Chapter 3 Concrete Repair & Restoration

197 Efficacy of MCI in Existing Concrete Structures (repair and rest) Corrosion inhibitors can also provide protection to existing concrete structures through topical coating or repair mortar application. Products in this category generally come in the forms of A) pure inhibitor solution to be applied on concrete surface – the inhibitors will then be transported to embedded steel rebar via capillary infiltration and vapor phase diffusion; B) Hydrophobic sealer with MCI component – this approach protects by reducing egression of corrosive species while simultaneously forming barrier layer on rebar surface though the action of MCI molecules; and C) MCI containing repair mortar that supplies the rebar with the migrating corrosion inhibitors.

MCI-2020, MCI-2020M, MCI-2020VO is a family of water-based impregnating migrating corrosion inhibitors. In testing protocol according to G109 that lasted 1500 days and over 200 cycles of 3.5%NaCl ponding/drying, Figure 10, it was found that the inhibitor MCI-2020 had increased polarization resistance (Rp) (60-80 kohms-cm2 with increasing trends) in the MCI coated concrete than un-coated concrete, for both low density and high density concretes. The untreated not only had lower Rp values, but also decreasing trends, Figure 11. Examination of the embedded steel rebar after corrosion tests showed no corrosion attack for the MCI treated concrete samples, while un-treated concrete showed corrosion, Figure 12. X-ray photoelectron spectroscopy (XPS) and depth profiling confirmed that the inhibitor had reached the rebar surface in less than 150 days. Depth profiling showed an amine-rich compound on the rebar surface that corresponded with the increase in Rp and improved corrosion protection for the MCI treated steel rebar even in the presence of chloride ions, Table 1. Based on measured corrosion rate the life expectancy of a concrete reinforced structure can be improved by more than 40 years.

Figure 10 – Modified ASTM G109 Test Set-Up (continuous submersion)

a) b) a) Samples prepared per ASTM G109 b) Samples modified for continuous immersion

198 Figure 11 – Comparison in Polarization Resistance (Rp) in Low & High Density Concretes – Treated (MCI 2020 & MCI 2020 M) vs. Untreated

199 Figure 12 – Rebar at the end of 1500 Days of Testing

a) b) a) Un-treated concrete, rebar showed localized corrosion attacks. b) MCI-treated concrete, rebar did not show any corrosion attacks.

Table 2: XPS analysis and spectrum of the rebar surface, untreated and MCI 2020M treated concrete after 1500 days in 3.5% NaCl

Atomic Conc (%) Mass Conc (%) Atomic Conc (%) Mass Conc (%) Peak Untreated Untreated MCI MCI Fe 2p 0.87 3.32 0.08 0.3 O 1s 30.19 33.06 31.4 35.91 C 1s 62.48 51.37 59.43 48.12 Ca 2p 0.15 0.42 1.08 3.01 Si 2p 4.72 9.08 1.26 4.14 Cl 2p 0.84 2.04 1.11 2.81 N 1s 0.74 0.71 5.64 5.71 Figure 13 - UV spectroscopy analysis of a concrete section 3” below a MCI-2020 treated surface 5 weeks after the treatment demonstrated the inhibitor presence at that depth

200

Adhesion testing of several traffic coatings applied over surfaces treated with MCI-2020 showed that MCI treatment had no adverse effect on the adhesion of the traffic coatings that followed .

A more severe test, the Cracked Beam Test modified from ASTM G109, on MCI-2020 showed that the inhibitor delayed onset of corrosion. The control started to corrode at average of 3.75 cycles while the MCI-2020 treated specimens at average of 9.25 cycles, an improvement of 150%, Table 2. After corrosion initiation, the treated specimens showed reduced amount of damage. For MCI-2020 treated concrete, the average corrosion was 28% of the control and the average corrosion current was 53% of the control, respectively, after 20 monthly cycles, Table 3.

Table 3: Time-To-Corrosion of Cracked Beams

Concrete Monthly Cycles before Initiation of Corrosion Mix Beam Ave

1 2 3 4

Control 0 0 5 10 3.75

MCI2020 11 8 12 6* 9.25

* Beam had bottom bar corrosion

201 Table 4: ElectroChemical Measurements in Cracked Beams

Concrete Number of Monthly Test Cycles

Mix Ave corr current, Resistance, Half-cell potential, Intergral current,

μA ohms negative Volts μA-days

1 10 20 1 10 20 1 10 20 1 10 20

Control -37 - - 67 131 135 0.155 0.349 0.379 131 15837 75839 145 228

MCI2020 5 -18 -91 70 130 158 0.103 0.192 0.346 -16 583 21329

Another MCI product in protecting existing structures is MCI-2018, a sealer with MCI component. Due to the MCI molecules, this sealer not only repels intrusion of corrosive species from the surface, but introduces migrating inhibitors to the concrete and the embedded rebar. The Cracked Beam Test shows that the resistance in the treated beam is 55% higher than untreated at 7th cycle, Figure 14.

Figure 14: Resistance in Cracked Beams (MCI-2018 treated and untreated)

202 Specification of MCI Surface Treatments by Product

MCI surface treatments are designed for use on existing structures. They are designed to be applied to clean, dry surfaces – free of dirt, grease, oils, laitance, presence of other sealers or coatings, etc.

The most concentrated application of MCI in a surface treatment is in a water-based solution (MCI 2020, MCI 2020 V/O, MCI 2020 M, MCI 2020 MSC, MCI 2020 M V/O). These products contain corrosion inhibitor only and are best for use direct to concrete or mortar. They can be followed by a top coat if desired.

The MCI technology has also been combined with water repellants to create two-in-one surface treatments – with 100% organosilane (MCI 2018, MCI 2018 V/O), 40% silane (MCI 2019, MCI 2019 W), silane/siloxane blends (MCI 2022, MCI 2022 V/O) and silicates (MCI 2021). UV Tracers or fugitive dyes can be added to MCI surface treatments to confirm application upon request.

Repair and Specialty

MCI admixtures have been combined into repair mortars and grouts (MCI 2023, MCI 2039 SC, MCI 2701, and MCI 2702). They have also been incorporated into specialty products such as a gel for injection to embedded reinforcing steel (MCI 2020 Gel), protection for post tensioned cables (MCI 309, MCI PTC Emitters), concrete cleaners (MCI 2060, MCI 2061), concrete removers (MCI Super Remover) and concrete curing compounds (MCI CorteCure).

203 Presented at the International Conference for Concrete Under Sever Conditions (ConSec), 2001, Vancouver, Canada

SURFACE APPLIED MIGRATING INHIBITORS FOR PROTECTION OF CONCRETE STRUCTURES

Prof. Dubravka Bjegovic University of Zagreb, Zagreb, Croatia Prof. Behzad Bavarian California State University, Northridge, USA Masaru Nagayama General Building Research Corporation of Japan, Osaka, Japan

Abstract This paper discusses the protection of reinforced concrete using surface applied Migrating Corrosion Inhibitors (MCI
). Concrete surface could be treated with migration corrosion inhibitor during maintenance life as the prevention measure to assure the extension of the structure service life. Migrating Corrosion Inhibitor could be also added in repair systems as an admixture. The experimental results are given for both applications from different independent laboratories in different countries around the globe.

1.Introduction

Corrosion of reinforcement has been recognized as one of the most prevalent durability factors, which affects the largest group of reinforced concrete structures as bridges, parking garages etc. Corrosion could be brought under such control by application of the protective measure. One of the possibilities is the topical application of the migrating corrosion inhibitor. Migrating corrosion inhibitors (MCI
’s) are a mixed (anodic /cathodic) amino-carboxylate based inhibitor (1). The inhibition of cathodic

204 process is achieved by incorporation of one or more oxidizing anions in an organic (amine) molecule of MCI. Inhibitor molecules are hydrolyzed when adsorbed on the metal surface. The nitrogen of the amine group is capable of entering into a coordinate bond with metals thus enhancing the adsorbtion process. Adsorption of cations increases the overpotential of metal ionization and slow down the corrosion. The mixed monomolecular film serves as a buffer to hold the pH at the interface in the optimum range for corrosion resistance. The inhibitor adsorption isn’t a momentary process and requires much time for completion resulting in a chemisorbed layer on the metal surface. The migrating corrosion inhibitors can be added to concrete as admixtures during concrete mixing, or topically applied to the concrete surface, or placed into cracks in concrete for injection application or inserted in the form of emitting capsules for easy and renewable corrosion protection of existing structures (2). In spite of many published studies a lot of conflicting opinions exist concerning the effectiveness of these products for corrosion protection. In this paper the effectiveness of the migrating corrosion inhibitor applied on the concrete surface is tested and the results of the investigation from different independent laboratories in different countries around the globe are presented.

2. Experimental Procedures

2.1. Laboratory 1 (University of Zagreb, Croatia) The concrete with w/c factor 0.7 was used for the preparation of the test slabs as concrete substrate (2). The reinforced concrete specimens were made in accordance with ASTM G 109. The specimens were demolded after 24 hours and kept in a wet chamber for 28 days (RH = 95%, T = 20+2oC). After 28 days the upper surface of the specimens was wire brushed and the topical application by brush was made according to supplier’s specification of 450 g/m2. After the topical application of the migrating corrosion inhibitor the specimens were cured for two weeks at 20°C and 65% RH.

205 0,000,501,001,502,002,503,003,504,004,505,00147101316192225283134374043

Fig 1. Total corrosion for untreated and topically treated specimens with migrating corrosion inhibitor

The measurements of electrochemical potential and corrosion current in accordance with ASTM G 109 were taken week during one year. The results are given in Fig.1. The values of total corrosion activity are significantly lower for migrating corrosion inhibitor treated concrete in relation to untreated concrete. The total corrosion activity in coulombs is three to four times less for MCI treated concrete as compared to untreated specimens after one year of the testing.

2. 2. Laboratory 2 (California State University, Northridge, USA Migrating corrosion inhibitors were investigated over a 400-day period. These investigations were made on steel rebar in concrete totally immersed in 3.5% NaCl in ambient temperatures using electrochemical monitoring techniques. Due to low conductivity of concrete, the corrosion behavior of steel rebar had to be monitored using AC electrochemical impedance spectroscopy (EIS). During this investigation, changes in the resistance polarization and the corrosion potential of the rebar were

206 monitored to determine the degree of effectiveness for the migrating corrosion inhibitors. The reinforced rebars (class 60, rebar #4 steel wire, 12.7mm diameter bar) were cast in concrete at one and two inches from the surface and allowed to cure for 28 days. After 22 days, the concrete blocks were sand blasted to remove loose particles, debris, and rust deposited on the metal. This process left the concrete with a marginally smoother surface. Red shrink-wrap was placed on each of the exposed rebars to prevent additional corrosion. Three combinations were made: control concrete specimens, concrete specimens with repair mortar applied on the specimen surface and repair mortar with migrating corrosion inhibitor applied on the concrete specimens surface. The samples were then submerged in 3.5% NaCl solution for the duration of the experiment. During this investigation, samples were tested once a week to measure the open circuit potential and resistance polarization (Rp). Corrosion potentials were recorded at the beginning of each AC impedance test. The Rp values obtained by curve fitting data from the Nyquist plots in the EG&G M398 corrosion software were used to estimate corrosion. The Rp values are Unprotected Concrete/Rebar (Reference) 25.4 mm (1 Inch) Rebar Concrete Coverage AC Impedance Tests 1.00E+05 Day 4 Day 55 Day 64 Day 71 1.00E+04 Day 115 day 187 day 253 day 324 1.00E+03 day 378 lZl (OHMS) 1.00E+02

1.00E+01 1.00E-04 1.00E-02 1.00E+00 1.00E+02 1.00E+04

FREQUENCY (Hz

Fig. 2. AC Impedance test for reference concrete inversely proportional to the rate of corrosion. A high Rp value could be an indication of a low corrosion rate. The Bode plots

207 were also obtained from this software to verify the Rp value for each sample.

Base Coating 25.4 mm (1 Inch) Rebar Concrete Covera AC Impedance Tests 1.00E+05

Day 3 Day 36 1.00E+04 Day 63 day 185 day 251 day 323 day 375 1.00E+03

1.00E+02

1.00E+01 1.00E-04 1.00E-02 1.00E+00 1.00E+02 1.00E+04

FREQUENCY (Hz)

Fig. 3. AC Impedance test for repair coating applied on specimen surface

Base & MCI Inhibitor 25.4 mm (1 Inch) Rebar Concrete Cover AC Impedance Tests 1.00E+05

day 3 day 43 day 57 day 78 1.00E+04 day 85 day 121 day 143 day 186 day 252 day 324 day 375 1.00E+03

1.00E+02

1.00E+01 1.00E-04 1.00E-02 1.00E+00 1.00E+02 1.00E+04

FREQUENCY (Hz)

Fig. 4. AC Impedance test for repair coating and MCI inhibitor applied on specimen surface

208 The migrating corrosion inhibitor tested in this investigation successfully inhibited rebar corrosion, Fig. 2-4. Also, the steel rebar corrosion potentials were maintained at approximately -120 mV, and rebar resistance polarization reached as high as 250,000 ohms. All results indicate excellent corrosion resistance performance.

2. 3. Laboratory 3 (General Building Research Corporation, Japan) Reinforced concrete specimens with the 0.6 w/c ratio were prepared with two polished rebars of 13 mm in diameter and 100 mm long embedded horizontally with a concrete cover of 20 and 30 mm. For corrosion monitoring, mini sensors were embedded in the vicinity of rebars in concrete specimens prepared with 0 and 3 kg/m3 chloride ions (3). After the 60-day initial curing the specimens were permeated with migrating corrosion inhibitor (MCI). The treated and non treated specimens were subjected to alternately wet (40°C and 100%RH) and dry (50°C and 30%RH) cycles during one week period.

Fig.5. Rebar and mini sensors arrangement in a mold

After 1311 days of testing non-treated test specimens showed severe cracking and high corrosion rate of 73-92μm/year in the case of 3 cm concrete cover. The test specimens protected with

209 MCI showed only minor cracks and low rate of corrosion of 10- 12 μm/year.

Fig. 6. Weight loss vs. time for untreated and treated with MCI specimens

The potential, the polarization resistance, the electrolyte resistance measurements and destructive test results (weight loss) showed the effectiveness in decreasing rebar corrosion in chloride contaminated concrete, Fig. 6. The appearance of the concrete surface of the specimens after 1311 days under the investigation is given in (3).

210 3. Conclusion

The migrating corrosion inhibitors for topical application were investigated in two methods of application: as topical treatment in an aqueous liquid carrier or as an MCI inhibited repair mortar. In both cases the experimental results indicate that migrating corrosion inhibitor offers an effective inhibiting system for protecting reinforced concrete. These results are reported by three independent laboratories and are in general agreement with works by other researchers shown in references.

4. References:

1. Miksic B., Gelner L., Bjegovic D., Sipos L.: Migrating Corrosion Inhibitors for Reinforced Concrete, Proceedings of the 8th European Symposium on Corrosion Inhibitors, 18-22. Sept. 1995. University of Ferrara, Italy, 569-588 2. Bjegovic D., Miksic, B.,: Migrating Corrosion Inhibitor Protection of Concrete, Materials Performance, USA, November 1999, pp. 52-56. 3. MCI 2020 Long Term Test Protection of Rebar in Concrete, Interim Report General Building Research Corporation of Japan, October 1998. 4. Martinola M., Viaduct N2 de Melide (T1): Assainissement des bordures, SIA , No. 18, Vol.122, Aug.21,1996, 320-324. 5. Soerensen H., Poulsen E., Risberg J., On the Introduction of Migrating Corrosion Inhibitors in Denmark - A Review of Documentation Tests and Applications, Proceedings of International Confrence Infrastructure Regeneration and rehabilitation Improving the Quality of Life Through Better Construction, Sheffield 28 June-2 July, 1999, pp. 1019-1029. 6. Bjegovic D., Miksic, B., Stehly R.: Effect of Migration Corrosion Inhibitor on Corrosion of Reinforcing Steel, Proceedings of the International Conference Creating with Concrete, held at the University of Dundee, Scotland, UK, September 1999, Vol. Controlling Concrete Degradation, pp. 81 – 91.

211 The Pentagon Lightwell Walls Repair, Rehabilitation, and Protection for the Next 50 Years

By Rick Edelson Reprinted with Permission by STRUCTURE® magazine, January 2007

onstructed in just 16 months during World C :DU,,WKH3HQWDJRQWKHZRUOG¶VODUJHVWRI FH building, is undergoing a complete renovation, rehabilitation, and modernization program. A program with the goal of a minimum 50-year design life has been mandated by Penren (www.pentagon. renovation.mil), the governing agency for the Pentagon renovation. That’s right, it is anticipated that repairs will last at least 50 years! Taking over 10 years to complete, every component—the walls, WKH RRUVWKHURRIVWKHwindows, the mechanical and electrical systems—is being renovated or replaced. This article is about one component—the most-used component in the Pentagon—concrete. All structural elements of the Pentagon, except one, are constructed of reinforced concrete. Sadly, that concrete is deteriorating. This article explains how to breathe at least 50 years of new life into deteriorating concrete. The one element of the Pentagon not constructed of reinforced concrete is the outermost peri- Fig. 1: Typical lightwell wall damage showing spalling and exposed, meter wall, made of limestone. This article rusting reinforcing bars focuses on the remainder of the 1 million ft2 (92,903 m2) of the lightwell walls, which are now undergoing a complete repair, rehabili- tation, and protection program. The Pentagon consists of five separate rings, each approximately 90 ft (27.4 m) wide with approximately 30 ft (9 m) between the rings. The space between the rings is known as the lightwells. Thus, we call the perimeter walls of each ring the lightwell walls. The lightwell walls, constructed of cast-in-place, reinforced concrete, are both bearing walls and shearwalls. The problem is corrosion, that is, rusting, of the reinforcing bars in the lightwell walls and related spalling damage caused by the expansive forces created by the rusting bars. As steel rusts, it expands 4 to 10 times its original size, creating extreme tensile forces in the surrounding concrete. From these tensile forces, the concrete cracks and spalls. The Pentagon program is about the repair and rehabilitation of the more than 250,000 ft2 (23,226 m2) of spalling. The typical damage is represented in Fig. 1. The program also includes an innovative protection system designed to resist the Fig. 2: Scaffolding constructed to allow direct access to walls damage for the next 50+ years.

22 CONCRETE REPAIR BULLETIN MAY/JUNE 2007

212 Concrete testing prior to the implementation of the program revealed that the lightwell walls were constructed of approximately 3500 psi (24 MPa) concrete. However, the reinforcing bars were often placed less than 1/2 in. (12.7 mm) from the outer surface, and testing revealed carbonation extending into the walls a distance of 3-1/2 in. (89 mm) or more. Reinforcing bars, normally protected against corrosion by highly alkaline concrete, lose their protection as a result of the carbonation process, which lowers the alkalinity concrete from a pH of over 13 to less than 11. Without corrosion protection, approximately 20% to 30% of the walls have suffered spalling damage; corrosion rate testing reveals active corrosion in virtually every other section of walls. Thus, the goal is to structurally repair and rehab- ilitate the corrosion-damaged concrete and protect Fig. 3: Jackhammer demolition in progress, exposing corrosion- the remainder of the walls to resist future damage damaged reinforcing bars for the next 50 years. The Structural Engineer of Record for the concrete repair program designed the concrete repair work closely following the International Concrete Repair Institute guidelines for concrete repair. All damaged and spalling concrete, some 3 to 4 in. (76 to 102 mm) deep, is removed with 15-lb jackhammers, fully exposing rusting reinforcing bars. Where corrosion has extended around a bar, the bar is undercut; this allows the full surface of the bar to be sandblasted clean, removing all rust. Working closely with U.S. Concrete Products, Timonium, MD, the manu- facturer of the repair concrete, a color-matching, low-shrinkage, pumpable repair concrete was developed to comply with the specifications, which require a color and texture match when viewed from a distance of 30 ft (9 m) (the view from any window across a lightwell). This is Fig. 4: Close-up view of corrosion-damaged reinforcing bars taken easier said than done. Although some of the after completion of jackhammer demolition. Note the severe loss of repairs are as much as 4 in. (102 mm) deep, some cross section at the bottom of the vertical bars in the photo repairs are less than 1 in. (25 mm) deep, and some are too small to economically build formwork. For the minor amount of hand-patching that is being performed on small repairs, a trowelable mixture was developed. For the remaining repairs, 86 &RQFUHWH GHYHORSHG D SRO\PHUPRGL HG plasticized, bagged material that is mixed on site. 7KLVPDWHULDO RZVHDVLO\LQWRWKHIRUPHGUHSDLUV with extremely little shrinkage cracking. The mixture allows repairs up to 4 in. (102 mm) deep without large aggregate extension, and almost no cracking. Simple external vibration is all that is needed for good consolidation. In addition, the concrete obtains at least 2000 psi (14 MPa) in less than 3 days to allow for early stripping. Concrete Protection and Restoration, Inc., the concrete repair subcontractor, developed a form- work system (Fig. 5) that allows for easy placement Fig. 5: Formwork in place constructed to match original formboard of the repair concrete, as well as matches the nish on the existing walls

MAY/JUNE 2007 CONCRETE REPAIR BULLETIN 23

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24 CONCRETE REPAIR BULLETIN MAY/JUNE 2007

214 Corrosion-rate reduction, however, is only half the battle. Without water, corrosion can be halted. The question arises: how to stop water from absorbing into the walls for 50 years? Further protection is provided by a system reducing the absorption of water into the walls. A 100% solids silane is applied to the wall surface, after the application of the corrosion inhibitor, to reduce absorption and to repel water. Silane repels only water and breaks down when exposed to ultraviolet light. To further protect the walls, a much more durable surface is needed, one which will last 50+ years and will prevent the breakdown of the silane. To accomplish this, potassium silicate was selected to enhance the surface and to protect both the water repellant and the corrosion inhibitor. Potassium silicate, originally developed and manufactured in Germany by Keim over 100 years ago, is reported in their literature to remain in service 100 years after initial application. The potassium silicate itself also resists water absorption by creating a tough, water-resistant mineral surface on the concrete. With both the potassium silicate and the silane, water now sheds Fig. 8: Corrosion-rate monitoring of corrosion activity in unrepaired off the surface of the concrete. In addition, a uniform portion of wall adjacent to exposed corrosion damage color is achieved with the addition of pigments to the potassium silicate, further improving the repair integrity and appearance of the lightwell walls, to meet the required speci FDWLRQRIDFRORUPDWFK and future corrosion damage is resisted with a as seen across the lightwells. system designed to protect the Pentagon concrete With four separate products applied to an existing for the next 50+ years. building, and on top of each other, compatibility was a major concern. During the design of the system, compatibility testing was performed by the Rick Edelson is the Vice President manufacturers of the corrosion inhibitor, the silane, of Tadjer Cohen Edelson Asso- and the potassium silicate. Each issued not only a ciates and the Principal in charge joint compatibility statement, but a 20-year warranty RIWKH UP¶V5HSDLUDQG5HVWRU for the performance of the system components. ation Division. He has over Quality control by the Prime Contractor, Hensel 20 years of experience in the Phelps, quality assurance by a third-party inspection evaluation, rehabilitation, repair, agency, and quality assurance by Penren all ensure and corrosion mitigation for the a complete installation. protection of concrete structures. Rick can be The Penren design goal of repairs to last 50 years reached at [email protected] or through is achieved. Concrete repair has restored both the www.tadjerco.com.

MAY/JUNE 2007 CONCRETE REPAIR BULLETIN 25

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221 SPINOFF National Aeronautics and Space Administration

222 FIGHTING CORROSION

ORIGINATING criteria of the National Association many shapes. The coating contains parti- NASA CONTRIBUTION of Corrosion Engineers for complete cles of magnesium and indium, as well as protection of steel embedded in moisture-attracting compounds that facil- Reinforced concrete structures such as concrete. Testing is being continued at itate the protection process. After the bridges, parking decks, and balconies are the Kennedy's Materials Science Beach coating is applied to the outer surface of designed to have a service life of over 50 Corrosion Test Site. reinforced concrete, an electrical current years. All too often, however, many struc- is established between the metallic parti- tures fall short of this goal, requiring cles and the surfaces of the embedded expensive repairs and protection work ear- PARTNERSHIP steel rebar. This electrical current is lier than anticipated. The corrosion of Cortec® Corporation, of St. Paul, Minne- responsible for providing the necessary reinforced steel within the concrete infra- sota, has licensed the NASA-developed cathodic protection for the embedded structure is a major cause for this prema- technology and markets it under the brand rebar surfaces. Without this protection, ture deterioration. Such corrosion is a name company manu- the embedded steel may continue to dete- particularly dangerous problem for the factures and supplies corrosion protection riorate until failure. facilities at NASA's Kennedy Space solutions to the petrochemical, Center. Located near the Atlantic Ocean electronics/electrical, utility, construc- GalvaCorr is a breakthrough technology in Kennedy is based in one of the tion, military/government, marine, basic with great commercial value for the trans- most corrosive-prone areas in the world. metals, automotive, and equipment main- portation, infrastructure, marine infrastruc- tenance markets. GalvaCorr is a compli- ture, civil engineering, and construction In order to protect its launch support ment to Cortec's line of Migrating industries. Without this technology, embed- structures, highways, pipelines, and other Corrosion ded steel structures will continue to cor- steel-reinforced concrete structures, rode and deteriorate until failure occurs, Kennedy engineers developed the costing companies billions of dollars to PRODUCT OUTCOME Galvanic Liquid Applied Coating repair their infrastructures. Cortec recom- System. The system utilizes an inorganic GalvaCorr is a room temperature liquid mends GalvaCorr for parking decks, ramps, coating material that slows or stops the coating that can be sprayed or hand and garages; commercial and civil engi- corrosion of reinforced steel members applied to concrete structures. is neered structures; bridges and concrete inside concrete structures. Early tests applied easily to vertical, horizontal, and piers; offshore platforms; and utility poles determined that the coating meets the overhead surfaces, and to structures of above water line.

Cortec® is a registered trademark of Cortec® Corporation. GalvaCorr™ and Migrating Corrosion are trademarks of Cortec® Corporation.

The GalvaCorr™ liquid coating is applied to concrete structures such as this bridge in order to protect the structures from corrosion.

34 PUBLIC SAFETY

223 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

Jure Franciškoviü*, Boris Mikšiü**, Ivan Rogan**, Mijo Tomiþiü***

*Longus Co. Ltd. Sachsova 4, 10000 Zagreb, Croatia, email [email protected]

** Cortec Corporation 4119 White Bear Parkway St. Paul MN 55110, USA, email [email protected]

** Cortecros Co.Ltd. Production & Supplay of Corrosion Control Systems Nova Ves 57, 1000 Zagreb, Croatia, email [email protected]

*** Škiljo Gradnja Co.Ltd. 21270 Zagvozd, Croatia

Key words: Migrating Corrosion Inhibitors (MCI)

Abstract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þH  

224 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

1. INTRODUCTION According to statistical indicators, damages of the reinforced concrete structures caused by the corrosion of the reinforcing steel make more than 80% of all damages of the reinforced concrete structures. Corrosion protection of the reinforcing steel and the protection of the new and the restoration of the old reinforced concrete structures by means of MCI-corrosion inhibitors and anticorrosion materials, as well as with the systems, which contain these inhibitors, represents important contribution and big step forward to the prolongation of the durability and the lifetime of the reinforced concrete structures, and herewith to the major reduction of the maintenance costs, as well as to the effectiveness of the building use. MCI-corrosion inhibitors and anticorrosion materials and the systems, i.e. those, which contain these MCI- inhibitors for the protection of the reinforcing steel and the protection of the new and the restoration of the old reinforced concrete structures, have been used successfully around the world for over 25 years. 3URGXFWRIWKHLURQFRUURVLRQ)HLVLURQR[LGH)H[2\ 2 Fe + 1 ½ O2 + H2O + heat 2 FeOH 1 vol ca. 2,5 vol -“Pure” iron oxide has ca 2,5 times bigger volume than metallic iron. -Reinforcing steel is not pure iron, but its alloy: steel. -Products of corrosion are iron oxide mixture, depending on the compound and concentration of the reactants, and on the thermodynamic conditions at which the electrochemical corrosion reaction unfolds, and the volume of the developed corrosion products is ca 3-12 times bigger than the initial volume of the reinforcing steel/iron. -Corrosion occurrence on the surface of the reinforcing steel causes not only decrease of adhesion/adherence between the reinforcing steel and the concrete, as well as the reduction of the reinforcing steel section, but also – due to the big increase of the volume of the corrosion products in relation to the initial reinforcing steel volume – huge pressures, which cause appearance of the fissures, setting apart, cracking and scaling of the concrete protection layer above the reinforcing steel.

2. MIGRATORY CORROSION INHIBITORS Migrating corrosion inhibitors are chemical compounds on the amine basis (e.g. aminocarbocsylates, amino alcohols, and o.), which through the process of chemical adsorption, so called chemisorptions, »bind»/adsorb on the surface of the reinforcing steel/iron (and other metals), making on the surface an firm and resistant micro layer thick ca 20 μm, resistant to many aggressive substances from the environment, primarily to the impact of the chloride, in the nature omnipresent, and simultaneously very aggressive against the iron oxides, which it chemically destroys. 0&,FRUURVLRQ LQKLELWRUV protect the reinforcing steel against the corrosion in both oxidation ranges: cathode and anode range, in distinction from some other types of corrosion inhibitors, such as e.g. nitrites – therefore are MCI-corrosion inhibitors also designate as mixed corrosion inhibitors. MCI-corrosion inhibitors on the basis of amine compounds belong to the group of so called cathode, respectively cathode-anode inhibitors, which adsorb (through chemisorptions) on the surface of the reinforcing steel, preventing diffusion of the corrosion reactants (O2,

225 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

H2O) to the do reinforcing steel, and in this way they protect it against the oxidation processes, in distinction from anode inhibitors on the nitrites and/or chromates basis, which protect the reinforcing steel from the corrosion through the anode passivisation, so that they themselves participate in the anode process, i.e. oxidize instead of main metal. Only the mechanically deteriorated concrete layer is removed, until the internal adhesion and the adhesion to the reinforcing steel of 1,5 N/mm2 is reached, and upon that: 1. Cleaned and made rough substratum is impregnated by means of MCI-inhibitor, 2. Concrete surface is reprofiled and open reinforcing steel closed by means of repair mortar, which contains MCI-inhibitor and 3. The concrete surface is finally worked out with the protective-decorative coat or hydrophobic impregnation, both containing MCI-inhibitor aiming at the protection of the reinforced concrete structure against moistening, impact of the atmospheric agents, freezing, salts and other aggressive impacts in the environment. It is important to stress that the protection of the reinforcing steel against the corrosion and the protection of the new, respectively old reinforced concrete structures needs to be performed applying complete protection system, as stated and not only partial, because only full protection system protects the reinforcing steel enduringly and efficiently against the corrosion and the reinforced concrete structure against the deterioration /damage.

3. QUALITY CRITERIA FOR THE CORROSIVE REPAIR- PROTECTIVE MATERIALS AND SYSTEMS 3.1. Quality criteria of the cleaned concrete Quality criteria of the cleaned concrete substratum and of the reinforcing steel of the reinforced concrete structures for the application of the Ac-repair-protective systems containing MCI-inhibitors: 1-Tensile strength of concrete substratum and adhesiveness of the concrete and reinforcing steel: 1,5 N/mm2 2-Surface roughness – depending on the repair mortar layer thickness: ca 5mm for layers with thickness ca 10-50 mm and ca 1mm for layers with thickness 2-10 mm 3-pH: alkaline range, >9 4-Chlorides concentration: without limit (some authors state max 1%) 5-Openness of the concrete surface structure: >50% visible aggregate grains, degree of coverage of the grains with the cement matrix ca 2/3 grain volume 6-Cleaness grade of the cleaned reinforcing steel: min SA 2 resp. St3 (according to international standards ISO 8501-1, SIS 05 59 00 1967, DIN 55 928-Teil 4, ASTM D 2200-67, SSPC VIS) depending on the cleaning method: sandblasting, shot blasting, hydro dynamically, manually.

3.2. Quality criteria of corrosion protective Quality criteria corrosive repair-protective system/layer materials above the reinforcing steel: concrete, resp. repair mortar, protective-decorative coat, resp. hydrophobic impregnations, all containing MCI-inhibitors:

226 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

1-Fluids impermeability: Gases permeability coefficient 1x10-16m2 (EN 993-4) 2-Chlorides diffusion: < 1x10-12 m2/s (GF) 3-Capillary water absorption coefficient: <10-1kg/m2h1/2 (HRN.U.M8.300) 4-Alkalinity: pH > 9,5 5-Anticorrosive reinforcing steel protection expressed in corrosion current intensity/density: - Accord. to ASTM STP 1065: < 0,1 A/cm2

4. PROCEDURE OF THE RESTORATION OF THE REINFORCED CONCRETE STRUCTURE OF THE MODULE NO.3 ON THE WHARF NO.5 IN THE PORT PLOýE CARRIED OUT DURING THE YEAR 2005 The works were carried out by the company ŠKILJO-GRADNJA, Zagvozd, according to the restoration project elaborated by the company GEOKON, Zagreb. The quality of the used materials and of performed works has tested and controlled IGH-Regional centre, Split.

Figure 1: The module No. 3 in port Ploe

4.1 Preparatory works Cleaning of the concrete surface and reinforcing steel through hydrodynamic removal of the deteriorated material with the high pressure water jet (>2000 bar) with a view to prepare the substratum for the application of the material of the repair-protective system: from the reinforcing steel separated and deteriorated protective concrete layer was removed all to the sound, clean and firm substratum (quality criterion: tensile strength of the concrete substratum and adhesiveness between the concrete and reinforcing steel: 1,5

227 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

N/mm2). Corroded reinforcing steel was cleaned with the hydrodynamic water jet to the cleanness grade min SA2 resp. manually to St3. High pressure pump was placed on the floating platforms from which the applying of the repair mortar and the final superficial treatment with the protective-decorative coat, resp. with the hydrophobic impregnation was performed. Transport of the material and the communication of people were performed through the openings in the reinforced concrete slab. Corrosion protection of the reinforcing steel was performed with the polymer cement coating, containing MCI-inhibitor. Application with the brush in 1-2 layers, consumption cca 0,2 kg/m 12 mm, for the12 mm diameter reinforcing steel.

4.2 Impregnation Impregnation of the entire concrete surface was with the water solution (1:4) of the corrosion inhibitor MCI – in powder. Application was with the brush or roller in 2 layer of the total yield cca 25 m2/kg.

Figure 2.: Impregnation concrete surface

4.3 Reprofilation Reprofilation of the concrete surface and the covering of the exposed reinforcing steel was performed with the repair mortar containing MCI-inhibitor, with the manual application in 1-3 layers depending on the total thickness of the mortar layer (on some areas mortar thickness even to 8 cm). Freshly applied repair mortar needed “curing”/protection against to fast drying and loss of technological moisture. On the concrete surfaces of the faces of the wharf, exposed to the insolation and to the air circulation, freshly applied repair mortar was protected from the to fast drying by means of the curing on the basis soya oil containing MCI inhibitor, applied with the brush or roller in one layer, yield ca 5 m2/l.

228 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

Figure 3.: Reprofilation concrete surface

4.4. Protection of the entire surface Protection of the entire surface, i.e. concrete and reprofiled with the repair mortar, from the impact of the moisture and atmospheric agents was performed with the protective- decorative coat, or hydrophobic impregnation: :KDUIIDFHwas treated with the protective-decorative coat (colour light grey) on the basis of 1-k acrylate binder containing MCI-inhibitor, applied with the brush or roller in two layers of the total yield ca 8 m2/l and, - &RQFUHWHVXUIDFHVRQWKHVRIILWDQGLQWKHLQWHULRURIWKHVWUXFWXUH were protected with treatment with the hydrophobic impregnation on the basis of sylane-syloxane in the water medium containing MCI-inhibitor, application with the brush or roller in 1-2 layers, treated surface does not change appearance or colour, yield, ca 3,5m2/l.

229 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

.

Figure 4.: MCI coating on the concrete surface

4.5 Report by the IGH-PC Split Report by the IGH-PC Split on the quality control of the built in material and on the quality of the realised works is positive, so it is stated in: - it.2.1. Preliminary testing of the quality of the chosen material: on the basis of the obtained test results, it was concluded that the restoration corrosive repair mortar conforms to the criteria stated in the Working project of the design company GEOKON - it.2.2. Preliminary testing of the quality of the readiness of the substratum: tensile strength of the concrete substratum „pull off“ comes to > 1,5 N/mm2, through which fact it conforms to the required criterion, as well as chlorides concentration, which comes to <0,4% - it.2.3. Control testing of the quality of the built in material: on the basis of the obtained continuous test results in relation to the repair mortar quality, it was concluded that the repair mortar built in at the wharf no.5, module no.3, in the port Ploe conforms to the conditions and criteria stated in the Working project - it.2.4. Control testing of the quality of the realised restoration system: on the basis of the daily obtained continuous test results in relation to the repair mortar quality, it was concluded that the repair mortar built in the every porthole of the module no.3, in the port Ploe conforms to the conditions and criteria stated in the Working project - it.3. Final evaluation of the continuous control quality: it was confirmed that the quality of the materials and works was proved through prescribed and documented testing and that it is in accordance with the conditions and criteria given in the Working design “Restoration of the soffit and the face of the reinforced concrete structure of the wharf no.5” elaborated by the company GEOKON, Zagreb.

230 J. Franciškoviü, B. Mikšiü, I. Rogan, M. Tomiþiü: PROTECTION AND REPAIR OF REINFORCED CONCRETE STRUCTURES BY MEANS OF MCI-INHIBITORS AND CORROSION PROTECTIVE MATERIALS

5. REFERENCES [1] Bjegovi D., Mikši B., Ukrainczyk V., Corrosion protection of the reinforcing steel through migratory inhibitors [2] Bjegovi D.., Designing of the lifetime of the reinforced concrete structures on roads, Scientific-research project [3] Haynes M., (1997), Use of migratory corrosion inhibitors, Construction Repair July/August [4] Mikši B., Gelner L., Bjegovi D., Sipos L., Migrating Corrosion Inhibitors for Reinforced Concrete, Proceedings of the 8th European Symposium on Concrete Inhibitors, University of Ferrara, Italy, 1995 [5] Broomfield J., The pros and cons of corrosion Inhibitors, Construction Repair July/August, 1997 [6] Alonso C., Andrade C., Effect of Nitrite as a Corrosion Inhibitor in Contaminated and Chloride-free Carbonated Mortars, American Concrete Institute Materials Journal, 1990 [7] Yongmo, X.; Hailong, S: Comparison of Amin- and Nitrite-Inhibitorsin Carbonation- Induced Corrosion; China Building Materials Academy, Materials Performance, Jan. 2004., p 42-46 [8] Berke N., Corrosion Inhibitors in Concrete, Concrete International 7, 1991 [9] Technical documentation of the company CORTEC Corporation, Minnesota, USA [10] Report IGH-PC-Split on the testing results of the quality of the built in materials and on the quality of the realised restoration works in 2005., No.3617/340-05/VN, November 2005.

231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 Paper 04323

IMPROVING DURABILITY OF REINFORCED CONCRETE STRUCTURES USING MIGRATING CORROSION INHIBITORS

Behzad Bavarian and Lisa Reiner Dept. of Manufacturing Systems Engineering & Management College of Engineering and Computer Science California State University, Northridge, USA

ABSTRACT

Steel corrosion poses formidable concerns for long term reliability of reinforced concrete structures. In the United States, with its vast infrastructure of concrete and steel bridges, superhighways, and reinforced concrete buildings, billions of dollars have been spent on corrosion protection. Among the commercial technologies available today, migrating corrosion inhibitors (MCIs) show versatility in their use as admixtures, surface treatments, and in rehabilitation programs. The effectiveness of two commercial inhibitors applied to the reinforced concrete surface was evaluated. The corrosion behavior of the steel rebar was monitored using AC electrochemical impedance spectroscopy (EIS). Corrosion potentials and polarization resistance values corroborated the inhibiting effects of the amine carboxylate and amino alcohol chemistry in an aggressive environment. The MCI products have successfully inhibited corrosion of the rebar in a 3.5% NaCl solution for duration of testing. MCI protected samples showed an average corrosion rate of 0.34 compared to untreated samples that were 1.50 This will increase the life expectancy by more than 15 years. XPS analysis demonstrated the presence of inhibitor on the steel rebar surface indicating MCI migration through the concrete.

Keywords: steel rebar, migrating corrosion inhibitors, electrochemical monitoring techniques

INTRODUCTION

Corrosion is one of the main concerns in the durability of materials and structures. Much work has been done to develop a corrosion inhibition process to prolong the life of existing structures and minimize corrosion damages in new structures. Carbon steel is one of the most widely used engineering materials despite its relatively limited corrosion resistance. Iron in the presence of oxygen and water is thermodynamically unstable, causing its oxide layers to break down. Corrosion undermines the physical

259 integrity of structures, endangers people and the environment, and is very costly. Because carbon steel represents the largest single class of alloys used [1], corrosion is a huge concern. The billions of dollars committed to providing protective systems for iron and steel have provided new ways of combating corrosion. Migrating corrosion inhibitors (MCIs) are one means of protection for reinforced concrete structures. Previous studies have established the benefits of using migrating corrosion inhibitors, the importance of good concrete, and the significance of the ingredients used to make the concrete [2-6]. Reinforcing steel embedded in concrete shows a high amount of resistance to corrosion. The cement paste in the concrete provides an alkaline environment that protects the steel from corrosion by forming a protective ferric oxide film. The corrosion rate of steel in this state is negligible. Factors influencing the ability of the rebar to remain passivated are the water to cement ratio, permeability and electrical resistance of concrete. These factors determine whether corrosive species can penetrate through the concrete pores to the rebar oxide layer. In highly corrosive environments (coastal beaches and areas where deicing salts are common), the passive layer will deteriorate, leaving the rebar vulnerable to chloride attack, thereby requiring a corrosion prevention system.

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 [2]. Organic inhibitors use compounds that work by forming a mono molecular film between the metal and the water. In the case of film 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 [3, 7]. 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 time to reach the rebar's surface and to form a protective layer. MCIs can be incorporated as an admixture or can be surface impregnated on existing concrete structures. With surface impregnation, diffusion transports the MCIs into the deeper concrete layers, where they will inhibit the onset of steel rebar corrosion. Laboratory tests have proven that MCI corrosion inhibitors migrate through the concrete pores to protect the rebar against corrosion even in the presence of chlorides [4, 5].

EXPERIMENTAL PROCEDURES

The main objective of this investigation was to study the corrosion inhibiting properties and to determine whether these inhibitors protect the steel rebar in concrete. Electrochemical monitoring techniques were applied while samples were immersed in 3.5% NaCl at ambient temperatures. Due to the low conductivity of concrete, the corrosion behavior of steel rebar was monitored using AC electrochemical impedance spectroscopy (EIS). Effectiveness of this MCI product was based on changes in the polarization resistance and the corrosion potential of the rebar, measurements that can be performed without destroying the sample. This data can provide early warning of structural distress and evaluate the effectiveness of corrosion control strategies that have been implemented. Once rebar corrosion has proceeded to an advanced state, where its effects are visually apparent on the concrete surface, it is too late for minor patchwork. The key to fighting corrosion is in preventative measures.

Prior to investigating the performance of two inhibitors, MCI 2020 and MCI 2020M, their potentiodynamic behavior was assessed. Studies were conducted in a saturated Ca(OH)2 solution with

260 and without chloride ions using EG&G M352 DC corrosion test software. Comparisons of the polarization behavior were made for the steel rebar in solution with varying concentrations of inhibitor and the introduction of a corrosive species (2000 ppm NaCl). The effects of the mixed inhibitor in an alkaline environment similar to the concrete medium were observed.

In this investigation, the steel rebar/concrete combination is treated as a porous solution and modeled by a Randies electrical circuit [8]. EIS tests performed on a circuit containing a capacitor and two resistors indicate that this model provides an accurate representation of a corroding specimen. EIS tests, by means of a small amplitude signal of varying frequency, give fundamental parameters relating to the electrochemical kinetics of the corroding system. The values of concern in this study are Rp and

The RP value is a measure of the polarization resistance or the resistance of the surface of the material to corrosion. is a measure of the solution resistance to the flow of the corrosion current. By monitoring the RP value over time, the relative effectiveness of the sample against corrosion can be determined. If the specimen maintains a high RP value in the presence of chloride, it is considered to be passivated or immune to the effects of corrosion. If the specimen displays a decreasing Rp value over time, it is corroding and the inhibitor is not providing corrosion resistance.

Concrete samples with dimensions 20cm x 10cm x 10cm were prepared using a 20 cm steel rebar (class 60, 1.27 cm diameter) and a 20 cm Inconel 800 metal strip (for the counter electrode). A concrete mixture containing commercial grade-silica, Portland cement, fly ash, and limestone (concrete mixture ratio: 1 cement/2 fine aggregate/4 coarse aggregate) were combined with one-half gallon water per 27.2 Kg (60-lb) bag in a mechanical mixer. The water to cement ratio was varied to achieve the two densities and the coverage layer was maintained at 2.5 cm (1 inch) concrete for all samples. Compressive strengths were roughly 27.6 MPa (4000 psi) for the low density and 41.4 MPa (6000 psi) for the high density concrete cured for 28 days per ASTM C387 [9], All samples were sandblasted to remove loose particles and provide surface uniformity. The experiments were conducted using an EG&G Potentiostat/Galvanostat (Model 273A with a 5210 Lock-in amplifier), EG&G M398 and Power Suite Electrochemical Impedance Software and a Gamry PC4-750 Potentiostat with EIS300 software and Echem Analyst. Bode and Nyquist plots were created from the data obtained using the single sine technique. Potential values were recorded and plotted with respect to time. By comparing the bode plots, changes in the slopes of the curves were monitored as a means of establishing a trend in the Rp value over time. To verify this analysis, the Rp values were also estimated by using a curve fit algorithm on the Nyquist plots (available in the software). In these plots, the Rp and combined values are displayed in the low frequency range of the bode plot and the value can be seen in the high frequency range of the bode plot. The diameter of the Nyquist plot is a measure of the Rp value.

As outlined in Table 1, there were six (6) concrete samples in total, two were surface impregnated with several coats of MCI 2020 and two were coated with MCI 2020M. The inhibitor was applied to the surface of the concrete with a paint brush while partially immersed in a shallow container of inhibitor. The remaining two samples were left untreated and used as standards for comparison. An additional coat of MCI 2022 sealer was used to prevent the inhibitor from washing off in solution. Clear silicon was applied to the concrete/metal interface to prevent easy access for ions. The testing environment was a solution of 3.5% NaCl and water with roughly 175 mm (7 inches) of each sample continuously immersed for 360 days. A Cu/CuS04 electrode was used as the reference and each sample was tested once every two weeks.

261 RESULTS

Many procedures have been developed for monitoring the corrosion of rebar in concrete, each method attempts to improve a shortcoming of an existing technique. Measuring the open circuit potential is very easy and inexpensive, but is not considered very reliable since the potential provides no information about the kinetics of the corrosion process. Linear polarization resistance (LPR) measurements are influenced by IR effects from the concrete. A significant potential drop in the concrete makes an accurate determination of the potential of the rebar surface very difficult. Electrochemical impedance spectroscopy (EIS) is able to overcome the difficulties of the concrete resistance, yet requires more testing time. The different analytical methods of electrochemical impedance spectroscopy are capable of giving more detailed information than LPR. The rebar potential, polarization resistance and current density data can provide information as to whether the rebar is in the active or passive corrosion state. Estimates made from these parameters for Tafel constants can be input into LPR analysis or can be used for corrosion rate measurement and cathodic protection criteria. Evaluation of the effectiveness of corrosion inhibitors and the effects of concrete composition is often based on these variables. For a more comprehensive approach to the corrosion process, several tests methods have been implemented in this investigation.

Corrosion Potentials The corrosion inhibition for the inhibitor identified as MCI 2020 has been investigated over a period of 360 days using AC electrochemical impedance spectroscopy (EIS). Throughout this investigation, changes in the corrosion potential of the rebar were monitored to determine the effects of this commercially available inhibitor. According to the ASTM (C876) standard [10], if the open circuit potential (corrosion potential) is -200 mV or higher, this indicates a 90% probability that no reinforcing steel has corroded. Corrosion potentials more negative than -350 mV are assumed to have a greater than 90% likelihood of corrosion. Figure 1 shows that the corrosion potentials for the samples (except the untreated low density sample) were between the range of 0 mV to -100 mV after 360 days of immersion in NaCl. Given an open circuit potential of-270 mV and declining, the untreated (low density) sample appears to suffer corrosion.

Polarization Resistance This electrochemical technique enables the measurement of the instantaneous corrosion rate. It quantifies the amount of metal per unit of area being corroded in a particular instant. The method is based on the observation of the linearity of the polarization curves near the potential Ecorr. The slope expresses the value of the polarization resistance if the increment diminishes to zero. This Rp value

is related to the corrosion current Icorr by the following Stern-Geary equation: Icorr = Where A is the area of the metal surface evenly polarized and B is a constant that may vary from 13 to 52 mV. For the case of steel embedded in concrete, the best fit with parallel gravimetric losses, results in B = 26 mV for actively corroding steel, and B = 52 mV for passivated steel. Figure 2 shows increasing trends for the samples with polarization resistance values between 60 and 70 The value for the untreated low density sample reached 40 before rapidly declining to 4 at 350 days of partial immersion in the aggressive solution.

Bode Plots Bode plots are not dependent on modeling the corroding system as are polarization resistance values. The electrochemical impedance spectroscopy data are obtained by applying a single sine wave

262 over a range of frequencies while measuring the corresponding impedance. Since the results are independent of an assumed model, the technique is highly reliable. Figure 3 shows a comparison of bode plots for the first day of testing and after 360 days of immersion. There is not much variation in the curves, except for the low density untreated sample which sharply contrasts with the rest.

Potentiodynamic Behavior Figure 4 shows a comparison of the polarization behavior from a potentiodynamic test of steel rebar in a saturated Ca(OH)2 solution. This graph shows the effects of a mixed inhibitor in an alkaline environment similar to the concrete medium with minor reduction in the corrosion current upon addition of MCI. Figure 5 shows the polarization results from the steel rebar tested in a saturated Ca(OH)2 solution with 2000 ppm NaCl. The effects of the inhibitor are far more noticeable in the presence of a corrosive species. The breakdown potential for the rebar tested with no inhibitor was around 350 mV SCE as compared to 600 mV for the rebar tested with 2000 ppm MCI. Figure 6 shows the corresponding current density for the various additions of MCI in column format. Consistent with the graph in Figure 5, the rebar tested in a saturated Ca(OH)2 solution with 2000 ppm NaCl and 2000 ppm MCI had the lowest corrosion rate. According to the data in Table 2, where a level of corrosion severity has been associated with a given icorr value, the sample tested with 2000 ppm MCI and having a corrosion rate of less than 0.34 will have "no expected corrosion damage."

X-ray photoelectron spectroscopy (XPS) The XPS analysis verified the inhibitor's ability to penetrate through the concrete pores by vapor phase diffusion, permeation along the microcracks, and capillary effects. Figure 7 shows the XPS analysis and spectrum for the rebar removed from the MCI treated sample after 320 days. The analyses show an organic compound carboxylate chemistry similar to the migrating corrosion inhibitor compound (nitrogen content, carbon and oxygen ratio is attributed to MCI compound). Depth profiling (using 4 kV Argon ions) measured a 100 nm layer of amine compounds on the rebar surface, confirming surface adherence after migration. Chloride was also found on the surface of the rebar. The XPS results demonstrate that both MCI and corrosive species had migrated in through the concrete capillary system, however, MCI had managed to coat the surface and neutralize the corrosive species (chloride ions and carbon dioxide) to protect the steel rebar.

CONCLUSIONS

At 360 days of immersion, all samples but one (low density-untreated), seem to have maintained a stable passivation layer that has protected the steel reinforcement from the corrosive environment. The MCI products have successfully inhibited corrosion of the rebar in a 3.5% NaCl solution for duration of testing. MCI protected samples showed an average corrosion rate of 0.34 compared to untreated samples that were 1.50 This will increase the life expectancy by more than 10-15 years. XPS analysis demonstrated the presence of inhibitor on the steel rebar surface indicating MCI migration through the concrete. Depth profiling showed a layer of amine-rich compounds and chloride ions on the rebar surface; however the neutralizing effects of the inhibitor assured satisfactory corrosion resistance.

263 ACKNOWLEDGEMENT

Thanks go to the National Aeronautics and Space Administration (NASA-IRA program) and CORTEC Corp. for their sponsorship of this project.

REFERENCES

1. http://www.corrosioncost.com/home.html 2. D. Bjegovic and B. Miksic, "Migrating Corrosion Inhibitor Protection of Concrete," MP, NACE International, Nov. 1999. 3. D. Stark "Influence of Design and Materials on Corrosion Resistance of Steel in Concrete." R & D Bulletin, RD098.01T. Skokie, Illinois: Portland Cement Association, 1989. 4. B. Bavarian and L. Reiner, "Migrating Corrosion Inhibitor Protection of Steel Rebar in Concrete," Materials Performance, 2003. 5. B. Bavarian and L. Reiner, "Corrosion Protection of Steel Rebar in Concrete using Migrating Corrosion Inhibitors," BAM 2001. 6. J. P. Broomfield et al, "Corrosion of Metals in Concrete," ACI 222R-96. 7. R. Dagani, "Chemists Explore Potential of Dendritic Macromolecules As Functional Materials," Chemical & Engineering News, American Chemical Society, June 3, 1996. 8. D. Jones, Principles and Prevention of Corrosion, 2nd Edition, Prentice Hall, NJ, 1996. 9. ASTM C387 Standard Specification for Packaged, Dry, Combined Materials for Mortar and Concrete, Vol. 04.02. 10. ASTM C876 Standard Test Method for Half Cell Potentials of Reinforcing Steel in Concrete, Annual Book of ASTM Standards, Vol. 04.02, 1983.

Table 1. Sample specifications.

Number of Concrete Surface Coating Density Water to cement samples ratio 1 No treatment-control sample Low = 2.08 g/cm3 0.65 1 No treatment-control sample High = 2.40 g/cm3 0.35 1 MCI 2020 Low = 2.08 g/cm3 0.65 1 MCI 2020 High = 2.40 g/cm3 0.35 i MCI 2020M Low = 2.08 g/cm3 0.65 i MCI 2020M High = 2.40 g/cm3 0.35

264 Figure 1: Corrosion Potential vs Time: Various Density Concrete (MCI 2020M, MCI 2020, untreated).

0

-50

-100

-150

-200

-250

-300 0 SO 100 150 200 250 300 350 400 Time of Submersion (Days)

Figure 2: Polarization Resistance (Rp) Versus Time; Comparison of treated (MCI 2020 & Md 2020M) low & high density concrete with untreated concrete.

8.0E+04 High denstty-MCI 2020M Low denslty-MCI 2020 7.0E+04 High density-untreated High denslty-MCI 2020 Low denslty-MCI 2020M 6.0E+04 Low density-untreated

5.0E+04

4.0E+04

3.0E+04

2.0E+04

1.0E+04

O.OE+00 0 so 100 150 200 250 300 350 400 TIME (Days)

265 Figure 3: AC Impedance Spectroscopy Results (Concrete density H = 2.40 g/cm3, L = 2.08 g/cm3) Bode Plot Comparison of MCI 2020 & 2020M with Untreated Concrete

1.0E+05

1.0E+04

1.0E+03

1.0E+02

1.0E+01 0.0001 0.001 0.01 0.1 1 10 100 1000 10000 100000 FREQUENCY (Hz)

Figure 4: Polarization Bahavlor of Steel Rabor In a saturated Ca(OH)2 solution +varlous ppm MCI additions, pH 12.5, 23 C 1.00E-03

1.00E-04

1.00E-05

1.0OE-06

1.0OE-O7

1.00E-08

1.0OE-09 -1000 -500 0 500 1000 1500 Potential, mVsce

266 Figure 5: Polarization Behavior of Steel Rebar In a saturated Ca(OH), solutlon+2000 ppm NaCI and various ppm MCI additions, pH 12.4, 23 C

1.00E-03

1.00E-04

1.00E-05

1.00E-06

Ca(OH)2 +2000ppm CI- +2000ppm MCI 1.00E-07 +2000ppm CI- +1200ppm MCI +2000ppm CI- + 1000ppm MCI +2000ppm CI- + 5OOppm MCI +2000 ppm CI-

1.00E-08

1.00E-09 -1000 -500 0 500 1000 Potential, mVsce

Figure 6: Polarization Behavior of Steel Rebar In a saturated Ca(OH)2 solution +2000 ppm NaCI and various ppm MCI additions, pH 12.4, 23 C

267 268 269

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349 Paper No. 06347

Current Progress in Corrosion Inhibition of Reinforcing Steel in Concrete using Migrating Corrosion Inhibitors

Bezad Bavarian and Lisa Reiner

Dept. of Manufacturing System Engineering and Management California State University, Northridge 18111 Nordhoff Street Northridge, California 91330-8332, USA

ABSTRACT

Several migrating corrosion inhibitors for reinforced concrete were investigated using ASTM G109 and Modified G109. XPS depth profiling showed a 90-100 nm amine-rich layer and chloride ions on the steel rebar surfaces indicating that the modified corrosion inhibitor molecules had suppressed chloride ion interaction and protected the steel rebar passivation layer. There is no indication of corrosion after 400 days of testing. The inhibitor treated samples showed improved resistance polarization (Rp was in the 50 kohm to 60 kohm range, corrosion potentials ranged between -64 mV and -103 mV) and potentiostatic tests showed a significantly lowered corrosion rate. These findings led to investigating the adsorption mechanism where comprehensive testing established a Langmuir adsorption isotherm and verified that chemisorption was responsible for the strong bonding between the inhibitor monolayer and the steel surface.

Keywords: reinforced concrete, migrating corrosion inhibitors, steel corrosion, XPS, adsorption mechanism

INTRODUCTION

The US infrastructure is heavily reliant upon construction materials that are vulnerable to corrosion. Conventional materials like reinforced concrete, prestressed concrete and steel that are used in bridges, highways and building foundations. Reinforcing steel embedded in concrete, however, shows a high amount of resistance to corrosion. Concrete is a highly alkaline material with a pH near 12 that Copyright ©2006 NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be in writing to NACE International, Conferences Division, 1440 South Creek Drive, Houston, Texas 77084. The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A.

350 provides a protective oxide layer for steel when embedded. Under corrosive conditions where oxygen and moisture can ingress through the pores of the concrete to reach the rebar surface, the alkalinity can change and cause the passive layer to breakdown. Carbonation of the concrete, where carbon dioxide reacts with calcium hydroxide or other cement hydrates, and ingress of chlorides are major causes of steel rebar corrosion in concrete. In the case of reinforced concrete samples placed in contact with a 3% NaCl solution, the stages for rebar corrosion deterioration would begin with chloride penetration into the concrete, then corrosion initiation or passive layer breakdown, more progressed corrosion, micro cracking and eventual spalling. Corrosion is a complex phenomenon with many interactions to consider (structural, physical, chemical and environmental considerations), for steel in rebar, as the passive film degrades by chloride ions or the pH drops due to carbonation, the metallic iron at the anode is oxidized to form ferrous ions. It is this simplified reaction that has to be prevented or at least mitigated. Much effort has been focused on the design of new structures to reduce or eliminate corrosion through increased concrete coverage using reduced permeability concrete, admixtures, migrating corrosion inhibitors and replacing the steel reinforcement with alternative materials.

The commercially available migrating corrosion inhibitors used to surface impregnate the concrete samples in this investigation are based on amino carboxylate chemistry [1]. They are designed to provide both anodic and cathodic protection with transport to the rebar surface in roughly 100 days. Transport begins through the concrete pores and proceeds through the capillary structure by liquid diffusion, high vapor pressure and by following microcracks to the rebar surface. At the rebar surface, the inhibitor forms a monomolecular layer of protection against corrosive species [2]. To better understand how the inhibitor works or by what mechanism it is able to adsorb to the surface, a surface adsorption isotherm has to be determined. Many models for adsorption isotherms have been defined (Temkin, Freundlich, Langmuir and Frumkin) and each explains a different relationship between concentration and inhibitor surface coverage on a metal or alloy surface [3, 4]. By measuring the corrosion current density of the non-inhibited solution (Blank) and inhibited solution (or by measuring polarization resistance), the surface coverage, ș, can be calculated from the following formula:

Icorr(B)  Icorr(I ) Rp(I )  Rp(B) ș = or ș = Icorr(B) Rp(I )

Where Icorr (B) and Rp (B) are the corrosion current density and polarization resistance of the Blank solution, respectively, while Icorr (I) and Rp (I) are the corrosion current density and polarization resistance of the inhibited solution. Based on the adsorption isotherm, the adsorption equilibrium T constant, Kad, can be calculated; for the Langmuir isotherm: KadC= ( ). This can then be used to 1  T calculate the free standard energy of adsorption, ǻGad = -RT Ln (Kad). By repeating the experiment at 0 different temperatures, the enthalpy of adsorption, ǻHad, can be calculated from Ln C = (ǻHad /RT) + constant. Chemisorption (chemical adsorption) makes strong covalent bonding between the chemical and the surface, so the ǻGad is usually much higher than for physisorption (physical adsorption) that involves van der Waals interaction. The criterion for chemisorption varies, it can require as little as -40 kJ/mol energy or as much as -100 kJ/mol energy [4-5]; physisorption requires energy between -5 to -25 kJ/mol [4]. The activation energy ('Ha) of corrosion is calculated using an Arrhenius type relationship where [5],

351  '+a Icorr v exp( ) RT

The slope of this graph will represent -'Ha /R where R is the gas constant.

EXPERIMENTAL PROCEDURES

The ASTM G 109-92 test structure provides a less aggressive corrosion environment compared with protocols for samples that were partially immersed in a 3.5% NaCl solution for the entire experiment. In the test method described in G 109, Plexiglas dams hold the 3.0% NaCl solution in contact with the surface of the concrete for two week periods and are then set to dry for 2 weeks with this cycle repeating for the duration of the experiment. As seen in Figure 1, three steel rebar were cast in concrete (density of 142 lbs/cu ft) with 1 inch coverage from the top and bottom rebar; concrete dimensions were 3 inches width x 6 inches height, Plexiglas dams were 3 inches x 3 inches. Two concrete samples were coated with Cortec’s MCI 2020M inhibitor (inhibitor 1) and MCI 2022 sealer; roughly 15 mL of inhibitor was absorbed into the concrete for 2 coats. Two concrete samples were coated with MCI 2022 inhibitor (inhibitor 2) and sealer. All inhibitor and sealer were painted on with a brush. The remaining 2 samples were untreated (references). Several days after the inhibitor and sealer were applied, the Plexiglas dams were fixed to the top of the concrete beams with silicone.

The rebar potential, polarization resistance and current density data can provide information as to whether the rebar is in the active or passive corrosion state. Estimates made from these parameters for Tafel constants can be input into LPR analysis or can be used for corrosion rate measurement and cathodic protection criteria. Evaluation of the effectiveness of corrosion inhibitors and the effects of concrete composition is often based on these variables. For a more comprehensive approach to the corrosion process, several tests methods were implemented in this investigation. These studies were conducted using an EG&G Potentiostat/Galvanostat (Model 273A with a 5210 Lock-in amplifier), EG&G M398 Electrochemical Impedance Software and a Gamry PC4/750™ Potentiostat/Galvanostat/ZRA using electrochemical impedance spectroscopy EIS300™ systems. The steel rebar/concrete combination can be treated as a porous solution and was modeled by a modified Randles electrical circuit. EIS tests performed on a circuit containing a capacitor and two resistors indicate that this model is an accurate representation of an actual corroding specimen. EIS testing was done by applying a small amplitude-alternating potential signal of varying frequency to the concrete/rebar system, providing fundamental electrochemical parameters. A standard CuCuSO4 reference electrode was used with a steel rebar counter electrode in a 3-electrode configuration with a steel working electrode.

In previous investigations using XPS depth profiling, it was determined that a 90-100 nm amine rich layer and chloride ions were present at the surface of the steel rebar. The XPS results demonstrated that both inhibitor and corrosive species had migrated in through the concrete capillary system, but the inhibitor had managed to coat the surface and neutralize the corrosive species (chloride ions and carbon dioxide) to protect the steel rebar [2]. This information led to investigating the mechanism by which adsorption occurs. To collect data for adsorption isotherms, flat samples were polished (600 grit sandpaper), placed in a flat cell and tested in solutions containing tap water and 3.5% NaCl with varying inhibitor concentration. The Rp value (determined from the EIS Bode plots) was used to fit the data into an adsorption isotherm model. To correlate the corrosion rate with the inhibitor concentration, a series of

352 linear polarization resistance (LPR) tests were conducted using Gamry’s DC105 software and a blank solution (no inhibitor) with 0.5% NaCl; inhibitor concentration was increased by 200 ppm for each subsequent test. To explore the activation energy and adsorption thermodynamics for the inhibitor, cyclic polarization was conducted in temperatures ranging from 23°C to 63°C.

RESULTS & DISCUSSION

Previous experiments (conducted on commercially available corrosion inhibitors) have shown noticeable differences in the treated and untreated samples around 250 days of constant immersion [2, 6- 8]. In Figure 2, corrosion potentials vs time are graphed for comparison; this was a constant immersion test. Inhibitor 1 was applied to the surface, mixed in the mortar and directly applied to the rebar before casting (concrete density: 140 lbs/ft3). The graph also shows untreated concrete samples and samples surface treated with other inhibitors (concrete density for L=130 lbs/ft3) [2]. Corrosion potentials for an untreated low density concrete sample measured 150 mV more negative than the other samples. The concrete sample was cracked open to physically verify that the rebar was corroding. Figure 3 shows a comparison of the corrosion potential versus time with little variation over the course of a year. The steel rebar appears to have formed a passive layer around day 150 and remained stable in the range of -40mV to 135 mV. Figure 4 shows Rp values versus time obtained by curve fitting the bode plots (Figure 5). The Rp values measured approximately 10000 ohms at the beginning of testing and increased to a range between 50000 to 60000 ohms by day 400. EIS bode plots for treated and untreated concrete are from initial tests and plots from data collected between day 371 and 400.

The potentiostatic tests (Figure 6) contrast the dramatic reduction in current density with increasing inhibitor concentration. The corrosion current density for the blank solution was 10.5 μA and decreased to 0.45 μA with 2000 ppm inhibitor; at saturation level (about 2000 ppm), the corrosion rate remained steady. From the corrosion current for the given concentrations, different adsorption isotherms were constructed to find the best fit for the data. Models were constructed based on surface adsorption which is a function of the corrosion current and the concentration of the solution. Table 1 contains the data obtained from linear polarization resistance. The EIS results showed that adsorption of inhibitor 1 on to the steel surface fits with the Langmuir adsorption isotherm [3, 4] since Ln C and Ln ș-Ln (1-ș) have a linear relation as is shown in (Figure 7). The extent of surface coverage is expressed as the fractional coverage, ș, or the ratio of adsorption sites occupied over the number of adsorption sites available. The changes in enthalpy of adsorption (ǻHad) and free standard energy of adsorption (ǻGad) were obtained with adsorption isotherms and elevated temperature tests [3]. Based on results from cyclic o polarization, Ln Icorr vs. 1000/T K was plotted (Figure 8); the slope of each line represents (-ǻHad /R). Figure 8 contains the data that was used to calculate the activation energy required to corrode the steel with inhibitor (-46 kj/mol) and without (-30 kj/mol). The value calculated for the inhibitor would indicate that the adsorption mechanism is achieved by chemically bonding to the surface.

CONCLUSIONS

Surface treated concrete samples with migrating corrosion inhibitors have been subjected to the ASTM G 109 corrosion test for more than 400 days to confirm effectiveness. Corrosion potentials

353 ranged between -64 and -103 mV(Cu/CuSO4); polarization resistance values measured between 50 kohm and 60 kohm. Potentiostatic tests showed a significantly reduced corrosion rate for steel rebar in the presence of inhibitor. From the LPR and EIS analysis and adsorption isotherms, it was determined that adsorption of inhibitor molecules to the steel surface most closely fit with Langmuir adsorption and was controlled by a chemisorption mechanism.

ACKNOWLEDGEMENT

Thanks go to the National Aeronautics and Space Administration (NASA-IRA NCC 5-513 program) for their sponsorship of this grant.

REFERENCES

[1] D. Bjegovic and B. Miksic, “Migrating Corrosion Inhibitor Protection of Concrete,” MP, NACE International, Nov. 1999. [2] B. Bavarian, L. Reiner & C. Y. Kim, “Corrosion Protection of Steel Rebar in Concrete by Migrating Corrosion Inhibitors, NACE Corrosion/2003 paper #03364 (San Diego, CA). [3] W. Durine, R. D Marco, A. Jefferson and B. Kinsella, Journal of the Electrochemical Society, 146 (5) 1751- 1756 (1999) [4] M. L. Free, “A new corrosion inhibition model for surfactants that more closely accounts for actual adsorption than traditional models that assume physical coverage is proportional to inhibition,” Corrosion Science, Volume 46, Issue 12 , December 2004, Pages 3101-3113 [5] M. Lagrenée, B. Mernari, M. Bouanis, M. Traisnel and F. Bentiss, “Study of the mechanism and inhibiting efficiency of 3,5-bis(4-methylthiophenyl)-4H-1,2,4-triazole on mild steel corrosion in acidic media,” Corrosion Science, Vol 44, Issue 3 , March 2002. [6] B. Bavarian & L. Reiner, “Improving Durability of Reinforced Concrete Structures using Migrating Corrosion Inhibitors,” NACE CORROSION/2004 Paper #04323 (New Orleans, LA). [7] B. Bavarian & L. Reiner, “Corrosion Protection of Steel Rebar in Concrete using Migrating Corrosion Inhibitors,” BAM, Germany, 2001. [8] B. Bavarian & L. Reiner, Corrosion Inhibition of Steel Rebar in Concrete using MCI Inhibitors, EUROCORR 2000, London UK, September 2000.

354

Figure 1: ASTM G 109-92 standard concrete/rebar specimens.

100 MS1-surface treated L2022 50 MR1-rebar treated L2021 MM1-mortar coated surface L untreated 0 RF1-untreated

-50

-100

-150

-200 Potential, (mV)

-250

-300

-350

-400 0 50 100 150 200 250 300 350 400 450

Time of Submersion (Days)

Figure 2: Corrosion Potential vs Time for inhibitors that were applied to the surface, mixed in the mortar and directly applied to the rebar before casting (Concrete density: 140 lbs/ft3); the graph also compares untreated samples with untreated concrete (L =130 lbs/ft3) [2].

355 0

-50

-100

-150

-200

-250 reference-1 Potential, (mV) inhibitor 2-1 -300 reference-2 inhibitor 1-1 -350 inhibitor 2-2 inhibitor 1-2 -400 0 50 100 150 200 250 300 350 400 450

Time of Submersion (Days)

Figure 3: Comparison of corrosion potentials for inhibitor treated and untreated concrete samples per ASTM standard G 109.

60000

50000

40000

30000 Rp (Ohms)

20000 inhibitor 2-2 inhibitor 1-1 inhibitor 1-2 10000 reference-1 reference-2 inhibitor 2-1 0 0 50 100 150 200 250 300 350 400 450

Time of Submerged (Days)

Figure 4: Comparison of polarization resistance (Rp) for treated concrete with untreated concrete per ASTM G 109.

356 1.00E+05 inhibitor 1-1 inhibitor 1-1 inhibitor 2-1 inhibitor 2-1 reference-1 reference-1 1.00E+04 inhibitor 1-371 inhibitor 1-371 inhibitor 2-400 inhibitor 2-400 reference-371 reference-397 1.00E+03 |Z| ohms

1.00E+02

1.00E+01 0.0001 0.001 0.01 0.1 1 10 100 1000 10000 100000 Frequency, Hz

Figure 5: EIS bode plots for treated and untreated concrete from initial tests and plots from data collected between day 371 and 400.

5.00E-04

4.50E-04

4.00E-04

3.50E-04 blank 500 ppm 3.00E-04 1000 ppm 1500 ppm 2.50E-04 2000 ppm

2.00E-04 Current Desnity (A/cm^2) Desnity Current 1.50E-04

1.00E-04

5.00E-05

0.00E+00 0 500 1000 1500 2000 2500 3000 3500 4000 Time (Sec.) Figure 6: Potentiostatic tests demonstrate a dramatic decrease in current density with higher concentration of inhibitor. Samples were polarized to +20 mV over the open circuit potential.

357

Figure 7: Langmuir adsorption isotherm for different migrating corrosion inhibitor concentrations.

-9.5 MCI Blank Linear (MCI) y = -5.255x + 6.2183 Linear (Blank) -10 R2 = 0.997

-10.5 Ln (Icorr) -11

y = -4.051x + 2.006 R2 = 0.9862 -11.5

-12 2.95 3 3.05 3.1 3.15 3.2 3.25 3.3 3.35 3.4

o 1000/T (1/ K) Figure 8: Activation energy calculations for corrosion reactions of steel with and without inhibitor at various temperatures.

358 Concentration (ppm) Icorr (μA) ș 1-ș Ln ș Ln (1-ș) Ln ș-Ln (1-ș) 010.501 200 6.32 0.398 0.602 -0.921 -0.508 -0.413 400 4.5 0.571 0.429 -0.560 -0.847 0.288 600 3.7 0.648 0.352 -0.434 -1.043 0.609 800 2.6 0.752 0.248 -0.285 -1.396 1.111 1000 1.7 0.8380.162 -0.177 -1.821 1.644 2000 0.45 0.957 0.043 -0.044 -3.150 3.106 Table 1: LPR test r esul ts for g ive n conc ent rations of i nhibitor 1.

359 Presented at EUROCORR 2003, Budapest, Hungary

Improving Durability of Reinforced Concrete Structures using Migrating Corrosion Inhibitors

Behzad Bavarian and Lisa Reiner

Dept. of Manufacturing Systems Engineering & Management College of Engineering and Computer Science California State University, Northridge, USA 91330

Abstract Corrosion creates long term reliability issues for reinforced concrete structures. Billions of dollars have been spent on corrosion protection of concrete and steel bridges, highways, and reinforced concrete buildings. Among the commercial technologies available today, migrating corrosion inhibitors (MCIs) show versatility as admixtures, surface treatments, and in rehabilitation programs. The effectiveness of the MCIs (mixture of amine carboxylates and amino alcohols) on reinforced concrete was evaluated throughout this project. Corrosion test results conducted over 1500 days, 200 cycles per ASTM G109) using immersion and ponding in 3.5% NaCl solution indicated that polarization resistance (Rp) for the MCI coated concrete was higher (60-80 kohms-cm2 with increasing trends) than non-coated concrete. The untreated not only had lower Rp values, but also decreasing trends. Examination of the embedded steel rebar after corrosion tests showed no corrosion attack for the MCI treated concrete samples, while non-treated concrete showed corrosion. X-ray photoelectron spectroscopy (XPS) and depth profiling confirmed that the inhibitor had reached the rebar surface in less than 150 days. Depth profiling showed an amine-rich compound on the rebar surface that corresponded with the increase in Rp and improved corrosion protection for the MCI treated steel rebar even in the presence of chloride ions. Based on measured corrosion rate the life expectancy of a concrete reinforced structure can be improved by more than 40 years.

1. Introduction Corrosion is one of the main concerns in the durability of materials and structures. Much work has been done to develop a corrosion inhibition process to prolong the life of existing structures and minimize corrosion damages in new structures. Carbon steel is one of the most widely used engineering materials despite its relatively limited corrosion resistance. Iron in the presence of oxygen and water is thermodynamically unstable, causing its oxide layers to break down. Corrosion undermines the physical integrity of structures, endangers people and the environment, and is very costly. Because carbon steel represents the largest single class of alloys used [1], corrosion is a huge concern. The billions of dollars committed to providing protective systems for iron and steel have provided new ways of combating corrosion. Migrating corrosion

360 inhibitors (MCIs) are one means of protection for reinforced concrete structures. Previous studies have established the benefits of using migrating corrosion inhibitors, the importance of good concrete, and the significance of the ingredients used to make the concrete [2-6]. Reinforcing steel embedded in concrete shows a high amount of resistance to corrosion. The cement paste in the concrete provides an alkaline environment that protects the steel from corrosion by forming a protective ferric oxide film. The corrosion rate of steel in this state is negligible. Factors influencing the ability of the rebar to remain passivated are the water to cement ratio, permeability and electrical resistance of concrete. These factors determine whether corrosive species can penetrate through the concrete pores to the rebar oxide layer. In highly corrosive environments (coastal beaches and areas where deicing salts are common), the passive layer will deteriorate, leaving the rebar vulnerable to chloride attack, thereby requiring a corrosion prevention system. 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 [2]. Organic inhibitors use compounds that work by forming a monomolecular film between the metal and the water. In the case of film 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 [3, 7, 14]. 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 time to reach the rebar’s surface and to form a protective layer. MCIs can be incorporated as an admixture or can be surface impregnated on existing concrete structures. With surface impregnation, diffusion transports the MCIs into the deeper concrete layers, where they will inhibit the onset of steel rebar corrosion. Laboratory tests have proven that MCI corrosion inhibitors migrate through the concrete pores to protect the rebar against corrosion even in the presence of chlorides [4, 5].

2. EXPERIMENTAL PROCEDURES This study focused on the usefulness of inhibitors and their means of application. Concrete samples were cast (dimensions 280 mm x 110 mm x 150 mm per ASTM G109 and 100 mm x 100 mm x 250mm for immersion tests) using commercial grade silica, Portland cement, fly ash, and limestone (concrete mixture ratio: 1 cement/2 fine aggregate/4 coarse aggregate). Five samples (low density concrete at 2.08 g/cm3) were prepared with a 0.65 water/cement ratio and five samples (high density concrete at 2.40 g/cm3) were prepared using a 0.35 water/cement ratio. All samples had three class 60 steel rebar (with dimensions of 381 mm length, 12.5 mm diameter) and were referenced to a Cu/CuSO4 electrode (Figure 1a). The rebar coverage layer was maintained at 25.4 mm of concrete. Concrete compressive strengths ranged about 21 MPa after 28 days of curing for the low density samples and 26 MPa for the high density. Migrating corrosion inhibitors, MCI 2020, MCI 2020M, and MCI 2022 (sealer) were applied to the concrete surface. The objective was to study the corrosion inhibiting properties and to determine whether these inhibitors protect the steel rebar. Due to the low conductivity of concrete, the corrosion behavior of steel rebar was monitored using electrochemical impedance spectroscopy

361 (EIS) was applied while samples were immersed in 3.5% NaCl at ambient temperatures. Effectiveness of this MCI product was based on changes in the polarization resistance and the corrosion potential of the rebar, measurements that can be performed without destroying the sample. This data can provide early warning of structural distress and evaluate the effectiveness of corrosion control strategies that have been implemented. Once rebar corrosion has proceeded to an advanced state, where its effects are visually apparent on the concrete surface, it is too late for minor patchwork. The key to fighting corrosion is in preventative measures.

a) b) Figure 1: a) Concrete samples prepared per ASTM G109; b) concrete samples modified for continuous immersion [8].

The experiments were conducted using Gamry EIS300 software and Echem Analyst. Bode and Nyquist plots were created from the data obtained using the single sine technique. Potential values were recorded and plotted with respect to time. By comparing the bode plots, changes in the slopes of the curves were monitored as a means of establishing a trend in the Rp value over time. To verify this analysis, the Rp values were also estimated by using a curve fit algorithm on the Nyquist plots (available in the software). In these plots, the Rp and R: combined values are displayed in the low frequency range of the bode plot and the R: value can be seen in the high frequency range of the bode plot. The diameter of the Nyquist plot is a measure of the Rp value. In this investigation, the steel rebar/concrete combination is treated as a porous solution and modeled by a Randles electrical circuit [9]. EIS tests performed on a circuit containing a capacitor and two resistors indicate that this model provides an accurate representation of a corroding specimen. Electrochemical impedance technique has been widely used as a corrosion measurement tool. A number of publications have reviewed both the theory and many areas of application [10-12]. EIS tests, by means of a small amplitude signal of varying frequency, give fundamental parameters relating to the electrochemical kinetics of the corroding system. The values of concern in this study are Rp and R:. The Rp value is a measure of the polarization resistance or the resistance of the surface of the material to corrosion. R: is a measure of the solution resistance to the flow of the corrosion current. By monitoring the Rp value over time, the relative effectiveness of the sample against corrosion can be determined. If the specimen maintains a high Rp value in the presence of chloride, it is considered to be passivated or immune

362 to the effects of corrosion. If the specimen displays a decreasing Rp value over time, it is corroding and the inhibitor is not providing corrosion resistance. During this investigation, changes in the polarization resistance (Rp) and the corrosion potential of the rebar were monitored to ascertain the degree of effectiveness for these MCI products. The samples were tested on a weekly basis and the data was collected for analysis for the first 500 days of exposures tests followed by monthly data collection. After 1,500 days of testing, four concrete samples (One reference sample and three MCI treated concrete samples) were cut open to remove the rebar for examination. A large area surface analysis was performed on several MCI treated concrete samples using a Kratos Axis Ultra XPS in electrostatic lens mode with resolution pass energy of 160 and an aluminum monochromator anode. The depth profiles were conducted using Argon ions at 4 kV. There were ten concrete samples in total, eight were surface impregnated with several coats of MCI 2020 and MCI 2020M. The remaining two samples were left untreated and used as control for comparison. Clear silicon was applied to the concrete/metal interface to prevent easy access for ions. The testing environment was a solution of 3.5% NaCl and water with roughly 175 mm (7 inches) (Figure 1b) of each sample continuously immersed during testing, while the ASTM G109 [8] was subjected to 3.5% NaCl salt solution ponding for every other two weeks for roughly 210 cycles.

RESULTS Many procedures have been developed for monitoring the corrosion of rebar in concrete, each method attempts to improve a shortcoming of an existing technique. Measuring the open circuit potential is very easy and inexpensive, but is not considered very reliable since the potential provides no information about the kinetics of the corrosion process. Linear polarization resistance (LPR) measurements are influenced by IR effects from the concrete. A significant potential drop in the concrete makes an accurate determination of the potential of the rebar surface very difficult. Electrochemical impedance spectroscopy (EIS) is able to overcome the difficulties of the concrete resistance, yet requires more testing time. The different analytical methods of electrochemical impedance spectroscopy are capable of giving more detailed information than LPR. The rebar potential, polarization resistance and current density data can provide information as to whether the rebar is in the active or passive corrosion state. Estimates made from these parameters for Tafel constants can be input into LPR analysis or can be used for corrosion rate measurement and cathodic protection criteria. Evaluation of the effectiveness of corrosion inhibitors and the effects of concrete composition is often based on these variables. For a more comprehensive approach to the corrosion process, several tests methods have been implemented in this investigation.

Corrosion Potentials The corrosion inhibition for the inhibitor identified as MCI 2020 has been investigated over a period of 1500 days using EIS techniques. Throughout this investigation, changes in the corrosion potential of the rebar were monitored to determine the effects of this commercially available inhibitor. According to the ASTM (C876) standard [13], if the open circuit potential (corrosion potential) is -200 mV or higher, this indicates a 90% probability that no reinforcing steel has corroded. Corrosion potentials more negative than -350 mV are assumed to have a

363 greater than 90% likelihood of corrosion. Figure 2 shows the corrosion potentials for the high and low density samples. The MCI treated samples showed a potential of roughly -100 mV after 1500 days of immersion in a salt solution. Given an open circuit potential of -570 mV for the untreated (low density) sample, it is highly probable that corrosion initiation has occurred. Figure 3a confirmed these findings. The untreated high density concrete maintained a potential of -240 mV, but had a high resistance polarization and did not suffer any corrosion.

Figure 2: Comparison of Corrosion Potentials for MCI Treated Concrete with Untreated Samples per ASTM G109 [8].

a) b) Figure 3: a) Non-treated concrete, rebar showed localized corrosion attacks. b) MCI-treated concrete, rebar did not show any corrosion attacks.

364 Polarization Resistance This electrochemical technique enables the measurement of the instantaneous corrosion rate.

This Rp value is related to the corrosion current Icorr by the following Stern-Geary equation [9]:

Icorr = B/( RpA) (1) where A is the area of the metal surface evenly polarized and B is a constant that may vary from 13 to 52 mV for the case of steel embedded in concrete. Figure 4 shows EIS data for polarization resistance that demonstrated an increasing trend for the MCI coated samples with polarization 2 2 UHVLVWDQFHYDOXHVEHWZHHQNȍ-cm DQGNȍ-cm . The Rp value for the untreated low density sample showed a declining trend of  Nȍ-cm2 at 350 days of partial immersion in the aggressive solution. The calculated corrosion rate of the steel rebar in concrete based on the measured polarization resistance values indicated a 1.6-2.2 mpy for the non-treated samples while MCI treated samples were in the range of 0.18-0.22 mpy. This can result in an additional 30-40 years of service life for protected concrete structures compared with non-protected concrete structures.

Figure 4: Polarization Resistance (Rp) Versus Time; Comparison of treated (MCI 2020 & MCI 2020M) low & high density concrete with untreated concrete.

X-ray photoelectron spectroscopy (XPS) The XPS analysis of the rebar surface verified the inhibitor’s ability to penetrate through the concrete pores by vapor phase diffusion and capillary effects. The data analyzed was consistent with an organic compound carboxylate chemistry similar to the migrating corrosion inhibitor

365 compound (nitrogen, carbon and oxygen presence was attributed to MCI compound). Depth profiling (using 4 kV Argon ions) measured an approximate 120 nm layer of amine compounds on the rebar surface, confirming surface adherence after migration. Chloride was also found on the surface of the rebar. The XPS results demonstrated that both the MCI and corrosive species had migrated in through the concrete capillary system. Table 1, however, shows that MCI managed to coat the surface and neutralize the corrosive species (chloride ions and carbon dioxide) to protect the steel rebar.

Table 1: XPS analysis and spectrum of the rebar surface, untreated and MCI 2020M treated concrete after 1500 days in 3.5% NaCl.

Atomic Conc% Mass Conc% Atomic Conc% Mass Conc% Peak Untreated Untreated MCI MCI

Fe 2p 0.87 3.32 0.08 0.3 O 1s 30.19 33.06 31.4 35.91 C 1s 62.48 51.37 59.43 48.12 Ca 2p 0.15 0.42 1.08 3.01 Si 2p 4.72 9.08 1.26 4.14 Cl 2p 0.84 2.04 1.11 2.81 N 1s 0.74 0.71 5.64 5.71

CONCLUSIONS Migrating corrosion inhibitors effectiveness were studied in continuous long duration corrosion tests, all samples but one (low density-untreated) have maintained a stable protective layer that has improved the steel reinforcement performance in the corrosive environment. The MCI products have successfully inhibited corrosion of the rebar in a 3.5% NaCl solution for the duration of testing. MCI protected samples showed an average corrosion rate of 0.4 ȝA/cm2 (less than 0.17 mpy) compared to untreated samples that were 5.10 ȝA/cm2 (2.2 mpy). This will increase the life expectancy of a concrete reinforced structure by more than 40 years. XPS analysis demonstrated the presence of inhibitor on the steel rebar surface indicating MCI migration through the concrete. XPS depth profiling showed a layer of amine-rich compounds and chloride ions on the rebar surface; however the neutralizing effects and film forming ability of the inhibitor assured satisfactory corrosion resistance.

366 REFERENCES 1. http://www.corrosioncost.com/home.html 2. D. Bjegovic and B. Miksic, Migrating Corrosion Inhibitor Protection of Concrete, MP, NACE International, Nov. 1999. 3. D. Stark, Influence of Design and Materials on Corrosion Resistance of Steel in Concrete, R & D Bulletin, RD098.01T. Skokie, Illinois: Portland Cement Association, 1989. 4. B. Bavarian and L. Reiner, Migrating Corrosion Inhibitor Protection of Steel Rebar in Concrete, Materials Performance, 2003. 5. B. Bavarian and L. Reiner, Corrosion Protection of Steel Rebar in Concrete using Migrating Corrosion Inhibitors, BAM 2001. 6. J. P. Broomfield et al, Corrosion of Metals in Concrete, ACI 222R-96. 7. R. Dagani, Chemists Explore Potential of Dendritic Macromolecules as Functional Materials, Chemical & Engineering News, American Chemical Society, June 3, 1996. 8. ASTM G109 Standard Test Method for Determining Effects of Chemical Admixtures on Corrosion of Embedded Steel Reinforcement in Concrete Exposed to Chloride Environments, Annual Book of ASTM Standards, Vol. 03.02, 1992. 9. D. Jones, Principles and Prevention of Corrosion, 2nd Edition, Prentice Hall, NJ, 1996. 10. G. Qiao and J. Ou, Corrosion Monitoring of Reinforcing Steel in Cement Mortar by EIS and ENA, Electrochimica Acta, Vol. 52, 2007. 11. D. A. Koleva, K. van Breuge, J. H. W. de Wit, E. van Westing, N. Boshkov, and A. L. A. Fraaij, Electrochemical Behavior, Microstructural Analysis, and Morphological Observations in Reinforced Mortar Subjected to Chloride Ingress, Journal of the Electrochemical Society, Vol. 154, 2007, pp. E45–E56. 12. H. Saricimen, M. Mohammad, A. Quddus, M. Shameem, and M. S. Barry, Effectiveness of Concrete Inhibitors in Retarding Rebar Corrosion, Cement and Concrete Composites, Vol. 24, 2002, pp. 89–100. 13. ASTM C876 Standard Test Method for Half Cell Potentials of Reinforcing Steel in Concrete, Annual Book of ASTM Standards, Vol. 04.02, 1983. 14. S. Sawada 1, J. Kubo, C.L. Page *, M.M. Page, “Electrochemical injection of organic corrosion inhibitors into carbonated cementitious Materials”, Corrosion Science 49 (2007) 1186–1204

367 Corrosion Protection of Steel Rebar in Concrete with Optimal Application of Migrating Corrosion Inhibitors, MCI 2022

Prepared for: The Cortec Corporation 4119 White Bear Parkway St Paul, MN 55110 (Report #1137)

Prepared by: Behzad Bavarian, PhD Professor of Materials Engineering

Lisa Reiner Dept. of Manufacturing Systems Engineering & Management College of Engineering and Computer Science California State University, Northridge March 2003

368 Steel corrosion is a major concern for any society with reinforced concrete structures. More specifically, the United States, with its vast infrastructure of concrete and steel bridges, superhighways, and reinforced concrete buildings has spent billions of dollars for corrosion protection. Among the commercial technologies available today, migrating corrosion inhibitors (MCIs) show versatility in that they can be incorporated as admixtures, surface treatment, or used in rehabilitation programs. The effectiveness of Cortec’s MCI 2022, a mixture of amine carboxylates, amino alcohols and siloxane, on reinforced concrete using various application methods was evaluated. Bode and Nyquist plots showed high polarization resistance values for inhibitor treated concrete. XPS analysis verified the presence of inhibitor chemistry and chloride molecules on the steel rebar surfaces. Depth profiling revealed a 100 nm amine-rich layer of inhibitor along with chloride ions on the rebar, confirming that MCI had migrated through the concrete coverage to suppress chloride ion corrosiveness. Eight concrete specimens were prepared with reinforcement placed at 1 inch (2.5 cm) concrete coverage and tested for a period of 400 days. MCI 2022 was applied directly to the rebar, by surface impregnation and combined in a mortar coating. Electrochemical monitoring techniques were applied to samples immersed in 3.5% NaCl at ambient temperatures. The corrosion behavior of the steel rebar was monitored using AC electrochemical impedance spectroscopy (EIS). The changes in the polarization resistance and the corrosion potential of the rebar were compared with previous investigations conducted on several admixtures and stainless steel rebar.

Introduction Corrosion is one of the main concerns in the durability of materials and structures. Much effort has been made to develop a corrosion inhibition process to prolong the life of existing structures and minimize corrosion damages in new structures. Carbon steel is one of the most widely used engineering materials despite its relatively limited corrosion resistance. Iron in the presence of oxygen and water is thermodynamically unstable, causing its oxide layers to break down. Corrosion undermines the physical integrity of structures, endangers people and the environment, and is very costly. Because carbon steel represents the largest single class of alloys used,1 corrosion is a huge concern. The billions of dollars committed to providing protective systems for iron and steel have provided new ways of combating corrosion. Migrating corrosion inhibitors (MCIs) are one means of protection for reinforced concrete structures. Previous studies have established the benefits of using migrating corrosion inhibitors, the importance of good concrete, and the significance of the ingredients used to make the concrete.2-7 Reinforcing steel embedded in concrete shows a high amount of resistance to corrosion. The cement paste in the concrete provides an alkaline environment that protects the steel from corrosion by forming a protective ferric oxide film. The corrosion rate of steel in this state is negligible. Factors influencing the ability of the rebar to remain passivated are the water to cement ratio, permeability and electrical resistance of concrete. These factors determine whether corrosive species like carbonation and chloride ions can penetrate through the concrete pores to the rebar oxide layer. In highly corrosive environments (coastal beaches and areas where deicing salts are common), the passive layer will deteriorate, leaving the rebar vulnerable to chloride attack, thereby requiring additional help to prevent corrosion damage.

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.2,3 Organic inhibitors

369 utilize compounds that work by forming a monomolecular film between the metal and the water. In the case of film 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.5 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 time to reach the rebar’s surface and to form a protective layer.

MCIs can be incorporated as an admixture or can be surface impregnated on existing concrete structures. With surface impregnation, diffusion transports the MCIs into the deeper concrete layers, where they will inhibit the onset of steel rebar corrosion. Bjegovic and Miksic recently demonstrated the effectiveness of MCIs over five years of continuous testing.2,3 They also showed that the migrating amine-based corrosion-inhibiting admixture can be effective when incorporated in the repair process of concrete structures.2 Furthermore, laboratory tests have proven that MCI corrosion inhibitors migrate through the concrete pores to protect the rebar against corrosion even in the presence of chlorides.6,7

Purpose The objective of this investigation was to further study migrating corrosion inhibitors, focusing on their usefulness and means of application. In many cases, there is thought to be an induction period, where time is required for the inhibitor to migrate through the concrete pores. A high density concrete may impede corrosive species from reaching the surface of the rebar and could also prevent inhibitor from reaching the surface of the concrete. Direct application of the inhibitor to the rebar surface would eliminate this concern. Also, a thicker coating of inhibitor and mortar was investigated; this combination may be necessary to protect steel rebar in extremely aggressive environments. Electrochemical monitoring techniques were applied while samples were immersed in 3.5% NaCl at ambient temperatures. Due to the low conductivity of concrete, the corrosion behavior of steel rebar had to be monitored using AC electrochemical impedance spectroscopy (EIS). Effectiveness of this MCI product was based on changes in the polarization resistance and the corrosion potential of the rebar, measurements that can be performed without destruction to the reinforcing steel. This data can provide early warning of structural distress and evaluate the effectiveness of corrosion control strategies that have been implemented. Once rebar corrosion has proceeded to an advanced state, where its effects are visually apparent on the concrete surface, it is too late for minor patchwork. The key to fighting corrosion is to introduce preventative measures.

Experimental Procedures For purposes of this study, the steel rebar/concrete combination is treated as a porous solution and modeled by a Randles electrical circuit. EIS tests performed on a circuit containing a capacitor and two resistors indicate that this model provides an accurate representation of a corroding specimen. EIS tests, by means of a small amplitude signal of varying frequency, give fundamental parameters relating to the electrochemical kinetics of the corroding system. The values of concern in this study are Rp and R:. The Rp value is a measure of the polarization resistance or the resistance of the surface of the material to corrosion. R: is a measure of the solution resistance to the flow of the corrosion current. By monitoring the Rp value over time, the

370 relative effectiveness of the sample against corrosion can be determined. If the specimen maintains a high Rp value in the presence of chloride, it is considered to be passivated or immune to the effects of corrosion. If the specimen displays a decreasing Rp value over time, it is corroding and the inhibitor is not providing corrosion resistance.

The experiments were conducted using an EG&G Potentiostat/Galvanostat (Model 273A with a 5210 Lock-in amplifier), EG&G M398 and Power Suite Electrochemical Impedance Software and a Gamry PC4-750 Potentiostat with EIS300 software and Echem Analyst. Bode and Nyquist plots were created from the data obtained using the single sine technique. Potential values were recorded and plotted with respect to time. By comparing the bode plots, changes in the slopes of the curves were monitored as a means of establishing a trend in the Rp value over time. To verify this analysis, the Rp values were also estimated by using a curve fit algorithm on the Nyquist plots (available in the software). In these plots, the Rp and R: combined values are displayed in the low frequency range of the bode plot and the R: value can be seen in the high frequency range of the bode plot. The diameter of the Nyquist plot is a measure of the Rp value.

Number of samples Application method 2 No treatment-control samples 2 MCI 2022 coated rebar 2 MCI 2022 treated concrete surface 2 2/8 to 3/8 inch mortar/MCI 2022 coating Table 1. Shows the application method used for each sample.

As seen in Table 1, several methods were used to treat the concrete samples. The objective was to determine whether the location of the inhibitor had any impact on its ability to protect the steel rebar. Prior to the concrete batching, two rebars were immersed for 20 minutes in MCI 2022 to ensure thorough coverage, then set to dry for several days. Concrete samples with dimensions 8” x 4” x 4” were prepared using an 8 inch steel rebar (class 60, 1/2” diameter) and one 8-inch Inconel 800 metal strip (for the counter electrode). A concrete mixture containing commercial grade-silica, Portland cement, fly ash, and limestone (concrete mixture ratio: 1 cement/2 fine aggregate/4 coarse aggregate) were combined with one-half gallon water per 60-lb (27.22 Kg) bag in a mechanical mixer. The mix resulted in a 0.5 cement to water ratio and the coverage layer was maintained at one inch concrete for all samples. Compressive strengths were roughly 3750 psi for this medium density concrete cured for 28 days per ASTM C387. After curing, samples were set to dry, then sandblasted to remove loose particles and provide surface uniformity.

Two of the concrete blocks were surface impregnated with several coats of MCI 2022 and set to dry. The inhibitor was applied to the surface of the concrete with a paint brush while partially immersed in a shallow container of inhibitor. Mortar samples were prepared using a 10 lb (4.5 kg) bag of Quikrete mortar mix, 100 ml MCI 2022 and 800 ml water. The remaining two samples were left untreated and used as standards for comparison. Clear silicon was applied to the concrete/metal interface to prevent easy access for ions. Figure 1 shows the samples partially immersed in a solution of 3.5% NaCl and water; roughly 7 inches of each sample was

371 continuously immersed in the solution for the entire testing period. A Cu/CuS04 electrode was used as the reference and each sample was tested approximately every two weeks. The results were compared with previous investigations conducted on several admixtures and stainless steel rebar.

Figure 1. This photo shows four of the concrete samples partially immersed in a 3.5% NaCl solution.

Results & Discussion

Many procedures have been developed for monitoring the corrosion of rebar in concrete, each method attempts to improve a shortcoming of an alternate technique. Measuring the open circuit potential is very easy and inexpensive, but is not considered very reliable since the potential provides no information about the kinetics of the corrosion process. Linear polarization resistance (LPR) measurements are influenced by IR effects from the concrete. A significant potential drop in the concrete makes an accurate determination of the potential of the rebar surface very difficult. Electrochemical impedance spectroscopy (EIS) is able to overcome the difficulties of the concrete resistance, yet requires more testing time. The different analytical methods of electrochemical impedance spectroscopy are capable of giving more detailed information than LPR. The rebar potential, polarization resistance and current density data can provide information as to whether the rebar is in the active or passive corrosion state. Estimates made from these parameters for Tafel constants can be input into LPR analysis or can be used for corrosion rate measurement and cathodic protection criteria. Evaluation of the effectiveness of corrosion inhibitors and the effects of concrete composition is often based on these variables. For a more comprehensive approach to the corrosion process, several tests methods have been implemented in this investigation.

Corrosion Potentials The corrosion inhibition for Cortec MCI 2022 was investigated over a period of 400 days using AC electrochemical impedance spectroscopy (EIS). Throughout this investigation, changes in the corrosion potential of the rebar were monitored to determine the effects of this commercially available inhibitor. According to the ASTM (C876) standard, if the open circuit potential (corrosion potential) is -200 mV or higher, this indicates a 90% probability that no reinforcing steel has corroded. Corrosion potentials more negative than -350 mV are assumed to have a greater than 90% likelihood of corrosion. Figure 2 shows that the corrosion potentials for all the samples were between the range of -25 mV to -150 mV after 100 days of immersion in NaCl.

372 0

-50

-100

-150

Potential, (m V) -200

RF1-untreated MR1-rebar treated -250 MS1-surface treated MM1-mortar coated surface

-300 0 50 100 150 200 250 300 350 400

Time of Submersion (Days)

Figure 2. Comparison of corrosion potential vs time for MCI treated and untreated samples.

Polarization Resistance This electrochemical technique enables the measurement of the instantaneous corrosion rate. It quantifies the amount of metal per unit of area being corroded in a particular instant. The method is based on the observation of the linearity of the polarization curves near the potential Ecorr. The slope expresses the value of the polarization resistance (Rp) if the increment diminishes to zero.

This Rp value is related to the corrosion current Icorr by means of the expression: § 'E · B p R ¨ ¸ 'E o0 Icorr © 'I ¹ Rp ˜ A Where A is the area of the metal surface evenly polarized and B is a constant that may vary from 13 to 52 mV. For the case of steel embedded in concrete, the best fit with parallel gravimetric losses, results in B= 26 mV for actively corroding steel, and B= 52 mV for passivated steel. Figures 3 & 4 show that MCI treated concrete samples have higher Rp values compared with the control sample. Figure 3 shows a declining trend for the untreated concrete sample and stable polarization resistance values after 400 days of testing for the treated concrete. Figure 4 shows Rp values obtained during linear polarization consistent with Figure 3. The inhibitor treated rebar had the highest polarization resistance, the next highest Rp values were for the concrete with mortar treatment, then surface treated concrete and finally the untreated concrete with somewhat lower values around 27000 (ohm) (cm2). The corrosion rate in PA/cm2 is shown in Figure 5 and the relative value is specified in Table 2. For example, at the present rate of corrosion, it is estimated that the untreated sample will suffer corrosion damage in 10-15 years.

373 p

35000 RF1-untreated MR1-rebar treated MS1-surface treated MM1-mortar coated surface 30000

25000 ) 20000 Ohms

p( 15000 R

10000

5000

0 0 50 100 150 200 250 300 350 400 450 Time submerged, Days

Figure 3. Comparison of polarization resistance (RP) for MCI treated & untreated concrete samples.

55000

50000

45000 , o hm .cm ^2

p 40000

35000

30000

25000 MCI on Rebar 20000 MCI in mortar MCI on Concrete

Polarization Resistance, R Resistance, Polarization 15000 Non MCI Treated

10000 0 2000 4000 6000 8000 10000 12000 14000 16000 Time, Second Figure 4. Linear polarization resistance tests on concrete samples partially immersed in 3.5% NaCl solution, day 365.

374 Non-treated 2 MCI on Concrete

MCI in Mortar

MCI on Rebar 1.5 A/cm^2 P

1 Corrosion Rate,

0.5

0 1234 Sample Figure 5. Bar chart obtained from LPR data quantifying the corrosion rate (PA/cm2) for concrete samples on day 365.

Corrosion rate (uA/cm2) Severity of Damage < 0.5 no corrosion damage expected 0.5-2.7 corrosion damage possible in 10 to 15 years 2.7-27 corrosion damage expected in 2 to 10 years > 27 corrosion damage expected in 2 years or less Table 2. Proposed relationship between corrosion rate and remaining service life.

Bode Plots Bode plots are not dependent on modeling the corroding system as are polarization resistance values. The electrochemical impedance spectroscopy data are obtained by applying a single sine wave over a range of frequencies while measuring the corresponding impedance. Since the results are independent of an assumed model, the technique is highly reliable. Figure 6 shows a comparison of the bode plots for the first day of testing. The similar results for day 1 are a good indication that the concrete samples were consistently cast. Figure 7, the bode plot results from day 400, shows an obvious decline in the impedance values measured for the control sample. The passivating layer for this sample appears to have been breached, indicating a high likelihood of corrosion. The MCI treated samples still have corrosion protection after 400 days in an aggressive environment.

1.00E+04 Mortar MCI-Day 1 Concrete+MCI-Day 1

1.00E+03 Rebar+MCI-Day 1 Control-Day 1

l Z l (Ohms) l Z 1.00E+02

1.00E+01 1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 FREQUENCY (Hz) Figure 6. EIS Bode plot for MCI 2022 treated & untreated concrete on day 1 of testing.

375 1.00E+05 Mortar MCI-Day 400 Concrete+MCI-Day 400 Rebar+MCI-Day 400 Control-Day 400

1.00E+04 l Z l (Ohms)

1.00E+03

1.00E+02 0.0001 0.001 0.01 0.1 1 10 100 1000 10000 100000 FREQUENCY (Hz)

Figure 7. EIS Bode plot for MCI 2022 treated & untreated concrete after 400 days of testing.

XPS Analysis After 415 days of immersion in a NaCl solution, several samples were removed from testing for XPS analysis and depth profiling. The rebar was removed from the concrete (Figures 8 & 9) and its surface chemistry was assessed. Figure 10 shows the XPS spectrum from untreated rebar sample after 450 days. It is similar to the spectrum shown in Figure 11 for the rebar removed from an MCI treated sample after 415 days.

Figure 8. This photo shows the treated rebar still embedded in the concrete and the portion of the rebar that was exposed to the corrosive environment.

376 Figure 9. Untreated rebar sample used for XPS analysis. Sample shows obvious indications of corrosion.

The major difference in the spectrums is the N 1s peak for nitrogen not seen on the untreated rebar. The amine-rich compounds found on the rebar surface are associated with the MCI 2022 chemistry (75% water, 20 % silane/siloxane based sealer, 1-2% amino alcohols, 3-4% amine carboxylate), derivatives of nitrogen. Figure 12 shows a narrow spectrum for the N 1s energy band region verifying the presence of nitrogen. XPS chemical quantification results (Figure 11) revealed organic compounds with carboxylate chemistry. Chloride was also detected at depths up to 50 nm from the analysis surface on the rebar and at a concentration of approximately 0.52 atomic %. The XPS results demonstrate that both MCI and corrosive species had migrated in through the concrete pores, but MCI had formed a protective film on the steel rebar surface. These results are promising for the MCI product in its ability to protect steel rebar in concrete in aggressive environments. Figure 13 shows several SEM micrographs of the rebar surface and the EDAX analysis.

Figure 10. XPS spectrum of steel rebar removed from untreated concrete after 450 days of immersion. Large area (1000 x 800 mm). Lens mode electrostatic; Resolution pass energy 160; anode: Mg (150 W).

377 peak position FWHM raw height RSF atomic mass atomic conc % mass conc % BE (eV) (eV) (CPS) C 1s 282.585 2.866 56290.7 0.318 12.011 53.88 41.91 O 1s 529.185 2.966 77068.9 0.736 15.999 32.79 33.98 N 1s 397.785 2.398 6550.4 0.505 14.007 3.99 3.62 Cl 2p 190.185 2.214 1641.7 0.964 35.460 0.52 1.18 Ca 2p 345.585 2.905 10461.1 1.950 40.078 1.64 4.25 Si 2p 100.185 2.587 7512.9 0.371 28.086 6.09 11.07 Fe 2p 742.785 5.120 9701.2 2.947 55.846 1.10 3.99

Figure 11. XPS spectrum analysis of steel rebar removed from MCI 2022 treated concrete after 400 days immersion and chemical quantification.

Figure 12. High resolution XPS spectrum for nitrogen peak (N 1s region) on surface of steel rebar removed from MCI 2022 treated concrete after 400 days immersion.

378

Elt XRay Int Kratio W% A% N Ka 4.8 0.00310 1.00 3.47 O Ka 50.6 0.01715 3.73 11.31 Si Ka 87.1 0.00969 1.87 3.23 S Ka 5.2 0.00070 0.09 0.14 Cl Ka 3.0 0.00048 0.35 0.27 K Ka 8.6 0.00149 0.14 0.18 Ca Ka 107.3 0.01837 1.77 2.14 Fe Ka 2720.8 0.89617 91.06 79.26 0.94657 100.00 100.00

Figure 13. SEM photos (magnification: 100, 50 Pm) showing the surface of an MCI treated rebar after 400 days in a 3.5% NaCl solution and the EDAX analysis.

379 Conclusion The MCI products have successfully inhibited corrosion of the rebar in a 3.5% NaCl solution for 415 days. Steel rebar corrosion potentials were maintained at approximately -150 mV, and rebar polarization resistance showed a gradual increase reaching as high as 27,000 ohms. MCI coated rebar and MCI added to mortar showed significant reduction in the corrosion rate. XPS analysis demonstrated the presence of inhibitor on the steel rebar surface indicating MCI migration through the concrete. Depth profiling showed a layer of amine-rich compounds and chloride ions on the rebar surface; neutralizing effects of the inhibitor assured satisfactory corrosion resistance in the presence of corrosive chloride ions.

References 1. http://www.corrosioncost.com/home.html 2. D. Bjegovic and B. Miksic, “Migrating Corrosion Inhibitor Protection of Concrete,” MP, NACE International, Nov. 1999. 3. D. Rosignoli, L.Gelner, & D. Bjegovic, “Anticorrosion Systems in the Maintenance, Repair & Restoration of Structures in Reinforced Concrete,” International Conf. Corrosion in Natural & Industrial Environments: Problems and Solutions, Italy, May 23-25, 1995. 4. D. Darling and R. Ram, "Green Chemistry Applied to Corrosion and Scale Inhibitors." Materials Performance 37.12 (1998): 42-45. 5. D. Stark “Influence of Design and Materials on Corrosion Resistance of Steel in Concrete." Research and Development Bulletin RD098.01T. Skokie, Illinois: Portland Cement Association, 1989. 6. B. Bavarian and L. Reiner, “Corrosion Inhibition of Steel Rebar in Concrete by Migrating Corrosion Inhibitors,” Eurocorr 2000. 7. B. Bavarian and L. Reiner, “Corrosion Protection of Steel Rebar in Concrete using Migrating Corrosion Inhibitors,” BAM 2001.

380 MIGRATORY VCI INHIBITORS FOR WET THERMAL INSULATION

By

B. A. Miksic 4119 White Bear Parkway St. Paul, MN 55110

Published: April, 1989 Presented at the Symposium “Corrosion Under Wet Thermal Insulation”, at Corrosion/89, New Orleans.

381 GENERAL

The corrosion of metals under thermal insulation is an industry wide problem, specifically during idle or cooling-down periods. The presence of condensed water, airborne contaminants and corrosive agents that are generated through thermal decomposition and aging of insulating materials further increases the rate of attack on underlying surfaces. Due to failure of outer barrier wraps or jackets, the moisture content of the insulation can often reach the point of saturation. This combined with elevated temperatures can cause the corrosion rates to multiply to exceedingly high levels.

M I G R A T O R Y V C I’S

The effectiveness of volatile corrosion inhibitors to inhibit corrosion of metals in recessed and hard-to-reach areas is well documented (1). The idea has occurred to utilize the unique transport mechanism of VCIs to stop the deterioration of metals under thermal insulation and thus to extend the useful life of the structures. However, for VCIs to be useful for this specific application, they must meet a specific set of requirements:

(1) VCI must be capable of migrating or penetrating to relatively great distance form point of injection or application.

(2) They must be effective in arresting further corrosion under existing corrosion or scale deposits.

(3) They must have balanced partial vapor pressure between VCI compounds in the formulation in order to provide rapid saturation of insulation jacket after application, and long term protection by minimizing the length of time between the application.

E X P E R I M E N T A L

Based on the above requirements, a formulation has been developed which utilizes a volatile, non-flammable liquid carrier (Cortec VCI-656x), to improve the migratory capability of the inhibitors. Sections of carbon steel pipe covered with wet calcium silicate thermal insulation were injected with the VCI at the metal/insulation interface. The entire system was kept wet at an elevated temperature to provide high possible rates of corrosion for the VCI to overcome. The rate of injection of the inhibitor was 1 gallon of liquid per 23 cu. feet of insulation. The test pipes were prepared with blast-to-white metal finish yielding maximum profile 1 to ½ mils, insulated with calcium silicate insulation 1½” thick and covered with 16 MIL aluminum jacketing prior to putting into test.

The test conditions were 200o F to 200o F surface temperature and 5 psig steam pressure which was maintained by continuous water injection at 5 ml/hr. (2)

R E S U L T S A N D C O N C L U S I O N S

382 After six months, the test was shut down and disassembled. The following visual observations were made:

- Control pipe was approximately 80% covered with the major part of the bottom half covered with a build-up of corrosion products.

- The pipe inhibited with liquid VCI was approximately 5% corroded at the two of the water injection points.

Considering the severity of the test, and experience with anti-corrosion coatings under similar conditions, it is believed that the VCI compounds show promise as an effective method of corrosion protection under existing insulation. It should be further mentioned that due to the unique transport mechanism, this method could result in significant material and labor savings in extending the useful life of the insulated structures, as the cost of reinsulating and repair could be considerable.

UNDERCOATING FOR INSULATED SURFACES

Another area of application is the new insulation work. Here the requirements for VCI are somewhat different as compared to injecting into the existing (wet) insulation. A typical case history involved a large Midwestern Utility that specified temporary coating for their ESP precipitators that have been fabricated on the location near the Gulf Coast.

Those large units were partially insulated at the fabrication yard with the additional requirement that the units had to withstand barge shipment to the Ohio location and up to one year field storage without appreciable corrosion attack. The limiting factor for the selection of temporary coatings were the start-up conditions, as the wall temperature of the precipitators is 475oF with excursions up to 700oF anticipated. Wax like coatings were ruled out due to high temperature conditions and concern for decomposition products that would form under the insulation. The conventional zinc rich primers could not be used because of Zn reversing the potential at elevated temperatures. Further obvious choice, the polyester lining material was excluded due to the marginal surface preparation, dampness in the yard and cost factor associated with the application of lining to large structures.

After careful review of the above requirements, a combination of contact and volatile corrosion inhibitors has been developed to provide temporary protection for ESP precipitators during fabrication, and in transit and storage before plant start-up. The formulation was designated VCI-619 X and utilizes water as a carrier assuring safe application from stand points of flammability and health hazard. The coating was designed to withstand high start-up temperature conditions, thus eliminating concerns about decomposition products that would be formed. The material is shop applied by spray or brush to steel surfaces using commercial equipment and it does not require stringent surface preparation as with the linings. It can be applied directly to the surfaces covered with tight oxide film or scale. Treated surfaces are allowed to air dry from ten to sixty

383 minutes (depending upon ambient conditions) before further handling or covering with insulation.

The temporary coating was submitted to laboratory and field tests to prove its effectiveness in retarding corrosion attack. Under laboratory conditions described above, it showed approximately 30% corrosion which, considering severity of the test was still acceptable (control pipe was covered over 80% with heavy corrosion product). The field experience showed even more promising results - a total of 20 ESP precipitators have been coated and insulated together with the associated equipment. All units have been transported by river to the Midwest location and stored on site for over 1 year. The periodic inspection show no or minimum amount of corrosion under thermal insulation.

R E F E R E N C E S

(1) B. A. Miksic, Chemical Engineering, September 1977

(2) E. I. Dupont Co., Internal memorandum Jan 15, 1988 (Haldeman & Hughes)

384 Presented at the 2nd International Congress on Studies in Ancient Structures, 2001, Istanbul, Turkey

Effects of Migrating Corrosion Inhibitors on Reinforced Lightweight and Common Mortars

G. Batis, E. Rakanta Section of Materials Science and Engineering Dept. of Chemical Engineering, National Technical University, Athens, Greece

ABSTRACT

In reinforced landmark, historical buildings, a series of mortars are commonly used for rendering of horizontal elements or filling of vertical ones. Corrosion of reinforcing steel represents the most important cause of concrete structure deterioration. This paper studies the protective effect of the reinforcement mortars, against rebars corrosion in mortar specimens containing corrosion inhibitors as admixture or as impregnation agent. The migrating corrosion effectiveness was assessed in lightweight concrete with Greek pumice stone and in common mortar specimens. The inhibiting behavior of organic aminobased migrating corrosion inhibitors against steel corrosion was evaluated by specimens’ immersion into 3,5%w.t. sodium chloride corrosive solution and by exposure to the atmosphere. The corrosion activity and inhibiting efficiencies (IE) were tested by measuring the rebars weight loss, their half - cell potential, carbonation depth and electrochemical measurements of chronicles corrosion rate of rebars in concrete specimens. The results of our experiments have shown that the presence of the inhibiting protection increases in the mortars systems with the usage of migrating corrosion inhibitor compared to the reference specimens without corrosion inhibitor. Furthermore, common mortar specimens exhibited lower rebar corrosion rate than the lightweight concrete specimens. Finally, specimens with corrosion inhibitor exhibited the best corrosion protection results in corrosive conditions without chloride ions.

385 1. INTRODUCTION

Corrosion of reinforcing steel embedded in concrete is becoming a significant structural and financial problem. As it is known, in Greece, many historical buildings and structures are located in coastal regions (islands) where the weather - is characterized by pollutants such as part particles Cl and carbon dioxide, CO2. This leads to an increased incidence of spalls, delimination and as a consequence the deterioration of concrete in reinforced structures. In restorations, a series of traditional construction materials such as mortars, steel and grouts are commonly used for repairing and filling elements of structures. They are generally composed of cement, sand, lime and water or cement, sand, superplastisizer, and water [1]. Due to the fact, that the rest of the construction and the repair mortar have high porosity, the durability of these mortars is questionable as far as the corrosion of the reinforcement steel. This results in an attack from probably all sides as the water can penetrate either from the foundation and leakages in the roof or from porous walls [2]. As a result to a all above mentioned, many times the use of chemical admixture is essential due to blocking the ingress of chloride ions and oxygen, increasing the resistance of the passive film on the steel to breakdown by chloride ions.[3-4] The use of chemical admixtures, which acts as corrosion inhibitors, is a method for preventing and delaying the onset of rebar corrosion. An ideal corrosion inhibitor has been defined as “a chemical compound, which, when added in adequate amounts to concrete, can prevent corrosion of embedded steel and has no adverse effect on the properties of concrete” [5]. Nowadays chemical corrosion inhibitors present an easily implemented solution to the growing problem of corrosion of reinforcing steel in concrete. However, to be considered viable, these additives should not only prevent or delay the onset of corrosion, they must not have any detrimental effect on the properties of the concrete itself, such as strength, setting time, workability and durability [6]. It must be clarified, that corrosion inhibitors do not totally stop corrosion, but rather increase the time to the onset of corrosion and reduce its eventual rate. Drawbacks of corrosion inhibiting admixtures are that they may not remain in the repair area, potentially reducing the concentration of the inhibitor bellowing necessary values and secondly, when used in a limited area long a continuous reinforcing bar, there is the potential for micro cell corrosion development [7]. The aim of this study is the examination of the performance, in chloride environment of two different sets of steel reinforced mortar specimens (lightweight and common mortar) together with corrosion inhibitor in an effort to lower the corrosion rate of steel reinforcement. Corrosion parameters such as corrosion rates, Icorr, Rp of reinforcing steel in mortar specimens from two differences types of mortar have been evaluated by electrochemical measurements and compared with that obtained from metal loss determination. Electrochemical corrosion measurements gives a snapshot of how the system mortar – steel behaved under corrosive environments versus time. Linear polarization, as well as

386 Tafel technique are not destructive methods for assessing the instantaneous corrosion current density. It has been widely used in monitoring corrosion of laboratory measurements and allowed to compare the performance of inhibitors in mortars specimens [8].

2. MATERIALS AND EVALUATION METHODS

2.1. Materials Greek Portlant cement was used for whole mortar specimens in this study. The chemical composition is given in Table 1. Half of the test specimens were constructed with lightweight aggregate and the rest of them were with Greek sand. The use of the porous lightweight aggregates results in porosity increase, which could negatively affect the corrosion rate if steel rebars. The lightweight aggregate used was a Greek porous pumice of 0 to 8mm diameter. The mean value of the sand grains diameter was 250_m < d < 4mm. Round deform med reinforcing steel, nominally 12mm in diameter (_12) was used for all test specimens. Fabrication of the steel for the test specimens simply involved cutting to the consistent length of 100mm. Their chemical composition is given in Table 1. Drinking water from Athens water supply network and INHIB-M, corrosion inhibitor alkanolamines based on, were used for the specimens’ construction. The corrosion-inhibiting admixture was used according to the manufactures instructions regarding dose rate and mixing into the concrete. INHIB-M protects both the anodic and cathodic parts of the corrosion all. It’s claimed to work by depositing a physical barrier in the form of the surface film that inhibits corrosion of the steel by preventing contact between moisture and oxygen. The inhibitor is able to diffuse through the concrete through either a vapor or liquid phase.

Table1: chemical composition % of OPC cement. SiO2 Al2O3 Fe2O3 CaO MgO K2ONa2OSO3 CaO(f) LOI 20.67 4.99 3.18 63.60 2.73 0.37 0.29 2.414 2.41 2.52

Table2: chemical composition % of steel rebars. CMnSP SiNiCrCuVMo 0.18 0.99 0.047 0.023 0.15 0.09 0.09 0.21 0.002 0.021

2.2. Specimens Casting The test specimens considered for the present study were 80mm long, 80mm wide and 100mm high. They contained four identical steel rebars in the position shown in figure 1. Copper wire cables were connected to each steel bar for electrochemical measurements. Prior to the preparation, the surface of the steel bars were washed with water, then immersed for 15 min in strong solution of HCl

387 with organic corrosion inhibitor washed thoroughly with distilled water to eliminate traces of the corrosion inhibitor and chloride ions. Following that, they were cleaned with alcohol and with acetone and then weighed to 0,1mg accuracy. Thereafter, the bars were placed in moulds, as shown in figure 1, where the mortars was cast and stored at ambient conditions in the laboratory for 24 hours. After being demolded, were cured in tap water at 25 oC for 24 hours. The specimens were stored for an additional 24h at ambient temperature and thereafter the part shown in Figure 1 was insulated with epoxy resin. Finally half of them were partially immersed in 3.5% w.t NaCl solution up to 20mm from the bottom of the mortar specimens and the rest of them were exposed to the atmospheric conditions.

80

20 100 Epoxy resin 80

(_) (_) Steel rebars Figure 1: Schematic representation of reinforced mortar specimen (a) upper, (b) latter view. Dimensions of specimens in mm

2.3. Evaluation Methods The objective of these experiments was to investigate mortar with corrosion inhibitor as corrosion protection system and evaluate its performance in reference to specimens without any addition of admixtures. The migrating corrosion effectiveness was assessed in lightweight concrete with Greek pumice stone and in common mortar specimens. The inhibiting behavior of organic alkanolamines based migrating corrosion inhibitors against steel corrosion was evaluated by specimens’ immersion into 3,5%w.t NaCl corrosive solution and by exposure to the atmosphere. The code numbers and the composition for the different sets of specimens used in this study are shown in Table 3. The experimental duration of this study was 1year. Whole experimental procedure will be discontinued at the conclusion of two full years of testing. Methods used to assess specimens’ performance included the corrosion potential, carbonation depth, corrosion rate, and mass loss time dependence of the rebars measurements.

388 Specimens with all categories were immersed in 3.5%w.t NaCl solution and their electro chemicals values were examined in order to evaluate the reinforcement corrosion in mortars. The test setup for both the Tafel plot as well as the linear polarization resistance techniques included a potensiostat / galvanostat, E.G & Model 263. Additionally, a computer program, Softcorr III developed by E.G & G Princeton Research was used for applying the potential scan, analyzing the parameters Icorr, Rp. Half – cell potential measurements for each of the test specimens were recorded at regular intervals versus a saturated calomel reference electrode (SCE), for the duration of this experiment. Initially, these measurements were taken every day, until equilibrium conditions were established. Following, half – cell measurements were recorded every week. Twelve months after the start of this experiment the specimens were removed from the corrosive environment and broken in order to measure the carbonation depth and weight loss of steel rebars.

Table 3: Type and Composition of specimens Specimens Composition ratio Corrosion Code Cement Pumice Sand Water inhibitor Remarks name (lt/m3) K-I 1 3 - 1 - Category I: KM-I 1 3 - 1 1.24 Immersed in S-I 1 - 3 0.6 - 3,5%w.t SM-I 1 - 3 0.6 1.24 NaCl K-II 1 3 - 1 - Category II: KM-II 1 3 - 1 1.24 Exposed in S-II 1 - 3 0.6 - Atmosphere SM-II 1 - 3 0.6 1.24

The steel rebars were cleaned from rust according to above mention procedure, the metal loss was determined and the corrosion rates were calculated by the following equation.

Corrosion rate (_m/y) = 8.76x107 W/ (A*T*D) (1) W: metal loss in [g], A: area of steel in [cm2], T: time of exposure in [h], D: density of steel in [g/cm3] The carbonation of the specimens was determined by the method recommended by RILEM CPC-18, on broken mortar pieces. The carbonation depth of mortar was calculated in the interval section of the specimen using phenolophalein and by measuring the area where the colour did not change to red.

389 3. MEASUREMENTS AND RESULTS

3.1. Category-I: Specimens immersed in 3.5%w.t NaCl Half-cell potential measurements given in figure 2 came out from the first category of specimens that were immersed in 3.5%w.t NaCl solution. According to the standard test method ASTM C 876, Standard test method for Half Cell Potentials of reinforcing Steel in Concrete, the more negative the voltometer reading, the greater the probability of active corrosion. Values less than –350mV, have as a result 90% probability of active corrosion. It is obvious that for all the specimens there is a tendency for the reduction of their potential value from the range of –300mV to –650mV.these measurements suggests a high probability of an active stage of corrosion throughout the test period.

K-I S-I SM-I KM-I 0

-100 024681012

-200

-300

-400

-500

reference electrode (SCE) -600

Potential (mV) vs saturated calomel -700 Time (months ) Figure 2: Half- cell potential measurements vs immersion time.

The results of mass loss measurements of reinforcing steel, after twelve months of exposure in chlorides solution are given in figure 3. It is obvious that mass loss differences are higher when lightweight mortars are compared to common mortars that contain as aggregate sand. From these results, the improvement of the mortars properties and consequently of the corrosion performance of steel rebars when the aminobased corrosion inhibitor added is evident. The INHIB-M, lowering the steel rebar mass loss after twelve months of exposured by about 45% in lightweight mortar and 50% in common mortar specimens.

390 250 192.475 200 152.82 150 104.225 100 77.725 Mass Loss (mgr) 50

0 K-I KM-I S-I SM-I Specimens immersed in 3.5%w.t Na C Figure 3: Mass loss measurements of lightweight and common mortars after 12 months of partially immerse to NaCl 3.5%w.t.

Carbonation of specimens versus time is shown in figure 4. Between mortars with sand and mortars with Greek pumice as an aggregate, it is observed that the specimens, which exhibit carbonation, were the latter mortars. Lightweight specimens without corrosion inhibitor, exhibit 3.5 times higher carbonation depth values than those with corrosion inhibitor. From these results, it seemed that the corrosion inhibitor addition in the lightweight mortars protect steel by a mechanism that seem to influence to carbon dioxide access. 14 12 12 10 8 6 3.5 4 2

Carbonation Depth (mm) 00 0 K-I KM-I S-I SM-I Specimens immersed in 3.5%w.t Na C Figure 4: Carbonation depth of lightweight and common mortars after 12 months of exposure to NaCl 3.5%w.t.

In Tafel plot technique, a potential scan was applied to the specimens starting from Ecorr and extending to 250mV either in the cathodic or anodic direction. The

391 current measurements in this case were the difference between anodic and cathodic currents. Figure 5 gives the Tafel curves generated at chloride level of 3.5% w.t.in solution that specimens were been immerse. In linear polarization technique, a controlled potential scan was applied to the specimens in a range much smaller than that used in the Tafel plot. It was from Ecorr-25mV to Ecorr+25mV. The Rp polarization resistance, which is the slope of the potential current curve at Ecorr is related to Icorr. Table 4 is a comparison of the corrosion rate values from electrochemical techniques with those from the mass loss determination technique.

SUM.DAT -275 S-I.DAT

K-I.DAT -400 KM-I.DAT

-525

E(mV) -650

-775

-900

-1025 -8-7 -6 -5 -4 -3 -2 log(I)(log(A)) Figure 5: Tafel plots curves for reinforcing steel in common mortar and lightweight specimens immersed in 3.5%w.t. NaCl

Table 4: Corrosion rates of reinforcing steel in mortars with and without corrosion inhibitor, calculated by different techniques. Linear polarization Weight loss Tafel plot technique Code technique determination Corrosion Corrosion Corrosio name Rp Icorr Rp Icorr Mass loss rate rate n rate (Ohms) (__) (Ohms) (__) (mg) (mpy) (mpy) (mpy) K-I 371.6 58.44 1.715 386.1 56.24 1.650 192.475 0.71193 KM-I 538.5 40.32 1.183 438.5 49.52 1.453 104.225 0.3855 S-I 460 47.20 1.384 480 45.15 1.325 152.82 0.5652 SM-I 1379 15.75 0.4617 1481 14.66 0.4298 77.725 0.2874

1.2. Category-II: Specimens exposed in atmosphere. The results of mass loss measurements of reinforcing steel, after twelve months of exposure in atmosphere are given in figure 6. The INHIB-M, lowering the steel rebar mass loss after twelve months of exposured by about 44% in lightweight mortar and 45% in common mortar specimens.

392 160 137.65 140 120 111.675 100 77.15 80 61.05 60 Mass Loss (mg) 40 20 0 K-II KM-II S-II SM-II Specimens exposed in atmospher e

Figure 6: Mass loss measurements of lightweight and common mortars after 12 months of exposure to atmosphere.

Carbonation of specimens versus time is shown in figure 7. From these results, it seemed that the corrosion inhibitor addition in mortars protect steel by a mechanism that does not seem to influence to carbon dioxide access. The carbonation depth in lightweight mortars is definitely higher than those in mortars with sand as aggregates.

30 25.5 24.4 25 19 19 20

15 10

Carbonation Depth (mm) 5

0 K-II KM-II S-II SM-II Specimens exposed in atmospher e

Figure 7: Carbonation depth of lightweight and common mortars after 12 months of exposure to atmosphere.

393 4. CONCLUSIONS The usage of corrosion inhibitors has decreased corrosion both in the specimens that were partially immersed in 3.5%w.t NaCl as well as in those that were exposed in atmospheric conditions exposed for about 45% and 50% respectively. The results of the electrochemical measurements for calculating the corrosion rate in order to have a first estimation of the corrosion of the mortar specimens that were partially immersed in 3.5%w.t NaCl solution are certified and confirmed by the results of the calculations of the reinforcements mass loss in the mortars for a twelve month corrosion period. The carbonisation with a high porosity aggregates is by far larger when compared with the one in the specimens that were mortars made with common sand. The corrosion in the lightweight mortars has reached the surface of the reinforcements in a about a year's time and in that case the corrosion inhibitor has decreased the reinforcements corrosion for about 45%. As a result the conclusions of this study are in line with the confession that the usage of corrosion inhibitors is doubling the lifetime of the constructions.

REFERENCES

1. Batis, G., Kouloumbi, N., Katsiamboulas A., 1996, “Durability of reinforced Lightweight Mortars with Corrosion inhibitors”, Cement, Concrete and Aggregates, CCAGDP, Vol. 18, No. 2, pp.118-125. 2. Batis, G., Chronopoulos, M., 1995, “Durability of mortars for restoration,” Structural Studies of Historical Buildings IV, Vol. 1, Architectural Studies, Materials and Analysis, International Coeference STREMA’95, Chania, Kreta, pp. 239-244 3. Kouloumbi, N., Batis, G., 1992, “Chloride Corrosion of steel rebars in mortars with fly ash admixtures”, Cement and Concrete Composites, Vol. 14, pp.199- 207. 4. Batis, G., Pantazopoulou, P., 1999, “Comperative Examination of the Durability of Reinforced Concrete through Coatings and Corrosion Inhibitors”, International Conference on Infrastructure Regeneration and Rehabilitation Improving the Quality of Life Through Better Construction, Sheffield, England, pp. 683-692. 5. Hanson, C.M., Mammoliti, L., Hope, B.B, 1998, “Corrosion Inhibitors in Concrete – Part I: The Principles”, Cement and Concrete Research, Vol. 28, No.12, pp. 1775-1781. 6. Mammoliti, L., Hanson, C.M., Hope, B.B., 1999, Part II, ibit Vol. 29, pp. 1583- 1589. 7. Miksic, B.A, ‘Use of vapor phase inhibitors for corrosion protection of metal products’, International Conference Corrosion 83,No.308, pp.307-315. 8. Abdul- Hamid, J., Al-Tayyib, Mohammand Shamim Khan, 1988, “Corrosion Rate Measurements of Reinforcing Steel in Concrete by Electrochemical Techniques”, ACI Materials Journal, pp. 172-177.

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398  

Evaluation of Migrating Corrosion Inhibitors Used in the Restoration and Repair of Reinforced Concrete Structures

Matt Drew Jessi Jackson Meyer Joshua Hicks Cortec Corporation Cortec Corporation Cortec Corporation 4119 White Bear Parkway 4119 White Bear Parkway 4119 White Bear Parkway Saint Paul, MN 55110 Saint Paul, MN 55110 Saint Paul, MN 55110

ABSTRACT

Corrosion inhibitors used in reinforced concrete structures can greatly increase service life and reduce long term maintenance costs. In this work, migrating corrosion inhibitors have been utilized in the repairs of concrete structures that were deteriorating due to corrosion of embedded reinforcement. These two projects show that migrating inhibitors have a direct and significant impact on the reduction of corrosion.

The Randolph Avenue Bridge in Minnesota was repaired using an overlay incorporating a migrating corrosion inhibitor in the westbound lanes. The repair of the eastbound lanes did not contain a corrosion inhibitor. The rehabilitation was part of a Federal Highway Administration project and measurements were also taken as part of a Virginia Tech study. Updated readings were performed in 2000, 2003, 2007, and 2011.

The Apple Street Parking Garage in Ohio contained precast double tees that had advanced corrosion which led to full depth concrete repairs. Repairs were completed using concrete that included a migrating corrosion inhibitor, and the application of a penetrating corrosion inhibitor to the rest of the structure.

This paper will cover the corrosion rate data collection and present findings, which will include chloride level analysis, half-cell potential readings, concrete resistivity readings, and linear polarization resistance techniques.

Key words: Migrating corrosion inhibitor, concrete, reinforcement, half-cell potential, linear polarization resistance, repair.

399  INTRODUCTION

Originally constructed in 1963, the Randolph Avenue Bridge spans Interstate 35E in Saint Paul, Minnesota. Due to chloride induced corrosion, embedded reinforcement deteriorated to the point of causing major cracking and spalling on the concrete bridge decks. In 1986, the top deck of the Randolph Avenue Bridge was repaired in a project sponsored by the Minnesota Department of Transportation. Both sides of the deck were repaired using a low slump, dense concrete overlay that incorporated a migrating corrosion inhibiting admixture into one side while the other was left untreated as the control. The treated westbound lanes have served as a real world comparison of corrosion current reduction versus the untreated “control” eastbound lanes.

The rehabilitation of this bridge was part of a Federal Highway Administration project from 1986 to 1990 and a Virginia Tech Study in 1991 and 1992. Updated readings were performed by the Minnesota DOT in 2003 and by Cortec Corporation(1) in 2000, 2007, and 2011.

The Apple Street Parking Garage in Dayton, OH is a pre-topped, precast, double tee garage. The lower two levels were constructed in 1986 and the upper levels were added in 1989. During an inspection in the early 2000s, the precast double tees were found to have advanced corrosion which led to necessary full depth repairs of the concrete. In 2006, repairs were completed using ready mixed concrete that included a migrating corrosion inhibiting admixture. Surface treatments were also made to existing concrete outside of the patchwork using a penetrating corrosion inhibitor.

EXPERIMENTAL

Randolph Avenue Bridge

Background.

The rehabilitation process included the application of a low slump dense concrete that varied in depth from 2.3 to 4.2 inches (58.4-106.7 mm). The mix design of the overlay can be seen in Table 1. An aminoalcohol based migrating corrosion inhibiting admixture was added to the concrete overlay at 1 pint/yd3 (0.62 L/m3) for the two westbound traffic lanes. The eastbound lanes were repaired with the same type of concrete which did not contain the corrosion inhibitor to act as the control. Prior to application of the overlay, the deck was milled to a depth of 0.5 inches (13 mm) and the areas of unsound concrete were removed. The cavities from the removal of the unsound concrete were filled with the overlay concrete. The general slope of the bridge for water runoff appears to be towards the northeast.

400  Table 1 Mix design parameters of the Randolph Avenue Bridge repair Control Treated Component (lbs/yd³) (lbs/yd³) Type I Cement 836 836 Water 270 270 w/c ratio 0.32 0.32 Coarse Aggregate 1385 1385 Fine Aggregate 1374 1374 Water Reducing Admixture 0.25 0.25 Air Entraining Agent 0.073 0.073 Corrosion Inhibitor - 0.95

Corrosion assessments were conducted on the eastbound (control) and westbound (aminoalcohol) travel lanes of the structure by Virginia Tech researchers on two occasions, June 1991 and August 1992. The assessments included visual inspection, delamination survey, cover-depth survey, chloride contents as a function of depth, corrosion potentials, and estimates of corrosion current densities (icorr) using 3LP(2) Meter (Linear Polarization Device 1). Prior to the assessments completed by Virginia Tech, the repair was part of a Federal Highway Administration Project until 1990.

In November 2000, technicians returned to the bridge and took new measurements. These included linear polarization readings obtained by a Gecor 6(3) (Linear Polarization Device 2) instrument, and copper/copper sulfate half-cell potentials. A new chloride analysis was also taken at various depths.

In June 2007 and July 2011, chloride analysis, alkalinity testing, and half-cell potential readings were performed. Linear polarization readings using a Galvapulse(4) (Linear Polarization Device 3) instrument, of corrosion current, corrosion rate, and concrete resistivity were also taken.

Apple Street Parking Garage

Background.

The concrete reinforcement is a steel mesh that is located 1.75-2 inches (44.5-50.8 mm) deep and is 0.19 inches (4.76 mm). The mesh was laid out in a 4 foot by 8 foot (1.22 m by 2.44 m) grid. In November 2006, patchwork was completed using ready mixed concrete that incorporated an amine carboxylate based migrating corrosion inhibiting admixture dosed at 1.5 pints/yd3 (1 L/m3).

Also in 2006, a water-based penetrating corrosion inhibitor was applied to both the deck and to the underside at a coverage rate of 150 ft2/gal (3.68 m2/L). The substrate was allowed to dry for a week and was then shot blasted prior to application of a 40% silane water repellant to the deck surfaces.

On July 1, 2009, linear polarization readings were obtained using Linear Polarization Device 3. Ten corrosion current readings were taken at five different locations within the garage.

401  Chloride Contamination Levels.

At the Randolph Avenue Bridge, powdered concrete samples for chloride analysis were taken at mean depths of 0-1, 1-2, and 2-3 inches (0-25, 25-51, and 51-76 mm) from six total locations, three on each side of the bridge.

Samples were taken using a rotary impact type drill with a 0.5 inch (12.7 mm) sized bit. Three-gram samples that passed through a #20 sieve were obtained from each depth. The powder was then mixed with 20 ml of digestion solution for a total of 3 minutes and then 80 ml of stabilizing solution was added. A calibrated electrode coupled to an Orion(5) Model 720-pH/ISE meter was then immersed in the solution, and the chloride-ion concentration was recorded. This method was consistent with the AASHTO: T260 Procedure C. The standard deviation for this chloride test was determined by testing the six pulverized concrete Quality Assurance (QA) samples of known chloride content. Each QA sample was tested five times.

Corrosion Current Measurements.

Corrosion current density (icorr) estimates were taken at the Randolph Avenue Bridge in June 1991 and August 1992 using Linear Polarization Device 1. Readings were also performed in November 2000, July 2007, and July 2011 using both Linear Polarization Device 2 and Linear Polarization Device 3. Corrosion current density readings were also obtained at the Apple Street Parking Garage in July 2009 using Linear Polarization Device 3.

The icorr measurement is proportional to the corrosion rate through Faraday’s Law. The instruments used measure the corrosion rate of steel in concrete by “polarization resistance” or “linear polarization” techniques. This is a non-destructive technique that works by applying a small current to the rebar and measuring the change in the potential. Then the polarization resistance, Rp, (the change in potential measured), is divided by the applied current. The corrosion rate, icorr, is obtained from the polarization resistance, Rp, by means of the “Stearn and Geary” relationship:

icorr = B/Rp, where B = 26 mV (1)

Each device used has different criteria for evaluating the corrosion rates which are described in Table 2, Table 3, and Table 4.1

Table 2 Corrosion intensity versus corrosion current and rate of corrosion found by Linear Polarization Device 1 Corrosion Current Corrosion Rate Intensity of Corrosion (μA/cm2) (μm/year) <0.5 <5.8 Passive Condition 0.5-2.7 5.8-31.3 Low corrosion (damage possible in 1-15 years) 2.7-27 31.3-313.2 Moderate corrosion (damage possible in 2-10 years) >27 >313.2 High corrosion (damage expected in 2 years or less)

402  Table 3 Corrosion intensity versus corrosion current and rate of corrosion found by Linear Polarization Device 2 Corrosion Current Corrosion Rate Intensity of Corrosion (μA/cm2) (μm/year) <0.5 <1.2 Negligible corrosion 0.5-2.7 1.2-5.8 Low corrosion 2.7-27 5.8-11.6 Moderate corrosion >27 >11.6 High corrosion

Table 4 Corrosion intensity versus corrosion current and rate of corrosion found by Linear polarization Device 3 Corrosion Current Corrosion Rate Intensity of Corrosion (μA/cm2) (μm/year) <0.5 <5.8 Passive condition 0.5-5 5.8 to 58 Low corrosion 5-15 58 to 174 Moderate corrosion >15 >174 High corrosion

Concrete Resistivity Measurements.

Linear Polarization Device 2 calculates the concrete resistivity by means of the formula,

Resistivity = 2 × R × D (2)

where R = resistance by the “iR drop” from a pulse between the sensor counter-electrode and the rebar network and D = counter-electrode diameter of the sensor

The value of the concrete’s resistance is used as an additional parameter for the interpretation of the rate of corrosion. Table 5 shows the interpretation of the results.2

Table 5 Correlation of resistivity measurements to corrosion rate using Linear Polarization Device 2 Resistivity Corrosion Rate >100-200 kȍ · cm Very low, even with high chloride and carbonation 50-100 kȍ · cm Low 10-50 kȍ · cm Moderate to high where steel is active <10 kȍ · cm Resistivity is not the parameter controlling corrosion rate

Half-Cell Potentials.

ASTM C 876 corrosion half-cell potentials were measured on the Randolph Avenue Bridge for both the eastbound and westbound travel lanes with Linear Polarization Device 2 in November 2000, June 2007, and July 2011. The Minnesota Department of Transportation also conducted half-cell potential readings in 2003. According to ASTM C 876, the results can be interpreted in Table 6.

403  Table 6 Corrosion potential using half-cell potential readings from Linear Polarization Device 2 Potential Probability of Corrosion >-200 mV Less than 10% -200 mV to -350 mV 50% <-350 mV Greater than 90%

Carbonation.

Carbonation of concrete is a process by which carbon dioxide from the air penetrates the concrete and reacts with the hydroxides, such as calcium hydroxide, to form carbonates. This process increases shrinkage on drying (promoting crack development) and reduces the alkalinity of the concrete. High alkalinity is needed to protect embedded rebar from corrosion; consequently, concrete should be resistant to carbonation to prevent steel corrosion.3 The carbonation of powdered concrete samples taken from the Randolph Avenue Bridge was determined by using phenolphthalein (alkalinity) measurements.

RESULTS AND DISCUSSION

Randolph Avenue Bridge

Chloride Threshold.

Chloride threshold refers to the concentration of chlorides at which corrosion in the steel is initiated. Based on the service life prediction model, Life 365, the chloride threshold of the concrete used in the Randolph Avenue Bridge is 0.05 percent of the concrete.4 This converts to 0.4% by weight of the cement and 3.35 lbs/yd³ (1.98 kg/m3).

Chloride content readings were taken at 0-1, 1-2, and 2-3 inches (0-25, 25-51, and 51-76 mm) from 3 different locations on each side of the bridge. These readings indicated that the overall chloride levels in the control side were slightly higher than in the treated side. As can be seen in Table 7, the chloride levels have continued to rise at the level of the steel.

Table 7 Average chloride levels of Randolph Avenue Bridge Treated Side (lbs/yd3) Control Side (lbs/yd3) Depth (0-1”) (1-2”) (2-3”) (0-1”) (1-2”) (2-3”) 1991 3.5 0 0.7 7.7 2.5 1.9 1992 6.5 1.1 1.9 9.5 3.5 2.5 2000 11.7 1.6 1.3 17.2 6.2 2.4 2007 11.7 1 2.6 20 7.4 2.3 2011 12.3 4.9 1.8 14.7 6.6 3.5

Corrosion Current Readings.

Corrosion currents of rebar have increased on both sides of the bridge since the year 2000, when the treated side had very low corrosion currents, an average of 0.0081 μA/cm2, approximately 42% below readings taken on the control side (average of 0.014 μA/cm2).

The corrosion current readings that were taken in July of 2011 are substantially higher at almost all points on the bridge. As shown in Table 7 the control side has reached the chloride threshold at the depth of the reinforcing steel. As seen in Table 8, the average corrosion rate of the treated side is 35% of the level on the control side. The highest rate of corrosion was measured in the center section of the ©2012control by NACE side International which was Requests 1.2755 for permission μA/cm² to publishcomp thisared manuscript to the in treated any form incenter part or insection whole must which be in writingis 0.4202 to NACE μ InternationalA/cm²,

404  a reduction of 67%. This reduction is confirmed by the half-cell potentials which show a high probability of corrosion in the control South Central section seen in Table 10.

In Table 8, the average corrosion current data is presented comparing segments of the bridge using Linear Polarization Device 2. In 2011 all readings taken on the treated areas of the bridge were much lower than the readings taken on the control side. Additionally, all three control locations had average corrosion rate readings that would be considered active, whereas the treated side readings were all in the passive range. This indicates the corrosion inhibiting admixture is functioning as expected.

Table 8 Average corrosion rates for each bridge section of Randolph Avenue Bridge Treated Lanes Control Lanes Northwest North Central Northeast Southwest South Central Southeast Year (μA/cm2) (μA/cm2) (μA/cm2) (μA/cm2) (μA/cm2) (μA/cm2) 2000 0.0081 0.0006 0.0077 0.093 0.175 0.145 2007 0.1258 0.2522 0.4231 0.2982 0.1878 0.368 2011 0.2659 0.4202 0.3196 0.6254 1.2755 0.8607

Figure 1 shows the comparison of corrosion rate readings on the control side versus the treated side using Linear Polarization Device 2. Prior to 2007, both sides of the bridge showed average corrosion rates in the passive range, however the treated side exhibited 40% lower readings. Now that the control side has entered active corrosion, the treated side is exhibiting corrosion rates that are approximately 85% less.

Figure 1: Average corrosion rates of the Randolph Avenue Bridge

Weather can be a factor that affects readings. Of particular importance is the humidity level as the moisture in the concrete affects the conductivity and readings that are taken. To mitigate the effects of the weather, the surface was prepared using ASTM C876. This method requires a specific pattern of adding moisture to the concrete so a consistent environment is achieved across all areas.

405  Alkalinity Levels.

The core samples from 2011 were tested and exhibited average alkalinity levels between 1640 and 1840 mg/L. The samples that were taken from the treated side of the bridge show results of higher alkalinity levels, which can signify the presence of corrosion inhibitor and resistance to carbonation. The data is compiled in Table 9.

Table 9 Alkalinity results organized by the section of the Randolph Avenue Bridge Treated Control Alkalinity Average Alkalinity Average Sample Sample (mg/L) (mg/L) (mg/L) (mg/L) NW 0-1" 1680 SW 0-1" 1800 NW 1-2" 1800 1800 SW 1-2" 1920 1800 NW 2-3" 1920 SW 2-3" 1680 NC 0-1" 1800 SC 0-1" 1920 NC 1-2" 1800 1840 SC 1-2" 1800 1800 NC 2-3" 1920 SC 2-3" 1680 NE 0-1" 1920 SE 0-1" 1560 NE 1-2" 1800 1760 SE 1-2" 1680 1640 NE 2-3" 1560 SE 2-3" 1680

Half-Cell Potentials.

The half-call potential readings taken in 2011 can be seen in Table 10. The average reading for each side of the bridge shows that the potential for corrosion is higher on the control side than that of the treated side according to Table 6.

Table 10 Half-cell potential values from each segment of the Randolph Avenue Bridge Treated Control Rebar NW (mV) NC (mV) NE (mV) SW (mV) SC (mV) SE (mV) 1 -378 -130 -130.3 -84 -332 -231 2 -331.3 -128.7 -93.3 -91.5 -397.5 -248.5 3 -294.3 -98.3 -59.7 -88.5 -381.5 -187 4 -239.7 -83.3 -68.3 -104 -400 -150 5 -227.3 -72.3 -82.7 -97.5 -392 -125.5 6 -183.7 -79 -37 -99 -400 -117.5 7 -185 -69.3 -36.7 -122 -404.5 -140 8 -170.3 -72 -46.3 -163.5 -381.5 -147 9 -156 -78 -79.3 -231 -397.5 -181 10 -172 -76.3 -167 - - -206.5 11 -190.7 -74.3 -192 - - -270.5 12 - -97.3 -189.7 - - - 13 - -96.3 -191.7 - - - 14 - - -218.7 - - - Average -229.8 -88.9 -113.8 -120.1 -387.4 -182.2

406  The time versus average half-cell potential results, shown in Figure 2, shows that the potential for corrosion within the bridge is higher on the control side and has been for 20 years. This data along with the rest of the supporting information suggests that levels of corrosion in the treated side are lower than in the control.

Figure 2: Average half-cell potentials of the Randolph Avenue Bridge

Apple Street Parking Garage

Corrosion Rate Readings.

All readings at the Apple Street Parking Garage were performed using Linear Polarization Device 3. All locations had average readings in the passive to low levels according to Table 4. Fifty readings were taken in total; 10 readings at 5 different locations throughout the garage. All readings can be seen in Table 11.

Table 11 Corrosion current readings for treated areas of the Apple Street Parking Garage Location 1 Location Location Location 4 Location 5 Reading (μA/cm2) 2 (μA/cm2) 3 (μA/cm2) (μA/cm2) (μA/cm2) 1 2.97 1.75 0.51 1.62 3.12 2 1.76 1.35 0.57 0.65 0.89 3 3.01 1.08 0.47 0.81 0.36 4 1.22 1.37 0.26 1.17 0.38 5 1.59 6.76 0.32 0.96 0.25 6 3.48 1.38 0.41 0.24 0.24 7 1.55 0.96 0.6 0.26 0.52 8 2.15 8.22 0.4 0.92 0.22

407  9 6.43 9.71 0.45 0.62 6.63 10 5.28 3.37 0.38 1.2 2.86 Average 2.94 3.6 0.43 0.84 1.55

CONCLUSIONS

Aminoalcohol and amine carboxylate based corrosion inhibitors have proven beneficial when used in repair of concrete that has cracked and spalled due to chloride induced corrosion of the embedded reinforcing steel. In the Randolph Avenue Bridge, corrosion was significantly decreased compared to the control due to the presence of the aminoalcohol corrosion inhibiting admixture. The Apple Street Parking Garage is showing very low corrosion currents due to the high affinity of the amine carboxylate corrosion inhibiting admixture and the penetrating corrosion inhibitor. The lower corrosion currents are due to the adsorption of the aminoalcohol and amine carboxylate molecules on the embedded reinforcing steel, showing that these molecules can displace existing chloride and water molecules. Thus, corrosion rates can be decreased significantly.

ACKNOWLEDGMENTS

Authors thank American Engineering and Testing, Inc for their assistance in obtaining readings on the Randolph Avenue Bridge. They would also like to thank Chris Przywara, Structural Engineer with THP, Ltd. and Rae Jean Nicholl of S.M.A.R.T. Distribution for their assistance with the Apple Street Parking Garage readings.

REFERENCES

1) Germann Instruments, Inc., Galvapulse TM GP-5000 Instruction and Maintenance Manual, 2005.

2) Andrade, C., Fullea, J., Alonso, C., “The Use of the Graph Corrosion Rate-Resistivity in the Measurement of Corrosion Current”, International Workshop MESINA, Instituto Eduardo Torroja, Madrid, Spain, 1999.

3) Kosmatka, Steven and Panarese, William, Design and Control of Concrete Mixtures Thirteenth Edition, Portland Cement Association, Skokie, Illinois, 1994 rev. pp. 72.

4) Thomas, M.D.A. and Bentz, E.C., Life-365 Computer Program for Predicting the Service Life and Life-Cycle Costs of Reinforced Concrete Exposed to Chlorides. University of Toronto, Toronto, Canada, April 21, 2000, pp. 9.

5) Alfred J Gardiner PE et al, Affects of a Migrating Corrosion Inhibitor on Bridge Decks in St. Paul, Minnesota, August 27, 2003.

408 Corrosion Inhibition of Steel Rebar in Concrete By Migrating Corrosion Inhibitors

Bezad Bavarian and Lisa Reiner Dept. of Civil and Manufacturing Engineering California State University, Northridge 18111 Nordhoff Street Northridge, California 91330-8347

Corrosion of embedded steel is one of the major causes of concrete deterioration in reinforced concrete structures. This type of corrosion results when a corrosive species, water and air, penetrate through the concrete pores to the steel’s surface. The key to inhibiting rebar corrosion is to restrict the permeability of concrete. Migrating corrosion inhibitors and concrete sealers can reduce the corrosive ion mobility and permeability by decreasing concrete porosity.

The effectiveness of several commercially available migrating corrosion inhibitors and concrete sealers for steel rebar (class 60) in concrete was investigated. Concrete specimens were prepared with reinforcement at 1 and 2 inches of concrete coverage. Corrosion inhibitors and sealers were applied to the surfaces of the concrete after they had been cured for 28 days. Specimens were immersed in a 3.5% sodium chloride solution. Using Electrochemical Impedance Spectroscopy, the specimens were tested to determine changes in their resistance polarization, Rp, over a 52-week period. The Rp values are significant because they are inversely proportional to the rate of corrosion. The open circuit potential versus a Cu/CuSO4 reference electrode (ASTM C876) was also monitored as a function of time to ascertain the probability of corrosion activity.

MCI 2022 has successfully demonstrated corrosion inhibition of steel rebar in 3.5% NaCl solution. This MCI product has exhibited promising corrosion inhibiting properties by maintaining a high resistance polarization (low corrosion rate) for the rebar in concrete. The reference concrete samples (non-protected), however, have shown a decline in their resistance polarization, indicative of corrosion.

INTRODUCTION

Corrosion of steel rebar is the major cause of concrete deterioration in reinforced and prestressed concrete structures. Billions of dollars each year are spent to repair the damages resulting from this type of corrosion that initiates when salts, water and air penetrate through the pores of concrete and reach the surface of the steel. In general, embedded steel rebar in concrete is stable; the concrete provides a highly alkaline, protective environment. Problems arise when the embedded concrete structure is exposed to the aforementioned corrosive species.

Chemical admixtures have been combined with concrete as a possible means of preventing chloride ions from reaching the steel's surface. Inhibitors have the effect of promoting a passive layer at the steel’s surface, which makes it more difficult for the chloride ions to remove electrons. A reduction in the corrosion rate can occur if the permeability of the concrete is restricted. Migrating corrosion inhibitors (MCI) can reduce the corrosive ion mobility and neutralize these corrosive species.

Migrating Corrosion Inhibitor (MCI) technology was recently developed to protect the imbedded steel rebar/concrete structure. MCIs are based on amino-carboxylate chemistry. They are very effective

409 “mixed” cathodic and anodic corrosion inhibitors. Under normal conditions these substances enhance the vapor pressure. Increased pressure causes the inhibitor molecules to diffuse through the concrete. This diffusion process requires a period of time to migrate through the concrete’s pores. Once the MCIs migrate to the rebar’s surface, a protective layer is formed. This suggests that the migratory inhibitors are physically adsorbed onto the metal surfaces1.

MCIs can be incorporated as an admixture or can be used by surface impregnation of existing concrete structures. With surface impregnation, diffusion transports the MCIs into the deeper concrete layers. They will delay and inhibit the onset of corrosion on steel rebar. Bjegovic and Miksic recently demonstrated the effectiveness of MCIs over four years of continuous testing1. They also showed that the migrating amine- based corrosion-inhibiting admixture can be effective when they are incorporated in the repair process of concrete structures2. Furthermore, laboratory tests have proven that MCI corrosion inhibitors migrate through the concrete pores and protect internal steel bars against corrosion even in the presence of chlorides3-4.

The objective of this investigation was to study the corrosion inhibition of several commercially available migrating corrosion inhibitors on steel rebar in concrete. Electrochemical monitoring techniques were applied while samples were totally immersed in 3.5% NaCl at ambient temperatures. Due to the low conductivity of concrete, the corrosion behavior of steel rebar had to be monitored using AC electrochemical impedance spectroscopy (EIS). During this investigation, changes in the resistance polarization and the corrosion potential of the rebar were monitored to ascertain the degree of effectiveness for these MCI products. The results were compared with previous investigations conducted on several admixtures and stainless steel rebars.

EXPERIMENTAL PROCEDURES

In theory, the steel rebar/concrete combination can be treated as a porous solution that can be modeled by a Randles electrical circuit. EIS tests performed on a circuit containing a capacitor and two resistors indicate that this model is an accurate representation of an actual corroding specimen. EIS testing allows for the determination of fundamental parameters relating to the electrochemical kinetics of the corroding system. This is attained through the application of a small amplitude-alternating potential signal of varying frequency to the corroding system. Because processes at the surface absorb electrical energy at discrete frequencies, the time lag and phase angle, theta, can be measured. The values of concern in this study are

Rp and R
. The Rp value is a measure of the polarization resistance or the resistance of the surface of the material to corrosion. R
is a measure of the solution resistance to the flow of the corrosion current.

By monitoring the Rp value over time, the relative effectiveness of the sample against corrosion can be determined. If the specimen maintains a high Rp value in the presence of chloride, it is considered to be "passivated" or immune to the effects of corrosion. If the specimen displays a decreasing Rp value over time, it is corroding and the inhibitor is not providing corrosion resistance.

The EG&G Instruments Potentiostat/Galvanostat Model 273A and EG&G M398 Electrochemical Impedance Software were used to conduct these experiments and to record the results. Bode and Nyquist plots were produced from the data obtained using the single sine technique. Potential values were recorded and plotted with respect to time. By comparing the bode plots, changes in the slopes of the curves were monitored as a means of establishing a trend in the Rp value over time. To verify this analysis, the Rp values were also estimated by using a curve fit algorithm on the Nyquist plots (available in the software).

Results from EIS tests were organized into bode and Nyquist plots. Based on these plots, the Rp and R
combined values are displayed in the low frequency range of the bode plot and the R
value can be seen in the high frequency range of the bode plot. The diameter of the Nyquist plot is a measure of the Rp value.

Ten concrete samples with dimensions 8” x 4” x 4” were prepared. Each sample consisted of one 8 inch steel (class 60) rebar (3/8” diameter) and one 8-inch Inconel metal strip (counter electrode). The rebar prior to being placed in concrete were exposed to 100% RH (relative humidity) to initiate corrosion. Teflon tape was wrapped around the top 2-3 inches of inconel and rebar to prevent corrosion rust at the

410 concrete/metal interface. Concrete was mixed with one-half gallon water per 60-lb. bag (.4-.5 cement to water ratio) in a mechanical mixer. Inconel and rebar were placed one inch apart and two inches from the bottom of the wood container before concrete was poured. Five rebars were placed one inch from the side of the box and five were placed two inches. The concrete was vibrated by machine after being poured into the boxes. This was done to minimize bubbles and slurry. The concrete was air cured for 24 hours, then removed from the wooden crates and placed in 8 inches of water to continue the curing process. The concrete specimens were removed from water and set out to dry (approx. 28 days; the attained compressive strength of concrete was about 2,800–3,200 psi). The concrete blocks were sandblasted to remove loose particles, debris, and rust deposited on the metal. This process left the concrete with a marginally smoother surface. Red shrink-wrap was placed on each of the exposed rebars to prevent additional corrosion.

CORTEC MCI 2021 BASE SEALER was applied on two concrete samples. CORTEC MCI 2021 INHIBITOR & BASE SEALER were applied on two concrete samples. CORTEC MCI 2022 BASE SEALER was applied on two concrete samples. CORTEC MCI 2022 INHIBITOR & BASE SEALER were applied on two samples. The remaining two concrete blocks were used as control references. These samples were immersed in 3.5 % NaCl solution (roughly 6-7 inches of each sample was immersed in the solution continuously). EIS (Electrochemical AC Impedance Spectroscopy) testing was started after 24 hours of immersion using a Cu/CuS04 electrode.

MCI 2021, the thicker of the two inhibitors, did not adhere to the concrete and fell to the bottom of the container after ten hours of immersion in solution. This resulted in a heavy white blanket of residue. Two coats of base and/or inhibitor were applied to each sample. There was nothing notable about the MCI 2022. The 2022 inhibitor and base sealer resembled a dilute (thin) milky white fluid.

RESULTS and DISCUSSION

The corrosion inhibition of two commercially available migrating corrosion inhibitors (Cortec MCI 2022 and 2021) was investigated over a period of 400 days using AC electrochemical impedance spectroscopy (EIS). Throughout this investigation, changes in the resistance polarization and the corrosion potential of the rebar were monitored to determine the degree of effectiveness for the Cortec MCI 2021 & 2022 products. According to the ASTM (C876) standard, if the open circuit potential (corrosion potential) is between 0 and -200 mV, this indicates a 90% probability that no reinforcing steel has corroded. Corrosion potentials more negative than -350 mV are assumed to have a greater than 90% likelihood of corrosion.

Figure 1 shows corrosion potentials for the MCI 2021 and untreated control samples dropped from –200 mV to –600 mV, which indicates a 90% probability of corrosion attack on the reinforcing steel. Figure 2 shows that the corrosion potentials for MCI 2022 without inhibitor were –200 mV; for samples with inhibitor, the corrosion potentials were –120 mV. All of the MCI 2022 samples had corrosion potentials in the non-corroding range per ASTM C876.

AC electrochemical impedance spectroscopy (EIS) showed that MCI 2021 and reference samples had a gradual reduction in their resistance polarization, from about 10000 ohms to less than 600 ohms, which is similar to the drop in their corrosion potentials and strongly indicative of steel rebar corrosion (Figures 3- 8). Figures 3-8 show that the resistance polarization for MCI 2022 without inhibitor (samples) gradually increased from 10,000 to 100,000 ohms; for samples with inhibitor, the Rp was 10,000 at the beginning of the experiment and ended at close to 200,000 ohms. An increase in the Rp value was observed after about 200 days, indicating that Migrating Corrosion Inhibitors (MCIs) require an induction period for diffusion into the concrete to reach the metal rebar.

The samples coated with the MCI 2022 Inhibitor and Base Sealer showed the greatest amount of corrosion resistance; the corrosion resistant behavior was similar to stainless steel rebar (investigated in a subsequent project)5-6. These results are extremely promising for the MCI 2022 product in its ability to protect steel rebar in concrete in aggressive environments.

411 CONCLUSION

Corrosion inhibition of two commercially available migrating corrosion inhibitors (Cortec MCI 2022 and 2021) on steel rebar in concrete was investigated while the concrete was totally immersed in 3.5% NaCl at ambient temperatures using electrochemical monitoring techniques.

The MCI 2022 products have successfully inhibited corrosion of the rebar in a 3.5% NaCl solution for 400 days. Steel rebar corrosion potentials were maintained at approximately -120 mV, and rebar resistance polarization reached as high as 200,000 ohms. Both results indicate excellent corrosion resistance performance. The MCI 2021 and untreated samples have shown a decline in their resistance polarization and corrosion potentials, indicative of corrosion. The lack of corrosion inhibition of MCI 2021 could be due to the lack of its adhesion to the concrete surface, thereby leaving the concrete with no protection.

In summary, the experimental results demonstrate that the MCI 2022 products offer an excellent inhibiting system for protecting reinforced concrete in an aggressive 3.5% NaCl solution. These results are extremely promising for the protection of steel rebar in concrete in aggressive environments.

REFERENCE

1. D. Bjegovic and B. Miksic, Migrating Corrosion Inhibitor Protection of Concrete, MP, NACE International, Nov. 1999.

2. D. Bjegovic and V. Ukrainczyk, “Computability of Repair Mortar with Migrating Corrosion Inhibiting Admixtures,” CORROSION/97, paper no. 183 (Houston, TX: NACE, 1997.

3. D. Rosignoli, L.Gelner, and D. Bjegovic, “Anticorrosion Systems in the Maintenance, Repair and Restoration of Structures in Reinforced Concrete,” International Conference Corrosion in Natural and Industrial Environments: Problems and Solutions, Grado, Italy, May 23-25, 1995.

4. R. Martinez , A. Petrossian, , and B. Bavarian, “Corrosion of Steel Rebar in Concrete,” presented at the 12th NCUR, April 1998.

5. R. Martinez , A. Petrossian, B. Bavarian, “Investigation of the Corrosion Behavior of Steel Rebar in Concrete in High Chloride Environments Through the Use of Electrochemical Impedance Spectroscopy,” June, 1998.

6. L. Reiner and B. Bavarian, “Corrosion of Steel Rebar in Concrete,” presented at the 14th NCUR, Missoula, Montana, April 2000.

412 413 414 415 416 417 Testing of Randolph Street Bridge

Background: In 1986, the deck of the bridge that carries Randolph Street over I-35E in St. Paul, Minnesota, was rehabilitated. The rehabilitation process included the application of a Low Slump Dense Concrete (LSDC) overlay that varied in depth from 2.28 to 4.2 inches. Cortec MCI-2000 was added to the LSDC at 1 lb/yd3 (0.6 kg/m3) for the two westbound traffic lanes. Prior to overlay, the deck was milled to a depth of 0.5 in (13 mm) and the areas of unsound concrete were removed. The cavities from the removal of the unsound concrete were filled with the overlay concrete. The general slope of the bridge for water runoff appears to be towards the northeast.

Corrosion assessments were conducted on the eastbound (control) and westbound (MCI) travel lanes of the structure by Virginia Tech researchers on two occasions, June 1991 and August 1992. The assessments included visual inspection, delamination survey, cover-depth survey, chloride contents as a function of depth, corrosion potentials, and estimates of corrosion current densities (icorr). SHRP-S-658 contains all information from the 1991 and 1992 study.

In November 2000, technicians from Cortec Corporation and American Engineering Testing returned to the bridge and took new measurements. These included Gecor 6 readings and copper/copper sulfate half-cell potentials. A new chloride analysis was also taken at various depths. Cortec report number 01-019-1425 contains the data obtained in 2000.

This report, 07-151-1425, will contain data obtained during the June 2007 evaluation. A technician from American Engineering Testing used a Profometer to locate rebars in concrete and did Chloride testing. Technicians from Cortec Corporation did alkalinity testing and took GalvaPulse readings of corrosion current and corrosion rate, and Gecor 6 readings of resistivity and half-cell potential.

Purpose: The purpose of this study was to follow-up on the benefit of MCI-2000 in reducing reinforcing steel corrosion.

Materials: Geocisa Gecor 6 GalvaPulse Proceq SA Profometer Rotary Impact Type Drill with a ½” bit Alkalinity Test Kit Tap water

Project #07-151-1425 Page 1 of 14 December 6, 2007 © 2007, Cortec Corporation. All Rights Reserved. Copying of these materials in any form without the written authorization of Cortec Corporation is strictly prohibited.

418 Methods: AASHTO: T260 – Procedure C, Sampling and Testing for Chloride-Ion in Concrete and Concrete Raw Materials Gecor 6 method for measuring concrete resistivity and half-cell potential GalvaPulse method for measuring corrosion current and corrosion rate Alkalinity

Procedures: Chloride Contamination Levels Powdered concrete samples for chloride analysis were taken at mean depths of 0-1, 1-2, and 2-3 in (0-25, 25-51, and 51-76 mm) from 3 different locations on each side of the bridge.

A diagram of these locations is included at the end of this report. Samples were taken using a rotary impact type drill with a ½” sized bit. Three-gram samples that passed through a #20 sieve were obtained from each depth. The powder was then mixed with 20 ml of digestion solution for a total of 3 minutes and then 80 ml of stabilizing solution was added. A calibrated electrode coupled to an Orion Model 720- pH/ISE meter was then immersed in the solution, and the chloride-ion concentration was recorded. This method was consistent with the AASHTO: T260 Procedure C. The standard deviation for this chloride test was determined by testing the six pulverized concrete Quality Assurance (QA) samples of known chloride content. Each QA sample was tested five times.

Corrosion Current Measurements Corrosion current density (icorr) estimates were taken with the Gecor 6 instrument in November 2000 and a GalvaPulse instrument in July 2007. These same estimates were taken in June 1991 and August 1992 using a 3LP device. The icorr measurement using the 3LP device is proportional to the corrosion rate through Faraday’s Law. The Gecor 6 and GalvaPulse measure the corrosion rate of steel in concrete by “polarization resistance” or “linear polarization” techniques. This is a non-destructive technique that works by applying a small current to the rebar and measuring the change in the half-cell potential. Then the polarization resistance, Rp, (the change in potential measured), is divided by the applied current. The corrosion rate, icorr, is obtained from the polarization resistance, Rp, by means of the “Stearn and Geary” relationship: icorr = B/Rp, where B = 26 mV.

The criteria for estimating the condition of the reinforcement in relation to the different devices’ measured value of the rate of corrosion have been defined as1:

Table 1. Corrosion intensity versus corrosion current and rate of corrosion found by LP3 device (K.Clear) Corrosion Current Corrosion Rate Intensity of Corrosion (PA/cm2) (Pm/year) <0.5 <5.8 Passive condition 0.5-2.7 5.8 to 31.3 Low corrosion (damage possible in 10-15 years) 2.7-27 31.3 to 313.2 Moderate corrosion (damage possible in 2-10 years >27 >313.2 High corrosion (damage expected in 2 years or less)

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419 Table 2. Corrosion intensity versus corrosion current and rate of corrosion found by Gecor 6 Corrosion Current Corrosion Rate Intensity of Corrosion (PA/cm2) (Pm/year) <0.5 <1.2 Negligible corrosion 0.5-2.7 1.2 to 5.8 Low corrosion 2.7-27 5.8 to 11.6 Moderate corrosion >27 >11.6 High corrosion

Table 3. Corrosion intensity versus corrosion current and rate of corrosion found by GalvaPulse Corrosion Current Corrosion Rate Intensity of Corrosion (PA/cm2) (Pm/year) <0.5 <5.8 Passive condition 0.5-2 5.8 to 58 Low corrosion 2-5 58 to 174 Moderate corrosion >27 >174 High corrosion

Concrete Resistivity Measurements Gecor 6 calculates the concrete resistivity by means of the formula:

Resistivity = 2 * R * D, where

R = resistance by the “iR drop” from a pulse between the sensor counter-electrode and the rebar network D = counter-electrode diameter of the sensor

The value of the concrete’s resistance is used as an additional parameter for the interpretation of the rate of corrosion. According to Andrade2, the following interpretation of the results is possible:

Table 4. GeCor 6 correlation of resistivity measurements to corrosion rate.

Resistivity Corrosion Rate >100 to 200 k: · cm Very low, even with high chloride and carbonation 50 to 100 k: · cm Low 10 to 50 k:· cm Moderate to high where steel is active <10 k: · cm Resistivity is not the parameter controlling corrosion rate

Half-Cell Potentials ASTM C 876 corrosion half-cell potentials were measured for both the eastbound and westbound travel lanes with a Gecor 6 in November of 2000 and June 2007. According to ASTM C-876, the results can be interpreted as follows:

Table 4b. Corrosion Potential Potential Probability of Corrosion >-200 mV Less than 10% -200 mV to -350 mV 50% <-350 mV Greater than 90%

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420 Carbonation Carbonation of concrete is a process by which carbon dioxide from the air penetrates the concrete and reacts with the hydroxides, such as calcium hydroxide, to form carbonates. This process increases shrinkage on drying (promoting crack development) and reduces the alkalinity of the concrete. High alkalinity is needed to protect embedded rebar from corrosion; consequently, concrete should be resistant to carbonation to prevent steel corrosion3. The carbonation of powdered concrete samples taken from the bridge was determined by using phenolphthalein (alkalinity) measurements.

Attached Figures/Tables: East and Westbound Randolph St. Bridge Deck Test Locations (Figure 1) East and Westbound Randolph St. Bridge Deck Average Half-Cell Potential, Resistivity and Corrosion Rates by Location (Figure 2) Average Half-Cell Potential versus Year (Figure 3) Average Corrosion Rate versus Year (Figure 4) Average Chloride Contamination levels (Table 5) Average Corrosion Currents using GalvaPulse (Table 6) Average Corrosion Rates using GalvaPulse (Table 7) GalvaPulse Measurements for Control Side of Bridge (Table 8) GalvaPulse Measurements for MCI-2000 Treated Side of Bridge (Table 9) Alkalinity Results (Table 10) Summary of Half-Cell Potentials (Table 11) Summary of Resistivity Measurements (Table 12)

Summary of Results: 1. In 2001, it was predicted the chloride concentration in the control side of the bridge would reach of 0.4wt% (of cementious materials) at the rebar in 19.5 years from the application of the overlay, or in the year 2005, if the chloride level continues to increase at its current rate. The MCI-2000 treated side was estimated to reach 0.4wt% (of cementious materials) of chlorides in 36 years from the application of the overlay, or in the year 2022. Revision of these predictions based on calculations from 2007 show that the Control side is estimated extended to the year 2016 and the MCI-2000 treated side is now estimated to the year 2013. It is not surprising that these would occur about the same rate, or even faster on the MCI side, where there is a tendency for water to pool at the bottom of the northeast corner.

The decrease in rate of ingress of chloride could be due to less being used to de-ice roads as winters have been milder the past few years. However, in 2000 and presently, the chloride content in all areas was over 300-400ppm, which has known to cause problems with corrosion and increase the freeze/thaw cycles. (See Table 5 for data and calculation.)

2. Corrosion currents of rebar have increased on both sides of the bridge since the year 2000, when the MCI-2000 treated side had very low corrosion currents, an average of 0.013 PA/cm2, approximately 40% below readings taken on control side (average of 0.022 PA/cm2). These reading were taken in cold weather, but the 2007 readings were taken when it was warmer. It hadn’t been raining, but areas were wetted very well before measurements were taken. The MCI-2000 treated side had an average of 0.21PA/cm2 and the control side had as average of 0.34 PA/cm2; giving the MCI-2000 treated side corrosion currents still approximately 40% lower. (Data is presented in Table 6.)

3. In two out of three locations on the MCI treated areas of bridge, the corrosion rate values were much lower than the control, showing the effectiveness of the MCI inhibitor. Only the SW (control) portion of the bridge had corrosion rate readings that would be considered an Project #07-151-1425 Page 4 of 14 December 6, 2007 © 2007, Cortec Corporation. All Rights Reserved. Copying of these materials in any form without the written authorization of Cortec Corporation is strictly prohibited.

421 active (although low level) versus the other 5 passive corrosion levels. Figures 1 and 2 show the location of rebar and readings, as well as the average half-cell readings, corrosion rates and concrete resistivities for both the control and MCI treated sides. Raw data from the GalvaPulse measurements of the bridge is included in Tables 8 and 9.

4. The concrete on the 21 year old bridge deck overlay showed alkalinity measurements between 1320 to 1680mg/L. The areas that had been treated with MCI show higher amounts, which can indicate the presence of MCI and resistance to carbonation. (See Table 10 for raw data.)

5. The resistivities measured by the Gecor 6 in 2000 ranged from 100 kohm.cm to 600 kohm.cm. In 2007, the range was 36 kohm.cm to 80 kohm.cm. This shows in increase in possible corrosion which is consistent in the rise of other parameters measured such as Cl-, Corrosion current, and corrosion rates. (See Table 12.)

6. The Average Half-Cell Potential versus Year (shown in Figure 3) and the Average Corrosion Rate versus Year (shown in Figure 4) show MCI treated side lower than control except for the first reading taken after the repair. It is important to note that three different instruments have been used for these measurements and that Tables 1 through 3 should be used to interpret the values. (A summary of half-cell potentials can be found in Table 11 and a summary of resistivity measurements can be found in Table 12.)

References: 1) Germann Instruments, Inc., GalvaPulse TM GP-5000 Instruction and Maintenance Manual, 2005

2) Andrade, C., Fullea, J., Alonso, C., “The Use of the Graph Corrosion Rate-Resistivity in the Measurement of Corrosion Current”, International Workshop MESINA, Instituto Eduardo Torroja, Madrid, Spain, 1999.

3) Kosmatka, Steven and Panarese, William, Design and Control of Concrete Mixtures Thirteenth Edition, Portland Cement Association, Skokie, Illinois, 1994 rev. pp. 72.

4) Thomas, M.D.A. and Bentz, E.C., Life-365 Computer Program for Predicting the Service Life and Life-Cycle Costs of Reinforced Concrete Exposed to Chlorides. University of Toronto, Toronto, Canada, April 21, 2000, pp. 9.

Project: 07-151-1425 Est. Project Cost: 25 hours For: Cortec Corporation From: Andrea Hansen Jessi Jackson Sara Johnson Brian Benduha

Date: November 30, 2007 cc: Boris Miksic Anna Vignetti Art Ahlbrecht Rita Kharshan

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422 Figure 1: Location of Rebar on Randolph Street Bridge Eastbound Lane = Control; Westbound Lane = MCI Treated (Note: this chart has been flipped from previous report so N is on top) CURB

LOCATION 1 (MCI) LOCATION 2 (MCI) LOCATION 3 (MCI) NORTH 35E 35E NORTH SOUTH 35E 35E SOUTH Å WEST BOUND TRAFFIC – MCI-2000 Å

Æ EAST BOUND TRAFFIC – CONTROL Æ

LOCATION 5 (Control) LOCATION 4 (Control) LOCATION 6 (Control)

CURB

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423 Figure 2: Randolph Street Bridge Half-Cell Potential, Corrosion Rate, Resistivity, and Chloride Results Eastbound Lane = Control; Westbound Lane = MCI Treated (Note: this chart has been flipped from previous report so N is on top)

CURB LOCATION 1 (MCI) LOCATION 2 (MCI) LOCATION 3 (MCI)

-104 mV (<10% probability of corrosion) -101 mV (<10% probability of corrosion) -302 mV (50% probability of corrosion) 2.42Pm/year (passive condition) 2.53 Pm/year (passive condition) 2.29 Pm/year (passive condition) 62 k:xcm (low corrosion rate) 65 k:xcm (low corrosion rate) 66 k:xcm (low corrosion rate) SOUTH 35E 35E SOUTH Å WEST BOUND TRAFFIC – MCI-2000 Å NORTH 35E 35E NORTH

Æ EAST BOUND TRAFFIC– CONTROL Æ

LOCATION 6 (Control) LOCATION 5 (Control) LOCATION 4 (Control) -85 mV (<10% probability of corrosion) -399 mV (>90% probability of corrosion) -112 mV (<10% probability of corrosion) 3.86Pm/year (passive to low corrosion) 1.83Pm/year (passive condition) 5.15 Pm/year (moderate corrosion) 70 k:xcm (low corrosion rate) 42 k:xcm (moderate to high corrosion rate) 36 k:xcm (moderate to high corrosion rate)

CURB

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424 Figure 3: Average Half-Cell Potential versus Year MCI CONTROL Average Half-Cell Potential (mV) 1980 1985 1990 1995 2000 2005 2010

-110

-160

-210

Ecorr (mV) Ecorr -260

-310 Year

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425 Figure 4: Average Corrosion Rate versus Year

25.000

MCI LP3 20.000 Control LP3 MCI GeCor 6 Control Gecor 6 MCI GalvaPulse 15.000 Control GalvaPulse

10.000

5.000

0.000 1990 1995 2000 2005 2010

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426 Table 5. Cl content in lbs/yd3 MCI Side (Average) Control Side (Average) Depth (0-1”) (1-2”) (2-3”) (0-1”) (1-2”) (2-3”) 2007 11.7 1.0 2.6 20.0 7.4 2.3 2000 11.7 1.6 1.3 17.2 6.2 2.4 1992 6.5 1.1 1.9 9.5 3.5 2.5 1991 3.5 0.0 0.7 7.7 2.5 1.9

Calculation for Time until Chloride Threshold of 0.4wt% (of cementious materials) is Reached Control 2.3 lbs/yd3 chlorides at 2” 21 years after overlay was placed. 836 lbs/yd3 of cement in mix 2.3/836 *100 = 0.28% Cl- by weight of cement in 21 years 0.28%/21 = 0.013%Cl- per year *30 years =0.4% Cl- 1986+30=2016 (expected year chloride threshold will meet 0.4wt% in control concrete.)

MCI 2.6 lbs/yd3 chlorides at 2” 21 years after overlay was placed. 836 lbs/yd3 of cement in mix 2.6/836 *100 = 0.3% Cl- by weight of cement in 21 years 0.3%/21 = 0.014% Cl- per year *27 years =0.4% Cl- 1986+27=2013 (expected year chloride threshold will meet 0.4wt% in MCI concrete.)

Table 6. Corrosion Current using GalvaPulse, PA/cm2 MCI-2000 CONTROL NW NC NE SW SC SE Rebar # Average Average Average Rebar # Average Average Average 1 0.164 0.196 0.127 1 0.345 0.129 0.419 2 0.235 0.235 0.109 2 0.778 0.151 0.268 3 0.180 0.177 0.205 3 1.008 0.156 0.292 4 0.210 0.204 0.241 4 0.371 0.156 0.341 5 0.193 0.260 0.261 5 0.294 0.180 0.345 6 0.202 0.237 0.284 6 0.314 0.172 0.346 7 0.200 0.232 7 0.321 Average 0.20 0.22 0.21 Average 0.52 0.16 0.33

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427 Table 7. Rate of Corrosion using GalvaPulse, Pm/year

MCI CONTROL NW NC NE SW SC SE Rebar # Average Average Average Rebar # Average Average Average 1 1.901 2.276 1.477 1 3.999 1.500 4.866 2 2.730 2.726 1.267 2 9.019 1.755 3.107 3 2.089 2.048 2.376 3 11.690 1.812 3.384 4 2.439 2.369 2.798 4 4.305 1.805 3.956 5 2.242 3.016 3.025 5 3.408 2.089 3.998 6 2.345 2.745 3.296 6 3.642 1.998 4.014 7 2.315 2.687 7 3.719 Average 2.29 2.53 2.42 Average 5.15 1.83 3.86

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428 Table 8. GalvaPulse Measurements for Control Treated Side of Bridge

SW rebar 19mm area 5659 current 19 point 17 27 37 47 57 67 ecorr -83.76 -127 -153.7 -120 -82.82 -68.32 Icorr 1.0982 0.3803 0.6393 0.3973 0.4059 0.3292 resistance 7.8 8 7.6 8.6 8.5 8.9 Corr Rate 12.73912 4.41148 7.41588 4.60868 4.70844 3.81872 point 18 28 38 48 58 68 ecorr -78.14 -90.07 -87.27 -83.76 -68.08 -69.95 Icorr 0.3527 0.3655 0.2171 0.2041 0.2198 0.2449 resistance 14 12 14 13 12 13 Corr Rate 4.09132 4.2398 2.51836 2.36756 2.54968 2.84084 point 19 29 39 49 59 69 ecorr -71.36 -58.49 61.53 -59.42 -44.92 -66.68 Icorr 0.1956 0.1359 0.1788 0.1915 0.3147 0.1991 resistance 16 16 15 16 13 13 Corr Rate 2.26896 1.57644 2.07408 2.2214 3.65052 2.30956 point 110 210 310 410 510 610 ecorr -74.16 -72.29 -75.1 -72.99 -68.55 -78.84 Icorr 0.1695 0.1488 0.2232 0.2288 0.1287 0.1872 resistance 14 17 15 14 12 15 Corr Rate 1.9662 1.72608 2.58912 2.65408 1.49292 2.17152 SC rebar 19mm area 5659 current 39 point 15 25 35 45 55 65 75 ecorr -246.3 -288 -318.4 -360.7 -288.4 -295 -282.8 Icorr 0.1848 0.2243 0.2236 0.1984 0.2067 0.1946 0.1988 resistance 8 8.9 7 5.1 6.6 8.3 10 Corr Rate 2.14368 2.60188 2.59376 2.30144 2.39772 2.25736 2.30608 point 16 26 36 46 56 66 76 ecorr -356.3 -362.4 -389.3 -396.8 -471.2 -442.4 -409.2 Icorr 0.1852 0.2099 0.1945 0.1768 0.2471 0.1952 0.2334 resistance 8.3 9.1 7.6 8.4 6 8.7 11 Corr Rate 2.14832 2.43484 2.2562 2.05088 2.86636 2.26432 2.70744 point 17 27 37 47 57 67 77 ecorr -348.3 -387.6 -427 -426.7 -405 -401.2 -392.8 Icorr 0.2132 0.1221 0.1413 0.2302 0.2129 0.2094 0.2166 resistance 10 12 11 6.2 8.1 8.9 10 Corr Rate 2.47312 1.41636 1.63908 2.67032 2.46964 2.42904 2.51256 point 18 28 38 48 58 68 78 ecorr -361.4 -387.6 -406.1 -382.3 -380.9 -359.3 -333.4 Icorr 0.1478 0.143 0.1678 0.1122 0.1471 0.1705 0.1521 resistance 12 10 6.3 12 12 12 17 Corr Rate 1.71448 1.6588 1.94648 1.30152 1.70636 1.9778 1.76436 SE rebar 19mm area 5659 current 39 point 14 24 34 44 54 64 74 84 ecorr -28.54 -43.75 -58.49 -72.99 -82.59 -35.09 -18.95 -5.147 Icorr 0.6206 0.5476 0.4054 0.5968 0.524 0.2966 0.4428 0.349 resistance 6.9 7.5 7.6 8.4 8.4 9.3 8.3 8.100 Corr Rate 7.19896 6.35216 4.70264 6.92288 6.0784 3.44056 5.13648 4.0426 point 15 25 35 45 55 65 75 85.000 ecorr -174.3 -193.2 -128.4 -91.71 -80.95 -88.2 -83.06 -91.950 Icorr 0.2649 0.5281 0.3879 0.2811 0.8402 0.3523 0.1732 0.263 resistance 9.4 7.6 10 12 11 11 12 11.000 Corr Rate 3.07284 6.12596 4.49964 3.26076 9.74632 4.08668 2.00912 3.05196 point 16 26 36 46 56 66 76 86.000 ecorr -190.6 -154.4 -125.4 -111.8 -110.9 -98.26 -97.33 -100.300 Icorr 0.2925 0.2117 0.3423 0.1697 0.2508 0.2541 0.1423 0.295 resistance 10 12 9.5 11 10 12 16 12.000 Corr Rate 3.393 2.45572 3.97068 1.96852 2.90928 2.94756 1.65068 3.42548

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429 Table 9. GalvaPulse Measurements for MCI-2000 Treated Side of Bridge NW rebar 19mm area 5659 current 34 point 11 21 31 41 51 61 71 ecorr -21.75 -54.51 -137.8 -138.9 -109.4 -47.02 -19.18 Icorr 0.1085 0.1443 0.1256 0.1816 0.1 0.1355 0.1241 resistance 11 9.2 11 7.5 12 11 10 Corr Rate 1.2586 1.67388 1.45696 2.10656 1.16 1.5718 1.43956 point 12 22 32 42 52 62 72 ecorr -59.89 -35.56 -48.9 -65.04 -68.32 -62.47 -115.1 Icorr 0.0961 0.1708 0.1224 0.0977 0.0829 0.2162 0.0778 resistance 15 8.8 12 11 8.9 8.9 12 Corr Rate 1.11476 1.98128 1.41984 1.13332 0.96164 2.50792 0.90248 point 13 23 33 43 53 63 73 ecorr -112.3 -97.8 -68.78 -70.42 -81.89 -92.41 -102.7 Icorr 0.074 0.1302 0.0829 0.0828 0.1079 0.1304 0.1215 resistance 18 13 15 16 13 12 14 Corr Rate 0.8584 1.51032 0.96164 0.96048 1.25164 1.51264 1.4094 point 14 24 34 44 54 64 74 ecorr -183.2 -110.4 -69.95 -82.82 -74.16 -88.44 Icorr 0.1237 0.1006 0.1134 0.1677 0.1654 0.2121 resistance 11 10 10 10 9.6 7.7 Corr Rate 1.43492 1.16696 1.31544 1.94532 1.91864 2.46036 0 NC rebar 19mm area 5659 current 39 point 11 21 31 41 51 61 ecorr -82.82 -108 -207.7 -193.9 -143.6 -164.2 Icorr 0.2269 0.2042 0.2297 0.2772 0.2794 0.3849 resistance 11 11 10 8.9 10 9.2 Corr Rate 2.63204 2.36872 2.66452 3.21552 3.24104 4.46484 0 point 12 22 32 42 52 62 ecorr -65.27 -91.95 -102.9 -110.2 -140.3 -157.6 Icorr 0.2152 0.3079 0.1957 0.2112 0.3639 0.3314 resistance 12 7.9 12 12 10 8.9 Corr Rate 2.49632 3.57164 2.27012 2.44992 4.22124 3.84424 0 point 13 23 33 43 53 63 ecorr -73.93 -48.66 -50.53 -68.08 -68.32 -101.7 Icorr 0.1946 0.1805 0.2039 0.2226 0.1734 0.3362 resistance 16 16 16 11 15 13 Corr Rate 2.25736 2.0938 2.36524 2.58216 2.01144 3.89992 0 NE rebar 19mm area 5659 current 39 point 11 21 31 41 51 61 71 ecorr -193.7 -236 -302 -334.8 -354.9 -398.9 -429.8 Icorr 0.2078 0.1198 0.3638 0.5317 0.2463 0.5523 0.2574 resistance 11 12 9.3 7 9.4 7.6 8.5 Corr Rate 2.41048 1.38968 4.22008 6.16772 2.85708 6.40668 2.98584 point 12 22 32 42 52 62 72 ecorr -281.9 -288.9 -320.5 -341.8 -375 -401.9 -432.6 Icorr 0.1932 0.2854 0.7807 0.4434 0.9579 0.6074 0.4858 resistance 8.6 11 9.9 8.2 6.8 7.2 6.8 Corr Rate 2.24112 3.31064 9.05612 5.14344 11.11164 7.04584 5.63528 point 13 23 33 43 53 63 73 ecorr -105.9 -124.9 -184.3 235.1 -331.3 -361.2 -435.8 Icorr 0.1474 0.0858 0.1639 0.1352 0.8829 0.8293 0.6082 resistance 18 23 13 16 5.7 5.1 6.4 Corr Rate 1.70984 0.99528 1.90124 1.56832 10.24164 9.61988 7.05512

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430 Table 10. Alkalinity Results

MCI Treated Concrete Control Concrete Alkalinity as Concrete Alkalinity as Concrete # of Average, # of Average, CaCO3 ppm (# Sample CaCO3 ppm (# Sample ID drops ppm drops ppm of drops x20x6) ID of drops x20) N.C. 0-1" 12 1440 S.C. 0-1" 11 1320 N.E. 0-1" 13 1560 1480 S.E. 0-1" 11 1320 1280 S.W. 0- N.W. 0-1" 12 1440 10 1200 1" N.C. 1-2" 13 1560 S.C. 1-2" 12 1440 N.E. 1-2" 13 1560 1560 S.E. 1-2" 13 1560 1520 S.W. 1- N.W. 1-2" 13 1560 13 1560 2" N.C. 2-3" 14 1680 S.C. 2-3" 13 1560 N.E. 2-3" 14 1680 1680 S.E. 2-3" 14 1680 1640 S.W. 2- N.W. 2-3" 14 1680 14 1680 3" All samples tested @ a 1:6 dilution All samples tested @ a 1:6 dilution Table 11. Summary of Half-Cell Potentials MCI-2000 CONTROL NW NC NE SW SC SE X X X X X X Average Average Average Average Average Average -99 -66 -191 -86 -355 -145 -93 -78 -211 -96 -395 -141 -107 -101 -258 -111 -423 -118 -125 -112 -298 -99 -427 -117 -111 -111 -342 -77 -411 -115 -101 -138 -385 -41 -402 -91 -94 -429 -381 -86 -78 Average of each horizontal bar -104 -101 -302 -85 -399 -112 Overall Average -169 -198

Table 12. Summary of Resistivity Measurements MCI-2000 CONTROL NW NC NE SW SC SE X X X X X X Average Average Average Average Average Average 67 65 90 51 70 55 66 83 79 64 62 38 59 70 68 74 50 33 49 53 62 56 50 30 64 68 50 63 36 37 63 47 47 41 44 70 67 36 62 65 66 70 42 36 Average Average 64 50

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431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454