Reinforcement corrosion in concrete is the predominant causal factor for the premature deterioration of reinforced concrete structures, causing various degrees of damage to the structure and leading to final structural collapse. The existence of reinforcement corrosion in concrete structures makes them increasingly vulnerable over time. This ultimately poses a potential risk to the public. The intention of the present paper is to propose a method to assess the vulnerability of reinforced concrete structures deteriorating over time due to reinforcement corrosion. The application of the proposed method to corrosion-affected flexural members is demonstrated, while in practice the limitations of the proposed approach need to be recognised due to the complexity of the corrosion process in real structures. The effect of design variables of reinforced concrete structures on their vulnerability is also studied using two sensitivity analysis techniques. It is found that corrosion-induced deterioration is the most important single factor that makes reinforced concrete structures vulnerable. The method presented in the paper can assist engineers, operators and asset managers in developing a risk-informed and cost-effective maintenance strategy in the asset management of corroded concrete infrastructure.
No abstract is provided for this article.
Long term deterioration of concrete sewer infrastructure costs the wastewater industry billions of dollars per year globally raising serious questions about how best to prioritize remedial and replacement work in order to maintain the sustainability of wastewater infrastructure. It follows that predicting the time to failure of existing reinforced concrete sewer systems is an important issue for wastewater utilities. A recently completed 6 year field trial examined the corrosion behavior of new and aged sewer pipe in Australian gravity sewers. The work shed light on the corrosion process timeline and the impact of the local sewer environment on the rate of corrosion experienced by concrete sewer mains. A service life prediction model for concrete sewer pipe which has been developed is discussed as well as methods for prolonging concrete sewer pipe service life.
Water pollution is often thought to cause accelerated corrosion of steels, particularly in harbors where levels of oxygenation of the waters may be low and where there may be industrial and shipping wastes. Harbors and coastal regions may also be prone to nutrient pollution from sewage or agricultural run-off. Offshore oil fields also are known to provide sources of nutrient pollution. There are some anecdotal observations but there appear to have been no systematic field or laboratory studies. Recent field observations have been reported on the effect of nutrient-based pollution on the corrosion of mild steel corrosion coupons. These are interpreted in terms of the phenomenological model previously described in the literature for the corrosion of mild steel under marine immersion conditions. A selection of field data previously reported in the corrosion literature is then considered and shown to have characteristics not inconsistent with nutrient-based water pollution. The effect of dissolved oxygen concentration is noted also.
The corroded external surfaces of older cast iron water mains buried in soils for many decades usually show a rough undulating topography. Sometimes, there also are areas of relatively smooth topography similar to uniform corrosion but over undulating surfaces. Investigations show this pattern is associated with localised pipe-wall perforation and sometimes pipe fracture. It is proposed that corrosion pitting from the outside surface of the pipe perforates the pipe-wall, allowing fresh oxygenated drinking water from inside the pipe to effuse through the orifice. This then causes a high rate of localised general corrosion under the graphitised layer. The resulting thinning of the pipe-wall may then lead to pipe fracture under high water pressure.
Infrastructure intended to contain or exclude fluids or gasses, or reinforced with glass or other fibres may be subject to failure caused by pitting corrosion of the containment system or of the reinforcement. To assess the reliability of the infrastructure then requires probabilistic models for the deterioration processes involved. Typically the critical deterioration is through localized pitting and in particular the most extreme pit depth as this governs containment capability and also fibre strength. The ‘arch-typical’ distribution for representing maximum pit depth is the Gumbel extreme value distribution, for which complying data plot linearly on a so-called Gumbel plot. However, there is increasing evidence that large, homogeneous datasets show significant deviations from linearity. This is demonstrated for steel plates continuously immersed in seawater, for the interior corrosion of water injection pipelines and for crude oil production pipelines. Further examples are given for the maximum pit depth on stainless steel rollers in the papermaking industry and for localized corrosion of glass fibre reinforcement in concrete structures. In each case the non-linear trends obtained permit a re-interpretation of, and new insights for, the underlying physico-chemical-material mechanisms. The results are important for accurate representation of deterioration processes and for best-practice structural reliability analyses.
It is well-known that bacterial activity can contribute significantly to corrosion in marine and buried conditions. Herein, the possibility of bacterial influence on corrosion under atmospheric conditions is investigated, using the commercially available LAB-BART ® system to identify and to some degree quantify the major groups of bacteria present in corrosion products, including the sulphate reducing bacteria (SRB), iron reducing bacteria (IRB), heterotrophic aerobic bacteria (HAB), denitrifying bacteria (DN), acid producing bacteria (APB) and slime producing bacteria (SLYM). This is sufficient for most engineering purposes to assess the likelihood of corrosion being influenced by atmospherically borne bacteria. Bacterial testing was conducted at nine widely different atmospheric test locations. Significant SRB were not identified at any of the locations, IRB were identified in significant populations at all locations including, surprisingly, at the desert location. HAB were identified in small amounts at some locations but in greater concentrations at a turf farm and at an inland dam site. DN were not present at any location except at the desert site. APB was present in significant amounts at all sites and SLYM varied from almost nil at the ocean beach to quite high populations at the turf farm and at the dairy. These results are compared with nutrient deposition at these sites.
No abstract is provided for this article.
Internal corrosion of steel pipelines before use, or temporarily taken out of use, and ‘parked’ on the seafloor for some time (months), suspended from operation or ‘abandoned’ for extensive period of time continues to be an issue for offshore operators and regulators. This is irrespective of whether the pipes are gas or oil production or water injection pipelines. Severe pitting corrosion, sometimes observed at the 6 o’clock position, conventionally often is assumed the result of microbiologically influenced corrosion (MIC), particularly if coupled with high bacterial concentrations in the rusts. Dosing with biocides is not always effective and increasingly is considered environmentally undesirable. This paper provides a brief overview of the fundamental requirements for long-term corrosion under low oxygen and essentially stagnant environmental conditions. It shows that any severe internal corrosion at the 6 o’clock position has similarities to that sometimes observed for water injection pipelines and likely the result of under-deposit corrosion resulting from the deposition of rusts and other debris. MIC may contribute providing there is availability of necessary nutrients. Generally similar issues apply for the external and interior corrosion of abandoned pipelines. Avenues for further research and development are outlined, including for pipelines proposed to be abandoned.
A methodology is described for the assessment of the service life of liquid carrying metallic pipelines subjected to pitting corrosion. The estimate of pipeline life is based on the loss of liquid through pit holes during transportation. The growth of corrosion pits is modelled by a two-parameter exponential function having time dependency and a decreasing rate of pit growth. Parameters which are related to corrosion, pipeline dimension and liquid flow are treated as probabilistic variables. The first-order reliability method is used to estimate the probability of failure and the relative contribution of the various uncertain parameters to it. Failure is defined in terms of a maximum allowable degree of loss or ingress of fluid. Numerical results are given for a typical example pipeline. A sensitivity study was also carried out for the example pipeline to reveal the effect of the level of variability of some of the random variables on the failure probability. The results show that the probability of failure increases nonlinearly with time and that the contribution of pit hole size and pitting corrosion parameters are very significant for long service lives.
In 2010 the disused railway bridge at St Lawrence on the Queensland Pacific Ocean coast was demolished after 90 years service across the St Lawrence Creek, Queensland, some 6 km inland from the Pacific Ocean and subject large (up to 9 m) seawater tidal movements. Detailed examination of samples about 300×300 mm square and larger cut from several of the bridge piers at various elevations showed corrosion loss varying on average between 2-3 mm for the immersion and tidal exposure zones. This is remarkably little for such aggressive environment and for such long duration of exposure. There was negligible corrosion in the atmospheric zone. The multiple samples allowed statistical analysis of the variability of corrosion losses at different elevations. The statistical results are unique for such long-term exposures and are of major importance for structural reliability analyses of similar old bridges. Also, the corrosion loss results were compared with results reported in the literature for which the longest period of observation is only a few years. Observations show that cast iron is not free from localized corrosion and pitting as sometimes assumed. The corrosion loss results were compared to patterns previously observed for corrosion of steel through the tidal zone. A pattern consistent with so-called accelerated low water corrosion was observed, suggesting that at some period of time in the history of the bridge the tidal seawaters suffered some degree of water pollution.
Despite being exposed to the harsh sea-spray environment of the North Sea at Arbroath, Scotland, for over 63 years, many of the reinforced concrete precast beam elements of the 1·5 km long promenade railing are still in very good condition and show little evidence of reinforcement corrosion. In contrast, railing replacements constructed in about 1968 and in 1993 are almost all badly cracked as a result of extensive corrosion of the longitudinal reinforcement. This is despite the newer concrete appearing to be of better quality than the 1943 concrete. Statistics for maximum crack width for each of the three populations, based on measurements made in 2004 and in 2006, are presented. In situ and laboratory measurements show that the 1943 concrete appears to have high permeability but it also shows high electrical resistivity. Chloride penetration measurements show the 1943 and 1993 concretes to have similar chloride profiles and similar chloride concentrations at the reinforcement bars. This is inconsistent with the 1943 beams showing much less reinforcement corrosion than their later replacements and casts doubt on the conventional practice for durability design focusing on reducing concrete permeability through denser concretes or greater cover.
Conventional Monte-Carlo integration for high reliability systems is extremely inefficient. It is possible to use a rather simple technique, known in the literature as importance sampling, to dramatically improve sampling efficiency (or the in the integral for a given amount of sampling). This technique, unlike some other variance reduction techniques, can be applied in a systematic manner to problems with one or more limit state functions, including unions and intersections of limit states. These applications as well as the theory, are outlined in this report. (Author/TRRL)
The evolution of corrosion loss and maximum pit depth of copper and copper alloys exposed for long periods of time in natural and industrial environments is shown to be more consistent with a bi-modal functional form than with the classical power law. Data from several long-term exposure test programs supports this proposition. The bi-modal behaviour signals a change from mainly cathodic oxygen reduction to a subsequent transitory corrosion process that may be modelled as involving pitting under earlier copper corrosion products. Possible reasons for some data sets showing decreasing maximum pit depths with increasing exposure time are discussed.
No abstract is provided for this article.
Keywords MONASH UNIVERSITY LOADS, STRUCTURAL, ELASTIC, PROPORTIONS, ULTIMATE, PROCEDURE, SERVICEABILITY, BENDING, UNITS, DEFLECTION, DESIGN, THEOREMS, BASIC, APPLIED, LIMIT STATE, ERRORS, MOMENTS, INTEGRATION, PLASTIC, SERVICE, LIMIT ANALYSIS, LIMITS, ANALYSIS, STRENGTH, DIRECT, LOWER BOUNDS, ESTIMATING, DIAGRAMS, FORMULAE... Show All
