• Magazine of the Korea Concrete Institute
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• v.9 no.3
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• pp.149-156
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• 1997

In order to improve compressive strength of cement mortar, powder admixture(FAS) was mmufactured by mixing fly ash. Il-anhydite and silica hume, and superplasticizer was used for the control of fluidity reduction with the use of this admixture. Cement was substituted by 10, 20wt% of FAS respectively. At W/S = 0.40, the fluidity of' cement paste substituted by PAS was decreased. NSF and NT-2 were very effective fbr the control of fluidity reduction. As the particle size of U -anhydrite was fine, the fluidity of cement mortar was increased. The fluidity reduction of cement mortar substituted by 10wt% of FAS was controlled. The compressive strength of cement mortar substituted by 10wt% of FAS showed higher. value than that of 20wt%, expecially specimen(C1) substituted by 10wt% of $\gamma$ had the highest compressive strength value.

• Journal of the Korea Institute of Building Construction
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• v.19 no.4
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• pp.299-306
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• 2019

In general, repair mortar is used to rehabilitate underground communities, but difficulties are encountered in the execution of long-term construction due to spatial co-operatives. In this study, the engineering properties of repair mortar according to the curing condition and accelerator type were reviewed. The results showed that the aluminate, alkali-free and calcium-aluminate precipitates in the water curing conditions showed higher compressive strength at the beginning of age than mortar specimens under air curing conditions, and increased. Especially in CA and AF test specimen with cement mineral quick setting, a large amount of ettringite products were observed compared with AL, thus reducing the pore volume and increasing the strength of the compound by micro-filling effect were found.

• Journal of the Korea Institute of Building Construction
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• v.21 no.3
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• pp.189-194
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• 2021

LIBS has been attracting attention as an analytical method capable of real-time measurement without sample preparation. In this study, a Lab. scale LIBS device was fabricated to examine the applicability and reproducibility of LIBS in the analysis of chloride contents in mortar. The existing analysis method and LIBS analysis were performed simultaneously on the mortar test specimen with the chloride content adjusted. Compared to the chloride content condition of the mortar, the XRF and Potentiometric Titration results also showed a similar trend. As a result of LIBS analysis, chlorine ions were detected at a wavelength of 837.59 nm according to the chloride content condition. In order to improve the precision in various concentration ranges, the LIBS signal amplification of about 50 times through the electric field enhancement was implemented. Through the verification of the aqueous solution-based reproducibility, a high correlation between the LIBS signal strength and the Cl concentration was confirmed, and the possibility of applying LIBS to the durability diagnosis of concrete damage by chloride was confirmed.

• Earthquakes and Structures
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• v.18 no.4
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• pp.451-466
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• 2020

In this paper, the effect of Engineered Cementitious Composites (ECC) on the lateral strength of a bearing unreinforced Masonry (URM) wall, was experimentally and numerically investigated. Two half scale solid walls were constructed and were tested under quasi-static lateral loading. The first specimen was an un-retrofitted masonry wall (reference wall) while the second one was retrofitted by ECC mortar connected to the wall foundation via steel rebar dowels. The effect of pre-compression level, ECC layer thickness and one or double-side retrofitting on the URM wall lateral strength was numerically investigated. The validation of the numerical model was carried out from the experimental results. The results indicated that the application of ECC layer increases the wall lateral strength and the level of increment depends on the above mentioned parameters. Increasing pre-compression levels and the lack of connection between the ECC layer and the wall foundation reduces the influence of the ECC mortar on the wall lateral strength. In addition, the wall failure mode changes from flexure to the toe-crashing behavior. Furthermore, in the case of ECC layer connected to the wall foundation, the ECC layer thickness and double-side retrofitting showed a significant effect on the wall lateral strength. Finally, a simple method for estimating the lateral strength of retrofitted masonry walls is presented. The results of this method is in good agreement with the numerical results.

• Corrosion Science and Technology
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• v.21 no.2
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• pp.100-110
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• 2022

Corrosion of steel reinforcement is the most important mode of concrete structures damages. It strongly depends on the composition and physicochemical properties of the cementitious medium. The use of waste materials as lightweight aggregates in concrete is environmentally recommended in polluted environments such as marine and/or industrial atmospheres in order to reduce its porosity and ensure the requested protection of reinforcing steel. The present study investigated the effect of waste cork addition on corrosion resistance of steel rebar in mortar specimen prepared in the laboratory. The main objective of this study was to improve the corrosion resistance of reinforcing steel. Another objective of this study was to valorize this ecological product and preserve the environment. Results obtained from various electrochemical tests indicated that the presence of a fine cork powder substantially improved the corrosion resistance of steel in the mortar contaminated by chloride ions. This improvement was reflected by a notable decrease in corrosion current density and a shift of corrosion potential of the steel towards more noble values. Moreover, the presence of a fine cork powder in the mortar had no adverse effect on its mechanical properties.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.195-196
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• 2021

The pore distribution of the cement mortar mixed with carbon nanotubes was found to have a large number of pores at (370~80)㎛, and the distribution ratio was larger as the carbon nanotubes were mixed. However, the pores with a fine particle diameter of (10-0.5) ㎛ were found to be larger as the carbon nanotubes were incorporated. However, the distribution of pores of the test specimens of conductive cement mortar with deterioration damage was found to be distributed in a number of particle diameters of (500 to 100) ㎛ and (10 to 0.5) ㎛. It is judged that the particle diameter of the internal pores increased due to the damage. However, as the mixing ratio of the test specimen with carbon nanotubes increased, the distribution of voids was relatively lower than that of plain, and it was judged to have excellent resistance to deterioration damage.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.43-48
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• 2002

This study is experiment results that carried out the sulfuric acid immersion of the mortar containing blast furnace slag powder, based ell the mechanism of the sulfuric acid corrosion for concrete which was caused by the H$_2$S gas. The used materials is OPC, slag powder and gypsum, and the proportion of cement is total 13 levels which are 0~70% of the contents of slag, 0~6％ of the contents of gypsum. The specimen is immersed by 5% H$_2$SO$_4$ solution after 28 days and its weight loss is measured at intervals of 7 days. The results of experiment showed that the substitution ratio of 70% slag was excellent at a point of view for the sulfuric acid resistance and the sulfuric acid resistance was not improved by tile increase of the blaine of slag(8, 000longrightarrow10, 000$\textrm{cm}^2$/g) and the addition of gypsum.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.211-216
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• 1998

Recently the shortage of good aggregate has encouraged the use of sea sand in construction field, and the corrosion damage of the reinforced steel in concrete structures has been increased due to chlorides from sea sand and deicing salt. Therefore, a number of researchs are proceeding to prevent the corrosion of the reinforced steel in concrete, especially in marine environments. This study focused on the effect of corrosion inhibitors to evaluate protection characteristics for mortar specimens containing clorides. Corrosion behaviors have been investigated by half-cell potential measurement, linear polarization method, AC impedance method, and cyclic polarization test after immersing in sea water for 7 years. A possitive effect of a corrosion inhibitor has been obtained.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.601-606
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• 2002

This study explored physical properties of a hardened cement and a concrete specimen using a high performance cement type solidification consisting of a weathered granite soil and a yellow soil mainly. Also the development of high performance cement type solidification was purposed for an intensity improvement and a long-term durability. As the experimental results, a mortar used by the weathered granite soil shows positive result, however using the yellow soil as a mortar Shows less positive result at the compressive strength. Also the dynamic modulus of elasticity measurement result, the concrete specimens used by the weathered granite and the yellow soil reached above 90%, so it seems to have the durability of freezing and thawing.

• Tunnel and Underground Space
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• v.7 no.3
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• pp.221-229
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• 1997

Disc-type and ring-type specimens of four different materials were tested to investigate the tensile characteristics and their brief results are presented. Materials tested were marble, granite, cement mortar and plaster. Unizxial tensile strengths are compared with Brazilian and ring test strengths. It was found that Brazilian strengths were usually greater than uniaxial tensile strengths and affected by loading rates. In the ring tests, tensile strengths were generally found to be decreased as relative hole radius being increased. Ring test strengths, however, converged to some value in r$\geq$0.45 of marble, r$\geqq$0.29 of cement mortar and r$\leq$0.5 of plaster specimens. In such range of r, furthermore, transverse cracking of specimens were observed.