• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.201-204
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• 2006

It should be noted that the critical chloride threshold level is not considered to be a unique value for all conditions. This value is dependent on concrete mix proportions, cement type and constituents, presence of admixtures, environmental factors, reinforcement surface conditions, and other factors. In this study, the accelerated corrosion test for reinforcing steel was conducted by electrochemical and cyclic wet and dry seawater method, respectively and during the test, corrosion monitoring by half-cell potential method was carried out to detect the time to initiation of corrosion for individual test specimen. For this purpose, lollypop and right hexahedron test specimens were made for 31%, 42%, and 50% of W/C, respectively, and then the accelerated corrosion test for reinforcing steel was executed. It was observed from the test that the time to initiation of corrosion was found to be different with the water-cement ratio and accelerated corrosion test method, respectively and the critical chloride threshold values were found to range from 0.91 to $1.47kg/m^3$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.4 no.4
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• pp.149-160
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• 2000

As systematic methodologies are required for the evaluation on the durability of reinforced concrete structure, it is necessary to study and examine every factor which deteriorates the durability of structures. This paper aims to define factors affecting rebar corrosion and to establish a basis for a prediction of serviceability, regarding a state of harmful corrosion as a state when crack begins on the surface of concrete. The study results are followings; The corrosive current has changed by types of mixture, and this property enables the evaluations of corrosion resistance by mixture and concrete cover. The specimen using AE superplasticizer has better corrosion-resistance properties than non-AE specimen, as well those having low W/C and high unit cement weight. The procedure for calculation of durable year in this study is able to use as an indicator to establish mixture factors such as unit cement weight, W/C, amount of admixture, etc.

• Computers and Concrete
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• v.15 no.4
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• pp.643-671
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• 2015

Chloride induced reinforcement corrosion is widely accepted to be the most frequent mechanism causing premature degradation of reinforced concrete members, whose economic and social consequences are growing up continuously. Prevention of these phenomena has a great importance in structural design, and modern Codes and Standards impose prescriptions concerning design details and concrete mix proportion for structures exposed to different external aggressive conditions, grouped in environmental classes. This paper focuses on reinforced concrete column section load carrying capacity degradation over time due to chloride induced steel pitting corrosion. The structural element is considered to be exposed to marine environment and the effects of corrosion are described by the time degradation of the axial-bending interaction diagram. Because chlorides ingress and consequent pitting corrosion propagation are both time-dependent mechanisms, the study adopts a time-variant predictive approach to evaluate residual strength of corroded reinforced concrete columns at different lifetimes. Corrosion initiation and propagation process is modelled by taking into account all the parameters, such as external environmental conditions, concrete mix proportion, concrete cover and so on, which influence the time evolution of the corrosion phenomenon and its effects on the residual strength of reinforced concrete columns sections.

• Steel and Composite Structures
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• v.29 no.6
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• pp.689-701
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• 2018

Corrosion of steel reinforcement is a principal cause of deterioration of RC columns. Making these corrosion-damaged columns conform to new safety regulations and functions is a tremendous technological challenge. This study presented an experimental investigation on steel-concrete jacketed corrosion-damaged RC columns. The influences of steel jacket thickness and concrete strength on the enhancement performance of the strengthened specimens were investigated. The results showed that the use of steel-concrete jacketing is efficient since the stub strengthened columns behaved in a more ductile manner. Moreover, the ultimate strength of the corrosion-damaged RC columns is increased by an average of 5.3 times, and the ductility is also significantly improved by the strengthening method. The bearing capacity of the strengthening columns increases with the steel tube thickness increasing, and the strengthening concrete strength has a positive impact on both bearing capacity, whereas a negative influence on the ductility. Subsequently, a numerical model was developed to predict the behavior of the retrofitted columns. The model takes into account corrosion-damage of steel rebar and confining enhancement supplied by the steel tube. Comparative results with the experimental results indicated that the developed numerical model is an effective simulation. Based on extensive verified numerical studies, a design equation was proposed and found to predict well the ultimate eccentric strength of the strengthened columns.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1035-1040
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• 2001

Recently, Sea-sand containing high levels of chloride is being applied to on reinforced concrete structures due to the exhaustion of river-sand and environmental problems, which affects directly corrosion of rebar in the RC structures. In this paper, characteristics of corroded rebar before and after casting were studied. Test results showed that bond strength of rebar corroded after casting was decreased with increase of corrosion level more rapidly than that of rebar corroded before casting.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.418-421
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• 1996

Carbon Fiber Sheet is very attractive for the upgrading damaged reinforced concrete due to its good tensile strength, handabilbity and resistance to corrosion. This paper discusses the applicability of continous carbon fiber sheet for a reinforcement of existeing reinforced concrete structure located in Pusan. Examples of site data and actual concrete rehabilitation project at slab structure related to construction method used carbon fiber sheet will be given.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.643-648
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• 1998

Despite many advantages of FRP materials, such as corrosion resistance, their linear elastic behavior up to rupture is likely to result in a lack of ductility. This paper discusses ductility improvement methods for prestressed concrete beams using FRP tendons. The methods were evaluated thorough extensive analytical and experimental investigations. The methods include optimization of sectional ductility through proper reinforcement, concrete confinement, concrete reinforcement with fibers, and prestressing with unbonded tendons.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.693-696
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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. It is , however, well known that moderate or minor cracks in reinforced concrete should be most serious causes to deteriorate the durability of RC structures. Furthermore, chloride contents penetrating through unexpected cracks in reinforced concrete bridges get to weaken corrosion resistance of reinforcement steel in concrete and than to accelerate the deterioration of concrete durability. The objective of this experimental research is 1) to evaluate the effect of various corrosion protection system for reinforced concrete specimens with moderate or minor cracks which are exposed to cyclic wet and dry seawater, and then 2) to develop effective corrosion protection system for reinforced concrete bridges under the exposure of various detrimental environments such as seawater, deicing and etc.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.158-162
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• 1994

Test results to evaluate the mechanical properties of epoxy-coated bars and corrosion protection characteristics of epoxy coating on the bars are described. The results show good adhesion and abrasion resistance satisfying the requirements in relevant standards. The test results also show that for a coating thickness ranging from 150${\mu}{\textrm}{m}$ to 300${\mu}{\textrm}{m}$, satisfactory results are obtained regarding bendability. Cautions shall be required when bending epoxy-coated bars at a high bending degree and at a low temperature. The results of accelerated corrosion tests show good corrosion resistance. However, surface defects from the steel itself and insufficient blast-clean process form weak points resulting blistering or disbonding of the coating. The use of epoxy-coated bars is expected to help protect corrosion of reinforcement and extend the service life of reinforced concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.203-206
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• 1998

In reinforced concrete carbonation of concrete leads to depassivation of the reinforcement, and hence to initiation of corrosion. As a result of carbonation accelerating experiment with using effect of wet-dry cycle and 15% concentration of CO ₂, the carbonation rate shows very distinct difference according to W/C ratio. OPC-40 estimated no carbonation depth, whereas OPC-60 estimated rapidly the carbonation rate. The comparative analysis of the carbonation rate accelerating depends on different kinds of cement shows fastest FAC-20. Also, highly W/C ratio's concrete shows low half-cell potential value and fast corrosion rate. During period for 14 weeks. corrosion rate was not severe. So, it can be concluded that only carbonation attack on concrete doesn't severly deteriorated except very poor qualitified concrete.