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Epoxy-coated reinforcement (ECR), with and without penetrations through the epoxy, was subjected to an accelerated weathering program under ultraviolet (UV) light following Cycle 1 of ASTM G154, simulating outdoor exposure in North America for periods ranging from 1.2 months to 1 year. The corrosion resistance of the bars was evaluated using the ASTM A955 rapid macrocell test. As a control, the corrosion resistance of bars not subjected to the accelerated weathering program was also evaluated. After accelerated weathering equivalent to approximately 1.2 months of outdoor exposure, the corrosion resistance of epoxy-coated bars with penetrations in the coating was reduced, with corrosion losses three to six times greater than ECR without UV light exposure. Even ECR without penetrations through the coating showed a loss in corrosion protection when subjected to the equivalent of 1 year of outdoor exposure. ECR should be stored in a manner that protects it from exposure to UV light. The existing guidelines in ASTM D3963 limiting unprotected exposure to 2 months are not sufficient to protect the coating from damage; limiting exposure to 1 month or less should be required. [ABSTRACT FROM AUTHOR]

The effects of settlement cracking in concrete on corrosion initiation and rate of reinforcing steel in the presence of chlorides are evaluated using uncracked southern exposure (SE) specimens, cracked beam (CB) specimens with 0.012 in. (0.3 mm) artificial cracks directly above reinforcing steel, and settlement cracking (SC) specimens in which cracks with widths ranging from 0.001 to 0.004 in. (0.025 to 0.10 mm) form in plastic concrete over reinforcing bars. The earliest corrosion initiation was observed in the CB specimens, followed, in turn, by the SC and SE specimens. Although narrow, settlement cracks can lead to early initiation of corrosion--on average of less than half the time than for uncracked concrete. Relative to uncracked concrete, specimens with settlement cracks exhibited a 30% increase in corrosion rate while specimens with the artificial 0.012 in. (0.3 mm) crack exhibited an over 200% increase in corrosion rate. [ABSTRACT FROM AUTHOR]

A test procedure was developed to evaluate the effect of different techniques to limit settlement cracking over reinforcing steel with low concrete cover. Various specimen configurations and methods of finishing and curing were investigated. It was found that a clear cover of 1-1/8 in. (29 mm) over a No. 6 (No. 19) bar and covering the specimens after placement with sloped hard plastic enclosed in plastic sheeting provided a suitable method for obtaining clearly visible settlement cracks for concrete with slumps ranging from under 2 in. (50 mm) to over 8 in. (205 mm). The test specimen was then used to evaluate the effectiveness of a rheology-modifying admixture and four types of synthetic fibers on settlement cracking. Eighty-eight concrete batches were tested for mixtures with a cement paste (cement and water) content of 27 percent by volume and a water-cement ratio (w/c) of 0.45. The results show that the addition of the rheology-modifying admixture or fibers greatly reduces settlement cracking over reinforcing steel with low concrete cover. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) are commonly used as a means of reducing cost, reducing environmental impact, or reducing permeability of concrete, but the current field of research has found mixed results in terms of the resulting time to corrosion initiation and corrosion rate of concrete containing SCMs. This paper examines the time to corrosion initiation, the water-soluble critical chloride corrosion threshold, and the corrosion rate after initiation for uncracked concrete specimens containing cementitious material consisting of 100% portland cement, mixtures with volume replacements of cement by 20% and 40% Class C fly ash, 20% and 40% Grade 100 slag cement, and 5% and 10% silica fume. Specimens had 1 in. (25 mm) concrete cover and a water-cementitious materials ratio (w/cm) of 0.45. Test results show that many specimens containing SCMs exhibited repassivation of the reinforcement after a "first" corrosion initiation. This "first" initiation occurred at chloride thresholds comparable to or lower than the chloride threshold for reinforcement in 100% portland-cement concrete. The reinforcement remained passive for varying lengths of time (from 3 to 50 weeks) before reinitiating. At reinitiation ("final" initiation), specimens with concrete containing SCMs exhibited times to corrosion initiation two to seven times that observed in specimens containing 100% portland cement and corrosion rates after initiation approximately an order of magnitude lower than that observed in specimens containing 100% portland cement. Increasing the amount of SCM generally lowered the corrosion rate after initiation. Chloride thresholds at final initiation for specimens containing fly ash or slag were 66 to 200% higher than that observed for specimens containing 100% portland cement. Chloride thresholds at final initiation for specimens containing silica fume were 40 to 60% higher those observed for specimens containing 100% portland cement. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

XM-28 (UNS S24100) and 2304 (UNS S32304) stainless steel reinforcing bars with different levels of pickling were evaluated for corrosion resistance using the rapid macrocell and cracked beam tests outlined in ASTM A955. Two heats of XM-28 from the same producer were evaluated using the rapid macrocell test. A single heat of 2304 was evaluated in two conditions; as-received from the manufacturer and re-pickled using both ASTM A955 tests. The poorly pickled heat of XM-28 reinforcement failed the rapid macrocell test with a peak individual corrosion rate exceeding 16 µm/y, while the properly pickled heat passed with no significant corrosion measured. The poorly pickled 2304 reinforcing steel failed the macrocell and cracked beam tests, with peak corrosion rates of 1.07 and 6.48 µm/y, respectively, while upon re-pickling, the same heat of steel passed both tests. These results suggest the need for a method to verify that the pickling process has been performed properly. Performance during the first week of the rapid macrocell tests or requiring that the bars exhibit a bright, shiny, uniformly light surface represent two potential methods for establishing the adequacy of pickling. [ABSTRACT FROM AUTHOR]

Anti-bleed grouts are often used to ill voids in post-tensioning ducts that result from bleeding and shrinkage of older portland-cement grouts. This repair, however, exposes the strands to environmental differences from dissimilar grouts, differences that may cause rapid corrosion. Portland-cement grout, gypsum grout, and four commercially available prepackaged grouts were analyzed to determine the chemical composition of the resulting pore solutions and tested to determine the potential for accelerated corrosion. Grouts and simulated pore solutions were paired to evaluate their potential to cause corrosion of, respectively, grout-encased and bare prestressing strands using the rapid macrocell test. Strands were also evaluated in simulated pore solutions containing chlorides and in deionized water. Unprotected prestressing strands can exhibit rapid corrosion. Gypsum grout, with its low pH and high sulfate content, will cause accelerated corrosion of strands when used in conjunction with any of the other grouts tested. None of the prepackaged grouts resulted in significant corrosion when used in conjunction with portland-cement grout. The highest corrosion measured for a prepackaged grout occurred for the grout with the highest pore solution sulfate content. [ABSTRACT FROM AUTHOR]

Three commercially available corrosion inhibitors--calcium nitrite, a solution of amines and esters, and an alkenyl-substituted succinic acid salt--are evaluated in conjunction with conventional reinforcement in concrete based on corrosion rate, metal loss, the critical chloride corrosion threshold (CCCT), pore solution analyses, and concrete compressive strength. All three inhibitors increase time to corrosion initiation and decrease corrosion rate, but are less effective in cracked concrete than in uncracked concrete. Of the three inhibitors, the alkenyl-substituted succinic acid salt results in the greatest decrease in corrosion rate, but exhibits the lowest CCCT--below that measured in concrete with no inhibitor. The compressive strengths of concretes containing the amine-ester inhibitor and the alkenyl-substituted succinic acid salt were 15% and 60% lower, respectively, than concrete without an inhibitor. For the latter inhibitor, pore solution analyses indicated elevated sulfate contents at 1 and 7 days, which may explain the low CCCT and strength. Paste containing the amine-ester inhibitor had an elevated sulfate content at 7 days. [ABSTRACT FROM AUTHOR]

The article focuses on the study that determines the critical chloride corrosion threshold of galvanized reinforcing bars. It states that the starting average content of critical chloride corrosion is greater than the starting time for conventional steel. Different types of metallic coatings are used to protect steel from corrosion. Among the principal metals being protected from corrosion is zinc, which is applied as a molten coating. Because zinc corrodes in alkaline and in acid environments, galvanized bars are used to passivate the zinc surface and prevent the zinc from reacting with hydroxyl ions in fresh concrete. Moreover, details on how to protect reinforcing steel from corrosion along with the conclusions made from the study are presented.

The article focuses on the chloride threshold level (CTL) for corrosion of chromium and galvanized-based steel reinforcing bars compared to normal steel. To calculate the CTL, the time of corrosion initiation and the chloride concentration at the steel depth has to be identified. Corrosion initiation is depicted by a sharp increase in the galvanic current, which shows an increase from a few micro amperes to hundreds or thousands of micro amperes.