• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.115-122
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• 2019

Steel Fiber Reinforced Wet-type Shotcrete improves the quality and stabilizes the tunnel by increasing the shear strength of the natural ground by constructing the concrete which attaches the fresh concrete to the predetermined position from the nozzle. The Steel Fiber Reinforced Wet-type Shotcrete improves and reinforces the strength and dynamic behavior characteristics of concrete to suppress the generation and growth of local cracks by increasing the tensile resistance ability. In addition, Steel Fiber Reinforced Wet-type Shotcrete is a shotcrete that improves tensile strength, bending strength, and crack resistance by dispersing discontinuous short steel fibers evenly in concrete. In this study, compressive strength test and bending strength test of shotcrete of NATM tunnel were measured and rebound reduction rate was measured by varying shotcrete putting pressure to 900 RPM, 1,000 RPM, and 1,100 RPM. Therefore, the data that can be applied to domestic NATM tunnel construction are presented.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.205-211
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• 2006

The purpose of this study was to evaluate the effects of fly-ash on strength development and durability of latex-modified concrete (LMC) and ordinary portland cement concrete (OPC). Main experimental variables were latex contents (0%, 10%, 15%) and fly-ash content (0, 10%, 20%, 30%). Air content and slump tests were performed to check the basic properties of fresh concretes, and compressive strength, flexural strength, rapid chloride ion permeability and chemical resistance were measured to analyze the basic properties of hardened concretes. The test results showed that air contents of LMC with fly ash decreased as fly-ash contents increased from 0% to 30%. Compressive and flexural strength developments of LMC with fly ash were quite similar to those of LMC without fly ash. However, the long-term flexural strength development of LMC with fly ash after 90 days were bigger than that of LMC without fly ash. Chloride ion permeability and chemical resistance decreased rapidly as the content of fly ash increased. Thus, fly ash could be used at LMC in order to reduce water permeability.

• Tunnel and Underground Space
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• v.13 no.5
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• pp.362-372
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• 2003

Since the occurrence of Portland cement, a great number of concrete structures were constructed. But the concrete structures have their own life times, which inevitably demand repairing treatments, especially on their surface parts. Currently many various methods have been developed and are being applied fer this purpose. In this study, a newly developed method using pneumatic chipping machine and anchor pin was adopted far repair of old concrete structure and the mechanical characteristics of cementing plane between existing and new concrete were tested. Comparing the removal methods for the decrepit part of existing concrete using pneumatic chipping machine and hydraulic breaker, the peak cohesion was higher when using chipping machine at the cementing plane. On the other hand, the residual cohesion was higher for the case of breaker. Step shaped chipping on the cementing plane was effective in increasing peak cohesion, which results 14% increase in the case of 30 mm step height and 22% in 50 mm height when compared with planar chipping plane. The use of anchor pin increased the residual cohesion, which restricted shear slip on the cementing plane after peak shear stress and the tensile strength of 32% compared with that of non-anchored case. According to the combined effect of step shaped chipping of 30 mm and anchor pin with an interval of 15 cm, the peak cohesion reached up to 77% and the residual cohesion showed 180% of the ones of the fresh concrete, respectively.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.179-188
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• 2007

Recently, the concern on the receipt of poor ready-mixed concrete in the construction field and the durability of concrete has been increased. Based on the such background, a large number of measuring methods of water content for fresh concrete have been developed and enforced in a developed country. In this study, to investigate practicality for quality control of ready-mixed concrete among various water content measurement techniques, microwave range method, air meter method and capacitance measurement method as measuring methods of water content were selected. Then, it was evaluated estimating performance of water content according to the change of binder types, fine aggregate types, absorption ratio, water content and water-binder ratio in series I and II. Also, it was examined influence on error occurrence of water content according to change of properties of used materials in series III. Finally, based on this study, it was proposed fundamental data to utilize measurement technique of water content to quality control of ready-mixed concrete in construction field.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.16-20
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• 2018

Steel Fiber reinforced self-compacting concrete (SFRSCC) has been widely used in a number of structures, such as ordinary civil infrastructures, sky scrapers, nuclear power plants, hospitals, dams, channels and etc. Thanks to its short and discrete reinforcing fibers, its performance, including tensile strength, ductility, toughness and flexural strength gets much better in comparison with ordinary self-compacting concrete (SCC) without any reinforcing fibers. Despite all these aforementioned advantages of SFRSCC, its performance highly depends on fiber's orientation. In case of short discrete fibers, the orientation of fibers is completely random and cannot be controlled during pumping process. If fibers distribution inside hardened state concrete are randomly distributed, it leads to less resistance potential of concrete element, especially in terms of flexural and tensile strength. The maximum expected strength may not be achieved. Therefore, fiber alignment has been considered as one of the important factors in SFRSCC. To address this issue, this study investigates the effects of concrete matrix's density and inlet velocity on fiber alignment during the pumping process using a finite element method.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.149-156
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• 2016

It has been well known that concrete structures exposed to chloride and sulfate attack environments lead to significant deterioration in their durability due to chloride ion and sulfate ion attack. The purpose of this experimental research is to evaluate the long-term durability against chloride ion and sulfate attack of the alkali activated cementless concrete replacing the cement with ground granulated blast furnace slag. For this purpose, the cementless concrete specimens were made for water-binder ratios of 40%, 45%, and 50%, respectively and then this specimens were cured in the water of $20{\pm}3^{\circ}C$ and immersed in fresh water, 10% sodium sulfate solution for 28, 91, 182, and 365 days, respectively. To evaluate the long-term durability to chloride ion and sulfate attack for the cementless concrete specimens, the diffusion coefficient for chloride ion and compressive strength ratio, mass change ratio, and length change ratio were measured according to the NT BUILD 492 and JSTM C 7401, respectively. It was observed from the test results that the resistance against chloride ion and sulfate attack of the cemetntless concrete were comparatively largely increased than those of OPC concrete irrespective of water-binder ratio.

• Asian-Australasian Journal of Animal Sciences
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• v.29 no.3
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• pp.428-435
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• 2016

The objective of this study was to clarify the most effective component of grazing for improving welfare of fattening pigs. This study compared welfare indicators of 20 fattening pigs aged 100 to 124 days (the prior period) and 138 to 164 days (the latter period) in an indoor housing system (IS), an outdoor pasturing system (OP), a concrete floor paddock system (CF), a concrete floor paddock system with fresh grass (FG), or a soil floor paddock system (SF). The last three treatments include important components of a grazing system: extra space, grass feed, and soil floor. Behavior, wounds on the body, and performances, measured as average daily gain (ADG) and feed conversion ratio, were observed. CF pigs behaved similarly to IS pigs. FG pigs showed higher levels of foraging, chewing and activity. SF pigs engaged in higher levels of foraging, exploring, activity, and rooting, and showed a similar amount of playing behavior as OP pigs. ADG was the same in all treatments at the prior period, and increased in the order FG, IS, CF, SF, and OP at the latter. The behaviors and performance of SF pigs resembled those of OP which seemed to indicate a consistently higher standard of welfare than the other treatments. In conclusion, the existence of a soil floor is the most important component of a pasture for improving the welfare of pigs.

• International Journal of Concrete Structures and Materials
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• v.7 no.3
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• pp.193-202
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• 2013

Geopolymer mortar compressed blocks were prepared using fly ash, ground granulated blast furnace slag, silica fume and metakaolin as binders and sand/quarry dust/pond ash as fine aggregate. Alkaline solution was used to activate the source materials for synthesizing the geopolymer mortar. Fresh mortar was used to obtain the compressed blocks. The strength development with reference to different parameters was studied. The different parameters considered were fineness of fly ash, binder components, type of fine aggregate, molarity of alkaline solution, age of specimen, fluid-to-binder ratio, binder-to-aggregate ratio, degree of saturation, etc. The compressed blocks were tested for compression at different ages. It was observed that some of the blocks attained considerable strength within 24 h under ambient conditions. The cardinal aim was to analyze the experimental data generated to formulate a phenomenological model to arrive at the combinations of the ingredients to produce geopolymer blocks to meet the strength development desired at the specified age. The strength data was analyzed within the framework of generalized Abrams' law. It was interesting to note that the law was applicable to the analysis of strength development of partially saturated compressed blocks when the degree of saturation was maintained constant. The validity of phenomenological model was examined with an independent set of experimental data. The blocks can replace the traditional masonry blocks with many advantages.

• International Journal of Concrete Structures and Materials
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• v.1 no.1
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• pp.11-18
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• 2007

In the recent design of high ductile engineered cementitious composites (ECC), optimizing both processing and mechanical properties for specific applications is critical. This study employs a method to develop useful ECC produced with slag particles (slag-ECC) in the field, which possesses different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or spray processing). Control of rheological modulation was regarded as a key factor to allow the performance of the desired processing while retaining the ductile material properties. To control the rheological properties of the composite, the basic slag-ECC composition was initially obtained, determined based on micromechanics and steady-state cracking theory. The stability and consequent viscosity of the suspensions were then mediated by optimizing the dosage of the chemical and mineral admixtures. The rheological properties altered through this approach were revealed to be effective in obtaining ECC-hardened properties, represented by pseudo strain-hardening behavior in uniaxial tension, allowing the readily achievement of the desired function of the fresh ECC.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.4
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• pp.173-177
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• 2017

A polynaphthalenesulfonate (PNS) superplasticizer and its relation to the fluidity of cement paste (w/c = 0.35) has been investigated for three cements at a given dosage of PNS superplasticizer. Chemical properties of three cements were characterized with a XRD, XRF. The additive effects of $Na_2SO_4$ on the fresh concrete with w/c = 0.33 were also estimated by the measurement of compressive strength, slump, air content. The experimental results exhibited that the addition of sodium sulfate 2.6 % to the cement A and C improves slump loss. In case of cement E, the addition of sodium sulfate 1.3 % was effective.