Template for SAMARIS documents

SAMARIS

Sustainable and Advanced MAterials for Road InfraStructure

EFFECTIVENESS OF CORROSION INHIBITORS IN LABORATORY STUDIES

Dr. Andraz Legat, Dr. Tayfun Altuğ Söylev, Dr. Mark Richardson

Competitive and Sustainable Growth (GROWTH) Programme

Document number:

SAM_GE_DE17v01_01

Version:

1

Date:

14/01/2005

Name and signature

Date

Drafted:

Reviewed:

Verified:

Validated:

Approved by SAMARIS Management Group:

TABLE OF CONTENTS

11.INTRODUCTION

2.MECHANISM STUDY2

2.1Introduction2

2.2Investigation of factors influencing inhibitor behaviour3

2.2.1Exposure of steel specimens3

2.2.2Electrochemical measurement5

2.3Investigation of passivation mechanism12

2.4Conclusions15

3.Further Experience from Selected Published STUDIES16

3.1Criteria for selection16

3.2Studies of Relevance to Task 13.1, Basic Mechanism Study16

3.3Studies of Relevance to Task 13.2, Chloride and inhibitor concentration20

3.3.1Chloride content20

3.3.2Degree of carbonation21

3.3.3inhibitor concentration21

3.3.4Concrete cover thickness22

3.4Studies of Relevance to Task 13.3, Concrete permeability22

3.4.1Strength22

3.4.2Solubility23

3.4.3Application direction, number of application, time between saturations of concrete23

3.4.4Concrete humidity23

3.4.5Penetration depth24

3.4.6Transport rate24

3.4.7Water/Cement ratio25

3.5Studies of Relevance to Task 13.4, Influence on mechanical properties25

3.5.1Freeze/thaw resistance25

3.5.2Compressive strength25

3.5.3Flexural strength26

3.5.4Permeability26

3.5.5Shrinkage27

3.5.6Reinforcement bond28

3.6Studies of Relevance to Task 13.5, Field trials28

4.Database of RECENT Relevant Publications29

1. INTRODUCTION

This report, a deliverable (D17) of Work Package WP13, presents key background information for the partners preparing the two later primary deliverables (D21 and D25) that will result from the Work Package. The information will be used to assist in the interpretation of the data generated in trials on concrete in the laboratory and the field. The primary deliverable (D25) will prepare the ground for addressing the specification issues for use of corrosion inhibitors in the maintenance of highway structures through technical documentation generated by the laboratory and field trials of inhibitors in WP13. The field trials will also be reported more fully as a separate main deliverable (D21) because of its particular interest to the end users of the SAMARIS project. The final conclusions regarding use of inhibitors as part of a repair strategy will be presented in Deliverable D31 of Work Package WP12.

The key background information presented in this report is structured as follows:

· mechanism study;

· literature findings of specific interest, presented by tasks (Task 13.1 to 13.5);

· database of relevant literature published in the last decade.

2. MECHANISM STUDY2.1 Introduction

Besides cathodic protection, the application of inhibitors is the most promising technique for the corrosion protection of concrete structures. Corrosion inhibitors are chemical compounds which can reduce, or even prevent, corrosion of metals. In general, these compounds act only if they are present in adequate concentration (otherwise their action is insufficient, or even aggressive localized corrosion may be induced). Their use has proved to be effective in the chemical process industry and power production. A group of mixed organic and inorganic compounds was proposed a few years ago as new effective corrosion inhibitors for reinforcing steel in concrete: they can be used as an admixture to the concrete, and also applied onto the concrete surface. It was claimed that they penetrate through the concrete to the steel and stop or retard corrosion.

The main goal of Task 13.1 of the SAMARIS project was to investigate the basic corrosion properties of mixed organic inhibitors for concrete. Three sub-goals were defined:

· to assess the efficiency of the inhibitors and to determine the factors which influence this efficiency,

· to determine the mechanism of steel passivation due to the inhibitors,

· to raise awareness of any eventual negative side-effects caused by the presence of the inhibitors.

In order to achieve these goals several laboratory tests in simulated concrete pore water were performed. These were as follows:

· exposure of steel specimens in water with analysis of corrosion damage and passive films,

· exposure of steel specimens in a salt-spray chamber and analysis of corrosion damage,

· determination of potentiodynamical polarization curves in simulated pore water,

· determination of electrochemical impedance spectra in simulated pore water,

· measurements of electrochemical noise with digitized imaging of corroded surfaces,

· investigation of passivation mechanism through measurements with ion-selective electrodes and Fourier-Transform Infrared Spectroscopy.

In the simulated pore water experiments the concentration of the inhibitors and the concentration of chlorides, were varied from the lowest to the highest values. In some experiments the inhibitor was added to the pore water at the very beginning (when the steel surface was still clean), whereas in the others the inhibitor was added after the corrosion already started. In the last group of experiments, the concentration of the inhibitor was gradually reduced after the passive condition was previously reached. The results of the measurements obtained in simulated pore water represent the basis for further investigations in concrete.

2.2 Investigation of factors influencing inhibitor behaviour2.2.1 Exposure of steel specimens

Exposure of steel specimens in aqueous solution with the added inhibitor showed that an adsorbed layer was formed on the steel surface. The layer protected the steel perfectly when the concentration of the chlorides was lower than 0,5%. No corrosion and no corrosion products were found (Figure 1). On the other hand, without the inhibitor rather general corrosion was observed.

In the second group of experiments steel specimens were, after the immersion into the inhibitor, exposed in a salt-spray chamber (Figure 2). Since this environment can be considered as a very corrosive, first corrosion spots were observed in less than an hour (the total duration of the exposure was approximately 20 hours). It should be noticed that at least in the first part of the test the corrosion damage of treated specimens was evidently more localized (Figure 2) than the damage of untreated ones (these specimens were not previously exposed to the inhibitor). After the test was finished, these localized corrosion areas were rather deep (Figure 3), and therefore the final corrosion condition of the treated specimens can be in general described as worse than the condition of the untreated specimens.

Figure 1: Exposure of steel specimens in aqueous solution with and without the added inhibitor

Figure 2: Exposure of steel specimens in a salt-spray chamber

Figure 3: Corrosion damage of steel specimen treated by the inhibitor after the exposure in a salt-spray chamber

2.2.2 Electrochemical measurement

In order to determine general corrosion properties of the inhibitor various electrochemical techniques were performed in simulated concrete pore water: potentiodynamic scans, electrochemical impedance spectroscopy, electrochemical noise combined with digitized imaging of electrode surfaces. As it was already mentioned, concentrations of the inhibitor and the chlorides were varied from the lowest to the highest values to obtain limiting conditions for passivation and corrosion initiation.

Retardation of corrosion (repassivation)

In this group of experiments the inhibitor was added after the corrosion already started in order to investigate whether and under which conditions the inhibitor could repassivate the steel. Measured potentiodynamic polarization curves indicated that by addition of the inhibitor the passive region appeared: by the increase of the inhibitor concentration this passive region became wider. On the other hand, the corrosion current and the corrosion potential were not evidently changed with the addition of the inhibitor. It could be therefore assumed that the potentiodynamic polarization curves could not reliably indicate the corrosion rate in the presence of the inhibitor. Since the corrosion potential does not change due to the inhibitor, it can be stated that the inhibitor can be classified as a mixed inhibitor. For this reason the reliability of the assessment of the inhibitor efficiency in concrete by using the potential-mapping and polarization rate measurements may be questionable.

Measured impedance spectra showed that after the initiation of corrosion the total impedance of the system was increased due to the addition of the inhibitor (Figure 4). However, even at the highest concentration of the inhibitor the total impedance was still lower than in pure simulated pore water. Presentation of the spectra as Nyquist plots indicated that under specific conditions (unstable passive state) two time constants appeared (Figure 5). Obviously in such cases the effects of the corrosion products and the initial passive layer due to the inhibitor are superimposed.

Measured electrochemical noise, especially current, proved that the inhibitor, which was added after the initiation, could retard the corrosion (Figure 6). It can be seen, however, that even at very high concentration of the inhibitor the corrosion process was not stopped completely – the current was still about 0,2 (A.

Figure 4: Electrochemical impedance spectra measured during successive additions of the inhibitor (presented as Bode plots)

Figure 5: Electrochemical impedance spectra measured during successive additions of the inhibitor (presented as Nyquist plots)

Figure 6: Electrochemical noise signals measured during successive additions of the inhibitor

Initiation of corrosion (prevention of corrosion)

In this group of experiments the inhibitor was firstly added to the pure simulated pore water, and afterward chlorides was successively added. The main goal of these experiments was to investigate whether the inhibitor additionally stabilize the passive state of clean, already passivated steel surface. It can be seen in Figure 7 that the inhibitor increased the total electrochemical impedance of the system, as well as changed the profile of the spectra. The significant reduction of the total impedance was observed when the chloride concentration reached a rather high value. From the measured spectra presented as Nyquist plots can be seen that the inhibitor considerably changed the shape of the spectrum (Figure 8). It can be therefore concluded that the structure of the passive layer due to the inhibitor differs from the layer in pure pore water.

Figure 7: Electrochemical impedance spectra measured during successive additions of chlorides after the passivation due to the inhibitor (presented as Bode plots)

Figure 8: Electrochemical impedance spectra measured during successive additions of chlorides after the passivation due to the inhibitor (presented as Nyquist plots)

Figure 9: Electrochemical noise signals measured during successive additions of chlorides after the passivation due to the inhibitor

Measured electrochemical noise did not exhibit any direct effect of the addition of the inhibitor: electrochemical voltage and current signals remained close to zero (Figure 9). Significant shifts in measured voltage and current were observed but not until the 8th addition of chlorides, when the total concentration of chlorides reached 1,5%. It can be therefore concluded that the inhibitor stabilized the passive layer and improved corrosion protection of steel.

Electrochemical noise measurements were performed also during alternate additions of chlorides and the inhibitor. It can be seen from Figure 10 that these additions of chlorides and the inhibitor induced alternating initiation of corrosion (regions II, VII, and XI) and repassivation processes. It can also be observed that, in the case of very high concentrations of chlorides and the inhibitor, an unstable repassivation/initiation of the corrosion process was generated (region XII). The phases of corrosion activity described above were confirmed by analysis of the digitized images captured by the computer visualization system in the first part of the test (up to region VII). After this, the thick layer of corrosion products combined by a precipitated layer due to the inhibitor made analysis of the images unreliable. It can be clearly concluded from this measurement that a critical ratio of concentrations inhibitor/chlorides exists: when the ratio is higher, the passive state is reformed, or corrosion is at least retarded; when the ratio is lower, the corrosion process in various forms (different degrees of localization) is initiated and continuing. Exact value of the critical parameter cannot be determined: in accordance with the results of previous measurements (Figures 4 to 9 inclusive) it can be stated that it is depended on various parameters, especially on the initial conditions of steel surface (presence of corrosion products).

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0

2000

4000

6000

8000

Real (Ohm)

-Imag (Ohm)

Simulirana porna voda

0,5% NaCl

0,1% inhibitor

0,2% inhibitor

0,5% inhibitor

1% inhibitor

2% inhibitor

Figure 10: Electrochemical noise signals measured during alternate additions of the inhibitor and chlorides

Stability of the passive layer (leaching of the inhibitor)

In the last group of experiments, the stability of the passive layer was investigated in order to simulate eventual leaching of the inhibitor from concrete. For this reason, the passive layer with the addition of the inhibitor was initially formed, and afterward the concentration of the inhibitor was gradually reduced. In accordance with previous electrochemical impedance measurements (Figures 4 and 7) can be seen in Figure 11 that the chlorides significantly reduced the total impedance of the system (initiation of corrosion), and that the subsequent addition of the inhibitor increased the total impedance again (repassivation). When afterward the concentration of the inhibitor was sequentially reduced (the concentration of chlorides remained constant), at a certain level the impedance of the system decreased once more (Figure 11). It can be therefore concluded that the passive state is actually a dynamic process influenced by the inhibitor and chlorides: obviously the ratio of inhibitor/chlorides concentrations should be maintained permanently for the long-term efficiency of the inhibitor.

A similar observation was made through electrochemical noise measurements: after the initiation of corrosion the passive state was re-established by the addition of the inhibitor (Figure 12). Afterward the concentration of the inhibitor was sequentially reduced and at a certain point significant shifts in voltage and current signals appeared. Evidently the corrosion process started when the ratio of inhibitor/chlorides concentrations decreased below the critical level, although the stable passive layer was previously formed.

Figure 11: Electrochemical impedance spectra measured during successive reductions of the inhibitor concentration (presented as Bode plots)

Figure 12: Electrochemical noise signals measured during successive reductions of the inhibitor

2.3 Investigation of passivation mechanism

All exposures and implemented electrochemical techniques confirmed that the inhibitor can, under certain conditions, repassivate steel in aqueous solutions. It was not clear, however, what the mechanism of the passivation was. Two main possible mechanisms were proposed:

· immobilization of chlorides,

· the formation of an adsorbed layer.

It was established that the ratio of inhibitor/chlorides concentration is the most important parameter for passivation. Therefore, one possible mechanism of the passivation could be immobilization of chlorides by the inhibitor. This would occur by transformation of free chlorides to a quaternary salt, which cannot influences the corrosion processes. In order to check this possibility, measurements with an ion-selective electrode (Ag/AgCl) were performed. As the basis, the response of the electrode at different concentrations of chlorides was determined (the electrode was not completely stable, but it was confirmed as reliable for the short-term indication of free-chloride concentrations). Measurements were performed at a certain level of chloride concentration with successive additions of the inhibitor (Figure 13): it can be clearly seen that even the significant increase of the inhibitor concentration only slightly affected the response of the ion-selective electrode. It was therefore concluded that the immobilization of chlorides by the inhibitor could not be the main mechanism of passivation.

In order to investigate eventual layers on steel surface, formed by the inhibitor, steel specimens were immersed into the inhibitor for a certain period (three times per hour, cyclically dried in air) and analysed. For the surface analysis of the passivated steel specimens FTIR (Fourier-Transform Infrared Spectroscopy) was chosen: this technique is able to detect a wide range of inorganic and organic compounds. Two main groups, which are very probably responsible for the passivation, were found by the analysis of measured FTIR spectra (Figure 14): amino-alcohol group, and phosphorous compounds. It was not the goal of this study to determine exactly the composition and the structure of these groups in the surface layer, neither their adsorption energy – we can only conclude at this stage, that the main mechanism of the passivation due to the inhibitor is the formation of an organic/inorganic adsorbed layer at the steel surface layer. For usual conditions in pore water this layer is very probably combined with the oxide/hydroxide passive layer at steel surface. In accordance with the results of our electrochemical measurements it can be assumed that the formation of this organic/inorganic adsorbed layer is more difficult when corrosion products already exist at the steel surface.

Figure 13: Response of ion-selective electrode during successive additions of the inhibitor

Figure 14: FTIR spectrum of steel specimen treated by the inhibitor

It can be expected that the concentration of the inhibitor near rebars (penetration) is crucial for its effectiveness in concrete and that the long-term concentration of the inhibitor near rebars must take account of the issues of decrease over time due to leaching and evaporation.

2.4 Conclusions

From the measurements in concrete simulated pore water the following main conclusions can be drawn:

1. all tests in simulated pore water solution proved that the inhibitor can reduce corrosion: the most important parameter is the ratio of inhibitor/chlorideconcentration,

2. the critical concentration ratio is strongly dependent on the steel surface conditions: after the initiation of corrosion this ratio should be quite high for the retardation of corrosion and if the steel is heavily corroded complete repassivation is practically impossible,

3. the efficiency of the inhibitor in pure water with lower pH (simulated carbonated concrete without chlorides) cannot be exactly assessed, because the inhibitor shows a buffering effect,

4. passivation due to the inhibitor is reached by the formation of an adsorbed layer on the steel surface,

5. when the critical concentration ratio is not reached, the layer is partly destroyed, and the corrosion damage is rather localized (localized corrosion spots can be relatively deep),

6. when the stabilization of the passive state is reached due to the inhibitor and consequently the concentration of the inhibitor is reduced, the initiation of corrosion might occur (the ratio of concentrations inhibitor/Cl- is critical also in such cases).

3. Further Experience from Selected Published STUDIES3.1 Criteria for selection

A review of over 50 papers and reports on corrosion inhibitors revealed a wide range of issues of general relevance to the objectives of Work Package WP12 and WP13 of the SAMARIS project. This will be used more extensively in later reports. A subset of issues of direct relevance to the interpretation of the results of Work Package WP13 Tasks 13.1 to 13.5 inclusive were identified for early dissemination to the WP13 partners to inform debate on the two main deliverables of the work package. A further criterion therefore was reference to inhibitor types of greatest relevance: aminoalcohol-based inhibitors.

Aminoalcohol-based inhibitors are typically dual effect inhibitors (or mixed inhibitors). They give both cathodic and anodic protection. They are layer forming and can be classified as adsorptive. The following results are primarily based on ethanolamine (EA), dimethylethanolamine (DMEA) and mixed Ferrogard (AMA-based with other organic and inorganic inhibitors). The results are set out in the sequence of the tasks of Work Package WP13.

3.2 Studies of Relevance to Task 13.1, Basic Mechanism Study

Two possible mechanisms of passivation are suggested: bounding of chlorides to the quaternary salt, and formation of the passive layer due to adsorption of the amino group on the steel surface (both processes probably take place simultaneously). It was found that the addition of the inhibitors to pore water solution formed gel-like complexes. For this reason, beside the mechanisms mentioned above, an additional mechanism for the retardation of steel in concrete is possible: the gel impregnates the steel surface, and thus the penetration of chlorides, oxygen, and water is reduced.

There exist several classification models. One of them divides the corrosion inhibitors in two categories:

· adsorptive,

· layer forming.

Most of the inhibitors have a double effect.

Adsorption inhibitors are the largest group of inhibitors. They are typically organic compounds (eg. amines, aminoalcohols, fatty acids) that suppress both the cathodic and anodic reactions on the metal surface. Research increased substantially during the last 20 years and various chemicals have been investigated, among these are benzoates of amines and morpholine. Amines, alkanolamines and salts have been patented for different applications such as reinforcement protection in concrete [1,2]

DMEA (dimethylethanolamine), a typical ingredient of such inhibitors, absorbs on mild steel in layers of roughly 20 Å and neutralized AMAs form layers of roughly 100 Å. XPS reveals that hydroxide groups and anions, normally strongly adsorbed on the steel surface, are replaced by AMA. AMAs can displace chloride, other ionic species and carbon from mild steel in a chloride environment, with chloride/AMA ratios varying from 1 to 20. The AMA layers cannot easily be removed by rinsing the steel with water due to the formation of chelate complexes with the iron ions [1,3].

Anodic inhibitors accept electrons. The reaction takes place on the anode. Cathodic inhibitors increase the pH of the medium and thereby decrease the solubility of ferrous ion. Mixed inhibitors contain molecules in which electron density distribution causes the inhibitor to be attracted to both anodic and cathodic sites.

AMA-inhibitor is an effective inhibitor in neutral and alkaline solution. The increased concentration correlates with an increased effect. This indicates a thicker layer formation. The protective layer is effective when it is built up. It was uncertain if the layer formation takes place when the chlorides are present in the solution at the beginning. Further work has shown that the layer is formed even at high chloride levels [3].

Contact angle measurements show increased hydrophilic behaviour of the surface with AMA-layer when the steel was exposed to AMA-solution [3].

Water-based organic admixtures, consisting primarily of amines and fatty acid esters, an admixture made up of organic amides in an aqueous medium, and a product, which is basically an aqueous solution of dimethylaminoethanol, functions by:

· reducing chloride ion ingress into concrete and

· forming a coating on the surface of the embedded steel [4]

Cathodic inhibitors act either by slowing the cathodic reaction or by selectively precipitating cathodic sites. Materials in this group are strong proton acceptors and their action, in contrast to anodic inhibitors, is usually indirect [5].

Organic-based corrosion-inhibiting admixtures (OCIA) function by providing a physical barrier to the ingress of aggressive agents or by chemically stabilizing the steel surface [9].

OCIA inhibit corrosion by the same mechanism as that of other organic corrosion inhibitors – by adsorption on the metal surface. It is generally accepted that organic corrosion inhibitors bond to metals by adsorption, physically and/or chemically, due to the polar or weakly polar characteristic of the organic compounds typically used in their formulation The following excerpt gives a basic understanding of organic corrosion inhibitor or filming inhibitor technology:

“ The mechanism by which all materials function is the same and requires their adsorption onto the metal through their polar group or head. The nonpolar tail of the inhibitor molecule is oriented in a direction generally vertical to the metal surface. It is believed that that the hydrocarbon tails mesh with each other in a sort of “zipper” effect to form a tight film which repels aqueous fluids, establishing a barrier to the chemical and electrochemical attack of fluids on the base metal. A secondary effect is the physical sorption of hydrocarbon molecules from the process fluids by the hydrocarbon tails of the adsorbed inhibitor molecules. This increases both the thickness and effectiveness of the hydrophobic barrier to corrosion.” (Corrosion Inhibitors, C.C. Nathan, ed., National Association of Corrosion Engineers, 1973, 279 pp.) This process also is applicable to OCIA [9]

The layer formed by OCIA, enhances the naturally occurring passive layer on the steel surface and offers a significant resistance to the detrimental effect of chloride ions [9].

The organic inhibitors used for the protection of steel in concrete are often amines, amino-alcohols or gluconates. In contact with a metallic surface in an alkaline medium, these products form a layer (film) that acts on the dissolution of the iron (anodic inhibitor). This layer is very thin and is fixed mostly on the surfaces [16].

An inhibitive effect was experienced particularly with triethanolamine, monoethanolamine, and methydiethanolamine. Alkanolamine salts of organic and inorganic salts were also found to reduce the steel corrosion rates and to be compatible with the concrete matrix [23].

Migrating Corrosion Inhibitor (MCI) technology was developed to protect the embedded steel rebar/concrete structure. Recent MCIs are based on amino carboxylate chemistry and the most effective types of inhibitor interact at the anode and cathode simultaneously. Organic inhibitors utilize compounds that work by forming a monomolecular layer between the metal and the water. In the case of layer forming amines, one end of the molecule is hydrophilic and the other hydrophobic. These molecules will arrange themselves parallel to one another and perpendicular to the reinforcement forming a barrier. The breakdown potential for the rebar tested with no inhibitor was around +350 mVSCE and improved +600 mVSCE for the rebar tested with 2000 ppm MCI. While only a minor improvement was observed in an alkaline environment similar to the concrete medium. The MCI treated concrete polarization resistance showed increasing trends (improved from 9-10 kohm to about 70-85 kohm) during these tests, while untreated samples had declining trends. MCI protected samples showed an average current density of 0.4(A/cm2 compared to untreated samples with 1.4(A/cm2. This behavior will increase the life expectancy by more than 15-20 years [31].

It is interesting that the measured values of half-cell potential for the bars showed no sudden rise in value that matched the observed drop in corrosion current. Instead the half-cell potentials showed a steady rise to more positive values in the region –300 to –400 mV. At such values the bars might still be expected to be corroding. That they are not suggests that in some way the changes in corrosion current and half-cell potential have become decoupled in a manner not exhibited in ponded samples. This may result from the multi-functional action of the amino alcohol inhibitor which is thought to form an adsorbed inhibitive layer (( 10-8 m thick) on the surface of the steel that is capable of displacing chloride and other ions. This layer and the associated retarding radicals are thought to suppress both anode and cathode reactions. Thus the gradual change in half-cell potentials observed may reflect the build-up of an increasing concentration of inhibitor which is eventually to close down the active corrosion sites [32].

In high performance concrete, the bars at 40 mm show virtually no change in behaviour over the first 20 days but subsequently show a steady drop in current reaching values of 0.1 mA/m2 after 40 days. This delayed action is thought to be related to the finite time the inhibitor takes to migrate through high quality, low permeability, cover concrete and raises the question: is there a level of concrete quality above which such surface applied inhibitors cannot reach bars at deep cover depths? [32]

Secondary ion mass spectroscopy (SIMS) has identified the surface layer to be composed of the parent AMA and the associated radicals, which completely cover all the anodic and cathodic sites. The results showed that AMAs form a continuous inhibitive layer and displace chloride and other ions from the surface. The investigations revealed that DMEA (dimethylethanolamine), a model compound in such inhibitors, absorbs on mild steel in layers of roughly 20 Å and neutralized AMAs form layers of roughly 100 Å thickness. The XPS (X-ray photoelectron spectroscopy) spectra reveals that hydroxide groups and anions, normally strongly adsorbed on the steel surface, are replaced by AMA. AMAs can displace chlorides, other ionic species and carbon from mild steel in a chloride environment, with chloride/AMA ratios varying from 1 to 20. The AMA layers cannot easily be removed by rinsing the steel with water. The formation of chelate complexes with the iron ions at the steel surface has therefore to be seriously considered [36].

Aminoalcohols such as ethanolamine (H2N-CH2-CH2-OH) and dimethylethanolamine ((CH3)2N-CH2-CH2-OH) control corrosion by attacking cathodic activity, blocking sites where oxygen picks up electrons and is reduced to hydroxyl ion. They may adsorb at anodic sites as well. One study examined the inhibition effect of a commercially available complex inhibitor containing 15% nitrite and an aminoalcohol on Type 304 stainless steel electrodes immersed in lime water solutions for up to 72 h using a potensiostat. A synergistic effect was observed, combining the effect of nitrite on ferric ion precipitation with the known layer-forming properties of hydroxyalkylamines. The corrosion current in the presence of 3% NaCl was reduced at pH 12.67 by a factor of 2.5 and at pH 9.37 by a factor of 5.4 [37].

Below 1 M (about 9% by weight), DMEA (dimethlyethanolamine) adsorbed on the steel oxide surface in slightly more than monolayer thickness (between 0.75 and 0.9 nm) (X-ray photoelectron spectroscopy). Higher concentrations (> 2 M) cause more adsorption, but only up to a bilayer thickness. DMEA is strongly and irreversibly adsorbed and cannot be completely rinsed off the iron oxide surface. Immersion of steel in solutions containing both DMEA and NaCl for 5 min was sufficient to reach equilibrium: DMEA was found to partially displace chloride from the iron oxide surface. These observations suggest that inhibition of corrosion occurs through a mechanism whereby DMEA displaces chloride ion and forms a durable passivating layer. In this view, although the aminoalcohols adsorb on non-corroding sites which may seem more cathodic than anodic, they can just as easily be said to adsorb on potentially anodic sites [37].

An organic corrosion inhibitor (OCI) comprising an aqueous emulsion of ester and aminoalcohol is a mixed inhibitor, affecting corrosion through a combination of active and passive mechanisms. A study extending over a decade investigated the active part, a layer-forming aminoalcohol which is generally taken to be a cathodic inhibitor. The passive part of the OCI mechanism reduces permeability by hydrolysis of an organic ester and deposition of insoluble calcium salts of fatty acid which hydrophobe the concrete pores to reduce ingress of chloride ions. A reduction of 56% in the capillary absorption rate was seen for the OCI-treated concrete. The OCI admixture reduces the chloride build-up rate, reduces the chloride diffusion coefficient, moderately increases the chloride threshold and slows the rate of corrosion after initiation. The insoluble salts appear to have long persistence in the concrete [37].

3.3 Studies of Relevance to Task 13.2, Chloride and inhibitor concentration

The effectiveness of the inhibitors is dependent on a number of variables, such as chloride content, concrete permeability, degree of carbonation and inhibitor concentration.

3.3.1 Chloride content

In many design and specification related references, it has been suggested that a total chloride content of:

· 0,4% produces a low risk of corrosion

· between 0,4% and 1% produces a medium risk

· greater than 1% produces a high risk

Hence, the inhibitors appears to be able to reduce the rate of corrosion in chloride contaminated concrete, that would normally have mid to high risk of corrosion (eg. improperly washed sea sand, salt bearing atmosphere, roads and bridge decks) [1].

Inhibitors’ effectiveness is strongly affected by the presence of chloride ions. To ensure this effectiveness the ratio between inhibitors and Cl- has to be relatively high (approximately 1) (Legat et. al. 1998, Elsener et. al. 1999). To ensure the required structural safety as well as effective corrosion protection, therefore, mechanical and durability properties of concrete with inhibitor, especially its compressive strength, should be tested prior to its use on site [2].

In tests with calcium nitrite, sodium monofluorophosphate and ethanolamine based treatments moderate reductions in the overall rates of corrosion were observed after the inhibitive treatments had been applied to those specimens in which levels of chloride contamination were fairly low (0.6% Cl- by weight of cement), particularly in the case of calcium nitrite. None of the inhibitors, however, functioned effectively in concrete with high levels of chloride contamination (2.4% Cl- by weight of cement) [22].

Similar behaviour was noted with an admixture type corrosion inhibitor (AMA) and a commercial nitrite based corrosion inhibitor at different concentration and different chloride contents. The pitting potentials indicate that the passive domain is left as soon as chlorides are present in some amount. However, it is difficult to draw conclusions about the critical chloride ratio, based on these measurements, as the measurements were performed in solution and not under real conditions in concrete or mortar. In the case of nitrite based inhibitors the nitrite/chloride ratio for effective corrosion prevention is given. The mixed corrosion inhibitors reduces the rate of corrosion in chloride contaminated concrete (1% of Cl- by weight of cement). Such a limit would also be in line of the measurements where a limit of approximately 1.2% was estimated [36].

3.3.2 Degree of carbonation

In tests on carbonated specimens the electrochemical monitoring results signified that no substantive inhibition of corrosion was produced by any of the three treatments if even low levels of chloride (0.3% Cl- by weight of cement) were present (calcium nitrite, sodium monofluorophosphate and ethanolamine based treatments) [22]. It should be noted in this context that chloride contents as low as 0.3% Cl- by weight of cement lie within the range permitted for reinforced concrete according to codes of practice such as BS 8110:1997.

Tests with penetrating corrosion inhibitor (PCI) showed excellent penetration into the test specimens in a relatively short period of time. The penetration of the inhibitor, however, is thought to be slower through carbonated concrete due to its denser microstructure. Inhibitors sometimes tend to simply migrate through concrete without leaving a protective layer around the reinforcement. In this study, the penetration results for both specimens treated with the inhibitor before and after carbonation showed that adequate amounts of the PCI were present at the level of the reinforcement at 1, 5 and 10 months. The corrosion rates of the specimens where the PCI was applied before and after the carbonation process showed much lower values of corrosion rates in comparison to the control samples. Further, the specimens treated with the inhibitor before and after the carbonation process showed a steady decrease in corrosion rate, gradually reaching the 0.1 (A/cm2 line [30].

3.3.3 inhibitor concentration

A unique organic-based corrosion-inhibiting admixture (OCIA), a combination of amines and esters in a water medium, has been developed as an alternative approach for protecting steel reinforcement. The recommended dosage for OCIA is 1 gal/yd3 (5.0 l/m3) of concrete [9].

As far as alkanolamine is concerned, its action depends of the concrete proportions tested. For concrete of lower density, with less than 6 l/m3 of alkanolamine, the equivalent of corrosion rate is lowered. However, when inhibitor content is higher, the inhibition action is no more effective. For concrete of higher density, the best inhibitor content is about 6 l/m3 . So, for the higher values of alkanolamine content, the inhibition is less efficient. The inhibition process is not clear. It is possibly due to the formation of a layer which is not stable in concrete when it is too thick. However, this assumption needs to be confirmed [17].

3.3.4 Concrete cover thickness

The results of the tests conducted on 20 MPa concrete indicated that the inhibitor did not delay the onset of corrosion when the reinforcement was embedded at 25 mm cover. The high permeability of the concrete caused a rapid ingress of chloride. At 50 mm cover (20 MPa concrete), the inhibitor appeared to delay the onset of corrosion and lower the actual corrosion thereafter. The corrosion rates of the specimens with 4% and 6% inhibitor were considerably less than their respective control specimens. Larger doses of the inhibitor may decrease the corrosion rate further. Corrosion rate data of 40 MPa concrete shows that at 25 mm and 50 mm cover, the inhibitor caused a significant delay in the onset of corrosion in all the specimens with the ACI (admixture inhibitor). Also, the corrosion rate of these specimens was considerably lower than that of the control specimens [30].

In the 20 MPa concrete specimens the inhibitor was found to be ineffective at 25 mm cover due to high chloride concentration (> 2.0%). Similarly, at 50 mm cover only short-term inhibition was observed (chloride concentration > 1.50%). In the 40 MPa specimens at 25 mm cover, chloride concentrations varied from 1.23% to 2.15%. Definite signs of corrosion inhibition were observed. At 50 mm cover chloride concentrations were well above the threshold value at the point the PCI (penetrating corrosion inhibitor) had reached the reinforcement. A positive performance of the inhibitor could therefore not be observed [30].

3.4 Studies of Relevance to Task 13.3, Concrete permeability

SAMARIS project WP13 is only investigating inhibitors applied as liquids to the surface.

There are a number of factors likely to influence the rate at which an inhibitor solution penetrates into a concrete. The inherent properties of the concrete (mix design, strength, age, degree of carbonation, chloride level etc), environmental conditions during application and subsequently, concentrations of inhibitor, and duration of treatment, could all be important.

3.4.1 Strength

It was found that the organic parts of the inhibitor (AMA) are transported through the concrete matrix with still an enrichment in the first layer (470 and 392 ppm respectively). In the concrete grade A the concentrations then decreased rapidly whereas in the concrete grade B significantly higher amounts were found, especially in deeper layers (23-30 mm and 33-40 mm). This clearly indicates that the transport is dependent on the concrete grade (w/c, degree of hydration) and the humidity conditions the concrete is stored at [32].

A true indication for a penetration of the corrosion inhibitor was also found by Alexander et al. where the determination of the AMA was performed qualitatively using a colour reaction caused by ninhydrine. In this study different grades of concrete were prepared (strength values of 20, 30, 40 and 50 N/mm2 after 28 days) and subjected to carbonation. The penetration found also shows a clear dependence on the grade of the concrete (hence porosity). However, a penetration beyond the depth of the reinforcement is clearly demonstrated [36].

On the other hand results of an investigation performed by Tritthart showed insufficient or no penetration at all. These tests were performed on laboratory specimens in pure cement paste. The active components of the corrosion inhibitor were determined by expressing the pore solution of the specimens and subsequent ion chromatography of this solution. It has been assumed that a pore blocking by gel formation of the inorganic component were made responsible for these results. However, in a real structure the author also found significant amounts of AMA in deeper concrete layers [36].

All these results at hand to date indicate that the mixed corrosion inhibitors actually penetrate the concrete, however at a lower rate than the previously supposed 10 mm/day [36].

3.4.2 Solubility

All but one inhibitor studied in tests (calcium nitrite and organic admixtures were sufficiently soluble to obtain a uniform mix. Even when mixed with warm water one of the organic admixtures proved impossible to disperse in solution [47].

3.4.3 Application direction, number of application, time between saturations of concrete

Whether is applied horizontally, vertically or overhead, the final distribution of the inhibitor is similar. Thus gravitation does not seem to have a significant influence on the transport properties of the inhibitors [1]. If the penetration is done by pure diffusion, the diffusivity of the product in the concrete may be replaced by the speed (penetration rate) expressed in length by mean-square of the time (cm.day-1/2). But it should be mentioned that this penetration is not done by simple diffusion and the fact of applying the product in several coatings changes the process of penetration and accelerates it [16].

Typical supplier’s recommendations for ethanolamine (14% aqueous solution with potassium di-hydrogen phosphate) involve five applications by brush at a recommended total inhibitor dosage of 750 g/m2 to surface dry concrete with intervening periods of drying [22,28].

3.4.4 Concrete humidity

Inhibitors tested at different humidity levels (50% and 95% RH) did not exhibit significantly different transport rates. However, somewhat higher rates are expected under dry conditions [1].

3.4.5 Penetration depth

Studies show an enrichment below the surface 3 days after the application and almost even distribution of the inhibitor within the concrete matrix 28 days after its application [1]. Ion chromatography, applied to aqueous extracts obtained from powdered concrete samples, yielded results indicating significant penetration of nitrite and ethanolamine at depths (12-18 mm) corresponding to the embedded steel bars [22].

For detailed reference on ion chromatography see reference 28. When ethanolamine and nitrite were applied to the surface of concrete, their penetration into concrete samples was readily detected by means of ion chromatography. In the case of monofluorophosphate-treated concrete, only the hydrolysis products, fluoride and phosphate, were detected in solution and not the monofluorophosphate ion itself [28].

Reference [31] includes SEM images of the concrete sample coated with MCI 2020M and rebar, its spectrum and the weight concentration percentage for elements typically found in concrete, corrosive species and steel rebar. For the untreated sample, nitrogen, the active component for MCI corrosion inhibitors was not detected. The presence of nitrogen on the rebar surface is significant in that it confirms the inhibitors are able to migrate through the concrete to reach the surface of the rebar.

An XPS detector (X-ray Photoelectron Spectroscopy) can analyze a much larger area than an SEM point analysis, providing a more comprehensive evaluation of surface chemistry. From the XPS depth profiling, chloride was detected at depths down to 60 nm from the analysis surface on the rebar; concentrations were approximately 0.44 weight percent for the untreated smple and roughly 0.14 wt % for the treated samples. Nitrogen was detected at levels down to 75 nm on the MCI 2020 sample and as far down as 85 nm on the MCI 2020M sample. The XPS results demonstrate that MCI and the corrosive species have comparable diffusion rates. The MCI inhibitors provided a protective layer on the rebar surface, the untreated samples, however, were attacked by localized corrosion [31].

3.4.6 Transport rate

An average transport rate of 10 mm/day in standard concrete and mortars have been reported [1]. The penetration rate occurs at values of about 2-20 mm per day. The transport rate was found not to be depending on neither the humidity level nor the transport direction. The transport distance of 70 mm was detected – this represented the maximum distance tested [3].

Penetrating corrosion inhibitor applied after a period of 4 months penetrated into the concrete at a very slow rate. After 4 months, the PCI reached the reinforcement at 50 mm cover in low concentrations and only after 9 months could be a sufficient concentration observed. The PCI was found to penetrate slowly into chloride-contaminated concrete but was still able to reach steel at covers of 50 mm. High moisture contents and surface chloride concentrations were thought to be responsible for the relatively slow penetration of the PCI into the concrete specimens. The relatively slow penetration of the PCI into chloride-contaminated concrete was also apparent when testing structures during field trials. Some concrete structures exposed to marine environments required periods of almost a year for the PCI to penetrate to depths of 50 mm [30].

Migrating corrosion inhibitors are able to penetrate into existing concrete to protect steel from chloride attack. The inhibitor migrates through the concrete capillary structure, first by liquid diffusion via the moisture that is normally present in concrete, then by its high vapor pressure and finally by following hairlines and microcracks. The diffusion process requires roughly 120 days to reach the rebar surface and to form a protective layer [31].

3.4.7 Water/Cement ratio

It has been recorded that the transport rate depends on W/C and the degree of hydration of the concrete matrix [1]. This is in addition to issues reported in the previous section.

3.5 Studies of Relevance to Task 13.4, Influence on mechanical properties

3.5.1 Freeze/thaw resistance

The presence of inhibitors has a beneficial effect upon freeze-thaw surface scaling resistance for both in-mass and surface inhibitors. However an over-dose of the inhibitor can lead to a slightly increased mass loss. Internal freeze-thaw resistance was tested according to the standard ASTM C 666 (1977). No significant influence of the presence of inhibitor upon the internal freeze-thaw resistance of concrete regardless of its content [2].

At the end of 300 freeze-thaw cycles (ASTM C 666), a durability factor of 96 percent was obtained for OCIA-treated concrete relative to the reference concrete. This indicates that OCIA will not affect the freezing and thawing resistance of concrete [9].

3.5.2 Compressive strength

There is no apparent detrimental effect of the AMA containing inhibitor (the one day strength was observed to increase in some cases and decrease in other cases) [1].

The influence of inhibitor is lowest when the concentration corresponds to the value recommended by the producer. Both lower and higher inhibitor concentrations results in a significant decrease of compressive strength (72-82%) when compared to the reference concrete with no inhibitor added (after 7, 28 and 90 days) [2]

Test data obtained through one year indicate that OCIA has a marginal effect on compressive strength [9].

Organic esters and amines (OEA) and commercial inhibitors (CI) had compressive strengths less than those of the control concrete. Indeed, the average compressive strengths observed for CI specimens were approximately 27 and 30% lower than the average control concrete strengths at 28 and 365 days of age, respectively. The average strength values of the next lowest series, OEA, compared with control concrete, were 11% lower at 28 days of age, and 13% lower at 365 days of age [27].

Strengths higher than that of the control concrete were observed in the concrete containing CNR (calcium nitrite solution), AA1 (amino alcohol), AA2 at all ages (3, 7, 28 and 365 days). The highest concrete strengths were observed in concrete containing CNR and AA1. At 28 days of age, both of these mixtures had compressive strengths approximately 20 to 22% higher than that of the control concrete. At 365 days of age, the average compressive strength for CNR and AA1 mixtures was approximately 17% higher than the average compressive strength of the control concrete [27].

The one day compressive strength was observed to increase in some cases and to decrease in other cases. The compressive strengths at 7 and 28 days were usually not adversely affected upon addition of 2-4% inhibitor (AMA) [36].

The addition of corrosion inhibitor to the OPC concrete led to reduction of compressive strength. The ultimate strengths of OCI and PMC (polymer modified cementitious repair material) mixes are similar for both curing conditions and 13% lower than that of the OPC concrete. The reduction in strength of the OCI mix may be attributed to the organic component of the corrosion inhibitor which interferes with the hydration process [41].

3.5.3 Flexural strength

Organic inhibitor OCIA had a marginal effect on flexural strength through 180 days. The strength differences between the references and treated concretes were less than 10 percent [9].

3.5.4 Permeability

OCIA had no effect on the coulomb rating of concrete. This indicates that OCIA does not decrease the electrical resistivity of concrete. At the end of the 48-week test period, the resistance of the concrete specimens containing OCIA was marginally higher than that of the reference specimens, 405 ohm versus 350 ohms [31].

Data indicate a decrease in chloride-ion content in the OCIA-treated concrete, particularly in the 0.5 to 1 in. (12 to 25 mm) depth. The trend is consistent with chloride-ion data obtained from time-to-corrosion tests, and further confirms that OCIA is effective in reducing chloride-ion into concrete [9].

ASTM C 1202-94 “Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration” is not an exact measure of permeability, but an indicator. Excerpted from ASTM C 1202-94, a total charge passed of 4000 coulombs is the threshold value above which concrete is considered to have high chloride ion penetrability. Average chloride penetrability by electrical conductance results for each series at 28 days of age were very close to or exceeded 4000 coulombs charge passed. At 365 days of age, however, the average charge passed for all series were within the moderate range for chloride ion permeability [27].

Diffused chloride was highest for the control concrete, even though the total charge passed under the electrical conductance test was near the median of all the groups [27].

The manufacturer of OEA (organic ester and amines) states that the OEA reduces the rate of ingress of chlorides and moisture as the product’s first line of corrosion defence. OEA did indeed exhibit a much lower level of diffused chloride than the control mixtures. Comparison of electrical conductance test results for OEA agree with the diffused chloride results, showing a lower average total charge passed. Previous research of a similar product produced by the same manufacturer demonstrated no significant difference in the ability to reduce chloride ingress for a single plant mixture batch [27].

For AA1 (amino alcohol), electrical conductance for chloride penetrability values and diffused chloride contents were both less than the control. The total charge passed for AA1 at 28 days age was less than 4000 coulombs, placing that material in the moderate range for permeability, while the control at that age was considered highly permeable. At 365 days of age, ASTM C 1202-94 results for AA1 and the control were comparable, and both would be considered moderately permeable to chloride ion. Diffused chloride in AA1 specimens after 2 years was significantly lower than the control. Therefore, early retarding effects were evident, but did not extend beyond the earliest phases of curing [27].

Concrete containing AA2 (amino alcohol) had significantly less diffused chloride at reinforcement depth, and electrical conductance values were very similar to the control. Concrete containing AA2 in this study would also be classified as moderately permeable. The AA2 admixture produced significant benefits in reduction of concrete permeability and long-term strength development. Of interest is the high variability in diffused chloride content of this CIA as compared with the control [27].

CI (commercial inhibitor) had significantly less diffused chloride at reinforcement depth, but its electrical conductance values were significantly higher than the control. The higher conductance values and lower compressive strengths seem to be complementary but are contradicted by reduction of diffused chloride [27].

OCI shows the highest oxygen and water permeability at all ages, in both curing conditions [41].

3.5.5 Shrinkage

Inhibitor can decrease the drying shrinkage. When used at concentrations recommended by the producer, shrinkage at 210 days decreased by approximately 20% for all inhibitor types [2].

The shrinkage characteristics of concrete are not affected by the use of OCIA (ASTM C 157) [9].

3.5.6 Reinforcement bond

The bond strength developed between concrete and steel is not affected by OCIA. In an independent evaluation, a normalized bond strength of 5920 lb/in. (1040 N/mm) was obtained for untreated concrete, with corresponding values of 6280 and 5750 lb/in. (1100 and 1010 N/mm) for concrete treated with OCIA at dosages equivalent to 1 and 2 gal/yd3 (5.0 and 10.0 l/m3), respectively. On the basis of equal compressive strength, it was concluded that, there is no difference in bond strength between the reference and OCIA-treated concretes, even at a dosage rate twice that recommended for corrosion inhibition [9].

3.6 Studies of Relevance to Task 13.5, Field trials

A detailed review will be included in Deliverable D21 however some initial points of general relevance to the laboratory programmes are worthy of note in the context of this report.

From Reference [33] three scenarios seem possible when considering applying inhibitor to a structure:

· The corrosion is very advanced (ie there is a high anodic activity) at the onset of treatment and an excessive quantity of inhibitor will be required to be available immediately and in the future.

· A high moisture/oxygen content is present within the concrete cover resulting in the cathodic reaction being “well-fed” at the cathode with the consequence that the corrosion reaction at the anode is high. This too may require a high usage of S-ACI (surface applied corrosion inhibitor).

· More commonly, a condition between the first two points may exist where the onset of corrosion may be staved off by the use of S-ACI. Alternatively where the existing corrosion rates, carbonation and chloride concentrations are at more moderate levels resulting in the S-ACI coping well for an acceptable period of time, perhaps five to ten years even without surface protection (although this should usually be considered).

See Reference [1] includes information on mortar and concrete tests in the marine environment:

· None of the specimens (W/C = 0,45, spray) with 3% inhibitor has started to corrode at the time of reporting;

· The chloride ion threshold value for W/C = 0,6 (sprayed) with 3% inhibitor was found to be 50% higher than for the reference mortar.

4. Database of RECENT Relevant Publications

The following publications have been assembled as a reference source for the Work Package.

1. Maeder, U., “A New Class of Corrosion Inhibitors for Reinforced Concrete”, Proceedings of the 9th Asian-Pacific Corrosion Control Conference, Corrosion Protection for Industrial Safety and Environmental Control, Kaosihung, 1995.

2. Selih, J., Legat, A., “Influence of Reinforcement Corrosion Inhibitors on the Durability and Mechanical Properties of Concrete”

3. Laamanen, P.H., Byfors, K., “Corrosion Inhibitors in Concrete – AMA (Alkanolamines) – based Inhibitors – State of Art Report

4. Nmai, C.K., Krauss, P.D., “Comparative Evaluation of Corrosion-Inhibiting Chemical Admixtures for Reinforced Concrete”, Concrete Durability

5. Vaysburd, A.M., Emmons, P.H., “Corrosion-Inhibiting Admixtures and Other Reinforcement Protection Systems in Concrete Repair: Desire and Reality”

6. Alonso, C., Andrade, C., “Effect of Nitrite as a Corrosion Inhibitor in Contaminated and Chloride-Free Carbonated Mortars”, ACI Materials Journal, V.87, No.2, March-April 1990, pp. 130-137.

7. Jin, S.X., Sagoe-Crenstil, K.K., Glasser, F.P., “Characteristics of corrosion inhibition admixtures in OPC paste with chloride additions Part I: Chemistry and electrochemistry”, Magazine of Concrete Research, 1991, 43, No. 156, Sept. 205-213.

8. Jin, S.X., Sagoe-Crenstil, K.K., Glasser, F.P., “Characteristics of corrosion inhibition admixtures in OPC paste with chloride additions Part II: Microstructures and mechanisms”, Magazine of Concrete Research, 1991, 43, No. 157, Sept. 275-280.

9. Nmai, C.K., Farrington, S.A., Bobrowski, G.S., “ Organic-Based Corrosion-Inhibiting Admixture for Reinforced Concrete”, Concrete International, April 1992.

10. Andrade, C., Alonso, C., Acha, M., Malric, B., “Preliminary Testing of Na2PO3F as a Curative Inhibitor for Steel Reinforcement in Concrete”, Cement and Concrete Research, Vol.22, pp.869-881, 1992.

11. Sagoe-Crenstil, K.K., Yilmaz, V.T., Glasser, F.P., “Corrosion Inhibition of Steel in Concrete by Carboxylic Acids”, Cement and Concrete Research, Vol. 23, pp. 1380-1388, 1993.

12. Sagoe-Crenstil, K.K., Glasser, F.P., Yilmaz, V.T., “Corrosion Inhibitors for Mild Steel: Stannous Tin (SnII) in Ordinary Portland Cement”, Cement and Concrete Research, Vol. 24, No. 2, pp. 313-318, 1994.

13. Raharinaivo, A., “Action des monofluorophosphates sur la corrosion des armatures dans le beton”, Synthese d’etudes faites au Laboratoire Central des Ponts et Chaussees avec le Laboratoire Regional de l’Est-Parisien et le LERM, Ref: DT/OAM/AR 81-96, 6 mai 1996.

14. Alonso, C., Andrade, C., Argiz, C., Malric, B., “Na2PO3F as Inhibitor of Corroding Reinforcement in Carbonated Concrete”, Cement and Concrete Research, Vol. 26, No. 3, pp. 405-415, 1996.

15. Gu, P., Elliott, S., Hristova, R., Beaudoin, J.J., Brousseau, R., Baldock, B., “A Study of Corrosion Inhibitor Performance in Chloride Contaminated Concrete by Electrochemical Impedance Spectroscopy”, ACI Materials Journal, V. 94, No. 5, September-October 1997, pp. 385-395.

16. Raharinaivo, A., “Les inhibiteurs de corrosion des aciers dans le beton”, LCPC, Juin 1998.

17. Dhouibi, L., Triki, E., Raharinaivo, A., “Laboratory experiments for assessing the effectiveness of inhibitors against steel corrosion in concrete”, 6th International Symposium on Advances in Electrochemical Science and Technology, Chernai (Madras), Nov. 26-28, 1998.

18. Raharinaivo, A., Malric, B., “Performance of Monofluorophosphate Inhibiting Corrosion of Steel in Reinforced Concrete Structures”, International Conference on Corrosion and Rehabilitation of Reinforced Concrete Structures, Orlando (USA), Dec. 7-11, 1998.

19. Hansson, C.M., Mammoliti, L., Hope, B.B., “Corrosion Inhibitors in Concrete – Part I: The Principles”, Cement and Concrete Research, Vol. 28, No. 12, pp. 1775-1781, 1998.

20. Sprinkel, M., Ozyildirim., C., “Evaluation of Exposure Slabs Repaired with Corrosion Inhibitors”,

21. Page, C.L., Ngala, V.T., Page, M.M., “Corrosion inhibitors in concrete repair systems”, Magazine of Concrete Research, 2000, 52, No. 1, Feb., 25-37.

22. Page, C.L., “Aspects of the Performance of Corrosion Inhibitors Applied to Reinforced Concrete”, Proceedings of the 9th European Symposium on Corrosion Inhibitors, 240th Manifestation of the European Federation of Corrosion, Volume 1, 4th – 8th September, 2000, University of Ferrara, Italy.

23. Monticelli, C., Frignani, A., Trabanelli, G., “A study on corrosion inhibitors for concrete application”, Cement and Concrete Research, Vol. 30, pp. 635-642, 2000.

24. Loulizi, A., Al-Qadi, I.L., Diefenderfer, B.K., “Effects of Nitrite-Based Corrosion Inhibitor on Concrete’s Rapid Chloride Permeability Values and its Dilelectric Properties”, ACI Materials Journal, V.97, No. 4, July-August 2000, pp. 465-471.

25. Saraswathy, V., Muralidharan., S., Kalyanasundaram, R.M., Thangavel, K., Srinivasan, S., “Evaluation of a composite corrosion-inhibiting admixture and its performance in concrete under macrocall corrosion conditions”, Cement and Concrete Research, V. 31, pp. 789-794, 2001.

26. Allyn, M., Frantz, G.C., “Corrosion Tests with Concrete Containing Salts of Alkenyl-Subtituted Succinic Acid”, ACI Materials Journal, V. 98, No. 3, May-June 2001, pp. 224-232.

27. Brown, M.C., Weyers, R.E., Sprinkel, M.M., “Effects of Corrosion-Inhibiting Admixtures on Material Properties of Concrete”, ACI Materials Journal, V.98, No. 3, May-June 2001, pp. 240-250.

28. Page, M.M., Page, C.L., Ngala, V.T., Anstice, D.J., “Ion chromatographic analysis of corrosion inhibitors in concrete”, Construction and Building Materials, Vol. 16, pp. 73-81, 2002.

29. Dhouibi, L., Triki, E., Salta, M., Rodrigues, P., Raharinaivo, A., “Studies on corrosion inhibition of steel reinforcement by phosphate and nitrite”, Materials and Structures, Vol. 36, October 2003, pp. 530-540.

30. Heiyantuduwa, R., Beushausen, H.D., Alexander, M.G., “The effectiveness of corrosion inhibitors in concretes subjected to chloride attack and carbonation”, BFT, Issue. 8, 2003.

31. Bavarian, B., Reiner, L., “Current Progress on Improving the Durability of Reinforced Concrete Structures using Migrating Corrosion Inhibitors”,

32. Mulheron, M., Nwaubani, S.O., “Corrosion Inhibitors for High Performance Reinforced Concrete Structures”, University of Surrey, SCI Conference, London, 2000.

33. Jones, G., “Performance of Corrosion Inhibitors in Practice”, Sika Ferrogard Corrosion Inhibitor Meeting, 13th January 2000.

34. Elsener, B., Cigna, R., “Surface applied inhibitors”, Corrosion of steel in reinforced concrete structures, COST Action 521,

35. Vaysburd, A.M., Emmons, P.H., “Corrosion inhibitors and other protective systems in concrete repair: concepts or misconcepts”, Cement & Concrete Composites, Vol. 26, pp. 255-263, 2004.

36. Wombacher, F., Maeder, U., Marazzani, B., “Aminoalcohol based mixed corrosion inhibitors”, Cement & Concrete Composites, Vol. 26, pp. 209-216, 2004.

37. Gaidis, J.M., “Chemistry of corrosion inhibitors”, Cement & Concrete Composites, Vol. 26, pp. 181-189, 2004.

38. Qian, S, Cusson, D., “Electrochemical evaluation of the performance of corrosion-inhibiting systems in concrete bridges”, Cement & Concrete Composites, Vol. 26, pp. 217-233, 2004.

39. Jang, J.W., Iwasaki, I., Gillis, H.J., Weiblen, P.W., “Effect of Corrosion-Inhibitor-Added Deicing Salts and Salt Substitutes on Reinforcing Steels: I. Influence of Concentration”, Advanced Cement Based Materials, Vol. 2, pp. 145-151, 1995.

40. Jang, J.W., Iwasaki, I., Gillis, H.J., Weiblen, P.W., “Effect of Corrosion-Inhibitor-Added Deicing Salts and Salt Substitutes on Reinforcing Steels: II. Influence of Temperature and Oxygen Content”, Advanced Cement Based Materials, Vol. 2, pp. 152-160, 1995.

41. Cabrera, J.G., Al-Hasan, A.S., “Performance Properties of Concrete Repair Materials”, Construction and Building Materials, Vol. 11, Nos 5-6, pp. 283-290, 1997.

42. Dry, C.M., Corsaw, M.J.T., “A Time-Release Technique for Corrosion Prevention”, Cement and Concrete Research, Vol. 28, No. 8, pp. 1133-1140, 1998.

43. Jeknavorian, A.A., Mabud, A.Md., Barry, E.F., Litzau., “Novel pyrolysis-gas chromatography/mass spectrometric techniques for the characterization of chemical additives in Portland cement and concrete”, Journal of Analytical and Applied Pyrolysis, Vol. 46, pp. 85-100, 1998.

44. Jang, J.W., Hagen, M.G., Engstrom, G.M., Iwasaki, I., “Cl-, SO42-, and PO43- Distribution in Concrete Slabs Ponded by Corrosion-Inhibitor-Added Deicing Salts”, Advanced Cement Based Materials, Vol. 8, pp. 101-107, 1998.

45. Li, L., Sagues, A.A., Poor, N., “In situ leaching investigation of pH and nitrite concentration in concrete pore solution”, Cement and Concrete Research, Vol. 29, pp. 315-321, 1999.

46. Jeknavorian, A.A., Barry, E.F., “Determination of durability-enhancing admixtures in concrete by thermal desorption and pyrolysis gas chromatography-mass spectrometry”, Cement and Concrete Research, Vol. 29, pp. 899-907, 1999.

47. Mammoliti, L., Hansson, C.M., Hope, B.B., “Corrosion inhibitors in concrete Part II: Effect on chloride threshold values for corrosion of steel in synthetic pore solutions”, Cement and Concrete Research, Vol. 29, pp. 1583-1589, 1999.

48. ACI Committee 212, “Chemical Admixtures for Concrete”, ACI Materials Journal, Vol. 86, Issue 3, May 1, 1989.

49. Hope, B.B., Ip, A.K.C., “Corrosion Inhibitors for use in concrete”, ACI Materials Journal, Vol. 86, No. 6, pp. 602-608, 1989.

50. Haran, B.S., Popov, B.N., Petrou, M.F., White, R.E., “Studies on Galvanized Carbon Steel in Ca(OH)2 Solutions”, ACI Materials Journal, Vol. 97, No. 4, July-August 2000.

51. Elsener, B., “Half-cell potential mapping to assess repair work on RC structures”, Construction and Building Materials, Vol. 15, pp. 133-139, 2001.

52. Batis, G., Routoulas, A., Pantazopoulou, P., “Reinforcement Corrosion Studies by the Strain Gauge Technique”, Proceedings, European Corrosion Congress EUROCORR, Nice, 2004.

53. Cigna, R., Mercalli, A., Grisoni, L., Maeder, U., “Effectiveness of Mixed-in Organic Corrosion Inhibitors on the Prolongation of the Service Life of Reinforced Concrete Structures”, Proceedings, European Corrosion Congress EUROCORR, Riva del Garda, 2001.

54. Cigna, R., Mercalli, A., Peroni, G., Grisoni, L., Maeder, U., “Influence of Corrosion Inhibitors containing Aminoalcohols on the Prolongation of the Service Life of Reinforced Concrete Structures”, Proceedings, International Conference on Corrosion and Rehabilitation of Reinforced Concrete Structures, Orlando, Florida, 1998.

55. Jamil, H.E., Shriri, A., Boulif, R., Montemor, M.F., Ferreira, M.G.S., “Electrochemical Behaviour of Amino Alcohol-Based Inhibitors to Control Corrosion of Reinforcing Steel”, Electrochimica Acta., No. 49, pp. 2753-2760, 2004.

56. Pedeferri, M.P. et al., “Mixed Inhibitors for Concrete Structures”, Proceedings, European Corrosion Congress EUROCORR, Riva del Garda, 2001.

�

�

�

�

�

�

�

�

1,50

2,00

2,50

3,00

3,50

4,00

-3,00

-1,00

1,00

3,00

Log Freq (Hz)

Log Modulus (Ohm)

Simulirana porna voda

0,5% NaCl

0,1% inhibitor

0,2% inhibitor

0,5% inhibitor

1% inhibitor

2% inhibitor

0

1000

2000

3000

4000

5000

6000

7000

8000

0

1000

2000

3000

4000

5000

6000

7000

8000

Real (Ohm)

-Imag (Ohm)

Simulirana porna voda

0,5% inhibitor

0,1% NaCl

0,2% NaCl

0,3% NaCl

0,5% NaCl

1% NaCl

1,60

2,10

2,60

3,10

3,60

4,10

4,60

-3,00

-2,00

-1,00

0,00

1,00

2,00

3,00

4,00

Log Freq (Hz)

Log Modulus (Ohm)

Simulirana porna voda

0,5% inhibitor

0,1% NaCl

0,2% NaCl

0,3% NaCl

0,5% NaCl

1% NaCl

2,00

2,50

3,00

3,50

4,00

4,50

5,00

-3,00

-2,00

-1,00

0,00

1,00

2,00

3,00

4,00

Log Freq (Hz)

Log Modulus (Ohm)

0,001% Ca(OH)2 + KOH

0,5% NaCl

0,5% NaCl + 2% inhibitor

0,5% NaCl + 0,5% inhibitor

0,5% NaCl + 0,2% inhibitor

U (zapisana) v odvisnosti od t

100,00

120,00

140,00

160,00

180,00

200,00

220,00

240,00

260,00

0

20

40

60

80

100

120

140

160

180

200

t [min]

U [mV]

raztopina

0,2% Cl

0,2%

inh.SLVP

0,5%

inh.SLVP

1%

inh.SLVP