference electrode were connected to each working electrode WE and a reference electrode RE of the constant potential / function generator 27. A 5 ohm resistor 28 and relay switch 29 were connected between the counter electrodes and the counter electrode terminal (CE) of the potentiometer / function generator. Sheathed copper core cables 30 were used for all of the above connections. The test was conducted indoors at a temperature of 7-15 ° C. Indentations of gypsum on the anodes were periodically wetted.

Measurements were made by briefly shutting off the current from the anode for less than 0.15 seconds using the anode current, the current-on potential of the anode measured relative to the reference electrode while the current was flowing, and the relay switch 29. And the instant-off potential of the anode, measured between 0.02 and 0.07 seconds. The moment-off potential of the anode is the correction potential where the geometry dependent voltage drop between the anode induced by the current and the reference electrode is subtracted from the current-on anode potential. These measurements were recorded using a high impedance data logger, which also controlled a relay switch. The potential of the anode was initially controlled to be close to its natural potential without any current. The controlled potential was then increased to about +2000 mV relative to the reference electrode at a rate of 0.1 mV / s to ensure polarization behavior.

3 shows the aluminum anode and MMO coated titanium anode current density outputs as a function of measured current-on potentials and instant-off potentials compared to the reference electrode 10 days after casting the concrete. The current density on the y-axis is expressed as current per unit area of the anode surface and is plotted against the potential of mV relative to the copper / saturated copper sulfate reference electrode on the x-axis. As the current-on potential of the aluminum anode increased to +2000 mV, the current density from aluminum increased to 16000 mA / m ² and the instantaneous-off potential of aluminum increased to +1000 mV. In contrast, the current from the MMO coated titanium anode was only noticeable when its potential increased above +1000 mV. At a current-on potential of +2000 mV, the MMO coated titanium anode current density approached 3000 mA / m ² and the instant-off potential was +1400 mV. Aluminum could thus produce much higher current densities at lower anode potentials. In fact, the current density applied by the aluminum anode was greater than 10000 mA / m ² when the instant-off potential approached the potential of the copper / saturated copper sulfate reference electrode.

In this example, a comparison of the anode polarization characteristics of the aluminum anode with those of the MMO coated titanium anode showed that significant peaks were obtained by using sacrificial metals mounted in the forced current role. The use of sacrificial metal mounted on porous material in the pores of the reinforced concrete allows substantially higher anodic forcing current densities to be achieved compared to any cases achieved using conventional forcing anode technology at the same drive voltage.

One issue that takes into account the use of sacrificial metal anodes mounted in porous materials applied to reinforced concrete is the lifetime of the anodes. The lifetime of a hybrid anode is related to its size and current output. The general size for long life is calculated using the following assumptions:

A 500 mA / m ² current applied to the steel for one week changes the local environment in the steel, leading to steel passivation.

-Average protection current of 1 mA / m ² maintains steel passivation and prevents corrosion initiation for the next 50 years.

The installation of four anodes per square meter achieves an adequate current distribution.

Separation aluminum alloy anodes are used with a density of 2700 kg / m ³ , a charge density of 2980 Ah / kg and an efficiency of 93%.

A current of 500 mA for 7 days followed by a current of 1 mA for 50 years corresponds to a charge of 522 Ah or 130 Ah per anode. The sacrificial metal properties indicate a useful charge of 7458 Ah per liter of anode metal and a 130 Ah anode can achieve an anode volume of 0.0174 liters. This can be achieved with an anode having a diameter of 15 mm and a length of 100 mm. The installation of four anodes of this size per square meter of the steel surface in the concrete structure is a relatively easy task.

As noted above, 500 mA / m ² applied to steel for one week will be more than sufficient to induce changes in the environment that make steel passivation in most cases. The cathode protection current density of 1 mA / m ² is in the middle of the expected range of cathode protection current densities disclosed in BS EN 12696: 2000. This calculation shows that it is practical to use sacrificial anodes mounted in hybrid electrochemical processing and achieve a long service life.

The invention will be explained in more detail in the following examples.

Example 1

An anode of 15 mm in diameter and 100 mm in length containing a rod of aluminum alloy known as US Navy definition MIL-A-24779 (SH) molded around a titanium wire to facilitate electrical connection to aluminum, the diameter in the concrete block It was mounted on lime putty in holes 25 mm and 130 mm deep. The basic arrangement is shown in FIG. A concrete block of 380 * 270 * 220 mm was prepared using a graded all-in-one 20 mm crushed stone and ordinary Portland cement in a ratio of 8: 1. The ratio of water to cement was 0.6 and 4% chloride ions were added to the mixture by weight of cement by dissolving sodium chloride in the mixture. Steel sheets with a surface area of 0.125 m ² were included in the concrete block. Lime putty was produced by filling and ripening quicklime and secured from the producers of lime putty and lime mortar. The hole in the concrete block containing the lime putty and anode was left open to the atmosphere. The concrete blocks were stored in a dry indoor environment and the temperature varied between 10-20 ° C.

The anode and steel were connected to a 12 Volt DC power source for 13 days while a 65 kC charge was applied from the anode to the steel. The current density applied from the anode for the first 11 days is shown in FIG. For most of this time, the current applied from the anode was greater than 5000 mA / m ² .

At the end of the forced current treatment period, the DC source was removed and the anode was connected to steel. The galvanic current from the anode was measured using a 1 ohm resistor as the current sensor in the connection between the anode and the steel. The current density applied from the anode, which acts in purely galvanic mode for the next 40 days, is shown in FIG. 5. For most of this period, the current density applied from the anode is between 500 and 600 mA / m ² .

It will be appreciated that the presence of 4% chloride in concrete is a very aggressive environment that results in a very high current output of the sacrificial anode when operating in both forced current and galvanic mode.

Example 2

Twenty five aluminum alloy anodes, 15 mm in diameter and 100 mm in length, described in Example 1 were mounted on a concrete column containing steel reinforcement with a steel surface area of 3.2 m ² . The pillars were protected from rain and moisture and were very dry but were exposed to chloride contaminants placed in the sea landscape and carried through the air. The anodes were installed by drilling a 25 mm hole into 180 mm in concrete, partially filling the hole with a mixture of lime putty and 10% polystyrene, and finally injecting the anodes into the putty until it was fully mounted in the putty. The anodes were evenly distributed across the columns and located between the reinforcing steel bars.

The anodes were connected to the positive terminal of a 12 Volt DC power supply and the steel was connected to the negative terminal for a period of 8 days when a 67 kC / m ² charge was applied to the steel surface. The current density applied from the anodes during this period is shown in FIG. 6. The current applied from the anodes varied between 4500 and 1500 mA / m ² . After this initial treatment the holes containing the anodes were sealed with standard cement mortar repair material.

At the end of the forced current treatment period, the DC source was removed and the anodes were connected to steel. Galvanic currents from the anodes were measured using a 1 ohm resistor as the current sensor in the connection between the anodes and the steel. The current density applied from the anode which acted in purely galvanic mode for the next 30 days is shown in FIG. 7. The galvanic current density applied from the anodes was between 80 and 150 mA / m ² , which is equated with the protective current on the steel surface between 3 and 5 mA / m ² .

The very dry ships represented a relatively non-aggressive environment and both the forced anode current density and the galvanic anode current density were both small compared to the data obtained in Example 2. However, the galvanic current applied to the steel as a preventive treatment is relatively high for cathodic prevention, especially in this environment. The remaining life of the sacrificial metal in anodes applying 3 mA / m ² to the steel was calculated as 28 years, assuming a 70% anode efficiency, which would be longer if the average applied cathode protection current density was stabilized at lower values. will be.

Industrial use of the disclosed technology relates to methods and products for preventing and preventing corrosion of steel in reinforced concrete structures. Advantages of the disclosed techniques include rapid suppression of steel corrosion, short on-site processing time, no regular long-term maintenance, ease of installation and self-correction of abnormal anode and steel shorts. Standards applicable to this technology include BS EN 12696: 2000 (cathode protection of steel in concrete) and prCEN / TS 14038-1 (electrochemical re-alkaline and chloride extraction treatments for reinforced concrete).

Claims (83)

By using an anode and a DC power source to protect the steel in the concrete structure, Driving a current from the anode to the steel using the DC power source to impart steel corrosion by applying a temporary impressed current treatmemt applied to improve the environment in the steel; And Then applying a first current treatment applied to prevent steel corrosion initiation from the same anode to the steel, The temporary forced current treatment is a second current treatment, and the anode includes a sacrificial metal member that undergoes sacrificial metal dissolution as its main anode reaction, And wherein the second current is greater in magnitude than the first current. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete The method according to claim 1, Wherein said transient forced current treatment is applied at an anode current density of greater than 200 mA per square meter of anode. The method according to claim 1, And said transient forced current treatment is applied at an anode current density of greater than 1000 mA per square meter of anode. The method according to any one of claims 1, 45 and 46, And wherein the average current in the transient forced current treatment is at least an order of magnitude greater than the average current in the first current preventive treatment. The method according to any one of claims 1, 45 and 46, And said first current prevention treatment comprises applying an average current of less than 5 mA per square meter of steel to said steel. The method according to any one of claims 1, 45 and 46, And said temporary forced current treatment is less than three months in duration. 50. The method of claim 49, And said temporary forced current treatment is less than three weeks in length. The method according to claim 1, And said anode is embedded in a porous material in contact with said concrete. The method according to claim 1, The anode is strongly attached to the concrete. 53. The method of claim 51 or 52, And said anode is a compact split anode mounted in a porous material in a cavity formed in said concrete. The method according to any one of claims 1, 45 and 46, And the period of the first current prevention treatment is longer than the temporary forced current treatment period. The method according to any one of claims 1, 45 and 46, And wherein said first current prevention treatment is effected by providing an electron conduction path from said sacrificial metal to said steel in said sacrificial metal member. The method according to any one of claims 1, 45 and 46, And said sacrificial metal member is connected to an inert conductor that remains passive at a potential more positive than +500 mV above the copper / saturated copper sulfate reference potential. The method according to any one of claims 1, 45 and 46, And said sacrificial metal member is formed around an inert forced current anode. 58. The method of claim 57, And wherein said first current prevention treatment comprises impressed current cathodic prevention. The method according to any one of claims 1, 45 and 46, And the sacrificial metal member comprises aluminum or zinc or magnesium or alloys thereof. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete The method according to claim 1, The anode is connected to the anode terminal of the DC power source in the temporary forced current processing; The anode is connected to the steel to provide an electron conduction path from the sacrificial metal member to the steel in the first current prevention process. 83. The method of any one of claims 1, 45 and 82, After the transient forced current treatment is applied, the DC power source is disconnected from the anode and the steel.

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