• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.12-23
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• 2024

In this study, a structural concrete square beam was developed using the centrifugal molding technique. In order to secure the bending stiffness of the cross section, the hollow rate of the cross section was set to 10% or less. Instead of using the current poor mixture of concrete and a concrete mixing ratio with a high slump (150-200) and a design strength of 100 MPa or more was developed and applied. In order to investigate the durability of centrifugally formed PSC square beams to be used as the superstructure of the avalanch tunnel or ramen bridge, the durability performance of ultra-high-strength centrifugally formed concrete with a compressive strength of 100 MPa was evaluated in terms of deterioration and chemical resistance properties.Concrete durability tests, including chloride penetration resistance, accelerated carbonation, sulfate erosion resistance, freeze-thaw resistance, and scaling resistance, were performed on centrifugally formed square beam test specimens produced in 2022 and 2023. Considering the information verified in this study, the durability of centrifugally molded concrete, which has increased watertightness in the later manufacturing stage, was found to be superior to that of general concrete.

• Magazine of the Korea Concrete Institute
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• v.7 no.6
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• pp.209-215
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• 1995

Corrosion of steel reinforcment is the most significant factor of deterioration in reinforced concrete structures. Chloride ion is considered one of the most common culprits in the corrosion of steel in concrete. It breaks down the passive film and allows the steel to corrode actively at a high rate. The main objective of this study is to determine the critical chloride ion concentrations in the pore solutions and chloride binding effect of cement pastes made with and without fly ash. Cement pastes with water-binder ratio of 0.5, allowed to hydrate in sealed containers for 28 days and to express pore solution. The expressed pore fluids were analyzed for chloride and hydroxyl ion concentrations. Evaporable water on paralled specimens was determined a.s the loss of weight per 100g of unhydreded cement when the specimens were heated to constant weight at 105'C. It was found that the replaced cement with fly ash has negligible influnce on the chloride binding and chloride binding capacity and rises the $Cl^-$ /$OH^-$ ratio in pore solution.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.769-772
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• 2008

Pores can become factors of reducing the capacity of concrete by being path of degradation factors and moisture can fill up pores inside of concrete, so evaluating the effect of unidirectional permeability due to moisture on pore structure of concrete structure is very important. Therefore, the change of pore structure in cases of 0%, 40%, 60%, 80% and 90% humidity being maintained on test specimens and in case of Lithium Silicate, which is chemical compound, being coated were evaluated. As a result, the condensation due to moisture could be confirmed since unidirectional permeability was decreased and the density of Pore Structure was improved as the percentage of water content was being increased. And, solution-type Lithium Silicate fills up pores of sizes around 1$\mu$m in the condition of carrying water and improves the density but the range of capacity improvement due to osmosis will be limited according to functional conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.104-111
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• 2013

Deterioration is accelerated due to additional intrusion of chloride ion in crack width in cracked concrete. In this paper, modeling on equivalent diffusion coefficient in cracked concrete is performed for 1-D (Anisotropic) and 2-D (Isotropic) diffusion based on steady state condition. In the previous research, rectangular shape of crack was considered but the shape was modified to wedge shape with torturity. For verification of the proposed model, crack is induced in concrete sample and migration test in steady state is performed for 1-D diffusion. For 2-D diffusion, previous test results are adopted for verification. Through considering wedge shape of crack with torturity, diffusion coefficients in 1-D and 2-D diffusion are reduced, and the more reasonable prediction is obtained. The results from the proposed model with torturity of 0.10~0.15 are shown to be in the best agreement with the test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.501-504
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• 2008

A concrete carbonation model has been constructed that takes account of the diffusion of carbon dioxide through a coating and reaction with calcium hydroxide, and this model has been validated by an accelerated carbonation experiment. (1) By using values for the coatings calculated on the basis of a diffusion.permeation theory as input data for the analysis of diffusion.reaction carbonation in an unsteady state, the effect of the coatings in reducing carbonation can be represented with high accuracy. (2) Through a sensitivity analysis of the diffusion.reaction carbonation model and the experimental results, we found that the diffusion coefficient of calcium hydroxide shows a high interrelationship at 1e-12($m^2/s$). The reaction rate constant for carbonation shows a high interrelationship at 5e-5($m^3/mol/s$).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.6
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• pp.575-582
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• 2008

Carbonation is one of major factors influencing on the durability of concrete structure. This paper investigates the effect of carbonation on the soundness of harbor concrete structure and quantifies the influence of carbonation based on in-situation data tested at 369 points in 69 harbor facilities. The relationships between carbonation depth and cover depth, and between carbonation depth and compressive strength are studied and the failure probability of durability, that is the initiation probability of steel corrosion, is evaluated on the basis of reliability concept. The in-situation test results showed that the ratio of carbonation depth to cover depth was less than 0.2, and the carbonation depth increased with age. In most cases, the failure probability of durability by carbonation was less than 10%. Therefore, it can be concluded that the influence of carbonation on the durability of harbor concrete structure is smaller than other factors deteriorating the durability of harbor concrete structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.197-205
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• 2020

In 2014, The Housing Act amended to allows vertical extension and increases the units of housing (or total floor area) to site. Currently, the feasibility of performing vertical extension is evaluated based on safety diagnosis provisions and manuals with 1st investigation stage on slope, uneven settlement, load-bearing capacity, and durability. However, a need for more reasonable evaluation criteria for the investigation is still required because there had not been any other case study on the diagnosis for the vertical extension, and the engineering basis on evaluation criteria were not suggested. Accordingly, this study is intended to suggest feasible evaluation criteria on the carbonation, chloride ion contents, corrosion of reinforcements, crack and surface deterioration of concrete for durability assessment by codes and standards of domestic and foreign countries. The results of this study are expected to be beneficial for establishing more reasonable durability evaluation criteria, and in turn, more reliable assessment protocol for vertical extension.

• The Journal of Engineering Geology
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• v.12 no.1
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• pp.95-109
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• 2002

A significant question is what role does newly-formed expansive mineral growth play in the premature deterioration of concrete. These minerals formed in cement paste as a result of chemical reactions involving cement paste and coarse/fine aggregate. Petrographic observations and SEM/EDAX analysis were conducted in order to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from lowa concrete highways that showed premature deterioration. Formation and expansive mechanisms involved in deterioration were Investigated. Brucite, Mg(OH)$_2$, is potentially expansive mineral that farms in cement paste of concretes containing reactive dolomite aggregate as a result of partial dedolomitization of the aggregate. No cracking was observed to be spatially associated with brucite, but most brucite was microscopic in size and widely disseminated in the cement paste of less durable concretes. Expansion stresses associated with its growth at innumerable microlocations may be retrieved by cracking at weaker locations in the concrete. Ettringite, 3CaO.Al$_2$O$_3$.3CaSO$_4$.32$H_2O$, completely fills many small voids and occurs as rims lining the margin of larger voids. Microscopic ettringite is common disseminated throughout the paste in many samples. Severe cracking of cement paste causing premature deterioration is often closely associated with ettringite locations, and strongly suggests that ettringite contributed to deterioration. Pyrite, FeS2, is commonly present in coarse/fine aggregates, and its oxidation products is observed in many concrete samples. Pyrite oxidation provides sulfate ions for ettringite formation.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.529-540
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• 2003

Recently, the researches on the durability design of concrete structures have been studied. As the examples, models to evaluate the service life prediction of the structure have been developed. The purpose of this article is to develop the model for predicting remaining service life. The final aim is to provide the user time for repairing the concrete structures. In addition, it makes possible to maintain the concrete structure economically. 70 reservoirs out of the inland concrete structures were selected and concrete structures of their components were surveyed. Two methods were used for measuring carbonation; TG/DTA method and Phenolphtalein indicator and, the value of pH was measured by the pH meter, After deriving correlations of calcium carbonate and used year, duration from completion year to 2002, pH value, and concrete cover depth the model was developed for predicting remaining service life by measuring data as small as possible. The conventional models had been developed on the basis of experiment data obtained from the restricted lab environment like as carbon gas exposure. On the other hand this model was developed on the basis of measuring data obtained from the real field that the complex deterioration actions are occurred such as freezing and thawing, carbonation, steel corrosion, and so on. The reliability of the developed model will be evaluated high in this point and this model can help to maintain concrete structures economically by providing the manager time to repair the deteriorated concrete structures in site of facility management.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.283-290
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• 2008

The repair technique using surface impregnation of reactive compound is so effective for deteriorated concrete structures that many researches are recently focused on these works. Particularly, inorganic impregnant is regarded as ecofriendly material because there is no air-pollution during manufacturing process as well as field coating works. Furthermore, The delamination between old concrete and impregnated surface does not occur, resulting from different material characteristics. In order to evaluate the durability performance of surface-impregnated concrete, durability evaluation through the long-term exposure tests is significant, however, experiments are usually limited to the temporary and qualitative laboratorial scope. In this study, durability characteristics for inorganic and organic/inorganic impregnated concrete specimens are evaluated through longterm chloride exposure test. The specimens with 21MPa and 34MPa strength have been prepared and exposed to chloride attack in the atmospheric, tidal, and submerged conditions. Evaluation for compressive strength, chloride penetration, and electrical potential (half cell potential) for steel corrosion are performed for the specimens exposed for 2 years. From the results, no distinct strength gaining is observed but the resistance to chloride penetration and steel corrosion is evaluated to be improved through surface impregnation. The more improved resistance to chloride attack is measured in the inorganic impregnated concrete and the results from atmospheric condition show more improved resistance to chloride attack than those from submerged and tidal condition.