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M G Alexander - One of the best experts on this subject based on the ideXlab platform.
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chloride induced corrosion of steel in cracked Concrete part ii corrosion rate prediction models
Cement and Concrete Research, 2016Co-Authors: Mike Otieno, H Beushausen, M G AlexanderAbstract:Chloride-induced corrosion rate (i sub corr) prediction models for reinforced Concrete (RC) structures in the marine tidal zone that incorporate the influence of crack width (w sub cr), cover (c) and Concrete Quality are proposed. Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in the tidal zone. Experimental variables were w sub cr (0, incipient crack, 0.4, 0.7 mm), c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). The two proposed models (one each for accelerated and natural i sub corr) can aid not only in quantifying the propagation phase, but also provide a novel way to select c, w sub cr and Concrete Quality.
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chloride induced corrosion of steel in cracked Concrete part i experimental studies under accelerated and natural marine environments
Cement and Concrete Research, 2016Co-Authors: Mike Otieno, H Beushausen, M G AlexanderAbstract:Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in a marine tidal zone. Experimental variables were crack width w sub cr (0, incipient crack, 0.4, 0.7 mm), cover c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). Results show that corrosion rate (i sub corr) was affected by the experimental variables in the following manner: i sub corr increased with increase in crack width, and decreased with increase in Concrete Quality and cover depth. The results also show that the corrosion performance of Concretes in the field under natural corrosion cannot be inferred from its performance in the laboratory under accelerated corrosion. Other factors such as corrosion process should be taken into account.
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corrosion in cracked and uncracked Concrete influence of crack width Concrete Quality and crack reopening
Magazine of Concrete Research, 2010Co-Authors: M G Alexander, H BeushausenAbstract:Cracks influence the durability of reinforced Concrete (RC) structures in aggressive environments by accelerating the ingress of corrosive agents to the embedded steel. This study investigated the influence of crack width (0·7 mm, 0·4 mm and incipient cracks), binder type (100% CEM I (ordinary Portland cement – OPC) and 50/50 OPC/Corex slag blend), water-to-binder (w/b) ratio (0·40 and 0·55) and crack reopening on chloride-induced corrosion in RC specimens with constant cover of 40 mm. Over the study period (31 weeks), corrosion rates varied from passive values of 0·01 μA/cm2 to active values of 1·50 μA/cm2. Results indicate that corrosion rate is sensitive to crack width, Concrete Quality (i.e. binder type and w/b ratio) and crack reopening. For a given binder type and w/b ratio, corrosion rate increased with increasing crack width; however, this increase was smaller in Corex slag specimens (increases of 40% or more) than in OPC specimens (increases 210% or more). Corex slag specimens generally had lower...
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a framework for use of durability indexes in performance based design and specifications for reinforced Concrete structures
Materials and Structures, 2008Co-Authors: M G Alexander, Y Ballim, K StanishAbstract:Durability of reinforced Concrete remains a pervasive concern. At present, as-built Concrete Quality and hence durability is inadequate in many cases. This relates partly to use of prescriptive specifications that do not appropriately address actual Quality concerns. Performance-based specifications may offer greater advantages in improving Concrete durability, but to be viable require suitable Quality parameters to be defined and measured. In South Africa, a ‘Durability Index’ (DI) approach has been developed to address these concerns. ‘Durability indexes’ are quantifiable parameters which characterise Concrete Quality and are sensitive to material, processing, and environmental factors. The approach is based on measurement of transport-related properties of the cover layer of laboratory and in-situ Concrete, thus reflecting the dual aspects of material potential and construction Quality. Rational durability design and performance-based durability specifications are being developed and in some cases applied in actual construction. The paper presents a framework within which the DI approach is used to craft performance-based specifications, based on service life models that utilise the relevant DI values. Steps to establish appropriate DI test values for a given structure are described, and a procedure for implementing their use as a Quality control measure is recommended. The approach is integrated, allowing for continual improvement and modification as additional data become available.
Shamsad Ahmad - One of the best experts on this subject based on the ideXlab platform.
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reinforcement corrosion in Concrete structures its monitoring and service life prediction a review
Cement & Concrete Composites, 2003Co-Authors: Shamsad AhmadAbstract:Reinforcement corrosion has been widely reported in the literature over the last two to three decades. It is one of the major durability problems, mainly when the rebar in the Concrete is exposed to the chlorides either contributed from the Concrete ingredients or penetrated from the surrounding chloride-bearing environment. Carbonation of Concrete or penetration of acidic gases into the Concrete, are the other causes of reinforcement corrosion. Besides these there are few more factors, some related to the Concrete Quality, such as w/c ratio, cement content, impurities in the Concrete ingredients, presence of surface cracks, etc. and others related to the external environment, such as moisture, oxygen, humidity, temperature, bacterial attack, stray currents, etc., which affect reinforcement corrosion. The assessment of the causes and extent of corrosion is carried out using various electrochemical techniques. Prediction of the remaining service life of a corroding RC structure is done with the help of empirical models and experimental methods. In this paper a review is presented on the mechanism of reinforcement corrosion, techniques utilized to monitor reinforcement corrosion and methodologies that are utilized for the prediction of remaining service life of structures.
Mark G Stewart - One of the best experts on this subject based on the ideXlab platform.
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predicting the likelihood and extent of reinforced Concrete corrosion induced cracking
Journal of Structural Engineering-asce, 2005Co-Authors: Kim Vu, Mark G StewartAbstract:Corrosion-induced cracking is observed to vary spatially over Concrete surfaces. A two-dimensional spatial time-dependent reliability model is developed to predict the likelihood and extent of corrosion-induced cracking. The spatial variability of Concrete cover, Concrete compressive strength, and surface chloride concentration are considered in the spatial time-dependent reliability model. The reliability analysis predicts: (1) probability of the first incidence of cracking, (2) proportion of an area subject to severe cracking, and (3) probability that a given percentage of a Concrete surface has cracked. Corrosion-induced crack initiation and propagation models are developed for limit crack widths up to 1 mm. The present paper presents results for a typical reinforced Concrete bridge deck. The effect of Concrete cover, Concrete Quality, limit crack width, and environment are considered. It was shown that for poor durability design specifications the likelihood and extent of spalling is high. When combined with a life-cycle cost analysis, this predictive capability enables the extent of future repair costs to be estimated and the optimal durability design specifications or repair/maintenance strategies determined.
Mike Otieno - One of the best experts on this subject based on the ideXlab platform.
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chloride induced corrosion of steel in cracked Concrete part ii corrosion rate prediction models
Cement and Concrete Research, 2016Co-Authors: Mike Otieno, H Beushausen, M G AlexanderAbstract:Chloride-induced corrosion rate (i sub corr) prediction models for reinforced Concrete (RC) structures in the marine tidal zone that incorporate the influence of crack width (w sub cr), cover (c) and Concrete Quality are proposed. Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in the tidal zone. Experimental variables were w sub cr (0, incipient crack, 0.4, 0.7 mm), c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). The two proposed models (one each for accelerated and natural i sub corr) can aid not only in quantifying the propagation phase, but also provide a novel way to select c, w sub cr and Concrete Quality.
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chloride induced corrosion of steel in cracked Concrete part i experimental studies under accelerated and natural marine environments
Cement and Concrete Research, 2016Co-Authors: Mike Otieno, H Beushausen, M G AlexanderAbstract:Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in a marine tidal zone. Experimental variables were crack width w sub cr (0, incipient crack, 0.4, 0.7 mm), cover c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). Results show that corrosion rate (i sub corr) was affected by the experimental variables in the following manner: i sub corr increased with increase in crack width, and decreased with increase in Concrete Quality and cover depth. The results also show that the corrosion performance of Concretes in the field under natural corrosion cannot be inferred from its performance in the laboratory under accelerated corrosion. Other factors such as corrosion process should be taken into account.
H Beushausen - One of the best experts on this subject based on the ideXlab platform.
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chloride induced corrosion of steel in cracked Concrete part ii corrosion rate prediction models
Cement and Concrete Research, 2016Co-Authors: Mike Otieno, H Beushausen, M G AlexanderAbstract:Chloride-induced corrosion rate (i sub corr) prediction models for reinforced Concrete (RC) structures in the marine tidal zone that incorporate the influence of crack width (w sub cr), cover (c) and Concrete Quality are proposed. Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in the tidal zone. Experimental variables were w sub cr (0, incipient crack, 0.4, 0.7 mm), c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). The two proposed models (one each for accelerated and natural i sub corr) can aid not only in quantifying the propagation phase, but also provide a novel way to select c, w sub cr and Concrete Quality.
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chloride induced corrosion of steel in cracked Concrete part i experimental studies under accelerated and natural marine environments
Cement and Concrete Research, 2016Co-Authors: Mike Otieno, H Beushausen, M G AlexanderAbstract:Parallel corrosion experiments were carried out for 2¼ years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in a marine tidal zone. Experimental variables were crack width w sub cr (0, incipient crack, 0.4, 0.7 mm), cover c (20, 40 mm), binder type (PC, PC/GGBS, PC/FA) and w/b ratio (0.40, 0.55). Results show that corrosion rate (i sub corr) was affected by the experimental variables in the following manner: i sub corr increased with increase in crack width, and decreased with increase in Concrete Quality and cover depth. The results also show that the corrosion performance of Concretes in the field under natural corrosion cannot be inferred from its performance in the laboratory under accelerated corrosion. Other factors such as corrosion process should be taken into account.
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Towards incorporating the influence of cover cracking on steel corrosion in RC design codes: the concept of performance-based crack width limits
Materials and Structures, 2012Co-Authors: M. Otieno, H Beushausen, M. AlexanderAbstract:This paper advocates for the adoption of performance-based limiting crack widths with respect to steel corrosion in reinforced Concrete structures. The authors argue that, from both durability and sustainability viewpoints, the practice of adopting a universal limiting crack width for a wide range of in-service exposure conditions and Concrete cover conditions and Quality is not valid. As new performance-based Concrete design codes are being developed and/or improved, the influence of cover cracking on steel corrosion needs to be incorporated in these codes. An experimental set-up was designed to investigate the influence of cover cracking, cover depth and Concrete Quality on chloride-induced corrosion. Beam specimens (120 × 130 × 375 mm) were cast using five Concretes made using two w/b ratios (0.40 and 0.55) and three binders (100 % CEM I 42.5 N (PC), 50/50 PC/GGBS and 70/30 PC/FA). Other variables in the experiments included cover depth (20 and 40 mm), crack width (0, 0.4 and 0.7 mm). A total of 105 beam specimens were cast and exposed to cyclic 3-days wetting (with 5 % NaCl solution) and 4-days air-drying in the laboratory (23 °C, 50 % relative humidity). Corrosion rate was monitored bi-weekly in the specimens. The results relevant to this paper are presented and discussed. For a given Concrete Quality and cover depth, corrosion rate increased with increasing crack width. If crack width and cover depth are kept constant, corrosion rate increases with decreasing Concrete Quality, and vice versa. A model framework that can be used to objectively select cover depth, Concrete Quality and crack width is proposed. Such a model can be improved into, for example, a nomograph and used in the design process for RC structures prone to corrosion. Performance-based crack width limits should be adopted in the design of RC structures prone to steel corrosion. These crack width limits should be dependent on a complex interaction of, inter alia, Concrete Quality, cover depth, crack characteristics and prevailing exposure conditions. This study showed the inter-relationship between crack width, cover depth and Concrete Quality in affecting chloride-induced corrosion rate. Accurate corrosion rate prediction models incorporating the influence of cover cracking on corrosion are a pre-requisite to implementing the influence of cover cracking in future Concrete design codes.
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corrosion in cracked and uncracked Concrete influence of crack width Concrete Quality and crack reopening
Magazine of Concrete Research, 2010Co-Authors: M G Alexander, H BeushausenAbstract:Cracks influence the durability of reinforced Concrete (RC) structures in aggressive environments by accelerating the ingress of corrosive agents to the embedded steel. This study investigated the influence of crack width (0·7 mm, 0·4 mm and incipient cracks), binder type (100% CEM I (ordinary Portland cement – OPC) and 50/50 OPC/Corex slag blend), water-to-binder (w/b) ratio (0·40 and 0·55) and crack reopening on chloride-induced corrosion in RC specimens with constant cover of 40 mm. Over the study period (31 weeks), corrosion rates varied from passive values of 0·01 μA/cm2 to active values of 1·50 μA/cm2. Results indicate that corrosion rate is sensitive to crack width, Concrete Quality (i.e. binder type and w/b ratio) and crack reopening. For a given binder type and w/b ratio, corrosion rate increased with increasing crack width; however, this increase was smaller in Corex slag specimens (increases of 40% or more) than in OPC specimens (increases 210% or more). Corex slag specimens generally had lower...