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Simulated reinforced concrete substructure element (piling) specimens were fabricated, cured for twelve months and exposed partially submerged in natural sea water. The specimens were made of mortar with 20% Fly Ash and a low water to cement ratio, simulating a FDOT Type V concrete. Exposure involved, first, intermittent spraying of the above waterline zone to simulate splash and spray and, second, electrically connecting the embedded reinforcement to submerged bare steel bars to affect a potential gradient from relatively negative in the submerged zone to positive in the atmospheric as occurs in actual members. Three different polarization levels were achieved by inserting resistors. On-potentials and 24 hrs depolarization tests at various elevations were used to better understand the influence of these polarizations on potential vs. elevation and how it affects time to activation. Chloride analysis and visual inspection was performed on selected terminated specimens. The proposed specimen geometry coupled to a submerged rebar provides a good alternative to investigate chloride threshold on partially immersed substructures.

The Florida Department of Transportation (FDOT) has been using high performance concrete since the late 1980s early 1990s. Some of the older bridge structures (assuming 1990 as the completion year) are reaching 35 year of age, and depending on the concrete cover thickness (those with thinner covers), and the diffusivity of the concrete, corrosion of the reinforcement might initiate in a few years on some of these structures. The corrosion propagation stage of carbon steel rebar in high performance concrete might last longer than the typically five years usually attributed for carbon steel rebar in concrete with type I/II Portland cement as the only cementitious material. It is well known that reinforcement corrosion typically initiates at a later time on specimens in which the concrete contains supplementary cementitious materials such as fly ash, silica fume, slag or a combination of these materials when compared to reinforced concrete with no cementitious materials of the same w/cm ratio, cementitious content, and concrete cover. There are some reports [1-2] that indicate that the chloride threshold is lower on concrete with supplementary cementitious materials, particularly for concrete with high fly ash content (i.e., 50%); thus, this needs to be considered when modeling service life. There are several reports [3-4] that indicate that the corrosion rate of carbon steel rebar embedded in high performance concrete is lower when compared to rebar corroding on concrete with no supplementary cementitious materials. This observation in part can be attributed to the higher concrete electrical resistivity for concrete with supplementary cementitious materials when comparing concretes with similar moisture content. It is possible that there are reduced macrocell effects. The higher resistivity is in part due to pore refinement and higher tortuosity that develop with time on concrete structures with supplementary cementitious materials. In this investigation chlorides were driven into reinforced concrete specimens via an electro-migration method, as a way to accelerate chloride transport and allow corrosion to initiate after a short period of time. Mature (samples prepared in 2008) and recently prepared (April/2016) reinforced concrete samples were used in this investigation to gain additional insight on the corrosion propagation stage. The cementitious in the concrete of the older samples: 1) ordinary portland cement (OPC), 2) OPC and 20% fly ash, and 3) OPC, 20% fly ash and 8% silica-fume. Recent concrete samples contained 1) OPC and 50% slag or 2)OPC and 20% fly ash composition. All specimens had a w/cm ratio of .41 and 390 kg/m 3 of cementitious material. The older specimens had either a single rebar embedded or four rebars (# 5 rebar/2 inch cover). Recently prepared samples had one rebar (#3 rebar/0.75 inch cover). Solution reservoirs ranged from one inch to 4 inches in length, as a way to vary the anode length. Rebar potential was used to determine if corrosion had initiated. The corrosion propagation was monitored via linear polarization measurements, solution resistance measurements, and rebar potentials. The corrosion propagation monitoring ranged from 300 days to several years. 1. M.D.A. Thomas and J.D. Matthews, “Chloride penetration and reinforcement corrosion in marine-exposed fly ash concretes”. In: Malhotra VM, editor, Third CANMET/ACI International Conference on Concrete in a Marine Environment, ACI SP-164, Detroit: American Concrete Institute; p. 317-38 1996 2. F. Presuel-Moreno, M. Paredes, “16 Years’ Exposure Of Fly Ash And Silica Fume Concretes On Salt Induced Reinforcing Steel Corrosion: Corrosion Potential, Resistivity And Diffusivity”, International Conference in Durability of Concrete, Trondheim, Norway, June 18-21, 2012 (Proceeding published on USB/Electronic form) 3. C Andrade, C Alonso “Test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method” Materials and Structures, v37 p623, 2004 4. W. Morris, A. Vico, M. Vázquez, “Chloride induced corrosion of reinforcing steel evaluated by concrete resistivity measurements” Electrochemica Acta, V 49 pp4447–4453 2004

A literature review was conducted with the goal of identifying alternative low-cost corrosion-resistant steel reinforcement materials. The most promising alternate reinforcing materials seen to date that are less expensive than 300 series stainless steels include low-nickel austenitic stainless steels and a variety of ferritic or martensitic 12-15 weight percent chromium steels. Steels with 2.5-10 weight percent chromium may also be of interest because they offer a marginal gain in corrosion performance at a very low cost. Several steel types that should undergo further evaluation are 201LN, 216, Duracorr, Enduramet 32 and Enduramet 33, HSS2, Lapealloy, S41425, S41426, and S42300. Corrosion-resistant steels are alloyed to ensure the steel itself has sufficient corrosion protection qualities; therefore, it is sensitive to cost fluctuations in raw materials. Based on the last 7 years, bars with higher nickel and molybdenum contents are sensitive to the cost of these alloying elements, whereas bars with higher chromium contents have been only slightly sensitive to the raw material cost. The cost of alloying materials also reflects the cost of different types of stainless steels. Both martensitic and ferritic stainless steels demonstrated slight increases in the average surcharge over a 7-year period, whereas austenitic, duplex, and precipitation hardening stainless steels increased dramatically. The most promising test for determining chloride threshold (initiation) in the laboratory is the +100 mV vs. SCE (or +200 mV vs. SCE) potentiostatic hold. The Clˉ threshold can be established for the new rebar materials by conducting potentiostatic holds at +100 mV vs. SCE at various fixed Clˉ levels. This method can also be extended to mortar-covered bars immersed in a simulated pore water solution with a thin mortar layer thickness. Propagation tests can also be conducted by conducting either potentiostatic holds at selected potentials or galvanic coupling in a split cell. A propagation law and repassivation potential (i.e., a “no propagation threshold” threshold potential) can be established. Concerning field testing, the ASTM G109 method is recommended primarily for comparison to existing research data. This test can be used to assess Clˉ thresholds either by varying Clˉ levels in the mortar mix or core drilling/sampling. Initial recording of galvanic current indicates initiation, whereas spalling provides an engineering indication of propagation. The Florida Department of Transportation’s tombstone method should also be considered as a variation of the ASTM G109 method in high-permeable/low-permeable concrete mixes in order to test candidate rebar in concrete. ASTM G109 and Florida Department of Transportation tombstone concrete specimens can be artificially cracked to accelerate the onset of corrosion. Finally, the mechanical properties for each steel will need to be determined. Data will need to be gathered on specimens that have been rolled to the final reinforcing steel dimensions, although some of the bars identified could potentially function in the same capacity as the MMFX-2. However, additional research is required for the higher strength steels for structurally critical areas.

Chloride-induced corrosion of carbon steel has been widely recognized as one of the main causes of premature failure on the reinforced concrete structures. Various strategies and measures such as employing stainless steel reinforcements have been developed to address this problem. Past studies have been concerned with the identification and characterization of chloride threshold since corrosion would not initiate as long as the chloride concentration values at the reinforcing stainless steel depth remains below this threshold value. It is therefore a critical parameter for the design of new stainless steel reinforced concrete structures and the assessment of existing concrete structures. This study presents the finding on the chloride threshold of stainless steel UNS32304 embedded in mortar with two different mixes. Reinforced mortar specimens were subjected to ponding exposure and wet/dry cycle exposure with a sodium chloride solution. The specimens were monitored by using the measurements of the open circuit potential, electrochemical impedance spectroscopy, and linear polarization resistance. The paper also discusses the chloride threshold values of such stainless steel embedded in mortar and concrete with other mixes reported by other researchers and the factors that may affect these values.

Two separate binary blended concrete mixes were prepared, one of which contains cement replacement of 50% slag (referred to as SL) and the other of which contains cement replacement of 20% fly ash (termed as FA). Concrete specimens were made using a water to cementitious ratio of 0.41. Different size reservoir lengths ranging from 2.5 cm to 17.5 cm were installed on the top surface of each specimen, and these reservoirs were ponded with 10 percent NaCl solution. Chloride transport was accelerated by electromigration, using an applied potential of 9V initially, and then reduced to 3V after around a week. Steel corrosion parameters were monitored using rebar potential measurements and galvanostatic pulse measurements, over a period of approximately 400 days. Corrosion current values obtained from experimental measurements were then converted to mass loss. Based on the results of experimental findings, the corrosion current values as well as the mass loss values were found to be significantly influenced by the length of the solution reservoirs. This study provides a guideline for subsequent research on accelerated steel corrosion in concrete.

Over the last few decades flexible fillers such as greases or waxes have been used in Europe as an alternative to cementitious grout. The Florida Department of Transportation (FDOT) is considering flexible fillers as alternative filler materials for post-tensioned (PT) tendons. In this study, the corrosion resistance of PT tendons is investigated experimentally as they are coated with flexible filler materials and contaminated with fungi. Three types of fungi were considered including Fusarium oxysporum (FO), Penicillium chrysogenum (PC), and Aspergillus flavus (AF). The flexible fillers investigated are commercially available microcrystalline waxes, and five different filler types were investigated. Both exposure and electrochemical corrosion tests were designed and performed. As for the exposure tests, two exposure conditions were considered including direct outdoor exposure test and indoor exposure test as the greases were contaminated with fungi. Electrochemical corrosion test showed that most of the PT tendons had impedances higher than 1 Gohm and galvanic corrosion currents lower than 1 nA. However, for PT tendons coated with filler type 3, an increase in the galvanic corrosion current and a decrease in the impedance were observed after two weeks of tests, indicating corrosion initiation. Direct outdoor exposure tests showed that rust was present on PT single wires coated with type 1, type 2, type 3, type 4, type 5 filler after 20 days, 43 days, 49 days, 114 days and 126 days of exposure, respectively. Indoor exposure tests showed that severe corrosion was present on PT single wires as their surrounding greases were contaminated by a fungi mixture. Different from the general corrosion observed on wires subjected to direct outdoor exposure tests, localized corrosion was present on indoor wires which were coated with flexible filler and contaminated with fungi.

Sea water induced reinforcing steel corrosion often results in high maintenance costs and can be service life limiting for concrete bridge substructure elements in marine environments. In the present research, a novel piling type specimen assembly and test protocol were developed to simulate performance of actual substructure elements undergoing marine exposure. Specimen mix design was based on the mortar component of a Florida Department of Transportation (FDOT) Class V high performance concrete, both with and without fly ash. The relatively low diffusion coefficient for such mixes and the long time that normally would be required for corrosion initiation was offset by employing covers of 12 mm for the non-fly ash mortar and 8 mm for the fly ash one. Exposures involved partial submergence in 15 wt% NaCl and in some cases periodic spraying of the above waterline zone to simulate splash. The rebar of some sprayed specimens was connected to submerged bare steel such that the lower portion of the simulated piling rebar was cathodically polarized, and it is demonstrated that the resultant potential profile was similar to that of actual marine pilings for which reinforcement below the waterline also exhibits a relatively negative potential because of oxygen concentration polarization. Consequently, the above waterline (splash) zone of the present specimens was cathodically polarized similar to what occurs in actual structures. Times to corrosion for the specimens were approximately the same for sprayed and unsprayed specimens but were greater for sprayed and polarized ones. In some cases, corrosion initiated above the waterline for sprayed and sprayed and polarized specimens, as typically occurs in actual bridge substructure elements. Threshold chloride ion concentrations to initiate corrosion, C sub T, were measured on the rebar mortar trace subsequent to corrosion initiation and specimen dissection using Energy Dispersive X-Ray Analysis and reported for various test conditions. Values for C sub T for corrosion initiation in both the submerged and above waterline zones are projected for both mix designs; however, these were based in some cases on limited data. It is recommended that the specimen design and test protocol investigated here be studied further.

Abstract As part of a recent experimental campaign several samples prepared in 1994 with various concrete compositions were terminated. These samples were exposed outdoors to seawater wet/dry cycles from 1994 till 2019, and since then to outdoor marine exposure. The remaining samples were monitored since 2021 with galvanostatic pulse measurements and more recently using a commercial device. The terminated samples showed cracks on the concrete surface, a negative rebar potential and a high corrosion rate. One or more rebars were removed from the selected samples. In some cases, the three top rebars were removed, in other cases only one rebar or two rebars were removed. The rebar surface condition upon exposure was recorded by photographing the sample, then the rebars were cleaned by sandblasting the rebars with walnut sand. The cross-section loss as a function of length was measured by using a caliper with conical tip. The pitting factor was calculated using only the sections that showed corrosion, the non-corroding sections were not included to calculate the pitting factor. The percentage mass loss (η) values were estimated by using the mass of the rebar section rebar embedded with respect to the mass a non-corroding rebar of the same length.

Cathodic polarization to elevate the corrosion threshold (“cathodic prevention”) was implemented with commercial Zn bulk anodes on laboratory columns to simulate a reinforced concrete marine system. Both a detailed computational model and another simplified, less computational intensive model of the polarization distribution in the laboratory columns were formulated and yielded results in reasonable agreement with the experiment. The simplified model was applied to predict cathodic prevention throwing power on field scale structures for a variety of plausible conditions. The calculations suggest that with an immersed anode useful levels of cathodic prevention may be reasonably expected, even under conservative assumptions, in the area immediately above high tide where conditions are otherwise very severe.

The ability of a SS 316L surface wetted with a thin electrolyte layer to serve as an effective cathode for an active localized corrosion site was studied computationally. The dependence of the total net cathodic current, I net, supplied at the repassivation potential E rp (of the anodic crevice) on relevant physical parameters including water layer thickness (WL), chloride concentration ([Cl−]) and length of cathode (Lc) were investigated using a three-level, full factorial design. The effects of kinetic parameters including the exchange current density (i o,c) and Tafel slope (β c) of oxygen reduction, the anodic passive current density (i p) (on the cathodic surface), and E rp were studied as well using three-level full factorial designs of [Cl−] and Lc with a fixed WL of 25μm. The study found that all the three parameters WL, [Cl−] and Lc as well as the interactions of Lc×WL and Lc×[Cl−] had significant impact on I net. A five-factor regression equation was obtained which fits the computation results reasonably well, but demonstrated that interactions are more complicated than can be explained with a simple linear model. Significant effects on I net were found upon varying either i o,c, β c, or E rp, whereas i p in the studied range was found to have little impact. It was observed that I net asymptotically approached maximum values (I max) when Lc increased to critical minimum values. I max can be used to determine the stability of coupled localized corrosion and the critical Lc provides important information for experimental design and corrosion protection.

No abstract is provided for this article.

This investigation was performed to gain insight and assist in determining the long-term durability of reinforced concrete structures where the external chloride concentrations are different than those typically observed at the permanently immersed, tidal, and splash zones of partially immersed bridges. Insight into the diffusion properties of the concrete at these locations may lead to changes in the state’s policy on corrosion control of reinforced concrete structures. Structures at locations where the external chloride concentrations may have spatial, let alone time, variation are of interest. Additionally, at elevations above the splash zone, the amount of chlorides deposited would be lower, and the concrete close to the surface not saturated. Similarly, the section of structures that extend inland would be subjected to seawater spray and the concrete close to the surface would usually not be water saturated. The performance in regard to chloride penetration of specimens made with three base compositions (the supplementary cementitious materials were: 20% fly ash; 20% fly ash + 8% silica fume; and 50% slag), and water-to-cementitious ratios of 0.35, 0.41, or 0.47 were investigated here. Experiments investigated the diffusion of chloride ions into concrete samples that were exposed in scenarios that simulated the splash, tidal, and immersed portions of a marine structure, with the solution ranging from brackish water to 10% seawater, to seawater. Bulk diffusion experiments were conducted in solutions that contained 0.6%, 3%, and 16.5% NaCl. Rapid migration tests and resistivity measurements were also performed several times over two years, and the non-saturated migration coefficient vs. resistivity values were correlated. The apparent diffusion values from the bulk diffusion tests were correlated to corresponding equivalent resistivity values. Samples exposed for over 18 years, simulating tidal exposure were also part of this investigation. The field component investigated the chloride concentration as a function of elevation. Other experiments were conducted which involved controlling the degree of saturation and exposing a designated surface to finely ground salt. These apparent diffusion results were compared to the apparent diffusion results from specimens in which the chloride transport was due to natural marine atmosphere.

Two duplex stainless steels rebars: UNS(1) S32304 and UNS S32101 were selected to investigate the corrosion initiation and propagation in reinforced concrete specimens. No chlorides were added to the concrete mix. Three of six embedded rebars had one inch concrete cover. A methodology was implemented to accelerate the chloride transport. The solution used was 20% NaCl by weight. First, cyclic ponding in a moderate elevated temperature (37°C) curing room took place, followed by a migration cell approach at laboratory room temperature. This methodology allowed corrosion to initiate in a relative short period of time (months rather than years). The electric field produced ionic current that polarized the rebars to potential range of values at which removal of Cr2O occurred, this likely lowered the amount of chlorides needed for corrosion to initiate. After corrosion had initiated and propagated for some time; selected specimens were terminated for visual examination. On specimens selected for autopsy, the rebars in the top row showed corrosion to various degrees. Corrosion had propagated to such extent on the terminated specimens that cracks had appeared at the concrete surface above one of the rebars. Stray current likely caused accelerated corrosion on rebars where corrosion had initiated first. Based on chloride concentrations measured at the rebar trace, corrosion initiated: on UNS S32101 rebars range 0.95 to 2.95 wt% cement, and on UNS S32304 rebars the chloride range 1.06 to 2.6 wt% cement. The findings also suggest that UNS S32304 rebars corroded at at a significantly slower rate than UNS S32101.

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