Search

To present resistivity-based chloride-induced corrosion rate prediction models and hypothetical framework for interpretation of resistivity measurements in cracked RC structures. Parallel corrosion experiments were carried out by exposing one half of 210 beam specimens (120 × 130 × 375 mm) to accelerated laboratory corrosion (cyclic 3 days wetting with 5 % NaCl solution followed by 4 days air-drying) while the other half were left to undergo natural corrosion in a marine tidal zone. The specimens were cast using five concretes made using two w/b ratios (0.40 and 0.55) and three binders (100 % CEM I 42.5N (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). Corrosion rate and resistivity were monitored bi-weekly in the specimens. The results relevant to this paper are presented and discussed. Experimental results (both natural and accelerated) show that there is an inverse relationship between corrosion rate and concrete resistivity in both cracked and uncracked RC structures. The results also show that for a given concrete resistivity value, corrosion rate of steel in concrete of a given binder type and w/b ratio increases with increase in crack width. Furthermore, for a given crack width, corrosion rate in cracked concrete is also shown to be influenced by concrete quality. Resistivity-based chloride-induced corrosion rate prediction models for cracked RC structures are proposed. This paper also advocates for the improvement in the interpretation of concrete resistivity measurements with respect to steel corrosion in cracked RC structures. A hypothetical framework to aid in this is proposed. [ABSTRACT FROM AUTHOR]

The ability of cementitious and acrylic coatings to protect concrete against carbonation was investigated by subjecting coated and uncoated samples to accelerated UV loads and subsequently measuring accelerated carbonation. Based on the correlation between accelerated and equivalent natural carbonation an equivalent oxygen permeability index (OPI) value was calculated for the coated samples using previously established correlations between carbonation and oxygen permeability. The OPI in turn was used as an input parameter in a performance-based carbonation prediction model, which resulted in the quantification of additional service life offered by the various coatings, depending on cover depth and exposure condition. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Structures is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

Tensile relaxation characteristics are important for the crack resistance of concrete members subjected to restrained contraction, for example bonded overlays and patch repairs. In the experimental research discussed in this paper, relaxation characteristics were measured for mortar specimens subjected to constant strain which corresponded to stresses close to the tensile strength of the mortar. Relaxation was found to relieve a considerable portion of tensile stresses. Ultimate relaxation values ranged from 20 to 45%, depending on w/c ratio and specimen age. As expected, a decrease in specimen age and an increase in w/c ratio resulted in increasing relaxation values. The rate of stress decay was found to be rapid, with approximately 80% of the ultimate relaxation occurring in the first 12 h after loading. A basic equation for the prediction of time development of relaxation is proposed and future research needs are discussed. [ABSTRACT FROM AUTHOR]

Bonded concrete overlays are widely used for repair and strengthening of existing structures as well as for precast elements which receive an in-situ topping. The performance of such overlays relates mainly to their resistance to cracking and debonding. Associated failure mechanisms are a result largely of differential volume changes between substrate and overlay. The objective of this paper is to provide an analytical tool to facilitate the design of bonded overlays for crack-resistance when subjected to shrinkage restraint. Fundamental strain characteristics of composite members are identified and existing analytical models for the prediction of strains and stresses in bonded overlays are evaluated. Results from experimental work indicate that existing models, which are based on simple beam theory, are deficient in modelling overlay strains realistically. The degree of overlay restraint was found to depend far less on relative section dimensions of substrate and overlay than is commonly assumed. Based on fundamental aspects concerning strain characteristics of bonded overlays, an analytical prediction model is introduced, based on localised strain conditions at the interface. [ABSTRACT FROM AUTHOR]

To investigate the influence of concrete quality and drying duration on steel corrosion rate when cyclic wetting and drying is used to accelerate corrosion propagation. To inform future similar experimental work in the area of accelerated steel corrosion in concrete. Concrete prisms (100 × 100 × 240 mm) were made using two w/b ratios (0.40 and 0.65) and three binder types. After elimination of the corrosion initiation phase using an impressed current technique, the specimens were exposed to cycles of wetting (2 days) and drying (1, 3, 5, or 7 days). Steel corrosion rate was monitored using a coulostatic technique, over a period of ca. 170 days. Both the duration of drying and concrete quality profoundly affect corrosion rate of steel in concrete in a cyclic wetting and drying regime. A general inference from the results is that with drying, the denser microstructure concretes with high resistivity exhibited resistivity corrosion control while the less dense microstructure concretes with low resistivity exhibited both cathodic and resistivity corrosion controls. In accelerated corrosion testing using cyclic wetting and drying, the combined effects of concrete quality and drying duration need to be considered in determining corrosion rate. [ABSTRACT FROM AUTHOR]