• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.388-395
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• 2016

This paper explores the photocatalytic sensitivity of cement mortar incorporated with recycled $TiO_2$ from waste water sludge. Basically, $TiO_2$ cluster sank down slowly to the bottom of cement mortar specimen before setting and hardening process. This leads the mismatch of $TiO_2$ concentration on the top and the bottom faces of a specimen. This poorly dispersed $TiO_2$-cement mortar naturally exhibits poor NOx removal efficiency especially on the top of cementitious structure. In architectural engineering application such as building or housing structures, one can simply filp over from the bottom so that more $TiO_2$ concentrated surface can be placed outward into the air. However, in highway pavement case, this could not be applicable due to in-situ installation of concrete pavement. Hence, the dispersion of $TiO_2$ cluster inside the cementitous material is getting important issue onto road construction application. To elaborate this issue, according to our results, silica fume, high-ranged water reducer, viscosity agent, blast furnace slag were not enhanced much of dispersion characteristics of $TiO_2$ cluster. The combination of foaming agent and accelerator of hardening with viscosity agent and small grain size of fine aggregate may help the dispersion of $TiO_2$ inside cementitious materials. Even though the enhanced dispersion were applied to the specimen, NOx removal efficiency doest not change much for the top surface of the specimen. This concurrently affected by the presence of tiny air voids and the dispersion of $TiO_2$ in that these voids could easily adsorbed NOx gas with the aid of large surface area.

• Journal of the Korea Institute of Building Construction
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• v.15 no.5
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• pp.483-489
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• 2015

The Purpose of this study was to establish the basic data on the mechanical properties of PCM in the high temperature range. To this end, an experiment was conducted on the characteristics of the residual compressive strength by temperature (100, 200, 400 and $600^{\circ}C$) with a fixed temperature heating. An after heating test was performed to investigate the properties after fire damage. The result showed that the residual compressive strength of PCM had a tendency to decrease, regardless of the type of polymer. It was also found that when the contents were low, the residual compressive strength started to greatly decrease from the high temperature range of $400^{\circ}C$, and that the specimen containing PAE showed a steeper slope than the specimen containing EVA. However, since little studies have been conducted on the mechanical properties of PCM with the high temperature, it is considered that, in addition to this study, basic studies must be preceded, including studies on the repairing methods.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.181-189
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• 2009

This study is to evaluate an effect of supports with respect to these supports after comparing the characteristic of support between rock bolt of a widely used type and spiral bolt of a new type. For these purposes, we performed pull-out test in laboratory about rock and spiral bolts in the case of cement-mortar grout curing periods, 7 and 28 days, then calculated pull-out load, displacement, external pressure, inner pressure and shear stress using data obtained from the results of pull-out test, respectively. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. We found that because adhesive force between supports and cement-mortar grout is increasing with compressive strength of grout according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.95-104
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• 2005

The research conducted to study the potential practicability of recycled aggregate concrete by analyzing the characteristics of concretes made of recycled quality aggregates produced by wet and dry process has found the following results. The air content of recycled aggregate concrete increased with increase of the substitut on rate due to mortar included while producing recycled aggregates. However, the concretes with aggregate produced by dry process had relatively low rate of increase in air content. The slump showed generally decreasing trend as the substitution rate of recycled aggregate increased regardless of the wet or dry process. It was assumed that the mortar particles remained in recycled aggregate absorbed the surplus hydration in concrete and decreased fluidity The compressive strength generally decreased as the substitution rate of recycled aggregate increased, however there was an increasing trend as well due to decreasing effect of water-cement ratio when the substitution rate of recycled aggregate reached 25, 50% after mix. This phenomena also appeared in early age, which meant that recycled aggregate concrete should not be retarded in setting when applied in the field. The tensile strength also reached the maximum when wet or dry recycled aggregate replaced with 25%. To conclude, recycled aggregates for concrete produced by wet or dry process are expected to demonstrate essential characteristics of concrete without significant decline in physical or dynamic quality when the substitution rate is below 25% although there are variations subject to water-cement ratio. However, slight differences are expected due to types of recycled aggregate and physical quality.

• 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 institute for structural maintenance and inspection
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• v.18 no.2
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• pp.117-125
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• 2014

This paper examines the fundamental properties of alkali-activated slag cement (AASC) activated by sodium hydroxide (NaOH). The water to binder (W/B) ratio was 0.4 and 0.5. And concentration of activator were 2M and 4M. Five mix design of each W/B ratios was considered. The N0 mixture was KS L 5109 method and N1~N4 were varied in different mixing time, mix step and entering points of fine aggregate. Test results clearly showed that the flow value, strength and drying shrinkage development of AASC were significantly dependent on the entering point of fine aggregate. The flow value tended to decreases with delaying entering point of fine aggregate. The compressive strength and flexural strength increases with delaying entering point. Moreover, the XRD analysis confirmed that there were sustain these results. The drying shrinkage increases with delaying entering point of fine aggregate. Futhermore, a modified mixing method incorporating all hereby experimentally derived parameters, is proposed to improvement the physical properties of AASC.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.77-86
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• 2013

This study investigates the fundamental properties of the water-binder (W/B) ratio and fine aggregate-binder (F/B) ratio in the alkali-activated slag cement (AASC) mortar. The W/B ratios are 0.35, 0.40, 0.45, and 0.50, respectively. And then the F/B ratios varied between 1.00 and 3.00 at a constant increment of 0.25. The alkali activator was an 2M and 4M NaOH. The measured mechanical properties were compared, flow, compressive strength, absorption, ultra sonic velocity, and dry shrinkage. The flow, compressive strength, absorption, ultra sonic velocity and dry shrinkage decreased with increases W/B ratio. The compressive strength decreases with increase F/B ratio at same W/B ratio. Also, at certain value of F/B ratio significant increase in strength is observed. And S2 (river sand 2) had lower physical properties than S1 (river sand 1) due to the fineness modulus. The results of experiments indicated that the mechanical properties of AASC depended on the W/B ratio and F/B ratio. The optimum range for W/B ratios and F/B ratios of AASC is suggested that the F/B ratios by 1.75~2.50 at each W/B ratios. Moreover, the W/(B+F) ratios between 0.13 and 0.14 had a beneficial effect on the design of AASC mortar.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.2
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• pp.135-142
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• 2021

In this work, multi-turn wings and guide plates are installed on recycled aggregate crushing devices to improve existing low recycled aggregate quality. Simulation analysis to evaluate the crushing efficiency of the new device shows enhanced crushing efficiency since the installation of guide plates shreds most of the inputs inside the crushing drum, and the multi-turn wings and guide plates induce rebound and circulation of the aggregate. Through this, the new device was found to be more economical and efficient than the existing recycled aggregate crushing device. Also, the amount of cement paste and mortar attached to the surface of the aggregate was smaller than that of the existing recycled aggregate, and it was found that the mechanical properties and elastic modulus deterioration were reduced. However, the carbonation resistance of concrete was not improved to the level of natural aggregates due to the remaining tiny cement paste and mortar on the surface of the new recycled aggregate. Therefore, it is deemed necessary to further research and experiment such as device improvement or binder development to reduce durability degradation of concrete mixed with new recycled aggregate.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.3
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• pp.86-91
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• 2024

In this study, the characteristics of mortar using carbondioxide conversion capture materials (CCMs), fabricated by reacting CO₂ with desulfurization gypsum (DG) by-produced from a oil refinery, as a cement mixture. Based on the chemical component and particle size analysis results, it estimated that desulfurized gypsum reacted with carbon dioxide to produce carbonate crystals such as CaCO₃. Using CCMs as a cement mixture, physical property and durability analysis were conducted by measuring such as workability, compressive strength, compressive strength ratio after freezing-thawing and accelerated carbonation depth. The experimental results showed that as the content of the admixture increased, workability and compressive strength characteristics decreased. Compressive strength after freezing-thawing and accelerated carbonation depth also showed similar characteristics to the physical property measurement results. In addition, compared to desulfurized gypsum, using CCMs showed better physical properties and durability. This was assumed to be due to differences in the crystal phases of the mixed materials such as free-CaO and CaCO₃.

• 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.