Reinforcement Corrosion in Marine Concretes—1: Initiation

Melchers, Robert E.; Chaves, Igor A.

doi:10.14359/51716827

Cited by 14 publications

(34 citation statements)

References 27 publications

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“…For the latter, air-voids are often observed on the underside of horizontal reinforcement bars, irrespective of whether they are "top" bars or bars in the lower parts of a beam or slab [72]. This has been observed also for laboratory specimens [12,73,74]. These observations provide one explanation to why spalling is mostly from the underside of beams rather than from the sides, even for a similar concrete cover and when exposure to seawater or seawater spray is similar.…”

Section: Discussionmentioning

confidence: 98%

“…A parallel project using specimens of the same size and with comparable water-cement and aggregate-cement ratios with exposures extending over more than 12 years has been reported recently [12,13]. This program used low-heat as well as blended commercial cement.…”

Section: Reinforcement Corrosion After Initiation (Parameters C Sc Anmentioning

confidence: 99%

“…The reasons for the poor performance of some practical reinforced concretes have become clearer as a result of recent long-term experimental findings [12,13]. These are reviewed briefly in the next section.…”

Section: Introductionmentioning

confidence: 99%

“…The severity of corrosion associated with an air-void depends on the amount of oxygen in the air-void and the local availability of pore water. It has been shown to commence as differential aeration, localized at the edges of the air-voids [1] that then causes localized (pitting) corrosion of the adjacent steel [12]. Once initiated, such localized corrosion is only very mildly inhibited by diffusion considerations and will increase rapidly until eventually limited by the availability of oxygen or water.…”

Section: Introductionmentioning

confidence: 99%

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Experience-Based Physico-Chemical Models for Long-Term Reinforcement Corrosion

Melchers

2021

CMD

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The long-term corrosion progression of steel reinforcement is important for estimating the life of reinforced concrete infrastructure. Reviews of field experience and results from recent controlled long-term experiments show that the development of reinforcement corrosion is much more complex than the classical empirical Tuutti model. A new, comprehensive model is proposed, referencing observations and inferences from many field and laboratory observations and built on the bi-modal model for the corrosion of steel. It includes the critical roles of air-voids in the concrete at the concrete-steel interface and the effect of long-term alkali leaching as accelerated by the presence of chlorides. Both are affected by compaction and concrete permeability. The role of chlorides in the early stages is confined to pitting within air-voids. These are critical for allowing initiation to occur, while their size influences the severity of early corrosion. Empirical data show that for seawater with an average water temperature in the range of 10–20 °C, the corresponding rate of long-term corrosion ra is in the range of 0.012–0.015 mm/y.

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Section: Discussionmentioning

confidence: 98%

Section: Reinforcement Corrosion After Initiation (Parameters C Sc Anmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experience-Based Physico-Chemical Models for Long-Term Reinforcement Corrosion

Melchers

2021

CMD

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“…Model concrete specimens exposed for up to 12 years and examined by breaking one or two open (at approximately yearly intervals) have shown that even with seawater used as mixing water (and therefore with very high available chloride concentrations at the steel bar and elsewhere, even after allowing for bound chlorides [24]) there is an initial degree of corrosion but that this then stops or much reduces [25]. Similar observations have been made elsewhere [26,27] for a number of RC beams, close to full size rather than the laboratory samples used in the 12-year study.…”

Section: Corrosion Initiationmentioning

confidence: 99%

Long-Term Durability of Marine Reinforced Concrete Structures

Melchers

2020

JMSE

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The sustainability of reinforced concrete is critical, particularly for structures exposed to marine environments. Chlorides are implicated in causing or accelerating reinforcement corrosion and potentially earlier expensive repairs, yet there are many older reinforced concrete structures in good condition for many decades despite very high chloride levels at the reinforcement. The reasons for this are reviewed briefly, together with recent experimental work that better defines the role of chlorides. One is initiation of reinforcement corrosion but only through localized pitting at air-voids in concrete at the interface with the steel reinforcement. These tend to be small or negligible for high quality well-compacted concretes. The other role for chlorides has been shown, in experimental work, to accelerate the long-term loss of concrete alkali material. On the other hand, a review of practical experience shows that what has been termed chloride-induced reinforcement corrosion often is not that at all, but is the end-product of factors that impair the protective nature of the concrete. As reviewed herein, these include poor compaction, physical damage to concrete cover, concrete shrinkage, and alkali-aggregate reactions. The various observations presented are important for the proper understanding, analysis, and design of durable reinforced concrete structures exposed to chloride-rich environments.

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