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The resistivity evolution vs. time of concrete prepared with three different compositions and subjected to various curing regimes for an extended period of time was studied. Two of the curing regimes consisted of immersing the specimens in either tap water or 3.5% NaCl solution. The other three curing regimes consisted of exposure to: fog room, high humidity and laboratory humidity. The measured resistivity values were then used to estimate the aging factor. It is found that the aging factor is time dependant for concrete with mineral admixtures. The curing exposure affects the magnitude of the aging factor.
Deterioration of concrete bridges because of reinforcing steel corrosion has been recognized for four-plus decades as a major technical and economic challenge for the United States. As an option for addressing this problem, renewed interest has focused on corrosion resistant reinforcements, stainless steels in particular. The present research study was performed jointly by Florida Atlantic University and the Florida Department of Transportation to evaluate reinforcements of this type. These reinforcements included solid stainless steels 3Cr12 (UNS-S41003), 2101LDX (ASTM A955-98), 2304 (UNS-S32304), 2205 (UNS 31803), two 316L (UNS S31603) alloys, and two 316 stainless steel clad black bar products, and MMFX-2 (ASTM A1035). Black bar (ASTM A615) reinforcement provided a baseline for comparison purposes. Results from short term tests and preliminary results from long-term exposure of reinforced concrete slabs were presented in the first Interim Report (FHWA-HRT-07-039) for this project. This report provides longer-term data and analyses of four different types of reinforced concrete specimens, two of which were intended to simulate northern bridge decks exposed to deicing salts and the remaining two to simulate substructure elements undergoing seawater exposure. Three different concrete mix designs were employed, and specimen types included variables such as 1) a simulated concrete crack, 2) a bent top bar, 3) corrosion resistant upper bar(s) and black steel lower bars, and 4) intentional clad defects such that the carbon steel substrate was exposed. Cyclic wet-dry ponding with a sodium chloride (NaCl) solution was employed for the former two specimen types, and continuous partial submergence in either a NaCl solution or at a coastal marine site in Florida for the latter two. The exposures were for periods in excess of four years. The candidate alloys were ranked according to performance, and an analysis is provided that projects performance in actual concrete structures. A subsequent final report is to be issued at a later time.
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Cathodic prevention was implemented with commercial Zn bulk anodes on laboratory columns simulating a reinforced concrete marine system. Two computational models of these laboratory columns were implemented. The results obtained from both models were in reasonable agreement with the experimental observations. One of the models was used to predict cathodic prevention throwing power on field scale structures, as a step towards field application. These predictions 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.
Purpose The purpose of this paper is to study the susceptibility of these three commonly used corrosion resistance fasteners in seawater. For a more practical scenario, a local Atlantic coastal seawater as received was used. Design/methodology/approach Carbon fiber reinforced polymer (CFRP) was fabricated with T700 carbon fiber (Toray Inc.) and VE8084 vinyl ester resin (Ashland) to make a unidirectional composite panel of thickness 1.8 mm. A conductive paint was applied to one of the sample edges that was perpendicular to the fiber direction, providing an electrical contact with carbon fibers to connect a copper wire. This external electric connection was used for potential measurements of both the open circuit potential (OCP) of the CFRP sample, and the mixed potential of the fastened set: consisting of the CFRP and the metallic fastener fastened to it. Three common fastener alloys were selected: 316SS, Monel and Titanium. For this purpose, a high impedance voltmeter was used in conjunction with a saturated calomel reference electrode. Measurements were taken daily. For longer time measurements, a four-channel high impedance analog data logger was used with 30 min sampling rate. Findings For both 316SS and Monel fastened sets, crevice corrosion occurred inside the occluded regions of the set, when immersed in coastal seawater. The attack was more severe for 316 stainless steel set. An isolated island attack of faceted surfaces morphology was seen for 316SS set. While, a circular ring of preferential grain boundary attack appeared for Monel set, indicating an IR (voltage) drop mechanism is more likely operating. Titanium-fastened sets showed high resistance to crevice corrosion when simmered in seawater. However, for long-time exposure, the sets became more susceptible to crevice corrosion attack supported by CFRP attachment (oxygen reduction reaction taking place at the carbon fibers). Originality/value Evidently, titanium, stainless steels and Monel are good candidates for galvanic corrosion resistance. However, their susceptibility to crevice corrosion when coupled with CFRP is a new challenging topic that needs further investigation. This is very important today because the vast application witnessed for CFRP material. This work involves developing an original methodology for this kind of investigation and was done at advanced laboratories of SeaTech at Florida Atlantic University by the Atlantic coastline.
A literature review has been conducted with the goal of identifying alternative low-cost corrosion resistant reinforcement materials compared to epoxycoated reinforcing steel. The new materials are evaluated on the basis of material attributes that are expected to improve initiation and propagation corrosion characteristics including an assessment of the impact of mill scale. Moreover, strength, ductility as well as low cycle fatigue behavior are considered where possible with endurance limit scaled to tensile strength. First, material characteristics that should contribute to improved initiation, propagation resistance, and oxide wedging damage mechanisms will be reviewed. Then, based on the literature survey, the individual materials are assessed and summarized. The most promising alternate reinforcing materials seen to date that are less expensive than 300 series stainless steels include low-Ni austentitic stainless steels, and a variety of ferritic or martensitic 12-15 wt. % Cr steels. Low Ni austentitic stainless steels and other 12-15% Cr steels will likely have inferior corrosion resistance compared to traditional 300 series stainless steels but may be significantly improved over traditional epoxy-coated rebar. It is recommended that a 200 series stainless steel and 12-15% martensitic or ferritic steel be considered for further investigation as reinforcing material in concrete.
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A set of partially immersed reinforced concrete columns with mature corrosion patterns was used to demonstrate that corrosion macrocell currents provided “cathodic prevention” to parts of the steel assembly that remained passive even though exposed to high chloride (~ 4.7% of the cement weight) concrete. Depassivation of that steel was observed upon macrocell decoupling.
A detailed computer model of corrosion distribution in reinforced concrete has been used to predict the extent of cathodic protection provided for partially submerged piles by a combination of bulk sacrificial anodes placed below water and surface anodes above water. The model predictions are directly compared with the experimental response to cathodic protection in laboratory piles having active corrosion in progress.
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Abstract Dry-cast reinforced concrete pipes (D-RCPs) are sometimes used in Florida at places in proximity to the ocean or at locations with high chloride concentrations where the water table seasonally saturates the D-RCPs. Previous studies suggest that corrosion would initiate after sometime in service once the critical chloride threshold has been exceeded at the reinforcement. However, very little is known as to how corrosion would propagate under the environmental service conditions. Instrumented segments obtained from two different types of D-RCPs in which corrosion had already initiated were used to investigate the corrosion propagation stage. During the propagation stage in different exposures, reinforcement eventually reached negative potentials values (< -600 mVsce), which suggest mass transfer limitations. The specimens show no visual signs of corrosion such as cracks or corrosion products. Moreover, the apparent corrosion rate values measured via linear polarization resistance suggest high corrosion rate. No crack appearance so far, could be explained by the corrosion products filling the pore system and also due to the small diameter of the reinforcement or longer exposure is required. Although there might be mass transfer limitations present, the current demanded by the anode is being matched by a larger cathode area due to macrocell effects, since the high moisture conditions likely lowered the concrete electrical resistance and hence increased the throwing power. This trend might change and longer exposure is planned to determine if the corrosion rate might become lower as a result of oxygen depletion at the cathode. Additionally, selected specimens are planned to be terminated to verify corrosion extent.
