• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.821-826
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• 2000

Reinforced concrete is in general known as high durability construction material under normal environments due to strong alkalinity of cement. Marine concrete specimens in the tidal and the splash zone at seashore have been exposed to cyclic wet and dry saltwaters which cause to accelerate corrosion of reinforcing steel in concrete. If corrosion resistance of concrete gets to weaken de to carbonations and cracks in cover concrete, furthermore, concrete durability rapidly decreases by the corrosion of reinforcement steel embeded in concrete. The objective of this study is to develop appropriate corrosion protection systems of marine concrete so as to enhance the durability of concrete by establishing pertinent cover depth of concrete and by using corrosion inhibitors as concrete admixtures.

• Advances in concrete construction
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• v.7 no.3
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• pp.167-174
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• 2019

Metakaolin (MK), which is increasingly being used to produce high performance concrete, is produced by calcining purified kaolinite between 650 and $700^{\circ}C$ in a rotary kiln. The carbonation resistance of metakaolin blended concrete is lower than that of control concrete. Hence, it is critical to consider carbonation durability for rationally using metakaolin in the concrete industry. This study presents microstructure modeling during the carbonation of metakaolin blended concrete. First, based on a blended hydration mo del, the amount of carbonatable substances and porosity are determined. Second, based on the chemical reactions between carbon dioxide and carbonatable substances, the reduction of concrete porosity due to carbonation is calculated. Furthermore, $CO_2$ diffusivity is evaluated considering the concrete composition and exposed environment. The carbonation depth of concrete is analyzed using a diffusion-based model. The proposed microstructure model takes into account the influences of concrete composition, concrete curing, and exposure condition on carbonation. The proposed model is useful as a predetermination tool for the evaluation of the carbonation service life of metakaolin blended concrete.

• Structural Engineering and Mechanics
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• v.64 no.2
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• pp.243-257
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• 2017

Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of high-strength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

• Steel and Composite Structures
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• v.45 no.5
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• pp.749-766
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• 2022

This paper investigates the seismic performance of exposed RCFST column-base joints, in which the high-strength steel bars (USD 685) are set through the column and reinforced concrete foundation without any base plate and anchor bolts. Three specimens with different axial force ratios (n = 0, 0.25, and 0.5) were tested under cyclic loadings. Finite element analysis (FEA) models were validated in the basic indexes and failure mode. The hysteresis behavior of the exposed RCFST column-base joints was studied by the parametrical analysis including six parameters: width of column (D), width-thickness ratio (D/t), axial force ratio (n), shear-span ratio (L/D), steel tube strength (f_y) and concrete strength (f_c). The bending moment of the exposed RCFST column-base joint increased with D, f_y and f_c. But the D/t and L/D play a little effect on the bending capacity of the new column-base joint. Finally, the calculation formula is proposed to assess the bending moment capacities, and the accuracy and stability of the formula are verified.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.755-758
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• 1999

Reinforced concrete is in general known as high durability construction material under normal environments due to strong alkalinity of cement. Marine and harbour concrete in the tidal and the splash zone at seashore are exposed to cyclic wet and dry saltwaters which cause to accelerate corrosion of reinforcing steel in concrete. If corrosion resistance of concrete gets to weaken due to carbonations and cracks in cover concrete, furthermore, concrete durability rapidly decreases by corrosion of reinforcement steel embedded in concrete. The objective of this study is to develop appropriate corrosion protection systems so as to enhance the durability of concrete by controlling the cover depth of concrete and by using corrosion inhibitors as concrete admixtures.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.241-247
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• 1997

Reinforced concrete is in general known as high durability construction material under normal enviroments due to strong alkalinity of cement. Marine and harbour concrete as well as concrete mixed with seasand for fine aggregate are exposed to detrimental saltwater wich cause to accel-eate corrosion of reinforcing steel in concrete. If corrosion resistance of concrete gets to weaken due to carbonation and crack in cover concrete, concrete durability rapidly decrease by corrosion of reinforcement steel embedded in concrete. This research is to investigate basic physical properties of various corrosion inhibitors and to evaluate their corrosion resistance in concrete mixed with seasand. The object of this study is develop appropriate corrosion protection systems so as to enhance the durability of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.747-750
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• 1999

Chloride ions are considered to be the major cause of steel corrosion in concrete structures exposed to seashore environments. Thus, estimating chloride ion concentrations by ages is needed to predict service life of seashore structures. Experimentally measured chloride profiles were used in this study for estimating chloride diffusion coefficients, and a relationship between mixing properties and chloride diffusion coefficients is proposed for predicting chloride penetrations.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.514-519
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• 2004

The paper discusses the general behavior of fire-damaged slender reinforced concrete columns on the basis of results obtained from parametric studies. Effects of slenderness ratio, concrete strength, cover thickness, reinforcement ratios, exposed time to fire, and eccentricity on the ultimate capacity of fire-damaged column are theoretically observed. With the increase of slenderness ratio, similar tendency of relative strength reduction was observed between fire-damaged columns and columns at room temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.625-628
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• 2003

This paper presents the behaviors of reinforced concrete columns under high temperature. When columns are exposed high temperature, temperature distribution of a section becomes nonlinear and it is calculated by using finite difference method(F.D.M). The interaction curves show the strength of columns at various exposure times. The strength of columns decreases according to the increase of the exposure time and the decrease of concrete cover.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.475-476
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• 2010

Hydration products formed on the steel surface may impose the resistance to corrosion of steel when a concrete is exposed to a salt environment. In the present study, ordinary Portland cement (OPC), calcium aluminate cement (CAC) and calcium hydroxide are applied as coating materials on the steel surface to consider the hydrations of each binder at corrosion. Corrosion is measured in terms of the corrosion potential and galvanic current to detect the effects in mitigating the corrosion behavior.