Fusion bonded thermoset epoxy-coated reinforcement is evaluated in conjunction with inorganic and organic corrosion inhibitors, bars initially coated with zinc prior to epoxy application, chemical pretreatments and epoxy formulations that increase the adhesion of the epoxy coating, and concretes with reduced water-cement ratios. The performance of corrosion protection systems is compared based on metal loss and disbondment between the epoxy-coating and the underlying steel using Southern Exposure and cracked beam tests in the laboratory and larger-scale slab specimens in the field. Findings after six years of this seven-year study indicate that conventional epoxy-coatings provide significant corrosion protection for reinforcing steel. The main potential weakness of this system is the loss of adhesion between the epoxy coating and the reinforcing steel, which is observed to be significantly greater for bars in cracked concrete than for bars in uncracked concrete. Bars initially coated with zinc prior to epoxy application exhibit lower disbondment than conventional epoxy-coated reinforcement. Concretes with reduced water-cement ratios provide better performance in uncracked concrete but only limited additional corrosion protection in cracked concrete.

Corrosion-related cracking in reinforced concrete is caused by expansive corrosion products and the resulting tensile stresses. While the amount of corrosion to cause cracking has been studied for uncoated conventional reinforcement, significantly less is known about the corrosion loss at cracking for galvanized reinforcement. Conventional and galvanized bars were cast in chloride-contaminated concrete. Clear cover to the bar ranged from 0.5 to 2 in. (12.7 to 51 mm). Specimens were tested both with and without the use of impressed current to drive corrosion. It was found that galvanized reinforcement requires greater corrosion losses to crack concrete than conventional steel reinforcement. Visual observations at autopsy suggest that the cracking of the concrete specimens containing galvanized reinforcement was not due to zinc corrosion products, but rather to corrosion products from intermetallic iron-zinc layers or from the underlying steel. Further study is needed to determine the exact nature of these corrosion products. Tests using impressed current may be used to establish the corrosion loss required to cause cracking.

The corrosion performance of MMFX and conventional reinforcing steels is compared based on macrocell and bench-scale tests. The conventional steel includes epoxy-coated and uncoated bars. Macrocell tests are conducted on bare bars and bars symmetrically embedded in a mortar cylinder. Specimens are exposed to a simulated concrete pore solution with a 1.6 or 6.4 molal ion concentration of sodium chloride. Bench-scale tests include the Southern Exposure and cracked beam tests. A 15% (6.04 m ion) NaCl solution is ponded on the top of both the Southern Exposure and cracked beam specimens. Mechanical properties are compared with the requirements of ASTM A 615. The uniformity and consistency in chemical composition is evaluated using a scanning electron microscope and an energy dispersive spectrometer. The microstructure of corrosion products is analyzed using a scanning electron microscope. The results indicate that MMFX steel exhibits better corrosion resistance than conventional uncoated steel, but lower corrosion resistance than epoxy-coated bars. In both the macrocell and bench-scale tests, MMFX steel exhibits a macrocell corrosion rate between one-third and two-thirds that of uncoated conventional reinforcing bars, while epoxy-coated reinforcement with the coating penetrated corrodes at a rate between 5% and 25% that of conventional steel. MMFX reinforcing steel is not recommended as a replacement for epoxy-coated reinforcement unless it is used in conjunction with a supplementary corrosion protection system.

The corrosion resistance of three microalloyed steels and two conventional reinforcing steels in concrete was evaluated. The microalloyed steels contain concentrations of chromium, copper, and phosphorus that, while low, are significantly higher than used in conventional reinforcing steel. Two of the microalloyed steels contain amounts of phosphorus that exceed the amounts allowed in ASTM specifications (ASTM A 615), while the other microalloyed steel has normal amounts of phosphorus. One of the conventional steels and the three microalloyed steels are heat treated by the Thermex process, which includes quenching and tempering of the steel immediately after rolling, while the other conventional steel is hot-rolled. The study was undertaken because earlier tests on similar steels indicated that the Thermex-treated, microalloyed steel corrodes at only one-half the rate of conventional reinforcing steel. The relative corrosion rate dropped to one-tenth if both steels were epoxy-coated. In the current study, the reinforcing steels were tested using two rapid evaluation tests, the corrosion potential and corrosion macrocell tests, and three bench-scale tests, the Southern Exposure, cracked beam, and ASTM G 109 tests. The corrosion potential, corrosion rate, and mat-to-mat resistance are used to evaluate the steel. Tension and bending tests were performed to evaluate the effect of the microalloying and heat treatment on the mechanical properties of the reinforcing steel. Results show that the corrosion potential of the five steels is approximately the same, indicating that they have a similar tendency to corrode. The results from the rapid macrocell test showed that the five steels had similar corrosion rates, with no improved behavior for the microalloyed steels. The microalloyed steel with regular phosphorus content (CRT) exhibited consistently lower corrosion losses than conventional steel in the bench-scale tests. Although CRT appears to be much more corrosion resistant than conventional steel in the G 109 tests (64% less total corrosion loss after 70 weeks), its overall performance does not show such an advantage. In the cracked beam test after 70 weeks, it had only 4% less corrosion loss than conventional steel, which indicates that in cracked concrete the two steels behave in a similar manner. In the Southern Exposure test, CRT steel had an 11% lower corrosion loss than conventional steel after the same period. This improved behavior is not enough to use the steel without an epoxy coating or to justify continued research on the steel as a superior epoxy-coated material. The mechanical properties of the microalloyed steels were similar to those of conventional steel, indicating that the increased phosphorus content did not affect the mechanical properties.

The corrosion performance of a prototype 304 stainless steel clad reinforcing bar and conventional reinforcing steel is compared based on corrosion potential and macrocell corrosion tests. Tests are conducted on bare bars and bars symmetrically embedded in a mortar cylinder. Test specimens consist of bars with ends protected with epoxy or with plastic caps filled with epoxy, and clad bars with a hole drilled through the cladding. Specimens are exposed to a simulated concrete pore solution with a 1.6 molal ion concentration of sodium chloride. Additional corrosion potential tests include specimens exposed to simulated concrete pore solution with and without pressurized air pumped into the solution and a conventional bar with a reduced thickness of mortar cover. Additional macrocell corrosion tests include sandblasted stainless steel clad bars, damaged stainless steel specimens connected to conventional steel cathodes, mortar covered conventional bars connected to bare conventional bars, and specimens with a reduced thickness of mortar. The thickness and uniformity of the stainless steel cladding is evaluated using a scanning electron microscope. The results indicate the prototype 304 stainless steel clad reinforcement exhibits superior corrosion resistance compared to conventional reinforcing steel, but requires adequate protection at cut ends, where the mild steel core is not covered by cladding. For bare stainless steel clad bars, the macrocell corrosion rate varies between 0.0 to 0.3 microns/yr (0.0 to 0.012 mpy), about 1/100 of the value observed for conventional bars. Stainless steel bars embedded in mortar exhibit corrosion rates between 0.0 and 0.2 microns/yr (0.0 and 0.008 mpy), averaging 1/20 to 1/50 of the value exhibited by conventional bars. The corrosion rates for clad bars with a drilled hole through the cladding range between 0.0 and 0.75 microns/yr (0.0 and 0.03 mpy), averaging about 1/70 of the value exhibited by conventional steel bars. The thickness of the stainless steel cladding on bars in the current study varies between 0.196 to 0.894 mm (7.7 to 35 mils). Imperfections in the form of an indentation in the base material and a crack in the cladding material filling the indention were observed. The crack did not penetrate the stainless steel cladding and cladding is of adequate thickness to protect the mild steel core. Longer-term tests are recommended, as is use of the bar in demonstration bridge decks.

ABSTRACT

Since the 1970s, research projects and field studies have been conducted on different methods for protecting reinforced concrete bridges from corrosion damage. The methods include alternative reinforcement and slab design, barrier methods, electrochemical methods, and corrosion inhibitors. Each method and its underlying principles are described, performance results of laboratory and/or field trials are reviewed, and systems are evaluated based on the results of the trials. Using performance results from the studies and costs obtained from transportation agencies, an economic analysis is used to estimate the cost of each system over a 75-year economic life using discount rates of 2%, 4% and 6%. Epoxy-coated reinforcing steel is the most common corrosion protection method used in the United States today. Although controversial in many areas, epoxy-coated reinforcement has performed well in many states, including Kansas, since it was introduced in the early 1970s and is a low-cost backup to many of the other corrosion protection options. Research on stainless steel reinforcement indicates that it may remain free of corrosion in chloride contaminated concrete for more than 75 years. At a low discount rate (2%), solid stainless steel reinforcement is a cost-effective option compared to other options, but at higher discount rates, the present value cost of a deck with solid stainless steel is significantly higher than that of an unprotected deck. Stainless steel clad reinforcement is much less expensive than solid stainless steel reinforcement. The performance of stainless steel-clad reinforcement will be similar to that of solid stainless steel bars if the stainless steel coating is continuous and if the black steel core, exposed at the bar ends, is protected so that it does not come into contact with the pore solution. The present value of the cost of a bridge deck built with stainless steel-clad reinforcement is significantly lower than the present value for the cost of any other corrosion protection system. This method should be considered for experimental use. Solid stainless steel should be considered, as well, if a low discount rate (around 2%) is used. Hot rubberized asphalt membranes are the least expensive option, other than stainless steel-clad reinforcement. Hot rubberized asphalt and spray-applied liquid membranes should be considered for use on future projects. In laboratory tests, corrosion inhibitors have been shown to provide protection to steel in chloride contaminated concrete, but information on their performance in the field is limited. Both calcium nitrite and organic corrosion inhibitors have the potential to be cost-effective, if they perform as well in the field as they have in the laboratory, and should be considered for experimental use.

This Innovations Deserving Exploratory Analysis (IDEA) project evaluated the corrosion resistance and mechanical properties of steel rebars produced by new microalloying and rolling procedures. Tests results confirmed that microalloying significantly decreased the corrosion rate of steel, and that quenching and tempering heat treatment further enhanced its corrosion resistance as well as yield and tensile strengths. Implementation of the new reinforcing steel will require extensive field validation, the development of standard specifications for the material, and the execution of demonstration projects in which the new reinforcing steel is applied in practice. Special attention should be given to using the new steel in conjunction with epoxy coating.

This handbook contains a structured selection of specific test methods for complete characterization of deicing chemicals. Sixty-two specific test methods are defined for the evaluation of chemical deicers in eight principal property performance areas: 1) physicochemical characteristics; 2) deicing performance; 3) compatibility with bare and coated metals; 4) compatibility with metals in concrete; 5) compatibility with concrete and nonmetals; 6) engineering parameters; 7) ecological effects; and 8) health and safety aspects. The 62 specific chemical deicer test methods are composed of 12 primary and 50 supplementary test methods. The primary test methods, which were developed for conducting the more important evaluations, are identified as follows: 1) ice melting tests for liquid and solid deicers; 2) ice penetration tests for liquid and solid deicers; 3) ice undercutting tests for liquid and solid deicers; 4) bare metal corrosion test; 5) concrete degradation test; 6) concrete scaling test; 7) friction characterization test; 8) ecological effects tests; and 9) rebar in concrete corrosion test.

Research to develop tests that can accurately predict the effects of deicing chemicals on the corrosion of steel in reinforced concrete structures is reported. The research includes the development and evaluation of a standard test specimen and the use of 3 deicing chemicals to determine the sensitvity of both corrosion potential and macrocell corrosion to molal ion concentrations ranging from 0.4 to 6.4. The standard test specimen consists of a No. 4 reinforcing bar embeded in a 1.18 in (930 mm) diameter, 4 in. (100 mm) long mortar cylinder. The mortar is made using portland cement, deionized water and standard graded Ottawa sand. Specimens cured in lime-saturated water reach a passive condition within 14 days. Based on limited test data using sodium chloride, calcium chloride, and calcium magnesium acetate, calcium chloride appears to be the most detrimental, followed in order by sodium chloride and calcium magnesium acetate.

Research to develop tests that can accurately predict the effects of deicing chemicals on the corrosion of steel in reinforced concrete structures is reported. The research includes the development and evaluation of a standard test specimen and the use of three deicing chemicals to determine the sensitivity of both corrosion potential and macrocell corrosion to molal ion concentrations ranging from 0.4 to 6.4. The standard test specimen consists of a No. 4 reinforcing bar embedded in a 1.18 in. (30 mm) diameter, 4 in. (100 mm) long mortar cylinder. The mortar is made using portland cement, deionized water, and standard graded Ottawa sand. Specimens cured in lime-saturated water reach a passive condition within 14 days. The tests are easy to perform, require no special training, and can normally be completed within 60 days. Of the two tests, the corrosion potential test provides more consistent results and should prove to be a useful tool for comparing the effects of deicing chemicals on the corrosion of reinforcing steel. Additional modifications are needed in the macrocell test before it is ready for general use. Based on limited test data using sodium chloride, calcium chloride, and calcium magnesium acetate, calcium chloride appears to be the most detrimental, followed in order by sodium chloride and calcium magnesium acetate. Corrosion in the presence of calcium magnesium acetate appears to be highly sensitive to relative concentration, with no corrosion occurring at a molal ion concentration of 0.4. In contrast, specimens exposed to both calcium chloride and sodium chloride exhibit measurable corrosion potential at a concentration of 0.4 m. At the highest concentration for which comparisons were made (6.4 m), both the CMA and the CaC12 appear to be equally detrimental, while the NaCl appears to cause somewhat less corrosion.

The corrosion performance of stainless steel clad reinforcing bars provided by Structural Metals, Inc. is compared with that of conventional (black) reinforcement. 304 stainless steel is used as the cladding material. The No. 19 (No. 61 bars are compared using rapid corrosion potential and macrocell tests. The tests are carried out in two stages, first with bare reinforcement and then with reinforcement encased in mortar. Test spe.cimens are placed in simulated concrete pore solution with a 1.6 molal ion concentration of sodium chloride. The continuity and uniformity of the cladding is measured using a scanning ele.ctron microscope. The study indicates that the cladding provides a significant improvement in corrosion performance, if the mild steel core of the clad bars is adequately isolated from chlorides. For bars not encased in mortar, the corrosion rate of the clad bars ranges between 0 and 0.3 μm/yr, about 1100 of the value observed for the black bars. For bars encased in mortar, the corrosion rate averages 0.1 μm/yr, I20 to /50 of the value exhibited by the black steel. Cladding thickness varies between 0.196 and 0.894 mm (7.7 and 35 mils), averaging 0.467 mm (18 mils). Based on an average corrosion rate of about 0.2 μm/yr for stainless steel bars not embedded in mortar (representing the corrosion rate that would be expected at a void adjacent to a bar in concrete), the cladding appears to be satisfactory if the current minimum thickness is maintained. Tests of bars clad with 316 stainless steel and longer-term tests are recommended.

The conditions in which stray currents contribute to the corrosion of highway structures, the tests to determine if these conditions exist, and the methods recommended to alleviate either the conditions or the damage caused by stray current corrosion are investigated. An extensive review of the literature concerning the fundamentals of stray current corrosion and the practices of utility cathodic protection is presented, including a comprehensive study of the history of stray current corrosion, from its conception with the direct current trolley systems of the late 1880s to its present day problems in the cathodic protection industry. Federal, state, and Kansas Department of Transportation (KDOT) rules and policy are reviewed as they pertain to utility cathodic protection and the damage it may cause to adjacent underground highway structures. Based on the research covered within this report, procedural changes for the prevention of stray current corrosion damage to highway structures and additions to the KDOT Utility Accomodation Policy (1994) are recommended. The research herein concludes that: (1) all construction close to cathodically protected utilities should be reported to the utility owners so that stray current interference can be assessed, (2) any utility pipeline found uncovered should be reported to its owner so it can be inspected for corrosion damage, and (3) no underground highway structure should be located within the area of influence of a cathodic protection groundbed. It is recommended that the KDOT Utility Accommodation Policy (1994) be modified to: (1) directly state the policy on stray current interference from utility cathodic protection systems, (2) require utilities installing cathodic protection systems to submit the design plans as part of the process necessary to obtain a permit agreement for operating in a highway right-of-way, and (3) state that KDOT may require additional inspections along pipelines where interference could jeopardize the structural integrity of an underground highway structure.

SMI-316 SCTM stainless steel clad concrete reinforcement is evaluated for corrosion resistance, mechanical properties, life expectancy, and cost effectiveness and compared with conventional mild steel reinforcement and epoxy-coated reinforcement (ECR). Corrosion performance is evaluated using rapid macrocell, Southern Exposure, and cracked beam tests. MMFX Microcomposite reinforcement is evaluated for the chloride content required for corrosion initiation, which is used to supplement corrosion test results from earlier research. Life expectancy and cost effectiveness of bridge decks containing the different reinforcing systems are evaluated using laboratory results for the chloride content required for corrosion initiation and rate of corrosion along with field experience and costs in South Dakota. The SMI-316 SC bars satisfy the mechanical properties specified by ASTM A 615 for Grade 60 reinforcing bars. The SMI-316 SC bars should be fabricated (bent) using protective equipment similar to that used for epoxy-coated bars to limit damage to the cladding. Cladding thickness is satisfactory for normal construction operations. The corrosion rates of both SMI-316 SC and ECR reinforcement are less than 0.4% or 1/250 of that for conventional reinforcement. Epoxy-coated reinforcement embedded in concrete can undergo a significant loss of bond between the epoxy and the reinforcing steel, although total corrosion losses are low compared to those observed for conventional reinforcement. Bridge decks containing SMI-316 SC reinforcing steel will not require repair due to corrosion-induced concrete cracking during a 75-year service life. In comparison, conventional bridge decks require repair 10 to 25 years after the construction, depending on exposure conditions. Bridge decks containing epoxy-coated reinforcement will not require repair due to corrosion-induced concrete cracking during a 75-year service life but are estimated to require repair approximately 40 years after construction due to corrosion near damaged areas where the bond between the epoxy and reinforcing steel has been lost. Bridge decks containing SMI-316 SC reinforcing steel are cost-effective compared to bridge decks containing epoxy-coated reinforcement. The critical chloride corrosion threshold for MMFX Microcomposite steel is three to four times the corrosion threshold for conventional reinforcement, and the corrosion rate is approximately one-half that of conventional steel. Bridge decks containing MMFX Microcomposite reinforcing steel will require repair due to corrosion-induced concrete cracking approximately 33 years after construction and do not appear to be cost-effective when compared to bridge decks containing epoxy-coated reinforcement.

The mechanism of corrosion of reinforcing steel in concrete is discussed based on electrochemical and electron microscopy observations. The importance of calcium hydroxide precipitation on the steel surf ace in the steel/mortar interface is evaluated by placing filter paper around reinforcing steel bar specimens prior to casting in mortar, thus preventing direct contact between steel and mortar. The voids created presumably prevent calcium hydroxide crystals from forming on the steel surface. Specimens with filter paper are compared to specimens with good steel/mortar adhesion using rapid macrocell and corrosion potential tests and a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The study included 21 macrocell and 16 corrosion potential tests run for periods of 25 to 89 days. Seven specimens were subjected to SEM/EDS analysis. Electrochemical results are mixed due to the influence of crevice corrosion. but it is generally shown that better protection is provided for steel with good steel/mortar adhesion than with filter paper. The filter paper, indeed, prevents calcium hydroxide crystals from forming on the steel surface. Corrosion products on active specimens with good mortar cover are shown to grow preferentially in voids created by air bubbles trapped in the mortar. The protective mechanism of calcium hydroxide crystals is proposed to be due to pH buffering by the hydroxyl ions released when the crystals are dissolved, a fact that cannot be proven easily, since many other factors may contribute to the protection of steel in concrete.