• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.885-892
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• 2005

Recently, the damaged concrete structures are often strengthened or repaired using the polymer concrete or the polymer cement mortar. In the repaired concrete structures at early ages, internal stresses could be developed due to the differential drying shrinkage of the repair material. Due to the difference of the thermal coefficients of the repair material and existing concrete, additional stresses also could be developed as the structures are subjected to the ambient temperature changes. Theses environmentally-induced stresses can sometimes be large enough to cause damage to the structures, such as debonding of the interface between the two materials. In this study, a rational procedure was developed where anchors can be designed and installed to prevent damages in such structures by thermally-induced stresses. Finally, through the experimental study and numerical study, the effects of the repair method using anchors with debonding was investigated and discussed the results.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.474-482
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• 2002

The purpose of the study is to establish an optimum geometry and optimum geometry factor through bond test of a structural synthetic fiber, which fully utilizes matrix anchoring without fiber fracturing with the maximum pullout resistance. Seven deformed structural synthetic fibers with widely different geometries were investigated and pullout test was conducted. Included parameters are seven different types of fiber and two of mortar matrixes. The test result shows that the crimped type structural synthetic fiber is significant improvement in the interface toughness(pullout energy) and pullout load. The pullout test was performed with various size of crimped type structural synthetic fiber in order to invest optimum geometry factor, In the basis of the test results, optimum geometry factor is established such as D=b$^{{\alpha}0{\alpha}}$h$^{λ{\beta}}$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.87-98
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• 2011

Clay bricks with lime mortar are recently popular since they are eco- and environment-friendly construction material being capable of air flow and moisture movement. However, there is little study on those of clay brick an lime mortar while relatively many researches on the structural characteristics of concrete bricks with cement mortar are available in Korea. Furthermore, the current Korean Building Code of masonry structures was established on the base of the Foreign Codes which does not reflect Korean masonry construction circumstance, such as material characteristics and section properties. To overcome these problems, experiments of masonry structures constructed using clay bricks with lime mortar were carried out to evaluate their structural characteristics such as, prism compressive strength, adhesive strength and diagonal tensile(shear) strength. Also this research compares the mechanical characteristics between clay bricks with lime mortar and concrete bricks with cement mortar to provide information that will be used for revisions of the domestic standards for masonry structures. As masonry structures constructed with clay bricks and lime mortar show different aspects over the ones constructed with concrete bricks and cement mortar, we suggest estimation equation of prism compressive strength and diagonal tensile strength on masonry structures constructed with clay bricks and lime mortar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.97-104
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• 2018

In recent years, more than 5,000 tons of sargassum honeri have been infested in the southern coast and the coast of Jeju Island, causing serious damage to the farms and fisheries, and environmental problems. The alginate contained in the sargassum honeri is a natural polymeric substance mainly used for medicines and foods. However, since there is no way to utilize it in large quantities, a study was carried out to utilize bio polymer obtained from sargassum honeri in producing polymer mortar for repairing deteriorated infrastructures. From the tests of setting time, it was found that the L0BP12 mixture containing 12% of bio polymer increased the setting time by 20% as compared with the L12BP0 mixture using only synthetic polymer. From the tests of water absorbtion, the LOBP12 combination decreased by 0.36% compared to Plain-URHC using ultra rapid hardening cement. This indicated that the watertightness of the mortar was increased by the incorporation of the bio polymer. In the compressive and flexural strength tests, the strength decreased as the amount of bio polymer increased. The incorporation rate of the maximum bio polymer satisfying the KS F 4042 standard was determined to be 12%. In addition, the bond strength of the mortar produced with biopolymer was higher than that of Plain-URHC specimens, and it was confirmed that incorporation of bio polymer improves bond strength of mortar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.235-242
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• 2005

This study is on the evaluation of performance of polymer cement mortar which is used for pre-wetting spray method. Pre-wetting spray method is an epoch-making method to repair concrete structures damaged, which is added a small quantity water preciously to dry mortar to reduce dust and rebound and spray mortar mixed with fixed quantity water at nozzle before spray. The result showed that physical performance such like compressive, flexural and adhesive strength of polymer cement mortar, TS 100 used for pre-wetting spray method was superior to other repair mortar. Also durable performance such as resistance on permeability of chloride ion, carbonation, chemical and freezing-thawing was excellent.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.189-198
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• 2006

The composition of most engineering materials is heterogeneous at some degree. It is simply a question of scale at which the level of heterogeneity becomes apparent. In the case of cementitious granular materials such as concrete the heterogeneity appears at the mesoscale where it is comprised of aggregate particles, a hardened cement paste and voids. Since it is difficult to consider each separate particle in the topological description explicitly, numerical models of the meso-structure are normally confined to two-phase matrix particle composites in which only the larger inclusions are accounted for. 2-D and 3-D concrete blocks(Representative Volume Element, RVE) are used to simulating heterogeneous concrete meso-structures in the form of aggregates in the hardened mortar with nearly zero-thickness linear or planar interfaces. The numerical sensitivity of these meso-structures are Investigated with respect to the different morphologies of heterogeneity and the different level of coupling constant among fracture mode I, II and III. In addition, a numerically homogenized concrete block in 3-D using Hashin-Shtrikman variational bounds provides an evidence of the effective cracking paths which are quite different with those of heterogenous concrete block. However, their average force-displacement relationship show a pretty close match each other.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.341-348
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• 2016

At present, about 40 million tons of concrete is dismantled each year, which accounts for the largest portion of the total amount of construction waste with 60.8%. It is known about 97.5% of it is recycled. However, most of the usage of waste concrete is limited to lower value-added business areas, and considering the increasing amount of waste concrete generated due to the deterioration of structures, the need for converting waste concrete to structural concrete is urgent. Therefore, this study aims at estimating the period for the optimum carbonation reforming to improve the quality of recycled aggregate, by making use of the method of accelerated carbonation reforming of the bonding heterogeneous (cement paste and mortar) for the purpose of converting recycled aggregate to structural concrete. Based on the period appropriate for the heterogeneous thickness and each bonding thickness of recycled aggregate which was drawn from previous studies, the changes in the characteristics and physical properties of pore structure according to progress of accelerated carbonation were analyzed. The result shows that with the progress of carbonation, the pore volume and the percentage of water absorption of the bonding heterogeneous decreased and the density increased, which indicates improvement of the product quality. But after certain age, the tendency was reversed and the product quality deteriorated. Synthesizing the results of previous studies and those of the present study, this study proposed 4 days and 14 days respectively for the period for the optimum carbonation reforming of recycled fine aggregate and recycled coarse aggregate.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.21-28
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• 2006

This paper presents both experimental and analytical studies for the development of an ECC(Engineered Cementitious Composites) using ground granulated blast furnace slag(slag). This material has been focused on achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, micromechanics was adopted to properly select optimized range of the composition based on steady-state cracking theory and experimental studies on matrix, and interfacial properties. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties of the fiber in a matrix and the fracture toughness of mortar matrix. The addition of the slag resulted in slight increases in the frictional bond strength and the fracture toughness. Subsequent direct tensile tests demonstrate that the fiber reinforced mortar exhibited high ductile uniaxial tension behavior with a maximum strain capacity of 3.6%. Both ductility and tensile strength(~5.3 MPa) of the composite produced with slag were measured to be significantly higher than those of the composite without slag. The slag particles contribute to improving matrix strength and fiber dispersion, which is incorporated with enhanced workability attributed to the oxidized grain surface. This result suggests that, within the limited slag dosage employed in the present study, the contribution of slag particles to the workability overwhelms the side-effect of decreased potential of saturated multiple cracking.

• Journal of the Korea Institute of Building Construction
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• v.22 no.5
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• pp.507-518
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• 2022

The purpose of this research is to obtain experimental data for developing a structural design of an external insulation system by evaluating the shear performance of a composite insulation system according to the adhesive type. The shear performance of the composite insulation system was experimentally evaluated by considering a simultaneous placement method, full and spot/edge coverage using adhesive mortar. As a result of the test, the shear strength of simultaneous placement and full coverage method was almost similar, the spot/edge coverage method was about 80% of them. Also, the simultaneous placement method is considered to be constructively advantageous when applied as an external insulation system to a high-rise building compared to using an adhesive mortar.

• Journal of the Korea Institute of Building Construction
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• v.23 no.3
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• pp.241-249
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• 2023

The objective of this research was to engineer a tile module that could efficiently curtail the incidence of tile defects during the construction phase. To assess the potential diminution in defect manifestation, we executed experiments centered on surface condition, the variation in mass before and after the freeze-thaw test, and adhesive strength. Our findings demonstrated that thermal contraction and expansion induced a relatively escalated frequency of defects in the underwater setting for the aluminum mesh, while the steel mesh saw a higher defect incidence in the air environment. Additionally, it was noted that the adhesive strength exhibited a trend towards augmentation as the mesh size dwindled. Collectively, these results suggest that the employment of smaller mesh sizes can foster improved adhesive strength, consequently diminishing tile defects. Further exploration and development of the tile module, informed by these insights, can substantially enhance the efficacy of the construction process.