The Experts below are selected from a list of 10143 Experts worldwide ranked by ideXlab platform
Ki Yong Ann - One of the best experts on this subject based on the ideXlab platform.
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Numerical Prediction of Chloride Penetration in Concrete Exposed to a Marine Environment at Tide
Hindawi Limited, 2018Co-Authors: Sung In Hong, Ki Yong AnnAbstract:Reinforced concrete structures under cyclic exposure to the corrosive environment such as the tidal zone as a part of marine structure entail the higher risk of steel corrosion. In this paper, Chloride penetration in concrete exposed to the tidal zone was predicted using a combined moisture and Chloride transport model. For the analysis of moisture transport, pore size distribution in concrete was determined from the experimental observation and used to determine the moisture permeability and degree of saturation. Then, the Chloride Profile through nonsaturated concrete cover was calculated by applying the moisture distribution along the penetration depth to the Chloride convection and diffusion model. To assess sensitivity of the service life to the environment and concrete mix conditions, this study used three types of tide levels and water to cement ratios in the simulation. Under 10 years of tidal exposure condition, the minimum required cover depth at which the threshold Chloride concentration reaches on the steel embedment increases only about 1.13 times as the tide level increases from the minimum to the highest while that for the w/c ratio increases about 1.69 times
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Influence of cementitious binder on Chloride removal under electrochemical treatment in concrete
Construction and Building Materials, 2016Co-Authors: Ki Beom Kim, Jun Pil Hwang, Ki Yong AnnAbstract:Abstract The present study concerns electrochemical treatment to extract Chloride ions and to repassivate the corroded steel in Chloride-contaminated concrete. As binder, ordinary Portland cement (OPC), ground granulated blast furnace slag (GGBS) and pulverised fuel ash (PFA) were used to produce different concrete mixes: OPC, GGBS and ternary mix containing the three binders, respectively. After 56 days of curing, a DC was supplied to the concrete specimens, ranging 250, 500 and 750 mA/m 2 for 4 weeks. Then, the corrosion rate was measured by the anodic polarisation. In fact, an increase in the current density applied to the specimens resulted in a decrease in the corrosion rate, imposing a reduction of the corrosiveness of steel in concrete. For a change in the Chloride Profile, a removal of Chlorides at the depth of the steel was more significant in GGBS and ternary mixes, presumably due to a release of adsorbed Chlorides on the hydration surface into free, which was further removed under electric charge. However, all Chlorides could not be removed by the immobility of Chlorides chemically bound into chloroaluminate and chloroferrite hydrates; a mostly half of Chlorides in cast were, in fact, present even after the treatment.
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the importance of Chloride content at the concrete surface in assessing the time to corrosion of steel in concrete structures
Construction and Building Materials, 2009Co-Authors: Ki Yong Ann, J H Ahn, Jaesuk RyouAbstract:Abstract A literature review in the present study has shown that the Chloride ions on the concrete surface exposed to a marine environment including tidal, splash and aerated zones can be accumulated then to increase with time. In order to take this effect into account in a model prediction of the rate of Chloride ingresses in concrete, the surface Chloride was expressed as a function of time such that (1) constant, (2) linear build-up, (3) square root build-up and (4) square root build-up with an initial set of the surface Chloride (a refined model), at a given diffusion coefficient (2 × 10 −12 m 2 /s). As a result, the constant surface Chloride model produced the greatest level of Chloride penetration, as an initial set of the surface Chloride content was overestimated. The rate of Chloride ingresses derived from the highest surface Chloride led to the greatest risk of Chloride-induced corrosion of steel in concrete, whereas the linear and square root build-up models indicated 2–3 times longer duration of corrosion-free service life. The refinement of a surface Chloride build-up suggested a more realistic prediction of Chloride Profile and corrosion risk, thereby imposing the rate of Chloride ingresses between the constant surface Chloride, and linear or square root build-up.
Feng Xing - One of the best experts on this subject based on the ideXlab platform.
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Chloride transport and microstructure of concrete with without fly ash under atmospheric Chloride condition
Construction and Building Materials, 2017Co-Authors: Jun Liu, Qiwen Qiu, Xiaochi Chen, Jing Hong, Feng XingAbstract:Abstract This paper presents a comprehensive investigation regarding the Chloride transport and microstructure of plain concrete and fly ash blended concrete under atmospheric Chloride environment. Experimental results demonstrate that all the free, bound, and total Chlorides show a build-up of ion concentration in the Chloride Profile. A linear relationship between the total and free Chloride content is observed. Both water-to-cement ratio and fly ash content have great impact on the Chloride binding capacity and the Chloride diffusion coefficient. Microscopic properties (e.g. morphology, pore size distribution, porosity) are evaluated for Chloride-contaminated concrete, and their correlation with the Chloride transport behavior is discussed.
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understanding the interacted mechanism between carbonation and Chloride aerosol attack in ordinary portland cement concrete
Cement and Concrete Research, 2017Co-Authors: Jun Liu, Qiwen Qiu, Xiaochi Chen, Feng Xing, Ningxu HanAbstract:Abstract An experimental study is carried out with the aim to understand the interacted mechanism between carbonation and Chloride aerosol attack in ordinary Portland cement (OPC) concrete. Effects of carbonation on the Chloride Profile, the Chloride binding capacity and the Chloride diffusion coefficient are evaluated. Besides, effect of Chloride aerosol attack on the carbonation rate is investigated. Concrete specimens with three water-to-cement ratios (0.38, 0.47 and 0.53) are fabricated in this work. Tested results demonstrate that carbonation remarkably affects the Chloride Profile, reduces the Chloride binding capacity, and also accelerates the rate of Chloride ion diffusion of concrete. Besides, the presence of Chloride aerosol can lead to lower the carbonation depth and increase the pH value of carbonated concrete. Microscopic properties such as morphology, porosity, and pore size distribution for the contaminated concretes are explored by scanning electron microscope and mercury intrusion porosimetry, which provide strong evidence to these research findings.
O. Alvarado - One of the best experts on this subject based on the ideXlab platform.
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Experimental and numerical study of electrochemical Chloride removal from brick and concrete specimens
Cement and Concrete Research, 2007Co-Authors: Ahmed Toumi, Raoul François, O. AlvaradoAbstract:The electrochemical technique for Chloride extraction (desalination) was applied in galvanostatic mode to cylindrical brick and concrete specimens with a steel bar as reinforcement placed in the centre. The specimens were initially contaminated by immersion in a solution of 35 g/l NaCl. Based on the Nernst–Planck equations, a numerical model was developed considering the interactions between the various ionic species in the pore solution. The model makes it possible to predict the evolution of the Chloride Profile with time. The numerical and experimental results are compared and the model parameters discussed.
Andrew Fahim - One of the best experts on this subject based on the ideXlab platform.
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performance of high volume fly ash concrete in marine environment
Cement and Concrete Research, 2017Co-Authors: Edward G Moffatt, Michael D.a. Thomas, Andrew FahimAbstract:Abstract This paper presents the durability performance of concrete incorporating high-volumes of fly ash exposed to a harsh marine environment for 19 to 24 years. Concrete specimens (305 × 305 × 915 mm [1 × 1 × 3 ft.]) were cast using W/CM in the range of 0.31 to 0.46, various types of fly ash with replacement levels of 56 or 58%, and various types of normal density and lightweight aggregates. Surface erosion/scaling was seen on all specimens; the extent of erosion was slightly worse for fly ash concrete with normal density aggregate compared to the controls (without fly ash), but fly ash concrete with two of the three lightweight aggregates exhibited severe surface erosion. Laboratory testing included taking cores from each block and determining the existing Chloride Profile, compressive strength and “Chloride permeability” (ASTM C1202). The depth of Chloride penetration was found to be in excess of 100-mm (4 in.) for the concrete specimens without fly ash, whereas the presence of fly ash significantly decreased the depth of penetration to approximately 30 and 40 mm in specimens containing either normal density or lightweight aggregate, respectively. The increased penetration in the concrete with lightweight aggregates is attributed to the surface erosion observed with these concretes. The results from the Chloride permeability testing also indicate significant increases in the resistance to Chloride-ion penetration for fly ash concrete.
Ouali Amiri - One of the best experts on this subject based on the ideXlab platform.
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study of electrical double layer effect on Chloride transport in unsaturated concrete
Construction and Building Materials, 2014Co-Authors: Phu Tho Nguyen, Ouali AmiriAbstract:In this paper, a physical model of Chloride ingress concretes is proposed. The originality of the model lies in its consideration of electrical double layer (EDL) phenomenon in unsaturated concrete. The EDL is occurring at the interface between pore walls and pore solution. The work is performed by solving the multispecies ionic transport equations coupled with those of humidity. To show the effect of slag and fly ash, several concretes were considered. The Chloride Profile was simulated. The results show that Chloride concentration increase for EDL negative more than EDL positive. The EDL effect is reduced in unsaturated concrete due to discontinuity of liquid phase. Finally, it is also shown that the concrete containing slag develops and EDL more important than those manufactured with fly ash.