• Journal of the Korea Institute of Building Construction
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• v.20 no.3
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• pp.213-221
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• 2020

The aim of the research is to provide thixotropy on cement-based materials. For this purpose, the linkage between polyvinyl alcohol (PVA) and borax was used. Namely, adding the suspensions of PVA and borax in cement paste, the thixotropy of cement paste was confirmed. The thixotropy of cement-based materials can have various advantages on construction process, especially, the placing method using pipe can have advantages. As a result of this research, the linkage between PVA and borax is valid inside of cement paste. Therefore, using PVA and borax, it is confirmed that the cement-based materials can have thixotropy with this method, and it can be expected to contribute on developing new method of placing cement-based materials with thixotropy.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.489-497
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• 2022

In this study, the fluidity, mechanical properties and microstructure of cement pastes with carbon nanotube (CNT) were experimentally investigated. The 6 types of cement paste mixes with different PCE:CNT and w/b had been manufactured, and several tests including flow, compressive strength, absorption and water porosity were performed on cement pastes with or without CNT.Additionally, microstructural observations such as x-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to examine hydrates formed in cement paste with CNT. As a result, it was found that the performance of cement pastes with CNT was better compared to that of control cement paste (OPC) due to both of hydration acceleration effect and filling effect. Furthermore, the SEM images clearly showed that CNT can bridge cracks formed in cement matrix. Conclusively, it is believed that the CNT, if mixed appropriately, could be an option as nono-materials to improve performance of concrete structures.

• Advances in concrete construction
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• v.2 no.3
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• pp.209-227
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• 2014

The use of limestone fines (LF) in mortar and concrete can in certain ways improve performance and thus has become more and more commonplace. However, although LF is generally regarded as a filler, it is up to now not clear how much filling effect it could have and how best the filling effect could be utilized. Herein, the packing density and filling effect of LF were studied by measuring the packing densities of LF, (LF + cement) blends and (LF + cement + fine aggregate) blends under dry and wet conditions, and measuring the performance of mortars made with various amounts of LF added. It was found that the addition of LF would not significantly increase the packing density of (LF + cement) blends but would fill into the paste to increase the paste volume and paste film thickness, and improve the flow spread and strength of mortar.

• International Journal of Concrete Structures and Materials
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• v.2 no.2
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• pp.161-167
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• 2008

Optimization of concrete mixing system is very important for the production of quality mixture of concrete and requires very complicated, specialized knowledge as there are a variety of variables that influence the result. One of the methods of optimizing the concrete mixing system is to minimize the volume of cement paste which, in turn, means maximizing the volume of aggregate. The purpose of this study is to determine the minimum volume of cement paste used in the design of concrete mixture and to design the optimum concrete mixing system based on the fluidity of mortar and concrete. In determining the minimum volume of cement paste, experiments of mortar and concrete were performed based on their workability, material segregation and bleeding. Type of aggregate, granularity distribution and sand percentage were used as test parameters and measurements were taken of the distribution of granularity, usage of HRWRA, minimum volume of paste and drying shrinkage and compressive strength of concrete.

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.532-540
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• 1988

Even the finest cement as having a specific surface area of 6.000~8.500$\textrm{cm}^2$/g (Blaine) is to convert into low-porosity hardened cement paste by the use of appropriate plasticizer. In this study, tests were carried out on such a special cement mix(fineness of 6.000$\textrm{cm}^2$/g, Ca-lignosulfonate plus k2CO3 as plasticizer and W/C=0.25) in comparison with ordinary Portland cement. Owing mainly to the high fineness of the cement powder and the low water-to-cement ratio, the hardened low-porosity cement paste showed a very tight microstructure, the pore texture of which consisted of micropores and wide pores only of small radii. The consequence of such mix was hence that the low-porosity special cement had excellent properties of early-high and very high strengths as compared to ordinary Portland cement. Its volume change when dried in the air or re-wetted, exhibited superor behaviour as well.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.5
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• pp.514-525
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• 2006

Statement of problem: The color change of final restoration resulting from resin cement is variable since the amount of the tooth is prepared is minimum. Purpose: The purpose of this study was to compare the color accuracy of try-in paste and their corresponding resin cements and the color stability of restoration intermediated resin cement according to two shades of three products(Rely-X. Variolink II. Choice). Material and method: Color was measured for porcelain disk sample without try-in paste, and porcelain disk sample intermediated by try-in paste and resin cement, then color differences were calculated. Results : 1. Color difference(${\Delta}E^*$) between try-in paste and resin cement showed the lowest value at Variolink II and increased in the order Choice and Rely-X statistically significant, and $?E^*$ of three resin cements was greater in A3 then A1. 2. The values of ${\Delta}L^*$ and ${\Delta}a^*$ between try-in paste and resin cement was in the increasing order of Variolink II, Choice and Rely-X. The ${\Delta}b^*$ value was increased in this order Choice, Rely-X and Variolink II in A1 on the other hand Variolink II, Rely-X and Choice in A3. 3. Color difference(${\Delta}E^*$) before and after resin cement showed the lowest value at Variolink II and increased in the order Rely-X and Choice. Conclusion : Above result revealed that the colors of try-in paste and resin cement were more or less accurate in the range of 0.35-1.95 of color difference which was unnoticeable with human eye, and Variolink II was superior to the other resin cements in color accuracy.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.2
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• pp.162-168
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• 2024

This study investigated the setting characteristics of cement paste with varying proportions of fly ash replacement using the electro-mechanical impedance (EMI) sensing technique. Cement paste samples were prepared with a water-to-binder ratio of 40 %, substituting fly ash for 10 %, 20 %, and 30 % of the cement weight. Piezoelectric (PZT) sensors were embedded in the center of each cement paste sample to continuously monitor the EMI signals. Vicat needle test and semi-adiabatic calorimetry test were conducted to validate the reliability of the EMI sensing technique in monitoring the setting of cement paste. Experimental results revealed notable changes in the magnitude and resonant frequency of the EMI resonant peaks during the setting time. It was confirmed that the setting times measured through the EMI sensing technique were correlated with those determined by the Vicat needle test and semi-adiabatic calorimetry test.

• Journal of the Korea Institute of Building Construction
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• v.14 no.1
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• pp.68-75
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• 2014

In order to increase the integrity of the wellbore which is used to prevent the leakage of supercritical $CO_2$, it is necessary to develop a concrete that is strongly resistant to carbonation. In an environment where the concentration of $CO_2$ is exceptionally high, $Ca^{2+}$ ion concentration in pore solution of Portland cement concrete will drop significantly due to the rapid consumption of calcium hydroxide, which decreases the stability of the calcium silicate hydrate. In this research, calcium phosphates were used to modify Portland cement system in order to produce hydroxyapatite, a hydration product that is strongly resistant to carbonation under such an environment. According to the experimental results, calcium phosphates reacted with Portland cement to form hydroxyapatite. The formation of hydroxyapatite was verified using X-ray diffraction analyses with selective extraction techniques. When using dicalcium phosphate dihydrate and tricalcium phosphate, the 28-day compressive strength was lower than that of plain cement paste. However, the specimen with monocalcium phosphate monohydrate showed equivalent strength to that of plain cement paste.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.144-145
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• 2020

Recently, the cement industry has been using various wastes as raw materials and fuel for cement as an eco-friendly business. However, most of these waste resources contain large amounts of chloride and alkali, which are concentrated in manufacturing facilities and adversely affect cement production products. Accordingly, in the cement production process, the chlorine ion contained in cement is managed by introducing the Chlorine Bypass System (CBS) into the manufacturing facility and releasing the dust. However, the processing volume of CBS-Dust has been limited due to the shortage of domestic processing companies, and the cost has also been raised, requiring measures to be taken in dealing with CBS-Dust. In this study, rheological properties of CBS-Dust incorporated paste are tested. With the increase of CBS-Dust, flow was decreased due to enhanced viscosity.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.345-346
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• 2018

In this study, various materials such as epoxy material, urethane material, cement material, and acrylic material are used to solve the water leakage occurring in underground structures. However, in the reality that the durability is insufficient and the effect is insufficient, it is aimed to improve the repairing effect by using cement and acrylics n combination. As a first study, we tried to verify the performance of rapid micro cement and cement paste and to improve the performance by checking the product properties. Three types of micro cement are evaluated. Three types of micro cement are used: fiber inclusion, fiber unfolding, and cement paste. When the material is selected for micro cement, it is applied to the field to understand the maintenance effect and durability.