Corrosion behavior of fastenings made with Hilti HIT-HY 150 and Hilti HIT-RE 500 injection systems

Transcription

1 Technoparkstr Zurich Tel Fax Schweizerische Gesellschaft für corrosionsschutz Swiss Association for protection against corrosion Report no a Dated September 17, 2002 Subject: Corrosion behavior of fastenings made with Hilti HIT-HY 150 and Hilti HIT-RE 500 injection systems This report consists of 16 pages. Order from: Hilti Corporation, FL-9494 Schaan Order dated Testing between June 27, 2001 and January 7, 2002 Contents Summary 2 1. Background information 3 2. Experiments 4 3. Test results Behavior of steel specimens in Hilti HIT-HY Behavior of steel specimens in Hilti HIT-RE Frequent questions: Sealing of Hilti HIT-RE 500 system Influence of chlorides Defects in coating of Hilti HIT-RE Reference literature 16 Zurich, October 07, 2002 for SGK:

2 - 2 / 16 - Summary The Schweizerische Gesellschaft für Korrosionsschutz (SGK) (Swiss Association for protection against corrosion) was given the assignment of evaluating the corrosion behavior of anchor fastenings post-installed in concrete using the Hilti HIT-HY 150 and Hilti HIT-RE 500 injection systems. HIT-HY 150 is a hybrid injectable adhesive mortar which is based on a fast-curing, organic binder (methacrylate) and cement. Its characteristics are comparable to those of concrete it is alkaline and porous. HIT-RE 500 is an injectable adhesive mortar which is based on a slow-curing epoxy resin with a polyamine hardener. As regards its characteristics, it is alkaline and dense. Corrosion tests were carried out. The behavior of the two systems had to be evaluated as regards their use in field practice and compared with the behavior of anchors cast in concrete (reference). The SGK can look back on extensive experience in this field, especially on expertise in the field of repair and maintenance work on bridges in the Swiss alps. To model the corrosion tests, the worst case with respect to corrosion, namely fastenings used during bridge repair for anchoring concrete cover to old concrete. The overall evaluation was made on the basis of the tests conducted, while including SGK s practical experience, theoretical considerations and reports from field practice found in the pertaining reference literature. The result can be summarized as follows: Hilti HIT-HY 150 The Hilti HIT-HY 150 system in combination with reinforcing bars (hereinafter referred to as rebars) can be regarded as being resistant to corrosion when it is used in sound, alkaline concrete. The alkalinity of the adhesive mortar safeguards the initial passivation of the steel and, owing to the porosity of the adhesive mortar, an exchange takes place with the alkaline pore solution of the concrete. If rebars are bonded in chloride-free concrete using this system, in the event of later chloride exposure, the rates of corrosion are about half those of rebars that are either cast in or bonded with cement mortar. In concrete containing chlorides, the corrosion behavior of the system corresponds to that of cast-in or cemented-in rebars. Consequently, the use of unprotected steel in concrete exposed to chlorides in the past or possibly in the future is not recommended because corrosion must be expected after only short exposure times.

3 - 3 / 16 - Hilti HIT-RE 500 If the Hilti HIT-RE 500 system is used in corrosive surroundings, a sufficiently thick coat of adhesive significantly increases the time before corrosion starts to attack the bonded-in steel. The HIT-RE 500 system may be described as resistant to corrosion, if a coat thickness of at least 1 mm can be ensured, even in concrete that is carbonated and contains chlorides. In this case, the unprotected steel in a concrete joint and in the new concrete is decisive. If the coat thickness is not ensured, the HIT-RE 500 system may be used only in sound concrete. A rebar may then also lie against the wall of the drilled hole. At these points, the steel behaves as though it has a thin coating of epoxy resin. In none of the cases investigated did previously rusted steel (without chlorides) show signs of an attack by corrosion, even in concrete containing chlorides. Neither during this study was an acceleration of corrosion found at defective points in the adhesive mortar bond nor was there any reference to this in literature. Even if a macro-element forms, the high resistance to it spreading inhibits a locally increased rate of corrosion. Information in reference data corresponds with the results of this study. 1. Background information The situation investigated is depicted schematically in fig. 1. There are the following possible risks of corrosion: The existing structural concrete might be carbonated. This could impair the passivity of the steel specimens. The existing structural concrete might have been impaired by chlorides. The chlorides could reach the surface of the concrete as a result of the anchor fastening and then initiate corrosion there. Chlorides can permeate into concrete and lead to corrosion on the surface of the steel. The main permeation route is through the joint between the existing structural concrete and the new concrete (fig. 1: Permeation route 1). Progressing from a joint, chlorides can advance into the new concrete and into the existing concrete (permeation routes 3 and 4).

4 - 4 / 16 - On the other hand, chlorides can also get into a structure quickly through cracks appearing in new concrete due to constrained shrinkage (permeation route 2) and then proceed to the steel specimens through the joints. Basically, chlorides can also permeate through the new concrete (permeation route 5), but this permeation takes place much slower than through permeation routes 1 and reinforcement new concrete steel specimens adhesive old concrete permeation routes Fig. 1: Schematic situation with a concrete extension containing bonded-in steel specimens and showing possible chloride permeation routes 2. Experiments In order to simulate the possible corrosion risk for the anchoring system experimentally, concrete test specimens were made which would be able to reproduce the various risk mechanisms in question. The set-up for the experiments is shown in fig. 2. First, concrete test specimens were made, these having a water-cement factor of 0.6. For this simulation of the various corrosion hazards, these test specimens were given different treatments. Series I: The old concrete was exposed in advance by letting it soak up a 2 M NaCl solution with chlorides. After the pretreatment, the chloride concentration reached a value of approximately 1 percent by mass in relation to the cement content (m%/c). Series II: The old concrete was carbonated by rapid carbonation at a relative air humidity of 60%. The carbonation depth after the pretreatment was 20 mm. Series III: The old concrete was not pretreated.

5 - 5 / 16 - reading of potential U I reading of macro-element current cathode 10 mm dia. 40cm old concrete concrete block 5 cm 5 cm 8 cm 16 mm 30 mm 17cm 10 cm 1cm solution (tap water/tap water + 1M NaCl) reference electrode anchor 12 mm dia. SCE adhesive mortar new concrete coating chloride sensor interface of new / old concrete Fig. 2: Schematic test set-up and measuring equipment As pretreatment of the concrete would have immediately led to corrosion of the cast-in reference steel specimens in series I and II, the reference specimens were installed using cement mortar after pretreatment of the concrete (coat thickness 6 mm). Only in the case of series III was it possible for the reference specimens to be cast-in when making the old concrete. After pretreating the concrete specimens, the steel specimens were installed in the old concrete using the two HIT injectable adhesive mortars (coat thickness 2 mm). As a rule, normal, untreated reinforcing steel with a diameter of 12 mm was used for the steel specimens. Several specimens were installed with intentional defects in the enveloping HIT-RE 500 adhesive mortar and previously rusted reinforcing steel was used for several specimens. After carrying out these preparations, the new concrete with a water-cement factor of 0.5 was applied. Permeation routes 1 and 2 were the main corrosion risks for the steel specimens. Consequently, the new concrete was coated with epoxy resin to seal off permeation route 5 and to make the joint the primary route for the water. In series I, the test pieces were submerged in tap water and, in series II and III, in 1 M NaCl solutions. To analyse the corrosion behavior, the potential and the corrosion current were recorded. Fig. 3 is a typical plot of the results. The activation of a specimen was determined on the basis of the drop in potential and an increase in the macro-element current. The rate of corrosion was ascertained from the current and the corroding area. By determining the area of corrosion after the test, it was possible to calculate and plot the rate of corrosion in millimeters per year from the corrosion current.

6 - 6 / 16 - Potential [V SCE] rate potential Time[h] Rate of corrosion [mm/year] Fig. 3: Typical plot of potential and rate of corrosion 3. Test results 3.1 Behavior of steel specimens in Hilti HIT-HY 150 Bonding in a steel bar with HY 150, gives the steel protection which is comparable to that of steel cast in concrete. Despite the prior carbonation of the old concrete, the HIT-HY 150 adhesive mortar was able to passivate the steel. Nonetheless, the system is unsuitable for use in concrete containing chlorides. Chlorides in salinized concrete quickly find their way to the surface of the steel through pores in the HIT-HY 150 where they cause an attack of corrosion. In this case though, the HIT-HY 150 system performs at least as well as concrete. All the same, differences do exist, depending on the corrosive testing conditions. These are discussed in the following. Series I: In the concrete containing large amounts of chlorides, steel specimens bondedin with HIT-HY 150 initiated corrosion of the reference specimens and the steel specimens in HIT-HY 150 within a short time. The 6 mm thick cement mortar coat in which the reference bars were embedded showed a behavior similar to that of the HIT-HY 150 system (with a coat 2 mm thick). Series II: After the bar had been put in place, the HIT-HY 150 passivated the steel by reason of its alkalinity, even though the surrounding concrete was carbonated. The infiltration of chlorides along the joint then soon caused the steel to corrode. In this case, a considerably better behavior of the reference specimens was observed. Most probably, this could be attributed to the steel being embedded in a very high-quality 6 mm thick cement mortar layer.

7 - 7 / 16 - Series III: Tendentially, the time required for the HIT-HY 150 system to trigger corrosion is longer than in series II. Immediately after the tests were started, the cast-in reference specimens were attacked by corrosion. Hilti HIT-HY 150 Reference Hilti HIT-HY 150 Reference Series I Series I Series II Series II Series III Series III Time [h] Fig. 4: Time to initiate corrosion Rate of removal [mm/year] Fig. 5: Max. rate of corrosion From the test readings, it could be seen that, on average, the rate of corrosion with the HIT-HY 150 system was slower than with the reference specimens. Among the reference specimens, no positive effect of the cement mortar on the rate of corrosion compared with the bonded-in with HIT-HY 150 specimens could be observed. 3.2 Behavior of steel specimens in Hilti HIT-RE 500 HIT-RE 500 significantly extended the time until corrosion began. Based on the available data, it could be assumed that corrosion could take place only on unprotected steel in the joint or in the new concrete, if they had been exposed to chlorides. After a test duration of 2,400 hours, steel used with the HIT-RE 500 system showed no significant signs of corrosive attack. In view of this, the testing conditions were made more stringent through exposure to an increased temperature. The test pieces were kept at 50 C for 7 days and then left at room temperature for approximately 21 days afterwards. This cycle was repeated three times. How these cycles affected the corrosion behavior was depicted fig. 6. Series I: The concrete containing chlorides was unable to cause the steel specimens in HIT-RE 500 to corrode. The contrary was the case with the reference specimens in cement mortar and the steel specimens in HIT-HY 150. If HIT-RE 500 enveloped the steel specimens, it prevented chloride access to the steel and inhibited an attack of corrosion in this way. Even the defects provided artificially in the HIT-RE 500 opened up no routes for the damaging substances to permeate to the specimen surfaces.

8 - 8 / 16-0 cycle: Fig. 6: Potential [V SCE] rate potential Time [h] Activation of specimen (example) during first temperature cycle Rate of corrosion [mm/year] Series II: At the start of the test, the HIT-RE 500 system displayed a clearly passive behavior in the carbonated concrete. Infiltrating chlorides were unable to initiate corrosion after the first temperature cycles. It was then found that the artificially provided defects had no negative effects. Only in the unprotected new concrete did both specimens with defect and specimens without defect corrode, and this during the same period. After stopping the tests, furthermore, several specimens were still not corroded. The previously rusted specimens installed with HIT-RE 500 showed no attack by corrosion throughout the entire test duration. The infiltrating chlorides were only able to initiate corrosion on the reference specimens bonded in with cement after a relatively long test duration. This good resistance could be attributed to the surrounding 6 mm thick, highly alkaline, cement mortar layer and the water-filled pores. Series III: By using HIT-RE 500, it was also possible to efficiently delay the start of corrosion in series III. Only when there was high chloride contents of up to 4 M%/C and, in some cases, only after additional exposure to heat were the specimens activated. After removal of the specimens, it was apparent that corrosion had been initiated primarily in the cast-in specimen section of the concrete cover. Consequently, the activation can be attributed to the high chloride content of the new concrete. The different activation times for the unprotected steel thus permitted the times to be deduced until the critical chloride content in the concrete cover was reached. None of the previously rusted specimens embedded in HIT-RE 500 showed signs of corrosion. The characteristic russet-brown coloration of the rust prior to installation changed to a black oxide layer under the HIT-RE 500 and a largely plain steel surface in the concrete cover.

9 - 9 / 16 - The activation times ascertained on the basis of the potential and rate of corrosion are depicted in 7. Reference RE 500 rusty Reference RE 500 rusty RE 500 RE 500 with defect RE 500 RE 500 with defect Series I Series I Series II Series II Series III Series III time [h] Fig. 7: Activation times rate [mm/year] Fig. 8: Max. rate of corrosion removal The rate of corrosion removal was calculated with the aid of corrosion current readings and measured sizes of the active zones. The results for die max. rate of corrosion were plotted in fig. 8. The graph shows that the rate of corrosion of the HIT-RE 500 system is less on average than that of the reference specimens. In no case, however, was a higher rate of corrosion observed than with the reference specimens. It was also seen that the rate of corrosion of specimens which corroded in the defective adhesive mortar in addition to corroding in new concrete was not higher. A visual examination of the installed bars, after the experiments had been stopped, indicated that corrosion of the reference specimens occurred primarily in the joint or in the old concrete. This means that the test arrangement led to the anticipated permeation of chlorides. In contrast to this, an attack of corrosion was observed on all HIT-RE 500 systems in the new concrete. In odd cases, corrosion also occurred at the defects. 4. Frequent questions about "sealing" of the HIT-RE 500 system 4.1 Effect of chlorides In the case of all systems installed with HIT-RE 500 which proved to initiate corrosion, corrosion always also occurred in the new concrete. This corrosion in the new concrete could be attributed to the penetration of chlorides. The results of the chloride analysis after stopping the tests were depicted in fig. 9. It was clearly shown that the critical chloride content of 0.4 percentage by mass in relation to the cement content (M%/C) had been

10 - 10 / 16 - exceeded in series II and III in the new concrete. As a result, corrosion had to be expected in the new concrete. By contrast, the chloride content in the new concrete in series I was below the critical value, as the chlorides could only diffuse from the old concrete to the new concrete. No attack of corrosion was observed in this case either. This means that the attacks of corrosion on the unprotected steel surfaces were primarily the result of chloride penetration into the new concrete. New concrete Old concrete Content of chloride [M%/Z] Series I Series II Series III depth [mm] Fig. 9: Chloride content in relation to cement at various depths in test pieces; the critical chloride content of 0.4 M%/C is indicated by the dotted line. 4.2 Defects in coat of HIT-RE 500 The excellent protection against corrosion of HIT-RE 500 cames from almost complete separation of the steel from the concrete (sealing), as it is achieved by the propper application of the system HIT.RE 500. As a result, corrosive substances can not access the surface of the steel and electro-chemical reactions can not take place. By reflecting on analogies with other applications with sealing systems as protection against corrosion, it became possible to put forward the following arguments against this protective principle: 1. The access of corrosive substances through defects in the coating is possible and corrosion could thus take place locally, e.g. (a) air voids, (b) cracks, (c) immediately on rebars in contact with the concrete and, possibly, (d) in connection with rebars previously exposed to chlorides. 2. Electro-chemical reactions are largely rendered impossible underneath the coating. Consequently, there is also no passivation of the surface, e.g. (d) for not cleaned, rusted rebars.

11 - 11 / When cracks are present, the solution in concrete pores (possibly, not alkaline or containing chlorides) could permeate to the steel surface, e.g. (a) air voids, (b) cracks. 4. The attack of corrosion is strongly localized in the defects. If the corrosion current is the same, there could bee rapid reductions in cross-sectional area, e.g. (a) air voids, (b) cracks and (c) rebars lying against the concrete. 5. If a bond is poor and the surface pretreatment inadequate, there could be corrosion beneath coats of paint applied as protection against corrosion and a rapid loss of the protective sealing effect, e.g. (c) rebars lying on the concrete, perhaps in combination with (d) non-cleaned or even chloride-contaminated rebars. In the following, the listed scenarios are discussed with respect to their potential risk. (a) Air voids Basically, it had to be expected that pores existed in the HIT-RE 500 coating. With this in mind, specific defects were made artificially in the adhesive mortar during the tests carried out. After removal of the specimens, natural air voids were actually found on one specimen which were comparable to the man-made defects. In view of this, it could be concluded that it was realistic to provide the defects in the way they were. During the experiments, it was found that it took around the same time for corrosion to begin on specimens with defects as on specimens without defects. Consequently, the conclusion was that pores had no pronounced negative effect on the corrosion behavior. On removing the specimens, the pores proved to be empty. This effect can be explained by the large diameter of the pores and the resulting lack of capillary action. (The same effect is used to achieve the resistance of concrete to freezing and thawing: Large pores do not fill with water because there is no capillary action. Only as a result of evaporation and condensation due to temperature fluctuations can an electrolytic solution get into these pores. Corrosion, which would be initiated by this process, cannot be analyzed by measuring potential and current because the origin of the corrosion has no electrolytic link with the concrete. Consequently, a macro-element cannot form either. The rate of corrosion thus remains extremely low, particularly as only internal corrosion can take place. Basically, the risk of corrosion from pores can be rated as very small, and this was also confirmed by the results of the experiments.) (b) Cracks in HIT-RE 500 In principle, defects are also conceivable which have a capillary action. First and foremost, they would be cracks which have a narrow opening and pass through both the concrete and the HIT-RE 500. If the crack opening is sufficiently narrow, the solution in the

12 - 12 / 16 - concrete pores is drawn towards the steel surface by capillary action. As, however, the alkalinity of the concrete pore solution is high, the surface of the steel will be passivated. If the concentration of chlorides in the concrete pore solution happens to be above the critical value, there will be a local attack of corrosion. The speed of the corrosive attack will most likely be dominated by the crack, according to the general geometric conditions. With a narrow crack opening, only a thin and thus high-resistance electrolytic contact exists with the surrounding medium. The so-called spreading resistance enters the corrosion current circuit directly and reduces the corrosion current. In view of this, the rates of corrosion of even a small corroding area would probably not increase disproportionally. A calculation of the spreading resistance has shown that a locally increased rate of corrosion will occur only if the crack width is larger than the thickness of the epoxy coating. With narrow cracks, the drop in voltage in the crack dominates and, even if a macro-element exists, there would probably be no locally accelerated rate of corrosion. (c) Points of contact with concrete If the steel is lying directly on the concrete, there is no positive effect from the spreading resistance. This can be the case if a rebar is angulated or touching. In alkaline and chloride-free concrete, the point of contact can passivate the steel. If the concentration of chlorides is high, however, local corrosion begins. The case of steel rebars touching the concrete is also discussed under point (d). (d) Surface quality of steel It is known from the use of anti-corrosion coatings that the success of this protective measure depends to a great extent on the quality of the surface treatment of the steel and on the coating thickness. A correspondingly large amount of time, money and effort is required to manufacture durable coatings for protection against corrosion. Experience with epoxy resins is available from, e.g. when used for repair and restoration purposes in reinforced-concrete construction. In these cases, the carbonated or chloridecontaminated concrete was removed, the surface of the reinforcing steel coated with an epoxy resin and the concrete reprofiled again. In many cases, however, the steel was badly attacked again in a short time. During respective studies, the causes, among others, were given as inadequate surface cleaning before applying the coating and the high chloride contamination of the concrete [5]. The renewed, strong attacks of corrosion in a very short time resulted in the bad reputation of epoxy resins as protection against corrosion in reinforced-concrete construction. This experience contradicts the results of the study presented here. It was shown that previously rusted rebars have an excellent corrosion behavior even if their rusty surfaces were not cleaned at all prior to being set in HIT- RE 500. In fact, their corrosion behavior is even superior to that of bright steels. The cause for this difference in behavior must be seen in the different type of prior corrosion,

13 - 13 / 16 - on the one hand, and, on the other hand, the considerably thicker coating used during the corrosion tests presented here. Condition of steel surface when coating: If prior corrosion steel took place when chlorides were present in the concrete, the steel surface is attacked locally. This leads to the formation of FeCl 3. This is a hygroscopic salt with a high redox (oxidation reduction) potential. During concrete repair and restoration, it is possible only to a limited extent for the steel surface to be cleaned owing to construction site conditions and roughening of the surface by the corrosion. FeCl 3 residues are probably always left on the surface. Moisture finds its way to the steel surface through pores in the thin coating or through the matrix by diffusion and osmotic processes, where it finds ideal conditions for corrosion. If the amount of aggressive ions, e.g. chlorides, is below the critical concentration when there are products of atmospheric corrosion, the outset situation is decisively different and, even if other soluble, trivalent iron salts are produced, e.g. Fe 3 (SO 4 ) 3, these might act as passivators. A prime reason for the contradiction is thus the different chemical contamination of the surface. Influence of coating thickness: Once corrosion begins, voluminous products of corrosion are produced on the surface. They split open thin coatings, thus facilitating the further access of corrosive substances to the surface. As a result of the sequence of corrosion and splitting, centers of corrosion form which spread along the surface. This phenomenon is referred to as corrosion beneath a coating or under rusting. Oxygen diffusion through the thin synthetic material coating is a further decisive step which, due to a local increase in ph value, destroys the bonding force between steel and coating and speeds up the electro-chemical reaction. If, however, in the case of rebars set in HIT-RE 500, the coating has a thickness in the millimeter range, this is a difference of at least one order of magnitude. This thick coating of epoxy resin resists the resulting compressive stresses with higher forces than a thin coating, whose build-up has to rely on the supporting structure of the steel. Even if corrosion occurs at the joint, the coating the risk of spliting is significantly decreased due to the high thickness of the coating. This inhibits the spread of corrosion along the surface. Whether or not oxygen diffusion through the thin coatings in concrete plays an important role for the progress of the corrosion in the case of the previously mentioned repair and restoration work, is still not clear. Basically, it should be less significant than attacks of atmospheric corrosion because the structural member is completely enveloped in a conductive electrolyte. Furthermore, it is possible for macro-elements to form and the oxygen diffusion is greatly retarded by the thick coating. A detailed study of these processes is presented in the paper by Nguyen and Martin [6].

14 - 14 / 16 - Consequently, the excellent behavior of HIT-RE 500 on previously rusted steels stems primarily from the fact that, although the surfaces were somewhat corroded, they were not contaminated with chlorides, and the coating was very thick. If a steel surface is contaminated with chlorides when the steel is used in maritime surroundings, the formation of FeCl 3 must be expected. By applying a comparatively thick layer of several millimeters of epoxy resin, this coating largely inhibits the mass transfer between steel surface and enveloping concrete. In general, it is found that epoxy resin coatings more than 300 microns thick are sufficient to produce a complete separating barrier. Water and oxygen diffuse if coatings are thin. This will result in a loss of bonding, blistering due to osmotic pressure, splitting of thin coatings and opening up of the steel surface. If the concrete is alkaline and free of chlorides passivation of the steel surface will occur. In presence of chlorides, however, pitting corrosion is expected to occur. These processes can be inhibited by applying a sufficiently thick coating. In the case of HIT-RE 500, the mass transport is efficiently stopped. In this way, possible attacks at coating defects are restricted. The comparatively thick coating of HIT-RE 500 on the steel surface, furthermore, confronts forming products of corrosion with higher mechanical strength. As a result, the splitting and thus the spread of an attack of corrosion under the coating will most likely be avoided as well. This situation was not investigated in the case in question. Theoretically, however, good performance by HIT-RE 500 can be expected, even if a surface of steel has been contaminated with chlorides, as long as the concrete is free of chlorides and non carbonated as long as the coathing thickness is sufficient and the concrete is alkaline and free of chlorides. If the benefit of a thick coating of HIT-RE 500 is put to use, e.g. with the aid of spacers, when installing rebars or other anchoring devices in old concrete, attention must, nonetheless, be paid to the anticipated scenarios at the unprotected zones, namely the concrete joint and the new concrete. If these zones are also at risk from chloride contamination, those responsible must use precoated steel or corrosion-resistant steel selected to suit the given conditions. (e) Rebar connections without guaranteed coat thickness When structural connections are made using rebars without spacers, the rebars can be in contact with their hole wall over a large area or at many points where the ribs might be touching. In these case, the effectiveness of the HIT-RE 500 system is impaired where the resistance to chloride exposure is concerned. Right next to the points of contact, the adhesive mortar will not be very thick. As long as there is no carbonation and no chlorides reach the steel surface, no corrosion will take place in this situation. In other words, the use of rebar connections made with HIT-RE 500 can be considered only if the concrete is sound and a minimum coating thickness of, for example, 1 millimeter is ensured.

15 - 15 / 16 - (f) Comparison of test results with data in reference literature on epoxy resin coated rebars Reports in pertaining literature are first and foremost about good experience with epoxy resin coated steel. There is, however, also mention of some negative results in the south of the USA. These studies carried out in Florida [5] showed a heavy attack of corrosion and large-area separation of the coating after a few years of exposure to a maritime environment. The causes were combinations of several mistakes made during work execution, such as very heavy concrete salinization, cracks in the coating caused by bending rebars, much to thin a concrete cover which resulted in cover cracking and inadequate pretreatment of the steel surface. Products of corrosion containing chlorides were left on the steel surface when the rebars were coated and they set off, among other things, the processes described under points (d and e). Other investigations into causes in Virginia showed that the coating had separated over a considerable area [7 and 8], but that no attacks of corrosion had taken place. Problems can also arise from delamination of the coating. This reduction in bond strength can occur if a structure is permanently saturated throughout. It has also been observed that the loss of bonding strength is reversible. On the other hand, irreversible delamination takes place when an increase in ph value at the interface occurs due to oxygen reduction [10]. This negative experience conflicts with numerous positive results [9]. The examination of 82 structures in the USA and Canada showed the corrosion behavior to be clearly better than that of uncoated reinforcement. Even misgivings about a small size of defect leading to a locally accelerated rate of corrosion were not verified during experiments [4]. The comparatively high resistance to spreading prevents this process from taking place. The evaluation in reference literature throws a positive light overall on the corrosion behavior of epoxy resin coated reinforcing bars. Prime requisites with these thin coatings are good surface pretreatment and, in particular, the absence of products of corrosion containing chlorides. The problems with epoxy resin coated steels referred to in reference literature are only vaguely relevant to the HIT-RE 500 system. For example, no cracks in the coating can be produced by bending. When rebars are bonded in with HIT-RE 500, the clearly thicker coating prevents oxygen and water from reaching the steel surface, and thus the bond is not lost. During the presented tests, it was observed with all specimens bonded in with HIT-RE 500 which had begun to corrode that there was always corrosion in the new concrete too. The occurrence of corrosion in the new concrete can be attributed to chloride penetration. In it, they can initiate corrosion on a bare steel surface.

16 - 16 / Reference literature [1] H. Kaesche, Die Korrosion der Metalle, Springer-Verlag, Berlin, (1990). [2] W. Richartz, Die Bindung von Chloriden bei der Zementerhärtung, Zement-Kalk- Gips, 10 (1969) [3] Y. Schiegg, Dissertation, ETH Nr [4] B. Elsener, Einsatz epoxidbeschichteter Stähle in Korrosion und Korrosionsschutz, SIA Dokumentation D021 (1988) [5] J. A. Read, Need for correct specification and quality control, Concrete, 23 (1989) 23. [6] T. Nguyen and J. W. Martin, Durability of building materials and components, 7 Volume 1 (1996) 491 [7] R. E. Weyers, M. M. Sprinke, W.A. Pyc, J. Zemaijtis, Y. Liu, and D. Mokarem, VTRC 98-R4 (1997) [8] R. E. Weyers, D. W. Morakem, J. G. Dillard, Concrete International (2000) 57 [9] J. L. Smith, Y. P. Virmani, Performance of epoxy coated rebars [10] J. J. Ritter, J. Kruger, Studies of subcoating environment of coated iron using ellipsometric and electrochemical technique, In Corrosion control by Organic Coatings (Ed. H. Leiheiser) (1981) 28.