• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.633-640
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• 2010

This study was performed to get basic information about properties of high blaine cement for shotcrete use. Particle size distribution, setting time and compressive strength test, analysis like as SEM, DSC thermal analysis, XRD was carried out to investigate principle properties of high blaine cement. Setting time of high blaine cement was shorter and compressive strength was higher than those of ordinary portland cement (OPC). Results of analysis showed early hydration products of high blaine cement is smaller and spread widely due to increased specific surface. From the SEM observation and analysis of DSC and XRD results, it was seen that the aluminates accelerators promoted calcium aluminium hydrates while the alkali free accelerators increased ettringite and monosulfates formation. Strength and setting time measurement of cement paste with aluminate accelerator is more effective than the alkali free accelerator in reducing the setting time and increasing early strength while alkali free accelerator is more effective in increasing the strength after 7 days.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.277-280
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• 2006

This paper presents the findings on the sulfate resistance of mortar specimens with or without alkali-free accelerator exposed to sodium sulfate solution for 270 days. Test results confirms a negative effect of alkali-free accelerator on the sulfate deterioration. Additionally, the influences of exposure concentration and temperature of sulfate solution on expansion were investigated. Especially, at a high concentration of solution a significant expansion of mortar specimens with alkali-free accelerator was observed. Further, low temperature also promoted the deterioration of the cement system due to sulfate attack.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.953-956
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• 2006

Sulfate resistance of mortar specimens with or without alkali-free accelerator exposed to sulfate solutions for 360 days was investigated. Test results confirms a negative effect of alkali-free accelerator on the sulfate deterioration, irrespective of attacking sources. Based on the ASTM C1012 expansion test, the experimental findings demonstrated that higher $C_3A$ content in cement led to the higher expansion, especially in the mortar specimens with alkali-free accelerator.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.514-519
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• 2020

In this study, cement clinkers were sintered at each temperature by replacing some of the clay components of cement clinkers with coal materials. The mineral phase change of sintered cement clinker was quantitatively analyzed by XRD-Rietveld method. As the sintering temperature of cement clinker increased, the amount of belite decreased, the amount of alite increased, and the amount of free-CaO decreased. The form of alite and belite could be distinguished at sintering temperature of 1450℃ or higher. The crystal size was greatly increased at 1500℃ sintering. It was confirmed that the excessive sintering was progressed. Free-CaO decreased with the increase of sintering temperature. At 1450 ℃ or higher, it was less than 0.5%. In 1450℃ or greater, it is determined that enough sintering is included. Therefore, the application of fly ash as a raw material of cement clinker was judged to be usable as a source of chemical components of alumina and iron raw materials.

• Journal of the Korean Ceramic Society
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• v.29 no.4
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• pp.298-304
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• 1992

Flexural strength, microstructure, hydration reaction and moisture sensitivity in macro defect-free (MDF) cement, which basically prepared of high alumina cement (HAC) and hydroxypropyl methylcellulose (HPMC) and polyvinylalcohol (PVA) as water soluble polymer were investigated. Cement composites based on HAC-PVA system were improved in flexural strength than that of HAC-HPMC system especially, the strength of specimens added to 10 wt% of polyvinylalcohol was 160 MPa. These improvements of flexural strength were attributed to not only the effect of water soluble polymer in elimination of macropores (above 100 $\mu\textrm{m}$) and cement grain bridging, but the effect of unhydrate cement as an aggregate. Moisture sensitivity and flexural strength in wet condition of MDF cement composites immersed in water at 80$^{\circ}C$ for 3 days were decreased.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.695-702
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• 2002

Shotcrete (or Sprayed concrete) has been used as an important support material in New Austrian Tunnelling Method (NATM). Since the mid of 1990, permanent shotcrete tunnel linings such as Single-shell, NMT (Norwegian Method of Tunnelling) has been constructed in many countries for reducing the construction time and lowing construction costs instead of conventional in-situ concrete linings. Among essential technologies for successful application of permanent shotcrcte linings, high performance shotcrete providing high strength, high durability, better pumpability has to be developed in advance as an integral component. This paper presents the Ideas and first experimental attempts to increase early strength and bond strength of wet-mixed Steel Fiber Reinforced Shotcrete(SFRS) in sump water condition. In order to increase early strength, a new approach using high-early strength cement with liquid alkali-free accelerator has been investigated From the results, wet-mix SFRS with high-early strength cement and alkali-free accelerator exhibited excellent early strength improvement compared to the ordinary portland content and good bond strength even under sump water condition.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.107-108
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• 2011

The purpose of present study is to examine the application of effective curing to hardener-free epoxy-modified mortars. The epoxy-modified mortars are prepared with polymer-cement ratios, subjected to two types of curing conditions, and tested for compressive, flexural and tensile strengths. As a result, hardener-free epoxy-modified mortars with steam curing is markedly improved with increasing air-dry curing period. High strength development of the epoxy-modified mortars may be achieved by the dense microstructure by cement and the hardener of the epoxy resin in the mortars.

• Restorative Dentistry and Endodontics
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• v.13 no.2
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• pp.307-322
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• 1988

The purpose of this study is to evaluate the pulpal responses to the base materials such as zinc oxide eugenol cement, calcium hydroxide, zinc phosphate cement, polycarboxylate cement and glass ionomer cement. The 100 caries free dog teeth were devided into 2 groups by remaining dentin thickness (Group A: 0.4-0.6 mm, Group B: 0.8-1.0 mm) and each group were devided into 5 subgroups. The intervals of observation period are 3days, 1 week, 2 weeks, 4 weeks and 8 weeks respectively after experiment. The specimens were fixed with 10% formalin and decalcifed in 5% nitric acid. All specimens were stained with Hematoxylin-Eosin and examined histopathologically. The results were as follows. 1. In group A, atropy or hyperplasia in odontoblasts were seen in zinc oxide eugenol cement, calcium hydroxide and zinc phosphate cement. No changes in odontoblasts were seen in polycarboxylate cement and glass ionomer cement. 2. In group A, increase of predentin were seen in all experimental materials. 3. In group A, vascular congestion were seen in all experimental materials and inflammation were seen on 3 days in zinc oxide eugenol cement, 8 weeks in zinc phosphate cement and hemorrage were seen on 3 days in zinc phosphate cement. 4. In group B, changes of odontoblasts were not seen all experimental materials. 5. In group B, increase of predentin and vascular congestion were seen in all experimental materials but inflammation were not seen.

• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.702-708
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• 2003

Cement paste, mortar or concrete specimens, substituting the content of Portland cement with fly ash up to 50 wt%, were prepared to investigate the effect of fly ash on the temperature, free lime content and strength etc. of mortar/concrete. Being compared with the concrete made of ordinary Portland cement, temperature increment of the concrete containing 50 wt% fly ash reduced, according to appropriate conversion formulae, to about 45％ at the 7 days curing time: the temperature increment of the former amounted to 33.4$^{\circ}C$, while that of the latter only to 18.7$^{\circ}C$. On the other hand, it is better to control the content of fly ash in the cement that is used for reinforced concrete not to exceed 30 wt％. In this study, more than 28 days curing time is necessary in order that the strength of concrete made of fly ash cement will be higher than that of pure Portland cement. In addition, 28-days concrete strength higher than 360 kg/$\textrm{cm}^2$ could be easily achieved even with 50 wt% fly ash cement.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.99-105
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• 1993

The purpose of this fundamental study is to investigate the mechanism of high strength concrete using the high calcium sulfate cement from a point of view in cement hydration and micro structure. As a results, it was found that the internal pores of concrete are decreased by using the high calcium sulfate cement, because the hydrates of Ettringite which is densified in structure is much formed in early ages at steam curing. In addition to the ettringite needs the 32 times of free water formed mixing water for hydration. This effect are not only decreased the water to cement ratio and also increase to comp, strength of concrete. It was conclude that these above the two facts are the main mechanism of high strength concrete using high calcium sulfate cement.