A method for rehabilitative and/or protective corrosion-inhibition of reinforcing steel embedded in a hardened concrete structure by means of surface-applied corrosion-inhibiting compositions

Abstract: The present invention provides methods and compositions for the reduction of the corrosion rate of already corroding steel reinforcements embedded in a hardened concrete structure as well as for the protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened concrete structure exposed to aggressive environments. The inventive new compositions employed for the novel method are essentially based on one or more amino- and/or hydroxyalkylamino compound(s), which are partially or completely neutralized with one or more inorganic acid(s) and/or derivatives thereof and/ or aliphatic carboxylic- and/or aromatic carboxylic acid(s), one or more surfactant(s) and optionally, one or more water-based or water-thinnable water repellent agent(s) selected from the group of organosilicones.

Description: Field of the invention The present invention is related to the inhibition of corrosion of reinforcing steel embedded in a hardened concrete structure. In particular, this invention provides compositions and a method for the reduction of the corrosion rate of already corroding steel reinforcements embedded in a hardened concrete structure as well as for the protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened concrete structure exposed to aggressive environments. Background of the invention Durability limitations of steel reinforced concrete are well documented. Corrosive environments (e.g. the presence of chlorides), carbonation of concrete structures, poor workmanship and other factors can quickly cause corrosion of the reinforcing steel. Chloride ions in concrete can originate from the ingress of de-icing salts, seawater or air-borne salts, diffusing to the reinforcement through the pore network of concrete, as well as from contaminated aggregates or from contaminated mixing water (cast in chlorides). Carbon dioxide as well as other acidic corrodents present in the air react with the free alkali contained in concrete. Over a period of time the pH value of the outermost concrete layer decreases, resulting in a reduction of the natural protection of the steel embedded in reinforced concrete. Normally, reinforcing steel embedded in concrete is protected because the concrete cover acts as a barrier and the high pH value of the pore fluid assures a passive state. Both the presence of chloride ions at concentrations above a given threshold level and carbonation can put reinforcing steel into an active state und result in corrosion rates that markedly decrease the expected service lives of reinforced concrete structures. Thousands of bridges and other structures made of reinforced concrete need to be repaired worldwide as a consequence of corrosion of the steel reinforcement. The present invention relates to corrosion-inhibiting compositions for the rehabilitative repassivation of corroded reinforcing steel embedded in hardened concrete as well as for the precautionary, protective corrosion inhibition of uncorroded reinforcing steel embedded in hardened concrete structures exposed to corrosive environments. Said corrosion-inhibiting compositions contain corrosion inhibitors with high buffer capacities as well as water repellent agents, and cause a reduction of the corrosion rate of corroding reinforcing steel embedded in a hardened concrete structure as well as delay the onset of corrosion of uncorroded reinforcing steel embedded in a hardened concrete structure respectively. Corrosion inhibitors are compounds or compositions that, when added in small concentrations to a corrosive environment, decrease the corrosion rate. The use of corrosion inhibitors is wide-spread and well established. For example protection systems based on corrosion inhibitors are used to limit the corrosion of process equipment such as cooling systems, pipelines, or central heating systems. Various types of corrosion inhibitors designed for different applications are available in the marketplace. Corrosion inhibitors may be classified into the following groups: Anodic oxidizing passivators (e.g. chromates, nitrites), anodic non-oxidizing passivators (e.g. molybdates), cathodic corrosion inhibitors (e.g. oxygen scavengers such as sulfites or cathodic poisons such as arsenates), film-forming inhibitors of the adsorption type (e.g. amines, alkanolamines). The film-forming corrosion inhibitors, which are typically organic compounds, represent the largest group of corrosion inhibitors and may exhibit anodic, cathodic or mixed behaviour. The prior art Several methods have been suggested to protect reinforcing steel embedded in concrete against corrosion : World Pat. Appl. No. 96/22951 (Berke et al.) discloses a corrosion-inhibiting admixture for hydraulic cement compositions. Said admixture is based on an anodic corrosion inhibitor such as calcium nitrite and a cathodic corrosion inhibitor such as calcium stearate or other organic acids of high molecular weights (C 17 to C 21 ) including salts and esters thereof. U.S. Pat. No. 5,262,089 (Bobrowski et al.) discloses an admixture for inhibiting the chloride-induced corrosion of steel reinforcements in concrete. Said admixture is based on an emulsion containing an ester of an unsaturated fatty acid, a surfactant and a saturated fatty acid ester as well as a saturated fatty acid, an amphoteric compound, a glycol and a soap; the admixture is added to the concrete prior to placement. World Pat. Appl. No. 96/27695 (Curatolo et al.) describes a method of controlling effectively chloride-induced corrosion of steel reinforcement members in concrete by addition of a corrosion-inhibiting admixture to fresh concrete. Said admixture comprises i) one or more waterproofing agents; ii) one or more mono-, di-, or trialkanolamines and iii) optionally, one or more additional corrosion-inhibiting agents, with the proviso that if the waterproofing agent is capable of forming a salt with ii) and / or iii), then at least a portion of i) and ii) and / or iii) are present in said admixture in their salt form in combination with each other. Swiss Pat. No. 686 368 (Buerge at al.) is related to corrosion-inhibiting admixtures for cementitious building materials which are containing metal parts, e.g. metallic reinforcements. Said admixtures are based on reaction products of amino compounds with one or more inorganic and/or organic acids. The admixtures may contain excessive amounts of the amino compound and/or unreacted amino- and acid compounds. According to the four patents above, corrosion inhibitors of the admixture type are added to concrete prior to placement, thus prior to hardening. None of these prior art methods, however, discloses a rehabilitative and/or protective application of corrosion-inhibiting compositions to the surface of a hardened, reinforced concrete structure. U.S. Pat. No. 5,435,846 (Tatematsu et al.) discloses a cement additive for inhibiting concrete deterioration. Said cement additive contains a powder mixture of inorganic ion exchangers as well as optionally nitrite ions. It inhibits the alkali-aggregate reaction and the corrosion of reinforcing steel, thereby protecting concrete from deterioration. Also disclosed is a method of inhibiting or repairing concrete deterioration, comprising charging or applying a cement composition to a concrete crack or to a concrete body whose surface has peeled or been damaged. However, said method of coating and/or patching damaged concrete structures with a cementitious material is labor-intensive and costly, as well as (regarding patching applications) limited to restorations of not fair-faced concrete structures. Canadian Pat. No. 1,258,473 (Martin et al.) describes a method of inhibiting corrosion of iron or steel reinforcements in concrete which comprises incorporating in a slurry of the concrete an effective quantity of a corrosion-inhibiting composition having as its major ingredient a water-soluble hydroxyalkylamine having a molecular weight in the range of about 48 to about 500. An additional method relates to placing a concrete slurry containing said hydroxyalkylamine in corrosion-inhibiting proximity to said reinforcement members embedded in cured concrete structures. This method relates to corrosion-inhibiting compositions of the concrete admixture type. Said corrosion-inhibiting compositions are mixed with concrete before placing the concrete to either cast or to repair reinforced concrete structures. According to the patent it is not intended to use a solution of said corrosion-inhibiting compositions to impregnate the surface of hardened reinforced concrete. Furthermore, many low to medium molecular weight types of hydroxyalkylamines are featuring disadvantages such as strong ammonia-like odors, high alkalinity and corrosiveness. U.S. Pat. No. 4,609,573 (Omata et al.) describes a process for inhibiting corrosion of steel built in an inorganic material by applying in a first step an aqueous solution of calcium nitrite, in a second step an aqueous solution of lithium silicate and optionally, in a third step, a cement composition containing a polymer dispersion (e.g. a styrene/butadiene rubber dispersion) to the surface of said inorganic material. Claimed corrosion inhibitors: only inorganic compounds such as calcium nitrite, sodium nitrite, tricalcium phosphate, sodium chromate. Said solution gradually penetrates the inorganic material by ionic diffusion. This method shows the following disadvantages: By applying a coat consisting of a polymer dispersion the anyway slow rate of ionic diffusion of the claimed inorganic corrosion inhibitors could be further slowed down. Furthermore the aspect of treated surfaces may alter by topcoating with a cement composition (important regarding fair-faced concrete fronts). Chromates are featuring problematic toxicity data. U.S. Pat. No. 5,391,349 (Hansen) discloses a method to inhibit the corrosion of ferrous-based metals embedded in concrete containing chlorides by drawing the chlorides away from the metal, (by applying water and electric current) and then applying a composition containing ammonium carbamate or ammonium carbonate to the concrete. Optionally, sodium silicate may be added to the solution. World Pat. Appl. No. 91/09153 (Hettiarachchi et al.) discloses a method for applying an anti-corrosive agent to a reinforcing bar in a cementitious structure. An electrolyte solution containing an anti-corrosive agent is placed in contact with a surface of the structure, and the agent is drawn into and trough the structure, into contact with the embedded reinforcing bar, by an electric field. Therefore an electrical connection between a first electrode placed in contact with said solution and a second electrode has to be made. The second electrode has to be positioned in the structure and may include the reinforcing member. Said anti-corrosive agent is selected from the groups of tetraalkyl-phosphonium compounds, nitrites or molybdates. European Pat. Appl. No. 0 723 947 A1 (Guerin) relates to a process for the restoration and protection of reinforced concrete structures. Solutions of alkaline electrolytes containing optionally a hydrophilic compound and/or a surfactant are filled into reservoirs which are installed on the surface of a concrete structure. An electrical connection is provided between external electrodes situated in the reservoirs and the reinforcing steel embedded in the concrete. Said electrolytes migrate by osmotic diffusion in direction of the reinforcement. Disadvantage of the three methods mentioned above: Reservoirs equipped with counter-electrodes have to be installed, which is difficult to perform at structurized concrete surfaces as well as labor-intensive and costly. Furthermore treatments according to said methods may cause undesirable efflorescences. The method according to the European Pat. Appl. No. 0 723 947 A1 is causing a reduction of the corrosion rate of the reinforcement by realkalization, but doesn't make use of the beneficial corrosion-inhibiting effect caused by the addition of corrosion inhibitors. U.S. Pat. No. 5,326,529 (Miksic et al.) describes a method of inhibiting corrosion of metal reinforcements embedded within cured concrete. The method comprises providing a plurality of exteriorly-accessible uniformly distributed openings in the concrete. In each of these openings a containers having a permeable wall structure and containing an adsorbent material as well as a migrating corrosion inhibitor is placed. The permeable wall structure of the containers allows the corrosion inhibitor to exit the container and to migrate through the concrete to the rebars to thereby inhibit corrosion. European Pat. Spec. No. 0 305 393 B1 (Banks) relates to a method for inhibiting corrosion of reinforcement of a reinforced porous structure by incorporating in the concrete of a vapour-phase corrosion-inhibitor, characterized in that the inhibitor is inserted in the structure, during or after its formation, and selectively positioned adjacent or in contact with the reinforcement, to cause the inhibitor to migrate through the structure and more particulary along an interface between the structural material and the reinforcement. The last two methods are featuring a common disadvantage: Before treating a hardened concrete structure according to these methods, a large number of holes has to be drilled into the surface of the concrete structure, which is both labor-intensive and costly, as well as has negative consequences regarding the aspect of fair-faced concrete fronts. U.S. Pat. No. 5,071,579 (Johnston et al.) describes corrosion-inhibiting systems which comprise at least one of the following compounds: sodium fluorophosphate and a water soluble salt of alkyl- and/or aminoalkyl- and/or N-hydroxyalkylphosphonic acid deriva- said above. The invention also discloses deicers, paints and other corrosion inhibitors in numerous carriers. U.S. Pat. No. 4,092,109 (Rosenberg et al.) discloses methods of protecting metal structures in hydraulic cement bridge decking against corrosion comprising applying an agent consisting of calcium nitrite to the bridge decking and to the juncture of the metal struc-ture with the bridge decking respectively. U.S. Pat. No. 5,422,141 (Hoopes et al.) discloses a rehabilitative solution for preventing or retarding the spread of corrosion of metal reinforcements in concrete, comprising a) one or more corrosion-inhibiting agent(s) selected from different groups of chemicals (e.g. nitrites) and b) an impregnation-increasing amount of penetration-enhancing agents selected from the group of C 1 to C 20 alcohols, alkali metal salts of gluconic acid, alkyl-substitutet benzene compounds or mixtures thereof. According to the literature underdosages of the anodic corrosion inhibitor nitrite in a reinforced concrete structure contaminated with chlorides may cause the adverse, undesirable effect of promoting the corrosion of the ferrous reinforcement. All the prior art methods have at least one of the following disadvantages: They comprise corrosion-inhibiting compositions to be added only to fresh concrete. They require the drilling of a multitude of holes into the concrete surface. They require the installation of auxillary devices like electrodes, reservoirs. They are labor-intensive and therefore costly. They require the application of electric current. They comprise inorganic corrosion inhibitors showing only limited rates of diffusion. They have the inherent risk of causing undesirable efflorecence. They are not very suitable for the restoration of structured concrete surfaces or fair-faced concrete fronts. None of the prior art methods, however, disclose a rehabilitative and/or protective corrosion inhibition of reinforcing steel embedded in a hardened concrete structure by means of applying an aqueous corrosion-inhibiting composition comprising corrosion-inhibiting compounds as well as organosilicone based water repellent agents to the surface of said concrete structure, featuring in addition to improved anti-corrosion action the following additional advantages: of being not labor-intensive, of implying moderate overall cost of rehabilitative treatment, of implying an easy application even on structured concrete surfaces, of not influencing the aspect of concrete surface. Description of the invention Hence, it was an object of this present invention to provide novel compositions being suitable for the reduction of the corrosion rate of already corroding steel reinforcements embedded in a hardened concrete structure as well as for the protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened concrete structure exposed to aggressive environments whereby said compositions do not display the above pointed out drawbacks. It was furthermore an object of the present invention to provide a novel method of reducing the corrosion rate of already corroding steel reinforcements embedded in a hardened concrete structure as well as for the protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened concrete structure exposed to aggressive environments. It was finally an object of the present invention to use novel compositions based on amino- and/or hydroxyalkylamino compound(s) for a process of of reducing the corrosion rate of already corroding steel reinforcements embedded in a hardened concrete structure as well as for the protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened concrete structure exposed to aggressive environments. The above objectives were met pursuant to the independent claims. Preferred embodiments are set forth in the dependent claims. Further aspects of the invention could be derived from the description. Thus, the aqueous corrosion-inhibiting compositions according to the present invention comprise the components as defined in claim 1. By mixing the aqueous corrosion-inhibiting composition consisting of components a) and b) with the further component c), an additional protection from rain water and/or from seawater and/or from the ingress of corrosive chemicals can be achieved. Said hardened concrete, particulary the outermost layer(s) of said hardened concrete in close vicinity of the outermost parts of the reinforcement, may be carbonated to any degree or uncarbonated and/or may contain chloride ions. The disclosed aqueous surface-applied corrosion-inhibiting impregnations are featuring the ability to reduce the corrosion rates of corroded steel reinforcement embedded in a hardened concrete due to their corrosion-inhibiting action as well as, in the case of a carbonated reinforced concrete structures, by realkalizing the carbonated concrete due to their alkalinities and their high buffer capacities. Additionally the corrosion rate of reinforcing steel, embedded in a hardened concrete structures exposed to moisture, rainfall and/or seawater, is further reduced due to the water repellent action of organosilicone compound(s) blended into said impregnations. The careful selection of the amino- and/or hydroxyalkylamino compounds as well as of the inorganic acid and/or carboxylic acid compounds allows the formulation of corrosion-inhibiting impregnations with high buffer capacities. When applied on the surface of a carbonated hardened reinforced concrete structure, said corrosion-inhibiting compositions are capable to raise the pH value of the concrete's pore fluid in the vicinity of the reinforcing steel to a level, where the corrosion rate is markedly reduced. Amines and alkanolamines and salts thereof have the unique feature to move a consiable distance through hardened reinforced concrete because of their physico-chemical properties. They interact with the reinforcing steel embedded in the concrete resulting in a protection of the reinforcing steel. Preferably, combinations of fast-penetrating and slow-penetrating corrosion-inhibiting compounds are selected, having the advantage of combining fast initial action with extended service life. Thus said corrosion-inhibiting composition preferably comprise at least two corrosion-inhibiting compounds, at least one which penetrates relatively quickly and at least one other which penetrates relatively slowly under the conditions to be encountered at building sites. In accordance with the present invention it was quite unexpectedly found that when certain amino- and/or hydroxyalkylamino compounds are combined with some inorganic acids and/or derivatives thereof and/or carboxylic acids, not only a corrosion-inhibition of uncorroded reinforcing steel embedded in hardened concrete can be achieved, but the corrosion rate of already corroded reinforcing steel embedded in a hardened concrete structure can be reduced significantly. A further reduction of the corrosion rate can be achieved by addition of water-based or water-thinnable water repellent agents based on organosilicones to said composition. Preferably, said amino- and/or hydroxyalkylamino compound(s) of component a) according to this invention is (are) selected from the group comprising: The most preferred amino- and/or hydroxyalkylamino compounds are selected from the group comprising 3-(Methylamino)propylamine 3-(Dimethylamino)propylamine 3-(Diethylamino)propylamine Cyclohexaneamine N-Methylcyclohexylamine N-Ethylcyclohexylamine 2-[(2-Aminoethyl)amino]ethanol 1-Amino-2-propanol 1-(Methylamino)-2-propanol 1-(Dimethylamino)-2-propanol 1-(Ethylamino)-2-propanol 1-(Cyclohexylamino)-2-propanol 3-Amino-1-propanol 2-Aminoethanol 2-(Methylamino)ethanol 2-(Dimethylamino)ethanol 2-(Ethylamino)ethanol 2-(Diethylamino)ethanol 2-(Butylamino)ethanol 2-[(1,1-Dimethylethyl)amino]ethanol 2-(Cyclohexylamino)ethanol 1,1'-Iminobis-2-propanol 2,2'-Iminobisethanol 2,2'-(Methylimino)bisethanol 1,1'-(Methylimino)bis-2-propanol 2,2'-(Butylimino)bisethanol 2,2'-[(1,1-Dimethylethyl)imino]bisethanol 1,1',1"-Nitrilotris-2-propanol 2,2',2"-Nitrilotrisethanol Said inorganic acid(s) and/or derivatives thereof and/or carboxylic acid(s) of component a) according to this invention is (are) selected from: The most preferred inorganic acid(s) and/or the derivates thereof and/or the carboxylic acid(s) and/or the derivatives thereof of component a) are selected from the group comprising Sodium hydrogen carbonate Potassium hydrogen carbonate Orthophosphoric acid Sodium dihydrogen phosphate Potassium dihydrogen phosphate Diphosphoric acid Sodium dihydrogen diphosphate Potassium dihydrogen diphosphate Monofluorophosphoric acid n-Hexanoic acid n-Heptanoic acid n-Octanoic acid n-Nonanoic acid 2-Ethylhexanoic acid Isooctanoic acid 1,6-Hexanedicarboxylic acid 1,8-Octanedicarboxylic acid Glycerophosphoric acid Glucosemonocarboxylic acid Benzoic acid 2-Hydroxybenzoic acid 4-Hydroxybenzoic acid 4-Nitrobenzoic acid 4-Methylbenzoic acid 4-(1-Methylethyl)benzoic acid 4-(1,1-Dimethylethyl)benzoic acid Suitable amounts of component a) according to this invention are between 8.0 % to 80.0 %, preferably between 25 % to 50, % by weight, based on the weight of said aqueous corrosion-inhibiting composition. Said surfactants of component b) according to this invention are preferably selected from the group comprising: N-(C 8 to C 22 -Acyl)sarcosine, alkanolammonium or sodium salt, preferably N-Lauroylsarcosine, alkanolammonium or sodium salt and/or N-Cocoylsarcosine, alkanolammonium or sodium salt and/or N-Oleylsarcosine, alkanolammonium or sodium salt N-(C 8 to C 22 -Acyl)-β-alanine, alkanolammonium or sodium salt, preferably N-Lauroyl-β-alanine, alkanolammonium or sodium salt and/or N-Cocoyl-β-alanine, alkanolammonium or sodium salt and/or N-Oleyl-β-alanine, alkanolammonium or sodium salt C 8 to C 22 -Fatty acid monoethanolamide C 8 to C 22 -Fatty acid diethanolamide 1-(C 6 to C 12 -Alkyl)-2-pyrrolidinone, preferably 1-Octyl-2-pyrrolidinone and/or 1-Dodecyl-2-pyrrolidinone Fluorosurfactants Examples: N-Oleylsarcosine, sodium salt 1-Octyl-2-pyrrolidinone Said alkanolammonium salts of the corresponding surfactant(s) are based on alkanolamines selected from 2-aminoethanol, 2-(methylamino)ethanol, 2-(butylamino)-ethanol, 2,2'-iminobisethanol, 2,2',2"-nitrilotrisethanol. Suitable amounts of said surfactants of component b) according to this invention are 0.05 % to 10.0 %, preferably 0.5 % to 5.0 %, by weight, based on the weight of said aqueous corrosion-inhibiting composition. Said water-based or water-thinnable organosilicone compound(s) according to this invention is (are) selected from: Silanes Alkylalkoxysilanes of the general formula R 15 -Si - (OR 16 ) 3 R 15 = C 4 to C 16 alkyl R 16 = C 1 to C 3 alkyl Oligomeric siloxanes and derivatives thereof Alkali siliconates Suitable amounts of said water repellent of component c), i.e. of the organosilicone compound(s) according to this invention are from about 0.1 % to 50.0 %, preferably 1.0 % to 20.0 %, and more preferably 5.0 % to 15.0 %,by weight, based on the weight of said aqueous corrosion-inhibiting composition. The compositions according to the present invention may also comprise further components such as biocidal agents, stabilizers etc. as desired. The disclosed corrosion-inhibiting compositions are showing a fast reduction of the corrosion rate of corroding reinforcing steel, as well as excellent corrosion-inhibition properties, ensuring the protection of reinforcing steel embedded in hardened concrete, thus securing the expected service life of such concrete structures. Furthermore, the application of said corrosion-inhibiting compositions to a.hardened reinforced concrete structure implies the following advantages: not labor-intensive moderate overall cost of rehabilitative treatment easy application even on structured concrete surfaces not influencing the aspect of the concrete surface. A further aspect of the present invention is a novel method for the rehabilitative reduction of the corrosion rate of corroded steel reinforcements embedded in a hardened, reinforced concrete structure as well as for the precautionary, protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened, reinforced concrete structure by impregnating the surface of said concrete structure with the novel aqueous corrosion-inhibiting compositions set forth above. According to said novel method, a solution and/or an emulsion and/or a micro-emulsion comprising the 3 components of the composition according to claim 1 is applied onto the hardened, reinforced concrete structure, whereby said solution and/or an emulsion and/or a micro-emulsion penetrates into the concrete material to reach the steel reeinforcements : In situations where the reinforcing steel embedded in a hardened concrete structure has undergone corrosion or is susceptible to corrosion, it is desirable to have a corrosion-inhibiting composition available which can be applied to the surface of the concrete structure and thereafter penetrates inwardly to protect the reinforcing steel. The method according to the present invention includes the improvement of an existing corrosion-inhibiting protection of reinforcing steel embedded in a hardened concrete structure which is containing corrosion inhibitors added as an admixture to the concrete at the time the concrete was cast. According to a preferred embodiment, in a first step, one or more coats of said aqueous corrosion-inhibiting composition consisting of components a) and b) are applied as a pretreatment to the surface of a hardened reinforced concrete structure. In a second step, one or more coats of a composition consisting of components a), b) and c) are subsequently applied to the same, already treated surface area. According to still another preferred embodiment, in a first step, one or more coats of said aqueous corrosion-inhibiting composition consisting of the components a) and b) are applied as a pretreatment to the surface of a hardened reinforced concrete structure, followed by an impregnation performed with one or more coats consisting of component c). Subsequent to the disclosed surface-applied treatment, corrosion-inhibiting compounds penetrate into the concrete and adsorb chemically on the surface of both, corroding and non-corroding reinforcing steel. The rates of penetration of said corrosion-inhibiting compounds are sufficient to cause a reduction of the corrosion rate of corroded reinforcing steel as well as to protect uncorroded reinforcing steel over extended periods of time. In a preferred embodiment of the present invention, the corrosion-inhibiting solution or emulsion or microemulsion is applied on the concrete surface in several coats by brush, by paint roller or by a spraying device in a total amount of 200-2000 g/m 2 , preferably 300-1000 g/m 2 . A final aspect of the present invention is the use of the above set forth novel compositions for the rehabilitative reduction of the corrosion rate of corroded steel reinforcements embedded in a hardened, reinforced concrete structure as well as for the precautionary, protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened, reinforced concrete structure by impregnation of said hardened reinforced concrete structure. The following examples I-V show that such compositions are able to reduce the corrosion rate of corroding reinforcing steel to a negligible value (repassivation effect) as well as to protect uncorroded steel from corrosion. They are included for the purpose of illustrating the invention, and are not intended to limit the scope of the invention in any manner. All component percentages are by weight unless otherwise indicated. Examples In the following examples the effect of the corrosion-inhibiting compositions No. I - V according to the invention on reinforcing steel will be set forth. The following corrosion-inhibiting compositions were used to perform the tests: Composition No. Ingredients [%] (w/w) I II III IV V 3-(Diethylamino)propylamin 4.2 ― ― 12.9 5.4 N-Ethylcyclohexylamine ― 2.8 2.1 ― ― 1-Amino-2-propanol 12.0 ― 11.6 ― 12.0 1-(Dimethylamino)-2-propanol ― ― ― 2.8 ― 2-Aminoethanol ― 12.7 ― ― ― 2-(Butylamino)ethanol ― ― 3.2 ― 4-Nitrobenzoic acid ― ― ― 5.7 ― Octanoic acid ― 4.9 4.8 8.6 ― Monopotassium phosphate 13.8 9.6 8.3 ― 12.6 N-Lauroylsarcosine, sodium salt 0.4 0.5 ― 1.2 ― N-Cocoyl-β-alanine, sodium salt 0.5 0.6 0.4 ― 1.0 1-Octyl-2-pyrrolidinone 0.1 0.1 0.1 0.2 0.2 Water 69.0 68.8 69.5 68.4 68.8 Σ 100.0 100.0 100.0 100.0 100.0 Example I In this example the influence of the corrosion-inhibiting composition No. I according to the invention in comparison to that of 1-amino-2-propanol on mild steel specimens was investigated by means of potentiodynamic polarization measurements, performed in aqueous, chloride containing solutions. The measurements were carried out using a potentiostat / galvanostat with scan option and a Camec II station. Test conditions: U max ± 5 V, v u = 1-8350 mV/min. working electrodes: polished steel plates (mild steel ST 37) 10mV/sec. concentration of corrosion-inhibiting compounds: 2.0 % based on solids The test solution was neither stirred, nor degased. The electrode was conditioned for one hour at i = 0.0 mA/cm 2 , then the polarization was started. Test period: 1 hour; i max = 0.5 mA/cm 2 , j o and j u depending on currents (i max = 30-50 mA) After a further conditioning at i = 0.0 mA/cm 2 for 30 minutes, the CV was performed in cathodic direction during 30 minutes. Cyclovoltammetry at a mild steel electrode (calcium hydroxide saturated + 0.09 M sodium chloride) Specimen Dosage [%] w/w Pitting potential vs SCE ø 3 scans [mV] Repassivation potential vs SCE ø 3 scans [mV] Control ---- + 240 - 540 1-Amino-2-propanol 6.5 + 660 - 430 Composition No. I 6.5 + 1050 + 890 As can be seen from the data in Table 2, the composition No. I performs substantially better than 1-amino-2-propanol as well as the control, showing more positive values of both, the pitting and the repassivation potentials. Example II In the following three examples IIA - IIC the effect of the corrosion-inhibiting compositions No. II, No. III and No. IV respectively on precorroded reinforcing steel is set forth. Pieces of rebars of job site quality were corroded in a 30 % sodium chloride solution to a potential of approximately -500 mV vs. a silver/silver chloride half cell (SSE). The corroded specimens were rinced with tap water and then dipped into aqueous test solutions showing different initial pH values each and containing 0.000 or 0.001 or 0.010 moles per litre sodium chloride respectively. After determination of the resulting corrosion potentials vs. SSE, 2.0 % w/w of the corrosion-inhibiting compositions No. II, No. III and No. IV respectively according to the invention were added to the test solutions. Subsequently the potentials vs. SSE of the test specimens were measured in function of time and the resulting shifts of the potentials were calculated. Example IIA This example shows the effect of the corrosion-inhibiting compostion No. II according to the invention on precorroded reinforcing steel in comparison to those of 2-aminoethanol and control specimens respectively (temperature: 25°C; dosage of corrosion-inhibiting composition No. II and of a 2-aminoethanol (solution 30% w/w) respectively: 2.0% w/w. Average shift of potential of precorroded reinforcing steel, 9 months after addition of corrosion-inhibiting composition; initial pH value of test solution: 10.0 Specimen Concentration of sodium chloride Shift of potential Control 0.000 M - 4.4 mV 2-Aminoethanol (aq.sol.30% w/w) 0.000 M +494.7 mV Composition No. II 0.000 M +517.5 mV Control 0.001 M +8.0 mV 2-Aminoethanol (aq.sol. 30% w/w) 0.001 M +482.1 mV Composition No. II 0.001 M +568.9 mV Example IIB This example illustrates the effect of the corrosion-inhibiting composition No. III according to the invention on precorroded reinforcing steel in comparison to those of 1-amino-2-propanol and control specimens respectively (temperature: 25°C; dosage of corrosion-inhibiting composition No III and of 1-amino-2-propanol (solution 30% w/w) respectively: 2.0% w/w. Average shift of potential of precorroded reinforcing steel, 9 months after addition of corrosion-inhibiting composition; initial pH value of test solution: 12.0 Specimen Concentration of sodium chloride Shift of potential Control 0.000 M - 4.4 mV 1-Amino-2-propanol (aq.sol.30% w/w) 0.000 M +380.5 mV Composition No. III 0.000 M +450.2 mV Control 0.001 M +4.6 mV 1-Amino-2-propanol (aq.sol. 30% w/w) 0.001 M +184.0 mV Composition No. III 0.001 M +296.5 mV Example IIC This example shows the effect of the corrosion-inhibiting composition No. IV according to the invention on precorroded reinforcing steel in comparison to those of 3-(diethylamino)propylamine and control specimens respectively (temperature: 25°C; dosage of corrosion-inhibiting composition No. IV and of 3-(diethylamino)propylamine (solution 30% w/w) respectively: 2.0% w/w. Average shift of potential of precorroded reinforcing steel, 9 months after addition of corrosion-inhibiting composition; initial pH value of test solution: 13.0 Specimen Concentration of sodium chloride Shift of potential Control 0.000 M - 45.5 mV 3-(Diethylamino)propylamine (aq.sol. 30% w/w) 0.000 M +127.2 mV Composition No. IV 0.00 0 M +196.3 mV Control 0.010 M - 210.5 mV 3-(Diethylamino)propylamine (aq.sol. 30% w/w) 0.010 M - 97.6 mV Composition No. IV 0.010 M - 20.8 mV As can be seen from the data in Tables No. 3 to 5, the compositions No. II, No. III as well as No. IV cause considerably larger shifts of the potentials of the precorroded reinforcing steel specimens in direction of more positive values, relative to both, the respective amino compounds alone and the control specimens. Example III This example demonstrates the corrosion-inhibiting effect of the compositions No. I and No. II as well as of a blend of composition No. I with a organosilicone compound according to the invention on corroded reinforcing steel embedded in hardened reinforced concrete. 550 g/m 2 of composition No. I and II, as well as of a blend of 85 % (w/w) of composition No. I + 15 % (w/w) of an aqueous emulsion of organosilicone based water repellent agents respectively were applied by paint roller according to the invention to carbonated concrete slabs containing corroded rebars (average carbonation depth: 25 mm; average concrete cover: 17 mm; chloride concentration: 22 ppm ; storage of test specimens during test period: weather-exposed). Measurements (performed by LP device) Prior to application of respective compositions (t = 0 months) After application of respective compositions (t = 17 months) Specimen Corrosion rate [µA/cm 2 ] Potential CSE [mV] Corrosion rate [µA/cm 2 ] Potential CSE [mV] Control / 1 0.228 - 372 0.251 - 409 Control / 2 0.173 - 340 0.184 - 361 Composition No. I/ 1 0.201 - 331 0.072 - 228 Composition No. I/ 2 0.247 - 392 0.098 - 306 Composition No. II/ 1 0.264 -356 0.117 -307 Composition No. II / 2 0.196 - 404 0.079 - 331 85 % (w/w) Composition No. I +15 % (w/w) organosilicone emulsion 30 % (w/w) / 1 0.239 - 388 0.083 - 251 85 % (w/w) Composition No. I +15 % (w/w) organosilicone emulsion 30 % (w/w) / 2 0.182 -365 0.049 -204 As can be seen from the data in Table 6, the compositions No. I and No. II, as well as a blend of 85 % w/w composition No. I + 15 % w/w organosilicone emulsion (30 % w/w) caused considerable reductions of the corrosion rates of the reinforcing steel embedded in carbonated concrete. After 17 months of weather-exposed storage of the specimens the average corrosion rates were 42 % [ composition No. II ], 38 % [ composition No. I ] and 31 % [ 85 % w/w composition No. I + 15 % w/w organosilicone emulsion (30 % w/w) ] respectively, based on the corresponding initial average corrosion rates, whereas the average corrosion rate of the control increased to 108 % of the corresponding average initial value. The results above show that the performance of corrosion inhibitors can be improved further by blending with organosilicone compounds. Example IV This example demonstrates the effect of the corrosion-inhibiting composition No. III on corroded reinforcing steel embedded in hardened reinforced concrete according to the invention. 600 g/m 2 of composition No. III were applied by paint roller to corroded, carbonated concrete slabs containing chlorides (average concrete cover: 25-38 mm; average carbonation depth: 31 mm; average chloride content, based on the cement weight: 0.74 %; relative humidity during test period: 50-90 %). Measurements (LP device) Results before application of composition No. III (t = 0 months) Results after application of composition No. III (t = 15 months) Specimen No. Corrosion rate [µA/cm 2 ] Potential CSE [mV] Corrosion rate [µA/cm 2 ] Potential CSE [mV] control / 1 0.404 - 417 0.411 - 431 control / 2 0.467 - 390 0.495 - 373 Composition No. III / 1 0.453 - 403 0.202 - 294 Composition No. III / 2 0.391 - 374 0.189 - 308 As can be seen from the data in Table 7, after a test period of 15 months the composition No. III caused an average reduction of the corrosion rates of the steel reinforcements embedded in hardened concrete to approx. 46 % of the initial average corrosion rate, whereas the average corrosion rate of the control increased to 104 % of the corresponding average initial value. Example V The following example illustrates the influence of the corrosion-inhibiting composition No. V according to the invention on the corrosion rate of corroded reinforcing steel embedded in reinforced concrete slabs. The concrete surface to be treated was washed using a high pressure jet of water. After drying, 450 g/m 2 of composition No. V were applied by paint roller to the surface of the carbonated concrete slabs. Storage of test specimens during test period: weather-exposed. Measurements (LP device) Average corrosion rate [µA/cm 2 ] Specimen before appliction of composition No. V (t = 0 months) after application of composition No. V (t = 10 months) Control / 1 0.238 0.251 Control / 2 0.275 0.306 Composition No. V / 1 0.247 0.089 Composition No. V / 2 0.302 0.167 Composition No. V / 3 0.214 0.060 As can be seen from the data in Table 8, after a test period of 10 months the composition No. V caused an average reduction of the corrosion rates of the steel reinforcements embedded in hardened concrete to approx. 40 % of the initial average corrosion rate, whereas the average corrosion rate of the control increased to 108 % of the corresponding average initial value.

Claims: A composition for the rehabilitative reduction of the corrosion rate of corroded steel reinforcements embedded in a hardened, reinforced concrete structure as well as for the precautionary, protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened, reinforced concrete structure by impregnation of said hardened reinforced concrete structure, wherein said corrosion-inhibiting composition comprises an aqueous solution and/or emulsion and/or micro-emulsion of a) one or more amino- and/or hydroxyalkylamino compound(s), partially or completely neutralized with one or more acid(s) and/or derivatives thereof, in an amount sufficient to inhibit corrosion of said steel reinforcement, whereby said acids are selected from Carbonic acid, monoalkali metal salts Orthophosphoric acid and derivatives thereof, including the mono-alkali metal salts thereof Monofluorophosphoric acid Glycerophosphoric acid Diphosphoric acid, including the dialkali metal salts thereof Hexanoic acid R 12 -COOH wherein R 12 = C 6 to C 8 alkyl wherein R 13 = H or C 1 to C 4 alkyl or -OH or -NO 2 HOOC-R 14 -COOH wherein R 14 = C 6 to C 8 alkylene b) one or more surfactant(s) providing an enhanced wetting and penetration capability by altering the surface tension, and c) optionally, one or more water-based or water-thinnable water repellent agent(s) selected from the group of organosilicones. Composition according to claim to 1, characterized in that the amount of the component a) represents from about 8.0 % to 80.0 % by weight, preferably from about 25.0 % to 50.0 % by weight based on the weight of said aqueous solution or emulsion or microemulsion. Composition according to any one of the claims 1 or 2, characterized in that the amount of the component b) represents from about 0.05 % to 10.0 % by weight, preferably from about 0.5 % to 5.0 % by weight based on the weight of said aqueous solution or emulsion or microemulsion. Composition according to any one of the claim 1 to 3, characterized in that the amount of component c) represents about 0.1 % to 50.0 % by weight, preferably about 1.0 % to 20.0 %, and more preferably about 5.0 % to 15.0 %, by weight, based on the weight of said aqueous solution or emulsion or microemulsion. Composition according to any one of the claims 1 to 4, characterized in that the amino- and/or hydroxyalkylamino compound is selected from the group consisting of 3-(Methylamino)propylamine 3-(Dimethylamino)propylamine 3-(Diethylamino)propylamine Cyclohexylamine N-Methylcyclohexylamine N-Ethylcyclohexylamine 2-[(2-Aminoethyl)amino]ethanol 1-Amino-2-propanol 1-(Methylamino)-2-propanol 1-(Dimethylamino)-2-propanol 1-(Ethylamino)-2-propanol 1-(Cyclohexylamino)-2-propanol 3-Amino-1-propanol 2-Aminoethanol 2-(Methylamino)ethanol 2-(Dimethylamino)ethanol 2-(Ethylamino)ethanol 2-(Diethylamino)ethanol 2-(Butylamino)ethanol 2-[(1,1-Dimethylethyl)amino]ethanol 2-(Cyclohexylamino)ethanol 1,1'-Iminobis-2-propanol 2,2'-Iminobisethanol 2,2'-(Methylimino)bisethanol 1,1'-(Methylimino)bis-2-propanol 2,2'-(Butylimino)bisethanol 2,2'-[(1,1-Dimethylethyl)imino]bisethanol 1,1',1''-Nitrilotris-2-propanol 2,2',2''-Nitrilotrisethanol. Composition according to any one of the claims 1 to 5, characterized in that the acid(s) and/or the derivatives thereof are selected from the group consisting of Sodium hydrogen carbonate Potassium hydrogen carbonate Orthophosphoric acid Sodium dihydrogen phosphate Potassium dihydrogen phosphate Diphosphoric acid Sodium dihydrogen diphosphate Potassium dihydrogen diphosphate Monofluorophosphoric acid n-Hexanoic acid n-Heptanoic acid n-Octanoic acid n-Nonanoic acid 2-Ethylhexanoic acid Isooctanoic acid 1,6-Hexanedicarboxylic acid 1,8-Octanedicarboxylic acid Glycerophosphoric acid Glucosemonocarboxylic acid Benzoic acid 2-Hydroxybenzoic acid 4-Hydroxybenzoic acid 4-Nitrobenzoic acid 4-Methylbenzoic acid 4-(1-Methylethyl)benzoic acid 4-(1,1-Dimethylethyl)benzoic acid. Composition according to any one of the claims 1 to 6, characterized in that the component b) is selected from the group consisting of N-(C 8 to C 22 -Acyl) sarcosine, alkanolammonium or sodium salt, preferably N-Lauroylsarcosine, alkanolammonium or sodium salt and/or N-Cocoylsarcosine, alkanolammonium or sodium salt and/or N-Oleylsarcosine, alkanolammonium or sodium salt N-(C 8 to C 22 -Acyl)-β-alanine, alkanolammonium or sodium salt, preferably N-Lauroyl-β-alanine, alkanolammonium or sodium salt and/or N-Cocoyl-β-alanine, alkanolammonium or sodium salt and/or N-Oleyl-β-alanine, alkanolammonium or sodium salt C 8 to C 22 -Fatty acid monoethanolamide C 8 to C 22 -Fatty acid diethanolamide 1-(C 6 to C 12 -Alkyl)-2-pyrrolidinone, preferably 1-Octyl-2-pyrrolidinone and/or 1-Dodecyl-2-pyrrolidinone Fluorosurfactants. Composition according to claim 7, characterized in that the amino alcohol compound of said surface-active alkanolammonium salts is selected from the group consisting of 2-Aminoethanol 2-(Methylamino)ethanol 2-(Butylamino)ethanol 2,2'-Iminobisethanol 2,2',2''-Nitrilotrisethanol. Composition according to any one of the claims 1 to 8, characterized in that said waterbased or water-thinnable organosilicone(s) of component c) is selected from silanes and/or oligomeric siloxanes and/or derivates thereof and/or polysiloxanes and/or derivates thereof and/or alkali-siliconates. Composition according to claim 9, characterized in that said silane is an alkyltrialkoxysilane having the formula R'-Si(OR'') 3 , wherein R' is a C 4 to C 16 - alkyl group and R'' is a C 1 to C 3 - alkyl group. Composition according to any one of the claims 9 or 10, characterized in that said organosilicone is either a mixture of one or more alkylalkoxysilanes and one or more oligomeric siloxanes and/or derivates thereof and/or one or more polysiloxanes and/or derivates thereof or is a mixture of one or more oligomeric siloxanes or derivates thereof and one or more polysiloxanes and/or derivates thereof or is a mixture of one or more alkali-siliconates and one or more oligomeric siloxanes and/ or derivates thereof and/or one or more polysiloxanes and/or derivates thereof. Composition according to any one of the claims 1 to 11, characterized in that it comprises a water-soluble dye, preferably featuring a low light fastness, to visualize the area on a hardened concrete surface upon which said corrosion-inhibiting composition is applied. A method for the rehabilitative reduction of the corrosion rate of corroded steel reinforcements embedded in a hardened, reinforced concrete structure as well as for the precautionary, protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened, reinforced concrete structure by impregnating the hardened reinforced concrete structure with a corrosion-inhibiting composition according of any one of the claims 1 to 12. A method according to claim 13, characterized in that said impregnation of the surface of a reinforced concrete structure is performed with a composition consisting of the components a) and b), to be applied in one or more coats as a pretreatment, followed by an impregnation performed in one or more coats with a composition consisting of the components a), b) and c). Method according to claim 13, characterized in that said impregnation of the surface of a reinforced concrete structure is performed with a composition consisting of the components a) and b), to be applied as a pretreatment in one or more coats, followed by an impregnation performed in one or more coats with a composition consisting of component c). Method according to any one of the claims 13 to 15, characterized in that the corrosion-inhibiting solution or emulsion or microemulsion is applied on the concrete surface in several coats by brush, by paint roller or by a spraying device in a total amount of 200-2000 g/m 2 , preferably 300-1000 g/m 2 . Use of a composition according to any one of the claims 1 to 12 for the rehabilitative reduction of the corrosion rate of corroded steel reinforcements embedded in a hardened, reinforced concrete structure as well as for the precautionary, protective corrosion inhibition of uncorroded steel reinforcements embedded in a hardened, reinforced concrete structure by impregnation of said hardened reinforced concrete structure.

Inventors: BUERGE THEODOR A, MAEDER URS DR, MARAZZANI BEAT, BUERGE, THEODOR A., MAEDER, URS, DR., MARAZZANI, BEAT, Bürge, Theodor A., Mäder, Urs, Dr.
Applicants: SIKA SCHWEIZ AG
Application year: 1998
Main classification: C04B41
IPC codes: C04B41