• Cement Symposium
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• no.29
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• pp.50-57
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• 2002

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.688-696
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• 2016

This paper evaluates the effect of hot weather conditions on the fresh concrete characteristics of 80-MPa high-strength concrete. The slump flow, packing ability, setting time, hydration heat, and compressive strength were evaluated under exterior temperatures of $20^{\circ}C$, $30^{\circ}C$, and $40^{\circ}C$. The slump flow, arrival speed of 500 mm, and their changes with the elapsed time were found to bring the occurrence of rapid slump loss forward by about 30 minutes when increasing the temperature by $10^{\circ}C$ from $20^{\circ}C$. The initial and final setting times of the concrete at $20^{\circ}C$ were 7 hours and 12 hours, which were reduced by 1 hour and 3 hours at $30^{\circ}C$ and by 2 hours and 5 hours at $40^{\circ}C$, respectively. The hydration heat characteristics at $20^{\circ}C$ and $30^{\circ}C$ were similar in terms of the highest temperature of the concrete casting depth and the time when the maximum temperature occurred. However, at $40^{\circ}C$, the maximum temperature occurred about 4 hours earlier, and the highest temperature per the concrete casting depth increased by about $12^{\circ}C$. Therefore, it is concluded that the characteristics can vary according to the exterior temperature. Thus, quality assurance should consider workability, temperature cracks due to hydration heat, the properties of strength development, and other characteristics.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.379-386
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• 2020

The present study examined the effect of bottom ash aggregate contents on the compressive strength gain and mechanical properties(modulus of elasticity and rupture and splitting tensile strength) of concrete. Main test parameters were water-to-cement ratio and bottom ash aggregate contents for replacement of natural sand. Test results showed that the 28-days compressive strength of concrete and mechanical properties normalized by the compressive strength tended to decrease with the increase in bottom ash fine aggregate content. When compared with fib 2010 model equations, bottom ash aggregate concrete exhibited the following performances: lower rates of compressive strength gain at early ages but greater rates at long-term ages; slightly higher measurements for modulus of elasticity and rupture; and lower measurements for splitting tensile strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.273-274
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• 2009

The curing method used on domestic sites for checking the concrete compressive strength of a structure. The curing method used for testing the specimens must be the standard ponding curing method (20${\pm}$%$2^{\circ}$C). However, because in-placed concrete is exposed to open air and cured under the seasonal temperature changes, the compressive strength of a real structure is different from the tested compressive strength. Therefore the curing method suggested in this research, which sets the internal conditions of the structural specimens as the conditions of the applied curing method. this thesis suggests the specimen curing method that most closely re-enacts the compressive strength of the concrete used on the structural specimens

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.749-752
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• 2008

The effects of fiber content on strength properties of ultrarapid-hardening polymer-modified concretes with fiber. As a result, the compressive and flexural strengths of ultrarapid-hardening polymer-modified concretes with fiber increase with increasing of fiber content. In particular, the ultrarapid-hardening polymer-modified concretes with a polymer-cement ratio of 20% and a fiber content of 0.08% provide approximately two times higher flexural strength than unmodified concretes. Such high strength development is attributed to the high tensile strength of polymer and fiber and the improved bond between cement hydrates and aggregates because of the addition of polymer and fiber.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.67-74
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• 2016

With several different dosages of multi-walled CNTs which was 0.1, 0.3, and 0.5% of the weight of binder, the fluidity in fresh CNT cement composites, as well as the strength and strength development with age of the hardened composites were investigated in this experimental study. The experimental results from flow test indicated that the increase in the dosage of CNTs badly impacted on the workability of fresh composites, and the results from rheological measurements presented the decrease in plastic viscosity and the increase in yield stress according to the amount of CNTs. In addition, the thixotrophy in the flow curve obtained from the rheology test was observed more noticeably in the composites with higher dosage of CNTs. With the experiments on the strength properties, the improvement of both compressive and tensile strengths with the increase of CNTs dosage could be obtained. Moreover, early strength development by adding CNTs was found when it was compared with plain cementious matrix without CNT.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.5
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• pp.63-71
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• 2010

This paper is about a research of steam curing which is one of the curing methods for accelerating the early-age strength of pre-cast concrete. With cylinder mold and mock-up specimen, the research was executed to study the best cycle of steam curing temperature through quantifying cycle of steam curing and maximum temperature, while the required strength is developed under the early-age. Moreover, causes and measurements for the high temperature of concrete, which is due to the steam curing, and the crack, which occurs when removing steel form, are stated. Ultimately, the economical method of producing, which satisfies early-age strength development and quality assurance while manufacturing PC structure, is stated.

• Magazine of the Korea Concrete Institute
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• v.10 no.5
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• pp.177-187
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• 1998

최근 국내에서 해양 구조물, 장대 교량의 하부구조물, LNG저장탱크 등 매스콘크리트의 증가추세에 따라 구조물의 고내구성과 관련하여 시멘트의수화열에 의한 온도균열의 발생을 최소화 시킬 수 있는 3성분계 혼합형 저발열시멘트가 개발되어 실 구조물의 적용단계에 있으나, 저발열시멘트가 개발되어 실 구조물의 적용단계에 있으나 저발열시멘트의 특성에 대한 전반적인 연구보고가 국내에서는 미진한 실정이다. 따라서 본 연구에서는 3성분계 혼합형 저발열시멘트의 특성 및 코\ulcorner리트의기초물성을 1종 보통포틀랜트 시멘트, 5종 내황산염시멘트, 슬래그시멘트와 비교하였다. 글 결과 저발열 콘크리트의 찹축강도는 초기재령에서 강도발현률이 적은 반면 장기강도발현률은 상당히 큰 경향을 보였다. 또한 수화열은 1종시멘트를 사용한 콘크리트에 비하여 1/3~1/2정도로 매스콘크리트의 수화열을 대폭적으로 저감시킬 수 있을 뿐만 아니라 염소이온에 대한 저항성이 상대적으로 높게 나타나 거대 해양 구조물의 적용에 매우 유리한 시멘트로 판단되었다.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.945-948
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• 2008

The effects of polymer-cement ratio on strength properties of ultrarapid-hardening acrylic-modified concretes. As a result, the flexural and tensile strengths of ultrarapid-hardening acrylic-modified concretes increase with increasing of polymer-cement ratio. In particular, the acrylic-modified concretes with a polymer-cement ratio of 20% provide approximately 1.5 times higher flexural and tensile strengths than unmodified concretes. Such high strength development is attributed to the high flexrul and tensile strengths of arcylic polymer and the improved bond between cement hydrates and aggregates because of the addition of acrylic polymer. However, the compressive strengths of ultrarapid-hardening acrylic-modified concretes decrease with increasing of polymer-cement ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.609-612
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• 2008

Ultra Super Early Strength Cement is a material that satisfies these requirements. early hydration heat however, is significant over regular concrete, thus discretion is advised for thermal cracks in accordance with heat generation when constructing a large-scale structures. In addition, the negative point that it is difficult to achieve required strength in a short period of time following rubbing process while retaining workability, the cement is being used conditionally for engineering material and Ultra Super Early Strength Cement for maintenance material for construction doesn't exist. Magnesia Phosphate Cement, which is currently under studies in overseas uses no extra admixture and has strong points of Ultra Super Early Strength as well as favorable construction-ability and adhesive stability to the prototype concrete. These factors stem recognition that it could be used as maintenance material for construction of diverse applicability. In order to provide necessary data to increase practicality of the magnesia phosphate cement for Ultra Super Early Strength Mortar, the study carried out simulate experiment on member of framework to review field applicability.