• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.593-596
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• 2008

Domestic area of most be happened chloride deicer damage. Because daily mean temperature is below 0$^{\circ}C$ from the area of domestic most. Use of deicing chemicals has been and will continue to be a major part of concrete structure in the highway. Chloride-containing chemicals such as calcium chloride or rock salt are main deicers for the road. Extensive use of chloride deicers is, however, not only the source of substantial cost penalties due to their corrosive action and ability to deterioration roadway surface materials but also the source of environmental damages. Chloride-containing chemicals such as calcium chloride or rock salt are main deicers for the road. Extensive use of chloride deicers is, however, not only the source of substantial cost penalties due to their corrosive action and ability to deterioration roadway surface materials but also the source of environmental damages. In this study, Use of deicing chemicals has been and will continue to be a major part of highway freeze-thaw durability and carbonation of concrete surface protecting materials

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.1
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• pp.1-6
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• 2011

To improve fire-resistance of a high strength concrete against explosive spalling under elevated temperature, fibers can be mixed with concrete to provide flow paths of evaporated water within concrete to the free surface. The fiber-mix concrete approach is effective against explosive spalling when the flow path generated from melting fibers at the elevated temperature is interconnected to transport high pressurized evaporated water from the inside concrete to the free surface. The percolation theory can identify the connectivity of the fibers and provide an estimate of the fire-resistance of concrete by investigating layout of fibers. In this study, the correlation between percolation theory and explosive spalling of fiber-mixed high strength concrete is analyzed and the connectivity of the fiber in concrete is stereologically investigated by using virtual specimens of fiber-mixed high strength concrete.

• Journal of the Korean GEO-environmental Society
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• v.6 no.3
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• pp.17-23
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• 2005

In Korea, the production of reclaimed concrete materials has been increased due to the increase in the concrete structures taken down every year. The reclaimed concrete materials have been reused as road materials. However, the studies on their mechanical and environmental properties have been very limited. The recycled rate of the materials is currently low in Korea. This paper presents the investigation of mechanical and environmental properties of the reclaimed concrete materials, as well as the comparisons with those of gravel. For the evaluation of the mechanical and environmental characteristics, following tests were conducted on both reclamed materials and gravel; liquid limit, plasticity index, CBR, sand equivalent test, abrasion test, pH test, and column leaching test. The test results showed that the reclaimed concretes satisfy the requirements for use as roadbase, subbase, and subgrade materials, except base materials. The pH of reclaimed concrete materials was less than 11 and the leaching test results satisfied the regulatory requirement of Waste Management Act in Korea. Based on the investigations, it appears that the reclaimed concrete materials are environmentally safe and applicable for use as road materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.35-42
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• 2024

This study evaluated the buildability and mechanical properties of 3DP concrete printed in air and underwater environments. Buildability was evaluated by green strength test on fresh concrete and height and deflection immediately and 1 hour after printing. The green compressive strength of the concrete was 5.0 kPa after 30 minutes and 7.9 kPa after 3 hours, an increase of 1.6 times the initial strength. The total height of the laminated parts met the design height regardless of the printing environment. The amount of deflection in air and under water 1 hour after printing was 1 mm and 0.2 mm, respectively, indicating a small amount of deflection under water. The apparent density of the sample appeared in the order of A-M > A-P > UW-P. This is believed to be because a large amount of air is mixed into the concrete during the printing process, and water infiltrates during the underwater printing process. The compressive strength ratio of UW-P/A-P was 0.86 at 1 day, but the compressive strength of the underwater printed concrete was high from 7 days.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.4
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• pp.403-409
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• 2013

Shear behavior of concrete beams reinforced with steel and/or FRP bar is studied through experimental tests. Experimental parameters includes the mechanical properties of reinforcements in shear and bending, and the ratio of shear reinforcement. The validity of the modified truss analogy, that has been widely accepted as a basis for the practical shear design of concrete beams, has been examined thoroughly by analyzing experimental results. The experimental results indicate that the modified truss analogy cannot be directly adopted to the shear problem of concrete beams reinforced with FRP bar.

• Economic and Environmental Geology
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• v.36 no.5
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• pp.365-374
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• 2003

Various deleterious chemicals can be introduced to existing concrete structures from various external sources. The deterioration of concrete by seawater attack is involved in complex processes due to various elements contained in seawater. In the present study, attention was paid to the formation of secondary minerals and characteristics of mineralogical and micro-structural changes involved in concrete deterioration caused by the influence of major seawater composition. The characteristics of deterioration occurred in existing concrete structures was carefully observed and samples were collected at many locations of coastal areas in Busan-Kyungnam. The petrographic, XRD, SEM/EDAX analyses were conducted to determine chemical, mineralogical and micro-structural changes in the aggregate and cement paste of samples. The experimental concrete deteriorations were performed using various chloride solutions (NaCl, CaCl, $MgCl_2$ and $Na_2SO_4$ solution. The experimental results were compared with the observation results in order to determine the effect of major elements in seawater on the deterioration. The alkalies in seawater appear to accelerate alkali-silica reaction (ASR). The gel formed by ASR is alkali-calcium-silica gel which known to cause severe expansion and cracking in concrete. Carbonation causes the formation of abundant less-cementitious calcite and weaken the cement paste. Progressive carbonation significantly affects on the composition and stability of some secondary minerals. Abundant gypsum generally occurs in concretes subjected to significant carbonation, but thaumasite ({$Ca_6/[Si(OH)_6]_2{\cdot}24H_2O$}${\cdot}[(SO_4)_2]{\cdot}[(CO_3))2]$) occurs as ettringite-thaumasite solid solution in concretes subjected to less significant carbonation. Experimentally, ettringite can be transformed to trichloroaluminate or decomposed by chloride ingress under controlled pH conditions. Mg ions in seawater cause cement paste deterioration by forming non-cementitious brucite and magnesium silicate hydrate (MSH).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.347-353
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• 2009

The qualitative factors influencing the ingress of chloride ion into concrete are water-binder (W/B) ratio, cement type, age, chloride ion concentration of given environment, wet and dry conditions, etc. Thus, an objective of this experimental research is to investigate the effects of cement types and environmental conditions on the chloride ion diffusion characteristics in concrete through the chloride ion diffusion test. For this purpose, the diffusion coefficients for chloride ion in concrete with three types of cement such as ordinary portland cement (OPC), binary blended cement (BBC), and ternary blended cement (TBC), were measured for the concrete specimens with W/B ratios of 32%, 38%, and 43%, respectively. The diffusion coefficients for chloride ion were also measured for the concrete specimens with W/B ratio of 43%, which were subjected to standard curing and field exposure conditions. It was observed from the test results that the resistance against chloride ion penetration increased with decreasing W/B ratio and those of BBC and TBC concretes were greater than that of OPC concrete. Therefore, it was revealed that the use of these cements containing mineral admixtures is required to extend the service life of RC structures exposed to chloride environment. On the other hand, it was noted that the resistance against chloride ion penetration of field exposure test specimens was slightly lower than that of standard curing test specimens due to the penetration of chloride ion under the irregular ambient temperature, splash of wave, and cycle of wet and dry.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.97-104
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• 2020

The present study conducted mock-up tests under the simulated sewage environments to examine the practical significance and limitation of coating materials that were previously developed on the basis of the bacterial glycocalix as a protection of concrete structures exposed to microbiological and sulphate attacks. The variations of the compressive strength and mass of the concrete due to the sulphate attack were measured using cylinder specimens. The bacteria growth and glycocalix formulation were calculated from the samples extracted from the sewage pipes. The next generation sequencing analysis was also conducted for environmental damage assessment due to the use of Rhodobacter capsulatus in the simulated sewage environments. The mock-up tests revealed that the developed coating materials have a good potential in resisting the sulphate attack, indicating no reduction on compressive strength and mass of the coated concrete under the sewage environment. At the age of 91 days, the concentrations of viable bacteria and glycocalix measured from the hardened coating materials were 1.4×10⁴cell/mL and 67.5mg/㎤, respectively. Moreover, harmful strains were not observed in the sewage water including glycocalix-coated concrete pipes. This implies that Rhodobacter capsulatus used in the coating materials does not influence negatively the microorganism cluster in the sewage environments.

• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.553-558
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• 2012

Airborne chlorides are transported to inland by sea wind to be attached to seashore concrete structure surface then penetrated into concrete structure members. Since the surface attached chloride amount are dependent on the amount of airborne chlorides, the prediction of distribution of airborne chlorides is important information in preventing chloride corrosion problems in seashore concrete structures. The prediction of surface chloride amount from airborne chlorides environment is extremely difficult than concrete directly in contact with seawater. In addition, their penetrating tendency is different from that of concrete immersed in seawater. In this study, properties of surface and penetrated chlorides under airborne chlorides environment are investigated. Concrete specimens were manufactured and exposed to marine environment for 3 years. The specimens were analyzed at the time durations of 1, 2, and 3 years to check surface chloride amount to penetrated chloride depth. The results revealed that there were certain differences according to surface roughness of concrete and with and without washing effect due to rainfalls. The evaluation results showed that penetrated chlorides depend on amount of airborne chlorides and duration of exposure. In addition, a notable tendency of having deeper chloride penetration and higher chloride content in concrete members under long-term exposure was observed.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2005.05a
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• pp.322-323
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• 2005

본 연구에서는 제주송이를 사용한 광촉매 콘크리트의 질소산화물(NO$_{X}$)의 제거 특성에 대하여 연구한 결과 다음과 같은 결론을 얻었다. 첫째, 제주 송이와 황토를 사용한 광촉매콘크리트는 28일 압축강도가 35MPa이상 발휘하는 배합비로 제조되었고, 디자인이 충분히 건자재로 사용될 수 있음을 알았다. 둘째, 송이 표면의 다공성구조로 인해 높은 비표면적과세공구조가 NO$_{X}$의 흡착 속도를 높이는 것으로 판단된다. 셋째, 자동차 배기가스 등의 대기오염이 심한 주차장 및 터널 등에 본 연구의 광촉매 콘크리트를 적용하면 NO$_{X}$를 효율적으로 제거 할 수 있을 것으로 예상된다.