U.S. patent application number 09/309290 was filed with the patent office on 2002-06-06 for method for rehabilitative and/or protective corrosion-inhibition of reinforcing steel embedded in a hardened structure by means of surface-applied corrosion-inhibiting compositions.
Invention is credited to BURGE, THEODOR A., MADER, URS, MARAZZANI, BEAT.
Application Number | 20020066889 09/309290 |
Document ID | / |
Family ID | 8231921 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020066889 |
Kind Code |
A1 |
MARAZZANI, BEAT ; et
al. |
June 6, 2002 |
METHOD FOR REHABILITATIVE AND/OR PROTECTIVE CORROSION-INHIBITION OF
REINFORCING STEEL EMBEDDED IN A HARDENED 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 one or more
water-based or water-thinnable water repellent agent(s) selected
from the group of organosilicones.
Inventors: |
MARAZZANI, BEAT;
(OBERENGSTRINGEN, CH) ; BURGE, THEODOR A.;
(GEROLDSWIL, CH) ; MADER, URS; (FRAUENFELD,
CH) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
8231921 |
Appl. No.: |
09/309290 |
Filed: |
May 11, 1999 |
Current U.S.
Class: |
252/390 ;
252/392; 252/396 |
Current CPC
Class: |
C04B 2111/26 20130101;
C04B 41/46 20130101; C04B 41/46 20130101; C04B 41/62 20130101; C23F
11/143 20130101; C04B 28/02 20130101; C23F 11/10 20130101; C04B
2103/54 20130101; C04B 2103/40 20130101; C04B 41/4905 20130101;
C04B 32/02 20130101; C04B 2111/723 20130101; C04B 41/009 20130101;
C04B 41/009 20130101 |
Class at
Publication: |
252/390 ;
252/392; 252/396 |
International
Class: |
C09K 003/00; C23F
011/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 1998 |
EP |
EP-98 108660.6 |
Claims
1. 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,
characterized in that said corrosion-inhibiting composition
comprises a solution and/or an emulsion and/or a micro-emulsion of
a) one or more amino- and/or hydroxyalkylamino compound(s),
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), in an amount sufficient to
inhibit corrosion of said steel reinforcement, whereby said organic
acid(s) contains one or more carboxylic groups and may additionally
contain one or more hydroxyl groups, and b) one or more
surfactant(s) providing an enhanced wetting and penetration
capability by altering the surface tension, and c) one or more
water-based or water-thinnable water repellent agent(s) selected
from the group of organosilicones.
2. Composition according to claim 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.
3. Composition according to claim 1, 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.
4. Composition according to claim 1, 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.
5. Composition according to claim 1, characterized in that the
amino- and/or hydroxy-alkylamino compound is selected from the
group comprising 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
6. Composition according to claim 1, characterized in that the
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 D-Gluconic 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
7. Composition according to claim 1, characterized in that the
component b) is selected from the group comprising N--(C.sub.8 to
C.sub.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.sub.8 to
C.sub.22-Acyl)-.beta.-alanine, alkanolammonium or sodium salt,
preferably N-Lauroyl-.beta.-alanine, alkanolammonium or sodium salt
and/or N-Cocoyl-.beta.-alanine, alkanolammonium or sodium salt
and/or N-Oleyl-.beta.-alanine, alkanolammonium or sodium salt
C.sub.8 to C.sub.22-Fatty acid monoethanolamide C.sub.8 to
C.sub.22-Fatty acid diethanolamide 1-(C.sub.6 to
C.sub.12-Alkyl)-2-pyrrolidinone, preferably 1-Octyl-2-pyrrolidinone
and/or 1-Dodecyl-2-pyrrolidinone fluorosurfactants
8. Composition according to claim 7, characterized in that the
amino alcohol compound of said surface-active alkanolammonium salts
is selected from the group comprising 2-Aminoethanol
2-(Methylamino)ethanol 2-(Butylamino)ethanol 2,2'-Iminobisethanol
2,2',2"-Nitrilotrisethanol
9. Composition according to claim 1, 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.
10. Composition according to claim 9, characterized in that said
silane is an alkyltrialkoxysilane having the formula
R'--Si(OR").sub.3, wherein R' is a C.sub.4 to C.sub.16-alkyl group
and R" is a C.sub.1 to C.sub.3-alkyl group.
11. Composition according to claim 9, 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 alkalisiliconates and one or
more oligomeric siloxanes and/or derivates thereof and/or one or
more polysiloxanes and/or derivates thereof.
12. Composition according to claim 1, 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.
13. 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 to claim 1.
14. 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), b)
and c), to be applied in one or more coats, followed by an
impregnation performed in one or more coats with a composition
consisting of component c).
15. Method according to claim 13, 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.sup.2, preferably 300-1000 g/m.sup.2.
16. Use of a composition according to claim 1 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.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] 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.
[0003] 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).
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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
[0008] Several methods have been suggested to protect reinforcing
steel embedded in concrete against corrosion:
[0009] 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.sub.17
to C.sub.21) including salts and esters thereof.
[0010] 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.
[0011] PCT Pat. Appl. No. 96/27695 (Curatolo et al.) describes a
method of controlling effectively chloride-induced corrosion of
steel reinforcement members in concrete by the addition of a
corrosion-inhibiting admixture to freshly prepared 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.
[0012] 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 un-reacted
amino- and acid compounds.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] Canadian Pat. No.1,258,473 (Martin et al.) discribes 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.
[0017] 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 odours, high alkalinity
and corrosiveness.
[0018] 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.
[0019] 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 top-coating with a cement composition (important
regarding fair-faced concrete fronts). Chromates are featuring
problematic toxicity data.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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 structure with the bridge decking respectively.
[0029] 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
[0030] a) one or more corrosion-inhibiting agent(s) selected from
different groups of chemicals (e.g. nitrites) and
[0031] b) an impregnation-increasing amount of
penetration-enhancing agents selected from the group of C.sub.1 to
C.sub.20 alcohols, alkali metal salts of gluconic acid,
alkyl-substitutet benzene compounds or mixtures thereof.
[0032] 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.
[0033] All the prior art methods have at least one of the following
disadvantages:
[0034] They comprise corrosion-inhibiting compositions to be added
only to fresh concrete.
[0035] They require the drilling of a multitude of holes into the
concrete surface.
[0036] They require the installation of auxiliary devices like
electrodes, reservoirs.
[0037] They are labor-intensive and therefore costly.
[0038] They require the application of electric current.
[0039] They comprise inorganic corrosion inhibitors showing only
limited rates of diffusion.
[0040] They have the inherent risk of causing undesirable
efflorecence.
[0041] They are not very suitable for the restoration of structured
concrete surfaces or fair-faced concrete fronts.
[0042] 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:
[0043] of being not labor-intensive,
[0044] of implying moderate overall cost of rehabilitative
treatment,
[0045] of implying an easy application even on structured concrete
surfaces,
[0046] of not influencing the aspect of concrete surface.
DESCRIPTION OF THE INVENTION
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] Thus, the aqueous corrosion-inhibiting compositions
according to the present invention comprise the following
components:
[0052] a) One or more amino- and/or hydroxyalkylamino compound(s),
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), in an amount sufficient to
inhibit corrosion of said steel reinforcement.
[0053] b) One or more surfactant(s) providing an enhanced wetting
and penetration capability by altering the surface tension is
applied in one or more coats to the surface of a hardened
reinforced concrete structure which has undergone or is susceptible
to corrosion of the reinforcing steel.
[0054] c) One or more water-based and/or water-thinnable water
repellent agent(s), selected from the group of organosilicone
compounds.
[0055] By mixing the aqueous corrosion-inhibiting composition
consisting of components a) and b) with the further component c),
quite surprisingly, an additional protection from rain water and/or
from seawater and/or from the ingress of corrosive chemicals can be
achieved. It turns out that the presence of component c) provides
unexpectedly a markedly improved resistance to the penetration of
water, while being permeable to vapor which is quite important
within the context of the drying process where the departure of
humidity in the form of vapor must not be hindered. Thus, through
the improved resistance to the water penetration, the
corrosion-inhibition could be significantly improved.
[0056] Said hardened concrete, particularly 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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, as well as one
or more surfactants b) and water-based or water-thinnable water
repellent agents based on organosilicones c) to said composition,
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.
[0062] Preferably, said amino- and/or hydroxyalkylamino compound(s)
of component a) according to this invention is (are) selected from
the group comprising: 1
[0063] The most preferred amino- and/or hydroxyalkylamino compounds
are selected from the group comprising
[0064] 3-(Methylamino)propylamine
[0065] 3-(Dimethylamino)propylamine
[0066] 3-(Diethylamino)propylamine
[0067] Cyclohexaneamine
[0068] N-Methylcyclohexylamine
[0069] N-Ethylcyclohexylamine
[0070] 2-[(2-Aminoethyl)amino]ethanol
[0071] 1-Amino-2-propanol
[0072] 1-(Methylamino)-2-propanol
[0073] 1-(Dimethylamino)-2-propanol
[0074] 1-(Ethylamino)-2-propanol
[0075] 1-(Cyclohexylamino)-2-propanol
[0076] 3-Amino-1-propanol
[0077] 2-Aminoethanol
[0078] 2-(Methylamino)ethanol
[0079] 2-(Dimethylamino)ethanol
[0080] 2-(Ethylamino)ethanol
[0081] 2-(Diethylamino)ethanol
[0082] 2-(Butylamino)ethanol
[0083] 2-[(1,1-Dimethylethyl)amino]ethanol
[0084] 2-(Cyclohexylamino)ethanol
[0085] 1,1'-Iminobis-2-propanol
[0086] 2,2'-Iminobisethanol
[0087] 2,2'-(Methylimino)bisethanol
[0088] 1,1'-(Methylimino)bis-2-propanol
[0089] 2,2'-(Butylimino)bisethanol
[0090] 2,2'-[(1,1-Dimethylethyl)imino]bisethanol
[0091] 1,1',1"-Nitrilotris-2-propanol
[0092] 2,2',2"-Nitrilotrisethanol
[0093] Said inorganic acid(s) and/or derivatives thereof and/or
carboxylic acid(s) of component a) according to this invention is
(are) selected from:
[0094] Inorganic acids:
[0095] Carbonic acid, monoalkali metal salts
[0096] Orthophosphoric acid and derivatives thereof, including the
mono-alkali metal salts thereof
[0097] Monofluorophosphoric acid
[0098] Diphosphoric acid, including the dialkali metal salts
thereof
[0099] Examples
[0100] Sodium hydrogen carbonate
[0101] Sodium dihydrogen orthophosphate 2
[0102] 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
[0103] Sodium hydrogen carbonate
[0104] Potassium hydrogen carbonate
[0105] Orthophosphoric acid
[0106] Sodium dihydrogen phosphate
[0107] Potassium dihydrogen phosphate
[0108] Diphosphoric acid
[0109] Sodium dihydrogen diphosphate
[0110] Potassium dihydrogen diphosphate
[0111] Monofluorophosphoric acid
[0112] n-Hexanoic acid
[0113] n-Heptanoic acid
[0114] n-Octanoic acid
[0115] n-Nonanoic acid
[0116] 2-Ethylhexanoic acid
[0117] Isooctanoic acid
[0118] 1,6-Hexanedicarboxylic acid
[0119] 1,8-Octanedicarboxylic acid
[0120] Glycerophosphoric acid
[0121] D-Gluconic acid
[0122] Glucosemonocarboxylic acid
[0123] Benzoic acid
[0124] 2-Hydroxybenzoic acid
[0125] 4-Hydroxybenzoic acid
[0126] 4-Nitrobenzoic acid
[0127] 4-Methylbenzoic acid
[0128] 4-(1-Methylethyl)benzoic acid
[0129] 4-(1,1-Dimethylethyl)benzoic acid
[0130] 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.
[0131] Said surfactants of component b) according to this invention
are preferably selected from the group comprising:
[0132] N--(C.sub.8 to C.sub.22-Acyl)sarcosine, alkanolammonium or
sodium salt,
[0133] preferably N-Lauroylsarcosine, alkanolammonium or sodium
salt and/or
[0134] N-Cocoylsarcosine, alkanolammonium or sodium salt and/or
[0135] N-Oleylsarcosine, alkanolammonium or sodium salt
[0136] N--(C.sub.8 to C.sub.22-Acyl)-.beta.-alanine,
alkanolammonium or sodium salt,
[0137] preferably N-Lauroyl-.beta.-alanine, alkanolammonium or
sodium salt and/or
[0138] N-Cocoyl-.beta.-alanine, alkanolammonium or sodium salt
and/or
[0139] N-Oleyl-.beta.-alanine, alkanolammonium or sodium salt
[0140] C.sub.8 to C.sub.22-Fatty acid monoethanolamide
[0141] C.sub.8 to C.sub.22-Fatty acid diethanolamide
[0142] 1-(C.sub.6 to C.sub.12-Alkyl)-2-pyrrolidinone,
[0143] preferably 1-Octyl-2-pyrrolidinone and/or
1-Dodecyl-2-pyrrolidinone fluoro-surfactants
[0144] Examples
[0145] N-Oleylsarcosine, sodium salt
[0146] 1-Octyl-2-pyrrolidinone
[0147] 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.
[0148] 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.
[0149] Said water-based or water-thinnable organosilicone
compound(s) according to this invention is (are) selected from:
[0150] silanes
[0151] alkylalkoxysilanes of the general formula
R.sub.15--Si--(OR.sub.16)- .sub.3
[0152] R.sub.15=C.sub.4 to C.sub.16 alkyl
[0153] R.sub.16=C.sub.1 to C.sub.3 alkyl
[0154] oligomeric siloxanes and derivatives thereof
[0155] alkali siliconates
[0156] 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.
[0157] The compositions according to the present invention may also
comprise further components such as biocidal agents, stabilizers
etc. as desired.
[0158] 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:
[0159] not labor-intensive
[0160] moderate overall cost of rehabilitative treatment
[0161] easy application even on structured concrete surfaces
[0162] not influencing the aspect of the concrete surface.
[0163] 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.
[0164] According to said novel method, a solution and/or an
emulsion and/or a micro-emulsion comprising the following 3
components 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 reinforcements:
[0165] a) One or more amino- and/or hydroxyalkylamino compound(s),
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), in an amount sufficient to
inhibit corrosion of said steel reinforcement, whereby said organic
acid(s) contains one or more carboxylic groups and may additionally
contain one or more hydroxyl groups.
[0166] b) One or more surfactant(s) providing an enhanced wetting
and penetration capability by altering the surface tension.
[0167] c) One or more water-based or water-thinnable water
repellent agent(s) selected from the group of organosilicones.
[0168] 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.
[0169] According to a preferred embodiment, in a first step, one or
more coats of said aqueous corrosion-inhibiting composition
consisting of the components a, b) and c) are applied as a
pretreatment to the surface of a hardened reinforced concrete
structure, optionally followed by an impregnation performed with
one or more coats consisting of component c).
[0170] 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.
[0171] 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.sup.2, preferably 300-1000 g/m.sup.2.
[0172] 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.
[0173] 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
[0174] 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.
[0175] The following corrosion-inhibiting compositions were used to
perform the tests:
1 TABLE 1 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-propan- ol -- -- -- 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-.beta.-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 .SIGMA. 100.0 100.0 100.0 100.0
100.0
Example I
[0176] 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.
[0177] Test Conditions
[0178] U.sub.max.+-.5 V, v.sub.u=1-8350 mV/min.
[0179] working electrodes: polished steel plates (mild steel ST
37)
[0180] 10 mV/sec.
[0181] concentration of corrosion-inhibiting compounds: 2.0% based
on solids
[0182] The test solution was neither stirred, nor degased. The
electrode was conditioned for one hour at i=0.0 mA/cm.sup.2, then
the polarization was started.
[0183] Test period: 1 hour; i.sub.max=0.5 mA/cm.sup.2, j.sub.o and
j.sub.u depending on currents (i.sub.max=30-50 mA). After a further
conditioning at i=0.0 mA/cm.sup.2 for 30 minutes, the CV was
performed in cathodic direction during 30 minutes.
2TABLE 2 Cyclovoltammetry at a mild steel electrode (calcium
hydroxide saturated + 0.09 M sodium chloride) Pitting potential
Repassivation Dosage vs SCE .o slashed. potential vs SCE Specimen
[%] w/w 3 scans [mV] .o slashed. 3 scans [mV] Control -- +240 -540
1-Amino-2-propanol 6.5 +660 -430 Composition No. I 6.5 +1050
+890
[0184] 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
[0185] 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.
[0186] 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 rinsed 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 liter sodium chloride
respectively.
[0187] 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
[0188] 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.degree. C.; dosage
of corrosion-inhibiting composition No. II and of a 2-aminoethanol
(solution 30% w/w) respectively: 2.0% w/w.
3TABLE 3 Average shift of potential of precorroded reinforcing
steel, 9 months after addition of corrosion-inhibiting composition;
initial pH value of test solution: 10.0 Concentration of sodium
Specimen chloride Shift of potential Control 0.000 M -4.4 mV
2-Aminoethanol (aq. sol. 0.000 M +494.7 mV 30% w/w) Composition No.
II 0.000 M +517.5 mV Control 0.001 M +8.0 mV 2-Aminoethanol (aq.
sol. 0.001 M +482.1 mV 30% w/w) Composition No. II 0.001 M +568.9
mV
Example IIB
[0189] 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.degree. C.; dosage of corrosion-inhibiting composition No III
and of 1-amino-2-propanol (solution 30% w/w) respectively: 2.0%
w/w.
4TABLE 4 Average shift of potential of precorroded reinforcing
steel, 9 months after addition of corrosion-inhibiting composition;
initial pH value of test solution: 12.0 Concentration of sodium
Specimen chloride Shift of potential Control 0.000 M -4.4 mV
1-Amino-2-propanol (aq. 0.000 M +380.5 mV sol. 30% w/w) Composition
No. III 0.000 M +450.2 mV Control 0.001 M +4.6 mV
1-Amino-2-propanol (aq. 0.001 M +184.0 mV sol. 30% w/w) Composition
No. III 0.001 M +296.5 mV
Example IIC
[0190] 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-(diethyl
amino)propylamine and control specimens respectively (temperature:
25.degree. C.; dosage of corrosion-inhibiting composition No. IV
and of 3-(diethylamino)propylamin- e (solution 30% w/w)
respectively: 2.0% w/w.
5TABLE 5 Average shift of potential of precorroded reinforcing
steel, 9 months after addition of corrosion-inhibiting composition;
initial pH value of test solution: 13.0 Concentration of Specimen
sodium chloride Shift of potential Control 0.000 M -45.5 mV
3-(Diethylamino)propylamine 0.000 M +127.2 mV (aq. sol. 30% w/w)
Composition No. IV 0.000 M +196.3 mV Control 0.010 M -210.5 mV
3-(Diethylamino)propylamine 0.010 M -97.6 mV (aq. sol. 30% w/w)
Composition No. IV 0.010 M -20.8 mV
[0191] 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
[0192] 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.sup.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 con-centration: 22 ppm ; storage of test specimens during
test period: weather-exposed).
6 TABLE 6 Prior to application of respective compositions (t = 0
After application of respective months) compositions (t = 17
months) Measurements Corrosion Corrosion (performed by LP device) *
rate Potential CSE rate Potential CSE Specimen [.mu.A/cm.sup.2]
[mV] [.mu.A/cm.sup.2] [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% 0.239 -388 0.083 -251
(w/w) organosilicone emulsion 30% (w/w)/1 85% (w/w) Composition No.
I + 15% 0.182 -365 0.049 -204 (w/w) organosilicone emulsion 30%
(w/w)/2 *Measurements of corrosion rates listed in this
specification were performed by a "Geocor 6" corro-sion rate meter,
manufactured by Geocisa S. A., Madrid, Spain. The "Geocor 6" device
measures the corrosion rate of reinforcing steel embedded in
concrete by the "linear polarization" technique (LP).
[0193] 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
[0194] 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.sup.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%).
7TABLE 7 Results before application of Results after application of
Measurements composition No. III (t = 0 months) composition No. III
(t = 15 months) (LP device) Corrosion rate Potential CSE Corrosion
rate Potential CSE Specimen No. [.mu.A/cm.sup.2] [mV]
[.mu.A/cm.sup.2] [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
[0195] 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
[0196] 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.sup.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.
8 TABLE 8 Average corrosion rate [.mu.A/cm.sup.2] before appliction
of before appliction of Measurements (LP device) composition No. V
composition No. V Specimen (t = 0 months) (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
[0197] 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.
* * * * *