• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.188-196
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• 2009

In Concrete, shrinkages occur like plastic shrinkage and drying shrinkage in the early age because of evaporation and transfer of moisture. Within the country, the crack test standardized by KS is used to test the drying shrinkage of the concrete by using the restricted drying shrinkage of Dumbbell type mold, but this test is for the cracking-point and the restricted shrinkage stress. Thus it is difficult to valuate the crack quantitative test. In this study, it is intended to develop the Flat-ring type restrained test method for the shrinkage deformation movement of the concrete and to provide the quantitative data for evaluating the cracks in concrete. And it suggest the proper specimen diameter and quantitative test method about shrinkage crack properties on Flat-ring type restrained test method. And Verified the suitability.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.329-335
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• 2009

The purpose of this study is to provide the efficient method and guideline of controlling the cracking in bridge deck concrete due to differential drying shrinkage. Drying shrinkage cracking is mainly influenced by the moisture diffusion coefficient that determines moisture diffusion rate inside concrete structures. In addition to the diffusion coefficient, surface coefficient of concrete surface and relative humidity of ambient air simultaneously affect the moisture evaporation from concrete inside to external air outside. Within the framework of cracking shrinkage cracking mechanism, it is necessary to conceive the numerical analysis, which involves these three influencing factors to predict and control the shrinkage cracking of concrete. In this study, moisture diffusion and stress analysis corresponding to drying shrinkage on bridge deck are performed with consideration of diffusion coefficient, surface coefficient, and relative humidity of ambient air. From the numerical results, it is found that cracking behavior due to differential drying shrinkage of bridge deck concrete shows different feature according to three influencing factors and the methodology of controlling of drying shrinkage cracks can be suggested from this study.

• Journal of the Korean Society for Railway
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• v.17 no.4
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• pp.270-280
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• 2014

In this study, to examine the causes of cracks in continuously reinforced concrete tracks (CRCTs) and the main factors affecting cracking, a field survey on the status of cracks and crack patterns in the Gyeong-bu high speed line was conducted, and the crack patterns of CRCT due to the temperature difference between the top of the slab (TCL) and the bottom of the subbase (HSB) and the drying shrinkage of concrete were predicted by a nonlinear finite element model considering the structure of CRCT. The results of the numerical analysis show that cracks will be developed at the interface between the sleeper and the TCL, and under the sleeper due to the temperature difference and concrete shrinkage. This corresponds well to the crack locations found in the field. Also, it is found that the most significant factors are the coefficient of thermal expansion with respect to the temperature difference, and the drying shrinkage strain with respect to shrinkage. According to the results, the reinforcement ratio should be carefully determined considering the structures of CRCT because the crack spacing is not always proportional to the reinforcement ratio due to the sleepers embedded in the TCL.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.296-302
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• 2016

Studies aimed at reducing the occurrence of cracks by the shrinkage of concrete are in demand because the repair and reinforcement for cracks caused by declining concrete durability costs the user to maintain the concrete structure. In particular, in underground power facilities for power transmission, the cost is a heavy burden to repair and reinforce. For this reason, underground power facilities demanded effective methods for crack reduction at the engineering design step. This study, as a part of the development of shrinkage reducing agent for low shrinkage concrete on underground power facilities, investigated TEA to complement the shrinkage reducing agent to improve the early strength of concrete. In the case of TEA 3% as a shrinkage reducing agent, the early strength was improved significantly, and the shrinkage reducing effect was excellent. In addition, TEA 3.0 % and the shrinkage reducing agent 2.0 % showed excellent shrinkage property and compressive strength. On the other hand, more study of shrinkage reducing materials, including performance reviews on the shrinkage reducing materials with variable factors and type of materials, will be needed to generalize these results.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.10
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• pp.163-170
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• 2019

In spite of various advantages, steel fiber reinforced concrete is still limited in its use due to the insufficient research results on the structural performance and design criteria. This study evaluated the long-term behavior of the steel fiber reinforced concrete slabs by long-term loading experiments based on the short-term load bearing capacity of steel fiber reinforced concrete slabs obtained from previous studies. In this study, long-term loading experiments were carried out on Total four 2-span continuous slab specimens were tested for examining the long-term behavior of steel fiber reinforced concrete members. Long-term behavior characteristics of members were evaluated by measuring the long-term deflection, drying shrinkage, the number and width of cracks. Experimental results showed that the instant deflection of the steel fiber reinforced concrete slab is about 50% of the normal reinforced concrete slab. And, it was analyzed that the long-term deflection of the specimen using steel fiber reinforced concrete was about 10~20% lower than that of normal concrete by the long-term deflection over 100 days. In addition, the slab specimen using steel fiber reinforced concrete was evaluated to have just 70% of the number and width of cracks compared with normal concrete specimens.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1095-1100
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• 2000

Concrete structure often exhibit cracks due to the combination of material construction and design error. Minor crack can be tolerated depending on exposure condition, but major cracks are aesthetically unpleasant and affect the durability and safety of the structure. All of the reinforced concrete structure have many inevitable cracks for various reason such as drying shrinkage, heat liberation of cement and over loads. Epoxy resin injection widely used for repairing cracks in concrete is too sensitive to high temperature. Besides, the problem in the epoxy resin injection is the difficulty of quality control after execution. Whereas, Ultra Fine Cement is similar in coefficient of thermal expansion and modulus of elasticity to concrete. The objective of the study is to find out that it is possible for Ultra Fine Cement to be used for repairing cracks in reinforced concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.773-776
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• 2008

Restraining cracks on concrete structures can be the basic condition to improve the durability, so in this research, the resistibility on the drying shrinkage of concrete structures in the long period was being confirmed and as the reason of this shrinkage, the density of minute textures was being analyzed using a wooden prototype of a full scale produced with ready-mixed concrete and agents of glycol which can be used as a surfactant. As result of those tests, PFB technology can reduce the drying shrinkage by approximately $-100{\sim}200{\times}10^{-6}$ on a wooden prototype of a full scale and can also reduce the pore volume as the obstruction to the movement of gas or liquid by approximately $2.4{\sim}3.5$% so that PFB technology can be used to assure the resistibility on the drying shrinkage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.93-100
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• 2009

This study forms part of a research project that was carried out on the development and application of high-strength concrete for large underground spaces. In order to develop 50MPa high-strength concrete, eight optimal mixtures with different portions of fly ash and ground granulated blast furnace slag were selected. For assessments of shrinkage characteristics, free shrinkage tests with prismatic specimens and shrinkage crack tests were performed. The compressive strength was more than 30MPa at 7days, and stable design strength was acquired at 28days. High-strength concrete containing blast furnace slag shows large autogenous shrinkage, while large shrinkage deformations and cracks will occur when mixtures are replaced with large volumes of cementitious materials. Hence, for these high-strength concrete mixtures, the curing conditions of initial ages that affect the reaction of hydration and drying effects need to be checked.

• Journal of the Korea Institute of Building Construction
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• v.16 no.6
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• pp.561-569
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• 2016

Concrete is cheap, easy to deal with, and the quality is satisfactory. Also, it is one of the easiest materials to get because chemical composition of cement is similar to chemical composition of surface. On the other hand, it is so vulnerable to transform because of weak binding capacity and low binding energy that it produces cracks. Cracks decline durability, usability, safety of structures and damage exterior. In order to decline drying shrinkage crack, this study used shrinkage reducing typed Superplasticizer, which is combination of and water-reducing agent for convenience, different with existing study using AE agent, water-reducing agent, shrinkage reducing agent,. Considering SRS field application possibility, this study planned to mix concrete and mortar generally used in ready-mixed concrete company and did basic experiment depending on a change of SRS content ratio and admixture. Based on the experiment result. It is judged that SRS admixture 2% is proper ratio when Given the intensity and length change. Also mass combination will conduct follow-up studies.

• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.685-691
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• 2022

This study was based on the steel composite concrete box structure (Transfer girder) which was installed to support the skyscrapers directly above the subway line. In this study, it was analytically proved that the cause of cracks on the steel composite concrete box structure were the shrinkage cracks by comparing the results of crack investigation and numerical analysis. As the results, it was found that the internal temperature difference between concrete and steel members occurred according to the shape of the steel frame embedded in concrete, the location of vertical stiffener, and the closed section area. The narrower spacing of vertical stiffener was occurred the internal temperature concentration of the structure and the temperature difference increased. And the location of higher thermal strain and temperature were similar to the location of actual cracks by the visual inspection. Therefore, the internal temperature concentration parts were formed according to the presence and spacing of the vertical stiffeners and the inspection passage in the central part of the structure. The shrinkage cracks were occurred by the restrained of temperature expansion and contraction of the concrete. As the results of this study, it was important to separate and manage the non-structural cracks caused by shrinkage and the structural cracks in the maintenance of serviced steel-composite concrete structures.