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A Study on Field Test of High-Strength Shotcrete using High-quality Additions and Accelerators (고품질 혼화재와 급결제를 적용한 고강도 숏크리트의 현장실험 연구)

  • Ma, Sang-Joon;Kim, Dong-Min
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.2C
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    • pp.121-131
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    • 2006
  • The strength standard of shotcrete in Korea is relatively lower than that in Europe where high-strength shotcrete has been developed and actively applied to the common practice, so it is hard to test a quality of high-strength shotcrete. In this study, field test was performed to find a solution improving the strength and a long-term durability on domestic shotcrete. In field test, a high-strength shotcrete was produced using high-quality additions and accelerators, and an effect of additions and accelerators was observed. In addition, quality test based on EFNARC was also performed. As a result of field test, a promotion ratio of early strength is 90~97% in case of using alkali-free accelerators, therefore, alkali-free accelerators had an effect on an increase of early strength on shotcrete. A compressive strength of shotcrete using Micro-silica fume was 45.2~55.8MPa and flexible strength was 5.01~6.66MPa, so a promotion ratio of strength was 37~79%, 17~61% respectively. It was showed that increment effect of strength by the silica fume replacement of 7.5~10% for cement mass was remarkable. As a result of test, it was possible to apply high-strength shotcrete to the domestic practice using high-quality additions such as Micro-silica fume and accelerators such as alkali-free.

A Vindication of Induction by Practical Inference (실천추론에 의한 귀납의 정당화)

  • Lee, Byeong-Deok
    • Korean Journal of Logic
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    • v.12 no.2
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    • pp.59-88
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    • 2009
  • According to David Hume, a deductive demonstration for inductive inference is not possible, because inductive inference is not deductive; and an inductive demonstration for inductive inference is not possible either, because such a demonstration is circular. Thus, on his view, there is no way of justifying inductive inference. Ever since Hume raised this problem of induction, a fair number of philosophers have tried to solve it. Nevertheless there is still no solution which is plausible enough to receive wide endorsement. According to Wilfrid Sellars, we cannot justify inductive inference by any theoretical reasoning; we can vindicate it only by a certain sort of practical reasoning. In this paper, I defend this Sellarsian proposal by developing and explaining it.

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Effects of Admixtures in Properties of Polymer Cement Mortar for Concrete Repair (혼화재료가 보수용 폴리머 시멘트 모르타르의 성질에 미치는 영향)

  • Song, Hyung-Soo;Lee, Chin-Yong;Min, Chang-Shik
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.11 no.1
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    • pp.85-94
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    • 2007
  • The EVA polymer is used as a modifier in the repair mortar, which contains various admixtures and mineral admixtures. It has been reported that the effect of polymer in cement mortar by the cement-polymer ratio only, but effect of admixtures over the polymer mortar was unknown. In this study, the fresh and mechanical properties of polymer cement mortar influenced by the range of admixtures(CSA expansive addictive, CSA accelerator, gypsum, silica fume) ratio were investigated.

Properties of High-Performance Concrete Containing High - Reactivity Metakaolin (고반응성 메타카올린을 사용한 고성능 콘크리트의 특성)

  • 원종필;권연성;이존자
    • Journal of the Korea Concrete Institute
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    • v.14 no.3
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    • pp.349-356
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    • 2002
  • This research deals with the properties of fresh and hardened high-performance concrete(HPC) incorporating high-reactivity metakaolin(HRM). The properties of fresh and hardened state concrete were investigated included air content, slump flow, setting time, heat of hydration, compressive strength, resistance to chloride-ion penetration, abrasion and repeated freezing and thawing. The properties of the HRM concrete were also compared with those of the portland cement concrete and silica fume(SF) concrete. The laboratory test results indicate that HRM material can be used as a supplementary cementitious material to produce high-performance concrete.

Improvement of Capturing Velocity in the Fume Hood using Computational Fluid Dynamics(I) - Uniform flow (전산유체역학을 이용한 흄후드 제어유속 개선(I) - 균일류)

  • Jung, Jong-Hyeon;Lee, Sang-Woon;Lee, Sang-Man;Shon, Byung-Hyun;Lee, Jung-Hee;Jung, Yu-Jin
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.2
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    • pp.962-969
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    • 2013
  • This study used Computational Fluid Dynamics(CFD) to assess the properties of the air current inflow and the flow velocity distribution in the fume hood. In order to verify the effect of improvement, it was also predicted the characteristics of the flow pattern in case the hood face is structurally improved. The assessment of the capture velocity with the existing fume hood confirmed maximum 23 to 30% difference as compared to the root mean square (RMS). And the hood face showed great difference in flow velocity, with the flow velocity in the upper part is 58 to 68% faster than that in the lower part of the hood. So, as a result of the improvement of the hood designed to maintain a steady exhaust at the hood face (that is, installing a baffle on the inner wall and designing the slot type face), a difference of maximum 7% as compared to RMS appeared while maximum 12% differentiation in flow velocity through sections was predicted, showing mitigation of much of the difference in control velocity as compared to the previous structure.

Characteristics of Compressive Strength Development of High Strength Cement Composites Depending on Its Mix Design (고강도 시멘트 복합체의 배합조건에 따른 압축강도 발현 특성)

  • Jeong, Yeon-Ung;Oh, Sung-Woo;Cho, Young-Keun;Jung, Sang-Hwa;Kim, Joo-Hyung
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.9 no.4
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    • pp.585-593
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    • 2021
  • This study investigates the compressive strength of high-strength cement composites with 64 mixture designs and 2 curing conditions. The cement composites were designed with varying water-to-binder ratios, silica fume content to cement, and binder content per unit volume of cement composite to explore compressive strength development depending on its mix design. An increase in the water-to-binder ratio decreased the compressive strength of the composites, having consistency with the trend in normal concrete. The compressive strength increased with ages at an ambient curing temperature, but it was not identified at high-temperature curing. The compressive strength development was negligible in case that silica fume content to OPC is 15%~25%, but a decrease in the con ten t below 15% reduced compressive stren gth. It was more obvious in the specimen of low water-to-binder ratio. The specimen with 840kg/m3 of binder content per unit volume had the highest compressive strength in this study, and the decrease in binder content reduced the compressive strength of high strength cement composites in low silica fume content.

An Investigation on the Long Term Durability of High-strength Shotcrete Using Field and Combined Deterioration Test (현장실험과 복합열화시험을 통한 고강도 숏크리트의 장기내구성 검토)

  • Ma, Sang-Joon;Choi, Jae-Seok;Ahn, Kyung-Chul;Kim, Sun-Myung;Kim, Dong-Min
    • Journal of the Korean Geotechnical Society
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    • v.22 no.10
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    • pp.77-91
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    • 2006
  • Domestic practices in shotcrete use have developed in many respects even now, but it still has issues about material, construction, quality standard and so on. In overseas, the construction using high strength shotcrete with $39.2{\sim}58.8 MPa$ of compressive strength is becoming common based on the shotcrete technology of high strength and durability. However, domestic shotcrete design strength is low at around 20.6 MPa of compressive strength and a long term durability is also insufficient. In this paper, field tests using high-quality additives and accelerators were performed to obtain the improvement of shotcrete strength and EFNARC standard was used to evaluate the field test results. In addition, deterioration test combined with the freezing-thawing and carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of the field test, the promotion ratio of early strength was $90{\sim}97%$ in case of using alkali-free accelerators. And the compressive strength of the shotcrete using Micro-silica fume was $45.2{\sim}55.8MPa$ and flexible strength was $5.01{\sim}6.66MPa$, so the promotion ratio of strength was $37{\sim}79%$ and $17{\sim}61%$ respectively. The promotion effect of strength by silica fine additives ratio of $7.5{\sim}10%$ for cement mass was much superior to the other cases. It was especially examined that using Micro-silica fume reduced deterioration due to mixed steel fiber and improved a long-term durability of shotcrete.