• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.721-728
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• 2000

The shear behavior of sawtoothed artificial joints grouted with cement milk was investigated in the laboratory under constant normal stress conditions. Tests were conducted on joints with asperities having inclinations of 16.7$^{\circ}$ and 26.6$^{\circ}$, compresive strengths having 15MPa and 47MPa under a given range of normal stresses varying from 0.76 to 1.91 MPa and at a free condition of pitching, rolling and dilatancy. Results show that the effect of asperities on shear strength increase is significant up to asperity height to grout thickness (t/a) ratio of 0.3∼1.0. Increase of cohesion is the main cause of shear strength increase in cement grouted sawtoothed artificial joints.

• Journal of the Korea Institute of Building Construction
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• v.18 no.2
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• pp.109-115
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• 2018

Since the current method of SCW cement milk pouring method uses one to one ratio of cement milk with OPC, there are some problems such as drying shrinkage, increased cost, difficulty of controlling mix proportions for various conditions of applied soil, and precipitation of $Cr^{6+}$ due to the excessively used cement. Specifically, in aspect of sustainability issues of cement manufacturing, the consumption of cement should be reduced. Hence, in this research, as a replacement of cement for SCW method, blast furnace slag with sulfate or alkali as a stimulant, and expansive admixture were used. By using blast furnace slag as a hardening composite of SCW, there are many advantages such as free controllable mix proportions, rapid setting time with less mud occurrence, less cost with less energy for mixing, constant strength development, and less precipitation of $Cr^{6+}$. Regarding the alternative composites for SCW, in this research, durability and chloride resistance were evaluated.

• Journal of the Korean Ceramic Society
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• v.43 no.7 s.290
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• pp.408-414
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• 2006

Properties of slag cement that contained 50 wt% of blast furnace slag were studied when replaced blast furnace slag powder with electric arc furnace slag powder. Electric arc furnace slag was aged for about 2 months in the air by being crushed to be 1-3 mm in size. As a result of the experiment, it was proven that the water content for obtaining the same consistency became decreased as slag is replaced with electric arc furnace slag instead of blast furnace slag. Also, the workability of mortar increased about 30% at the same ratio of water to binder when blast furnace slag was completely replaced with electric arc furnace slag. The compressive strength of mortar on the 28 days increased when a slag replacement rate became 10 wt%, however, it rather decreased when the slag replacement rate exceeded 10 wt%. The heat of hydration became higher for the first 14 h in case of the replacement of slag cement by electric arc furnace slag. Yet, it decreased when 14 h had passed. Therefore, when all blast furnace slag was replaced with electric arc furnace slag, about 15 cal/g heat of hydration decreased when it passed about 72 h.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.325-326
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• 2009

The present study concerns the acid neutralization capacity (ANC) of cement paste, mortar and concrete depending on a free water-cement ratio. The ANC of paste at 30%, 40% and 50% of water-cement ratio was measured and simultaneously the effect of aggregate on the ANC was evaluated. It was found that an increase in the acid concentration resulted in a decrease in the pH of the suspension, in particular, at 10 in the pH, a sharp decrease was observed. The ANC showed some peak resistances to acid at particular pH values.

• Nuclear Engineering and Technology
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• v.54 no.4
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• pp.1456-1463
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• 2022

The aim of this work is to study the radiation shielding properties of cement samples with waste glass incortated into its composition. The mass attenuation coefficient (MAC) of the samples were experimentally determined to evaluate their radiation shielding ability. The experimental coefficient was evaluated using NaI detector for gamma energies between 59.53 keV and 1408.01 keV using different radioactive point sources Am-241, Eu-152, Co-60, and Cs-137, and the gamma transmission parameters half-value layer, mean free path, and transmission factor were calculated. The theoretical coefficient of the composites was determined using Geant4 and XCOM software. The results were also compared against Geant4 and XCOM simulations by calculating the relative deviation between the values to determine the accuracy of the results. In addition the mechanical properties (including Compressive and porosity) as well as the thermogravimetric analysis were tested for the present samples. Overall, it was concluded that the cement sample with 50% waste glass has the greatest shielding potential for radiation shielding applications and is a useful way to reuse waste glass.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.1011-1018
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• 2005

The influence of liquid shotcrete accelerators(alkali aluminate, two types of alkali-free) was investigated. Comparing to the existing alkali aluminate accelerator, new alkali-free accelerator, AF2, shortened initial and final setting of cement system, and after curing for 1 day compressive strength was analogous with others. On the other hand, compressive strength of specimen cured for 12 hour was the highest by the addition of alkali aluminate accelerator, but final strength was the lowest by that. But compressive strengths of AF1, AF2 were similar to Plain up to 28day. Further from XRD(X-Ray Diffractometer) and DSC(Differential Scanning Calorimeter) analyses, we confirmed that setting promoted by alkali aluminate was mainly because of Ca(OH)2(calcium hydroxide), but the accelerating behavior of alkali-free was influenced by the needle-like ettringite$(6CaO{\cdot}Al_2O_3{\cdot}3SO_3{\cdot}32H_2O)$ crystal.

• Journal of the korean academy of Pediatric Dentistry
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• v.49 no.2
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• pp.197-205
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• 2022

This study was conducted to investigate the fluoride release of fluoride-containing restorative materials in fluoride recharging according to the concentration of fluoride toothpaste used in Korea. Samples of glass ionomer cement, resin-modified glass ionomer cement, alkasite restorative material, and composite resin were prepared and fluoride release was measured on days 1, 3, 7, 14, 21, 28. Thereafter, fluoride-free, 500 ppm, and 1450 ppm fluoride toothpaste was applied to each restorative materials, and the fluoride release was measured on days 1, 3, 7. Glass ionomer cement showed the highest cumulative fluoride release until the 7th day of measurement, and from the 14th day onwards, the resin-modified glass ionomer cement showed the highest cumulative fluoride release, but there was no significant difference. When restorative material groups were recharged with 500 ppm of fluoride toothpaste, the fluoride release was significantly higher only for the alkasite restorative material compared to the fluoride-free toothpaste group (p < 0.017). When restorative material groups were recharged with 1450 ppm of fluoride toothpaste, the fluoride release was significantly higher in all restorative groups compared to the fluoride-free toothpaste group (p < 0.017).

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.380-385
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• 2016

Nanocelluloses, mainly cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC, i.e., defect-free, rod-like crystalline residues after acid hydrolysis of fibers), have been the subject of recent interest. Due to the presence of hydroxyl groups on the surface of nanocelluloses, their surfaces are reactive, making them suitable candidates for reinforcing materials for manufacturing polymer composites. In this study, CNF was used as a reinforcing material for manufacturing cement composites. CNF was prepared by TEMPO (2,2,6,6,-tetramethyl piperidine-1-oxyl radical) oxidation procedure combined with extensive homogenization and ultrasonication. Transmission electron microscopy (TEM) analysis of the suspension showed the width of CNF between 10 and 15 nm. The compressive strength of cement composites containing 0.5% CNF was comparable to that of conventional cement composites. On the other hand, the tensile and flexural strength were improved by 49.7% and 38.8%, respectively, compared to those of conventional cement composites. Also, at an ambient condition, the degree of self-shrinkage reduction reached to 18.9% in one day, followed by 5.9% in 28 days after molding.

• Journal of the Korean Ceramic Society
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• v.11 no.1
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• pp.29-35
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• 1974

Effect of calcium sulfate and barium sulfate on the formation of portland cement clinker was studied by means of chemical analysis. DTA and X-ray diffraction analysis. In the presence of liquid phase, effect of the additives on the formation of tricalcium silicate was examined according to the reaction, 2CaO.$SiO_3$＋CaO$\longrightarrow$3CaO.$SiO_3$, which is the principal reaction in portland cement clinkerization, and optimum conditions in firing clinker concerning amount of additive, firing time and temperature were determined, and its kinetics was referred to. The experimental results are summerized as follow: (1) Appropriate burning temperature range of cement clinker is more limited as the content of calcium sulfate in clinker is increased. Amount of calcium sulfate, firing time and temperature in proper condition of clinkerization is related to each others. Being added suitable quantity of calcium sulfate, firing temperature of clinker can be lowered about $100^{\circ}C$. (2) When 3-5 mole% of calcium sulfate is added, firing time of 15-30 minutes at about $1380^{\circ}C$ is reasonable, and if the content is over7 mole %, firing for 1 hr. or more at $1350^{\circ}C$ is anticipated to be optimum condition. (3) In the reaction of tricalcium silicate formation, the role of barium sulfate as a mineralizer is similar to that of calcium sulfate, but the optimum firing temperature of cement clinker containing barium sulfate tends to be 20-$30^{\circ}C$ higher than that of clinker containing calcium sulfate. (4) When barium sulfate is used as mineralizer, 2-3 mole % of it to tricalcium silicate is recommended and if it is added more than this amount, free CaO is increased rapidly in clinker and alite formation is inhibited.

• The Journal of Advanced Prosthodontics
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• v.12 no.4
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• pp.197-203
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• 2020

PURPOSE. The aim of this study was to evaluate the effect of multiple firings on the bond strength between yttriatetragonal zirconia polycrystals (Y-TZP) and 2 types of resin cements. MATERIALS AND METHODS. Sixty 3Y-TZP specimens (LAVA Frame Multi) were divided into 3 groups depending on the following firing procedures: (1) 2-firing cycles, (2) 5-firing cycles, (3) 10-firing cycles. Two samples from each group were investigated by using SEM to determine the morphological changes. All specimens were treated with 125 ㎛ airborne-particle abrasion and the surface roughness of each specimen was measured. The specimens from each firing group were then further divided into 2 subgroups (n = 9) to apply 2 types of resin cement (MDP-free resin cement: RelyX Unicem-RU, and MDP containing resin cement: Panavia F 2.0-PA). The shear bond strength (SBS) test was performed and failure types of all the debonded specimens were classified by using a stereomicroscope as adhesive, cohesive, and mixed. The statistical analysis of surface roughness and SBS data were performed by using 1-way ANOVA and 2-way ANOVA followed by Tukey-HSD tests (α=.05). Failure modes were calculated as a percentage for each group. RESULTS. The bond strength of RU and PA to the specimens obtained with 2 firings were not statistically different from each other (P=.1). However, the SBS values of PA were found to be significantly higher than RU for the specimens obtained with 5 and 10 firing cycles (P=.001 and P=.02, respectively). Surface roughness analysis revealed no statistical difference between groups (P=.2). The SEM analysis of samples fired 5- and 10- times showed irregularities and boundary loss in zirconia grains, and empty spaces between zirconia grains. CONCLUSION. The bond strength of PA cement was higher than that of RU to the zirconia subjected to repeated firings (5 and 10 firing cycles). When zirconia is subjected to multiple firings, using MDP-containing resin cement can be recommended.