• Economic and Environmental Geology
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• v.56 no.1
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• pp.103-114
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• 2023

The Christian Museum of Gongju Jeil Church was first built in 1931 and was largely damaged during the Korean War, but the walls and chimneys have been preserved. This building has a high architectural values in that the chapel was reconstructed in 1956, and maintains its original form through repair of damaged parts rather than new construction. The stained glass windows were as installed in 1979 and has a great significance in the Dalle de Verre method using lump glass. However, some of the stained glass damaged partially, such as various cracks and splits, and vertical and horizontal cracks in the joint fillers of supporting the colored glass. As the structural materials of the stained glass window, an iron frame and cement mortar filled with it were used, and corrosion of iron, cracking of mortar and granular decomposition appear partially due to weathering. In the joint fillers, the content of Ca and S is very high, indicating that gypsum were used as admixtures, and the gypsums grow in a rhombohedral and forms a bundle, which is investigated to have undergone recrystallization. As a result of modeling the ultrasonic velocity at the joint fillers, the left and right windows at the entrance show relatively weak in the range of 800 to 1,600m/s, and the lower right corner of the altar window and the upper left corner of the center window were also 1,000 to 1,800m/s, showing relatively low physical properties. And gypsums produced during the neutralization of lime mortar were detected in the joint fillers and contaminants on the surface. Such salts may cause damage to the joint material due to freezing and thawing, so appropriate preventive conservation is required. Also, since various damage types are complexly appearing in stained glass window and joint filler, customized conservation treatment should be reviewed through clinical tests.

• Korean Journal of Agricultural Science
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• v.31 no.2
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• pp.105-114
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• 2004

This study was performed to examine the physical and mechanical properties of eco-concrete using soil, natural coarse aggregate, soil compound and polypropylen fiber. The mass loss ratio was decreased with increasing the content of coarse aggregate and soil compound. The compressive strength, flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity were increased with increasing the content of coarse aggregate, soil compound and polypropylene fiber. The compressive and flexural strengths were showed in 8.07 MPa and 2.641 MPa at the curing age 28 days, respectively. The coefficient of permeability was decreased with increasing the content of coarse aggregate and soil compound, but it was increased with increasing the content of polypropylene fiber. The lowest coefficent of permeability was showed in $5.066{\times}10^{-9}cm/s$.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.389-397
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• 2010

Concrete has excellent mechanical properties, high durability, and economical advantages over other construction materials. Nevertheless, it is not an easy task to apply concrete to long span bridges. That's because concrete has a low strength to weight ratio. Ultra high performance concrete (UHPC) has a very high strength and hence it allows use of relatively small section for the same design load. Thus UHPC is a promising material to be utilized in the construction of long span bridges. However, there is a possibility of crack generation during the curing process due to the high binder ratio of UHPC and a consequent large amount of hydration heat. In this study, adiabatic temperature rise and mechanical properties were modeled for the stress analysis due to hydration heat. Adiabatic temperature rise curve of UHPC was modeled superposing 2-parameter model and S-shaped function, and the Arrhenius constant was determined using the concept of equivalent time. The results are verified by the mock-up test measuring the temperature development due to the hydration of UHPC. In addition, models for mechanical properties such as elastic modulus, tensile strength and compressive strength were developed based on the test results from conventional load test and ultrasonic pulse velocity measurement.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.33-40
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• 2013

The cement industry brought very severe environment problems with massive carbon dioxide during its production. To solve this problem, attempts on Alkali-Activated Slag (AAS) concrete that perfectly substitutes industrial by-products such as ground granulated blast furnace slag (GGBFS) for cement are being actively made. AAS concrete is possible to have high strength development at room temperature, however, it is difficult to ensure the working time due to the fast setting time and the loss of workabillity because of the alkali reaction. In this study, the early age properties of alkali activated slag mortar are investigated to obtain the fundamental data for AAS concrete application to structural members. The water-binder ratio (W/B) was fixed at 0.35 and sodium hydroxide and waterglass as alkali activator was used. The compressive strength, the flow and the ultrasonic pulse velocity were measured according to the type of superplasticisers, which were naphthalene(N), lignin(L), melamine(M) and PC(P), up to a maximum of 2 percent by the mass of GGBFS. The results showed that adding melamine type of superplasticizer improved the fluidity of AAS mortar without decreasing the compressive strength, while naphthalene and polycarbonate type of superplasticizer had little effect on the fluidity of AAS mortar.

• Journal of Conservation Science
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• v.26 no.3
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• pp.277-294
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• 2010

The Seosanmaaesamjonbulsang (National Treasure No. 84) consists of light gray and coarse to mediumgrained biotite granite with partly developed pegmatite and quartz vein. The host rock is divided into dozens of rock blocks with various shape along irregular discontinuity plane. The evaluation results of discontinuity systems reveal that the host rock were exposed to instable sloping environments. Results of deterioration diagnosis show that the degree of damage has been made worse by physical weathering and surface discoloration laying stress on part that vertical and horizontal joints are massed. Generally, deterioration rate of the triad Buddha surface cover with 42.7%, however, the rate of physical weathering and surface discoloration are subdivided to 9.6% and 33.1%, respectively. Ultrasonic measurements indicate that the triad Buddha was reached highly weathered grade in general. And the rock material was weaken to show low velocity zone of 1,000m/s along irregular joint systems. Indoor and outdoor mean relative humidity of the shelter was recorded more than 70% during every season, and high frequency appears in high relative humidity range over 95%. Such environments seem to have produced dew condensation on the rock surface with rainfall and supply water, promoted physical, chemical and biological weathering along crack and joint, resulting in high permeation of water and percentage of water content. Therefore, it is judged that for scientific conservation of the triad Buddha it needs environment control through persistent preservation environment monitoring including water problem.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.593-600
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• 2016

The paper presented investigates the effects of kaolinite on strength properties of alkali-activated multi-component cement. The binders of this study was blended of ground granulated blast furnace slag (GGBFS), fly ash (FA), silica fume (SF) and kaolinite (KA). In this study, the specimens of combination of 20%~70% GGBFS, 10%~60% FA, 10% SF (constant ratio) and 10%~50% KA binder were used for strength properties tests. The water/binder ratio was 0.5. The binders (GGBFS + FA + SF + KA) was activated by sodium hydroxide (NaOH) and sodium silicate ($Na_2SiO_3$) was 10% by total binder weight (10% NaOH + 10% $Na_2SiO_3$). The research carried out is on the compressive strength, water absorption, ultrasonic pulse velocity (UPV) and X-ray diffraction (XRD). The compressive strength decreased as the contents of KA increase. One of the major reason for this is the low reactivity of KA compared with other raw materials used as precursors such as GGBFS or FA. The presence of remaining KA indicates that the initially used quantity has not fully reacted during hydration. Moreover, the results have indicated that increased of KA contents decreased UPV under all experimental conditions. The drying shrinkage and water absorption increased as the content of KA increase. Test result clearly showed that the strength development of multi-component blended cement were significantly dependent on the content of KA and GGBFS.

• Journal of Conservation Science
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• v.32 no.3
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• pp.353-364
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• 2016

The materials of sculptured stone property around the Hyeonleung Royal Tomb in Guri consist mainly of high weathered of granitic rocks with magnetite-series. Deterioration characteristics occurred highly with microorganism, soil inflow and black contaminants at the burial mound zone. As a result of deterioration evaluation, stone surface around the burial mound zone show serious comprehensive damage of soil inflow (50.5%) and lichen coverage (47.6%) which are the major damaging factors, and there are about 8.6% of biological growth noticeably in the north side. Surface contaminants and the discoloration had the complex causes. Gypsum occurred between joints of stones and the major contaminant type, darkening which was analyzed organic bodies caused discoloration. From result of ultrasonic velocity measurements, there are mean value of 2,195 m/s with highly weathered (HW) grade. Most of the stone properties showed 4 to 5 weathered grade. Therefore, it turned out that sculpture stone properties require conservation treatments. To remove soil accelerating damage factors and lichen occupying high percents, the cleaning process is necessary and consolidation, rejoining and filling are needed as well. Also, consideration on removing conservation materials containing Ca and e fflorescence is required and retreatments need to be considered.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.205-212
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• 2016

This research investigates the influence of ground granulated blast furnace slag (GGBFS) composition on the alkali-activated slag cement (AASC). Aluminum oxide ($Al_2O_3$) was added to GGBFS binder between 2% and 16% by weight. The alkaline activators KOH (potassium hydroxide) was used and the water to binder ratio of 0.50. The strength development results indicate that increasing the amount of $Al_2O_3$ enhanced hydration. The 2M KOH + 16% $Al_2O_3$ and 4M KOH + 16% $Al_2O_3$ specimens had the highest strength, with an average of 30.8 MPa and 45.2 MPa, after curing for 28days. The strength at 28days of 2M KOH + 16% $Al_2O_3$ was 46% higher than that of 2M KOH (without $Al_2O_3$). Also, the strength at 28days of 4M KOH + 16% $Al_2O_3$ was 44% higher than that of 4M KOH (without $Al_2O_3$). Increase the $Al_2O_3$ contents of the binder results in the strength development at all curing ages. The incorporation of AASC tended to increases the ultrasonic pulse velocity (UPV) due to the similar effects of strength, but increasing the amount of $Al_2O_3$ adversely decreases the water absorption and porosity. Higher addition of $Al_2O_3$ in the specimens increases the Al/Ca and Al/Si in the hydrated products. SEM and EDX analyses show that the formation of much denser microstructures with $Al_2O_3$ addition.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.349-356
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• 2016

This report presents the results of an investigation on the early strength development of pastes high volume slag cement (HVSC) activated with different concentration of sodium carbonate ($Na_2CO_3$). The ordinary Portland cement (OPC) was replaced by ground granulated blast furnace slag (GGBFS) from 50% to 90% by mass, the dry powders were blended before the paste mixing. The $Na_2CO_3$ was added at 0, 2, 4, 6, 8 and 10% by total binder (OPC+GGBFS) weight. A constant water-to-binder ratio (w/b)=0.45 was used for all mixtures. The research carried out the compressive strength, ultrasonic pulse velocity (UPV), water absorption and X-ray diffraction (XRD) analysis at early ages(1 and 3 days). The incase of mixtures, V5 (50% OPC + 50% GGBFS), V6 (40% OPC + 60% GGBFS) and V7 (30% OPC + 70% GGBFS) specimens with 6% $Na_2CO_3$, V8 (20% OPC + 80% GGBFS) and V9 (10% OPC + 90% GGBFS) specimens with 10% $Na_2CO_3$ showed the maximum strength development. The results of UPV and water absorption showed a similar tendency to the strength properties. The XRD analysis of specimens indicated that the hydration products formed in samples were CSH and calcite phases.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.307-315
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• 2008

In this study, it is investigated the properties of high strength concrete using mineral admixture, on the purpose of use of meta kaolin for the substitutive materials to silica fume which is so expensive. The plain mixtures are 3 degrees which are ordinary portland cement, blast furnace slag cement and OPC included fly ash 20%, and silica fume and meta kaolin are substituted for the each plain mixtures in the range of 20%. The results of experiment showed as follows. In case of silica fume was only used, the viscosity and slump flow of fresh concrete were much decreased, on the contrary air content increased. But as usage of meta kaolin increased, to being increase the viscosity of fresh concrete, slump flow increased and air content and usage of super-plasticizer were decreased. Accordingly the workabilities of concrete were against tendency between silica fume and meta kaolin. The compressive strength, velocity of ultrasonic pulse and unit weight were increased according to usage of meta kaolin, the properties of hardened concrete were judged that they are affected with air content of fresh concrete, so it is very important to control air content of high strength concrete. Therefore, the use of meta kaolin is prospected to the substitutive material of silica fume, in case of using silica fume and meta kaolin, it is judged that the optimum usage of silica fume and meta kaolin is about 10% respectively, considering workability and strength of concrete.