• Journal of Korean Society of Environmental Engineers
• /
• v.29 no.7
• /
• pp.810-819
• /
• 2007

Investigation of alkali activation of fly ash and blast furnace slag was carried out using waterglass and sodium hydroxide. XRD, FTIR, $^{29}Si$ and $^{27}Al$ NMR, TGA and SEM were used to observed the reaction products and microstructure of the fly ash/slag cement (FSC) pastes. The reaction products were amorphous or low-ordered calcium silicate hydrate and aluminosilicate gel produced from alkali activation of blast furnace slag and fly ash, respectively. On the basis of this investigation, waterglass solution with a modulus(Ms) of 1.0 and 1.2 is recommended for alkali activation of fly ash and blast furnace slag. Morphology of FSC pastes alkali-activated with Ms of 1.0 and 1.2 shows a more solid and continuous matrix due to restructuring of gel-like reaction products from alkali-activated fly ash and blast furnace slag together with another hydrolysis product(i.e., silica gel) from water glass.

• Journal of the Korea Concrete Institute
• /
• v.21 no.1
• /
• pp.21-27
• /
• 2009

In this study, experimental findings on the resistance to magnesium sulfate attack of portland cement mortar and paste specimens incorporating metakaolin (MK) are presented. Specimens with four replacement levels of metakaolin (0, 5, 10 and 15% of cement by mass) were exposed to solutions with concentrations of 0.424% and 4.24% as $MgSO_4$ at ambient temperature. The resistance of mortar specimens was evaluated through visual examination and linear expansion measurements. Additionally, in order to identify the products formed by magnesium sulfate attack, microstructural analyses such as XRD, DSC and SEM/EDS were also performed on the paste samples incorporating metakaolin. Results confirmed that mortar specimens with a high replacement level of metakaolin exhibited lower resistance to a higher concentration of magnesium sulfate solution. It was found that the negative effect of metakaolin on the magnesium sulfate attack is partially attributed to the formation of gypsum and thaumasite. Conclusively, it is necessary to pay a special attention when using metakaolin in concrete structures, particularly under highly concentrated magnesium sulfate environment.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.89-92
• /
• 2008

The seismic behavior of the lightly reinforced concrete frames (LRCFs) was controlled by the nonductile behavior of the critical regions. These critical regions require retrofit to improve the seismic behavior of the lightly reinforced concrete frames. Critical column end regions must be retrofit to increase the global ductility capacity. The objective of this research is to evaluate structural strengthening performance of lightly reinforced concrete frame with Strain hardening cement composite(SHCC) experimentally. The experimental investigation consisted of a cyclic load tests on 1/3-scale models of precast infill walls. Reinforcement detail of infill wall was variables in the experiment. The experimental results, as expected, show that the multiple crack pattern, strength, ductility and energy dissipation capacity are superior for specimen with SHCC infill wall due to bridging of fibers and stress redistribution in cement matrix.

• Proceedings of the IEEK Conference
• /
• 2001.10a
• /
• pp.453-458
• /
• 2001

This study was performed to reuse the dyeing wastewater sludge treated by Fenton process through the solidification/stabilization technique. To solidify the dyeing sludge the industrial by-products such as blast furnace slag, fly ash and waste sand with cement were used. The laboratory scale and pilot scale test were conducted at room temperature to make construction brick which has high compressive strength and low leaching of heavy metals. The experimental results showed that blast furnace slag and fly ash could be used instead of cement and the products satisfied the regulation of Korean Standards. The blast furnace slag increased the compressive strength and the optimum ratio of slag/dyeing sludge on dry basis was found 0.4. The solidifying agent of SB series could increase rapidly the compressive strength and the optimum ratio of solidifying agent/sludge on dry basis was 0.26 at which the strength was two times compared with non-added condition. The portion of waste and industrial by-products in matrix was over 80%. From the pilot test the optimum pressure in molding was 100kg/$\textrm{cm}^2$ at which the compressive strength was over 100kg/$\textrm{cm}^2$. And the strength increased continuously to 160kg/$\textrm{cm}^2$ until 120 days curing time due to pozzolanic reaction. When SB-20 as a solidifying agent was used, the unconfined compressive strength of dyeing sludge could be obtained 110kg/$\textrm{cm}^2$ which satisfied the regulation of cement brick in Korea Standard(KS).

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.1
• /
• pp.75-83
• /
• 2014

In order to prevent brittle failure of concrete, steel fiber reinforcement is effective composite material. However ductility of steel fiber reinforced concrete may be limited due to shrinkage caused by large content of cement binder. Chemical prestressing for steel fiber reinforcement in cement matrix can be induced through expansive admixture and this can increase reinforcing effect of steel fiber. In this study, mechanical performances in concrete with CSA (Calcium sulfoaluminate) expansive admixture and steel fiber reinforcement are evaluated. For this work, steel fiber reinforcement of 1 and 2% of volume ratio and CSA expansive admixture of 10% weight ratio of cement are added in concrete. Mechanical and fracture properties are evaluated in concrete with steel fiber reinforcement and CSA expansive admixture. CSA concrete with steel fiber reinforcement shows increase in tensile strength, initial cracking load, and ductility performance like enlarged fracture energy after cracking. With appropriate using expansive admixture and optimum ratio of steel fiber reinforcement, their interactive action can effectively improve brittle behavior in concrete.

• The Journal of Korean Academy of Prosthodontics
• /
• v.24 no.1
• /
• pp.125-138
• /
• 1986

It is considered that etching solution or material itself of phosphoric ester cement will induce not a little pulpal irritation, if applied directly onto unsealed dentinal tubules. This study was designed to confirm above consideration by comparing two different conditions between $Ca(OH)_2$-based and non-$Ca(OH)_2$-based group. Posterior teeth of 15 male dogs were selected for this experiment. One experimental group was filled with cement after $Ca(OH)_2$-basing and enamel-etching, the other experimental group after enamel etching without $Ca(OH)_2$-basing. And both of two experimental groups were observed at 2 hours, 15 hours, 3 days, 1 week, 2 weeks, 4 weeks, and 6 weeks after filling. The findings reached to the following conclusions histologically. 1. In both groups, the damaged odontoblasts were atrophied and eventually disappeared. 2. In non-based group at early stage, odontoblasts were severely atrophied and defective areas were appeared between odontoblast cell layers. However, in based group, the odontoblasts were arranged slight irregularly. 3. In non-based group, a small number of undifferentiated cells below the odontoblast cell layers started to appear at 1 week after filling. However, in based group, the undifferentiated cells were appeared at 15 hours after filling. 4. In non-based group, formation of reparative dentin was not begun until late stage of experiment. However, in based group, formation of reparative dentin matrix was begun at 2 weeks after filling and very thickened reparative dentin was formed at 6 weeks after filling. 5. In odontoblast cell layers of both groups, dilated capillaries were observed. 6. Argyrophilic fibers were reticularly condensed in zone of Weil, and they were connected to the pulp tissue and dentin.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.909-912
• /
• 2008

Fiber is an important ingredient in strain-hardening cementitious composite (SHCC), which can control fracture of cementitious composite by bridging action. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of SHCC. But SHCC has serious problem as drying shrinkage because silica powder is used to make SHCC in order to improve bond strength between reinforcing fibers and cement matrix. Therefore, curing method (period and temperature) is very important for SHCC to show high tensile performance. a variety of experiments have being performed to access the performance of SHCC recently. This research emphasis is on the mechanical properties of SHCC made in Polyvinyl alcohol (PVA), Polyethylene (PE) fibers and steel cord (SC), and how curing method affects the composite property, and ultimately its strain-hardening performance.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.04a
• /
• pp.913-916
• /
• 2008

Direct tensile response of strain hardening cement composites(SHCC) depends primarily on the material's tensile response, which is a water cement ratio, direct function of fiber and matrix characteristics, the bond between them, and the fiber volume fraction. This paper discusses effect of aspect ratio of the direct tensile response of SHCC with PET and PVA fibers. The main variables considered include the aspect ratio of PET fibers(Aspect ratio, ${\ell}/d_f$ : 150, 300, 600). For the same mixture proportion, PET1.5+PVA0.5-300 and PET1.5+PVA 0.5-600(Aspect ratio 300, 600) showed better overall behavior(Pseudo strain-hardening, Multiple cracking) than specimens with PET1.5+PVA0.5-150(Aspect ratio 150). Tensile strain of PET1.5+PVA0.5-300 and PET1.5+PVA 0.5-600 at ultimate tensile stress were 0.5, 2.0% respectively.

• Journal of the Korea Institute of Building Construction
• /
• v.15 no.3
• /
• pp.299-306
• /
• 2015

In construction materials area, many research on polymer for cement-based materials have been conducted. In spite of these research, general research scope is limited to the normal strength range, and thus in this research, for both normal and high strength range mixtures, the strength and mechanical properties of high strength cement mortar incorporating Vinyle Acetate-Ethylene(VAE) type powder polymer are evaluated. As a result of experiment, in the case of high strength mixture, as the amount of VAE polymer addition was increased the compressive and flexural strengths were decreased while the tensile and bonding strengths were increased because of the formation of the polymer membrane inside of the mortar matrix.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.7 no.3
• /
• pp.210-215
• /
• 2019

Concrete members with wide surface area are vulnerable to cracking due to material behavior such as hydration heat and drying shrinkage. Recently many researches have been performed on improvement of strength and cracking resistance through fiber reinforcement, which are mainly focused on enhancement of tensile strength against cracking due to material behavior. In this paper, CFs(Cellulous Fibers) are manufactured for slurry type, and the engineering properties in cement mortar incorporated with CFs are evaluated for flow-ability, compressive, and flexural strength. Through SEM analysis, a pull-off characteristics of CF in matrix are analyzed. With CF addition of $0.5kg/m^3{\sim}1.0kg/m^3$, flexural strength is much improved and enough toughness of pull-off is also observed unlike plastic fiber containing smooth surface.