• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.1
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• pp.173-179
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• 2003

Currently, in the mix design of high strength concrete, cement content depend on the target slump which is fixed with tests. However this cause high content cement use because it is based on the mix design of normal strength concrete. Also, comparatively high content cement might decrease the durability of the concrete. Therefore, in this study, we investigated proper cement content satisfying durability, workability, compressive strength, and reviewed use of admixtures, proper sand-aggregate ratio to the cement content. The results indicate that cement content ranging $370{\sim}550kg/m^3$ did not affect the compressive strength. The field workers should consider durability, workability as well as compressive strength for determining the optimal cement content in the mix design of the high strength concrete.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.51-60
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• 2009

This study investigates the fresh state characteristics, strength, chloride ion penetration resistance and freeze-thaw resistance of the suggested high strength-high durability cement concrete pavement. The required workability and air content could be achieved by using an appropriate admixtures. However its dosage should be carefully determined through field trial batches. Compressive strength increased with the increased cement content and, in particular, high cement volume concrete continuously developed strength up to 90 days. No clear relationship, however, existed between flexural strength and cement content. Chloride penetration resistance seemed as a function of curing age rather than the cement content. Freeze-thaw resistance test was conducted using two different coolants, tap water and 4% NaCl solution. When the tap water was used no severe damage was observed up to 300 cycles regardless the air content. Under 4% NaCl solution, specimens of 326kg/$m^3$ cement content showed severe damage with surface scaling. Based on the experimental investigations herein, it is highly recommended that the cement content be greater than 400kg/$m^3$ for strength-high durability cement concrete pavement structures.

• Journal of the Korea Concrete Institute
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• v.20 no.4
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• pp.415-421
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• 2008

Reinforced concrete starts to corrode when the chloride ion concentration which is the sum of included in concrete and penetrated from environments exceeds a certain level of critical chloride concentration. Therefore each country regulates the upper bounds of chloride amount in concrete and the regulations are different for each country due to its circumstances. In this study, the critical threshold chloride content according to unit cement amount is empirically calculated to propose a reasonable regulation method on the chloride amount. As a result, the critical threshold chloride content increases considerably according to cement content and it agrees with the established theories. The present regulations on total chloride amount 0.3 or 0.6 kg chloride ions per $1\;m^3$ of concrete does not reflect the influences of mix design, environmental conditions and etc. So it can be said that it is more reasonable to regulate the critical threshold chloride content by the ratio of chloride amount per unit cement content than by the total chloride content in $1\;m^3$ of concrete.

• Magazine of the Korea Concrete Institute
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• v.4 no.3
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• pp.135-146
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• 1992

프리텐션 방식 원심력 고강도콘크리트 말뚝이 KS F4306 규격에 제정되어 콘크리트의 압축강도가 800kg/$ extrm{cm}^2$ 이상의 제조가 불가한 실정이 것으로 평가 된다. 따라서 본 연구에서는 고강도콘크리트 말뚝 제조에 적용하기 위한 고황산염 시멘트의 실험적 연구로써 석고계 첨가량 및 단위 시멘트량 변화가 증가양생 콘크리트의 제 강도 특성에 미치는 영향을 규명하는데 목적이 있다. 연구결과로부터 석고첨가량이 증대하면 콘크리트강도가 향상되지만, 7.5% 이상 첨가시에는 오히려 강도 저하현상이 나타나는 것으로 분석되었으며, 특히 단위 시멘트량 변화에 따른 압축강도 영향은 그다지 크지 않은 것으로 나타났다. 한편 최고 압축강도 발현은 석고첨가량 5~7.5% 첨가와 단위시멘트량 500~540kg/㎥ 조건에서 800kg/$\textrm{cm}^2$ 이상의 고강도 콘크리트 제조가 가능함을 확인하였다.

• Magazine of the Korea Concrete Institute
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• v.14 no.1
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• pp.53-60
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• 2002

매스 콘크리트 구조물에서는 콘크리트 타설 후 시멘트의 수화열로 인한 온도응력에 의해서 온도균열의 발생 가능성이 매우 높다. 따라서, 매스 콘크리트 시공시, 온도균열을 구조물의 내구성 관점에서 최대한 억제시킬 필요가 있다. 최근에는 국내에서도 단위시멘트량이 많은 배합을 이용하는 고강도 콘크리트 구조물의 시공이 증가되고 있다. 이와 같은 매스 콘크리트 구조물은 단위시멘트량이 많기 때문에 부재내 수화열에 의한 온도의 상승 속도가 빠르기 때문에 시공에 앞서 사전에 설계, 재료 및 시공 측면에서 온도균열 제어 대책을 검토할 필요가 있다.(중략)

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.41-49
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• 2009

Cement concrete pavement has become more common in Korean highway systems. However, as its service period increases, there are some technical problems occurs and no clear solution is available primarily due to the lack of active researches. This research, hence, aims to develop a new mix proportion that may provide better strength and durability with extended service life. Based on a variety of literature reviews, the experimental variables were determined as unit cement content, S/a ratio and W/C ratio. From the experimental works, it is recommended to increase the unit cement content up to 375kg/$m^3$, 400kg/$m^3$ and 425kg/$m^3$. The target slump and air content were set 40mm and 5%, respectively. The maximum size of coarse aggregate was decided to be 25mm because of the easiness of supply in the field. The reduction of W/C ratio was necessarily required and decreased to 0.4 which was proven not to cause any mixing problem with the increased unit cement contents along with polycarbon-based high range water reducing agent. In addition, it was known that the S/a ratio could be reduced to 0.34. The lowered S/a might be possible because of the increased cement paste and hence increased cohesiveness and workability.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.745-752
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• 2009

This paper presents the optimized mixing design of lightweight aerated concrete using hydrogen peroxide. Design of experiments in order to the optimized mixing design was applied and commercial program (MINITAB) was used. Statistical analysis was used to Box-Behnken (B-B) method in response surface analysis. The influencing factors of experimental are unit cement content, water ratio and hydrogen peroxide ratio. According to the analysis of variance, at the hardened state, water ratio and hydrogen peroxide ratio affects on dried density, compressive strength and bending strength of lightweight aerated concrete, but unit cement content affects on only dried density. In the results of response surface analysis, to obtain goal performance, the optimized mixing design for lightweight aerated concrete using hydrogen peroxide were unit cement content of 800 kg/$m^3$, water ratio of 44.33% and hydrogen peroxide ratio of 10%.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.2
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• pp.132-139
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• 2015

In this study, the different unit cement content by the ratio of water absorption and water-cement ratio are applied to examine the properties of the concrete used the aggregate recycled by the crushing treatment. According to the experimental results, in the mix of low strength and high water-cement ratio, both of the compressive strength is almost equal in the concrete using the recycled aggregate by the crushing treatment and the concrete using broken stones. It means that the recycled aggregate has the low effect of the amount of bonded mortar. But, in the mix of high strength and low water-cement ratio, the concrete using the recycled aggregate by the crushing treatment has 40% less of the compressive strength than that using broken stones by the effect of the amount of bonded mortar. On the other hand, after 8 weeks, the dry shrinkage of the recycled aggregate with 7% of the ratio of water absorption doubles that of the broken stones with 1% ($-350{\times}10^{-6}$), in other words $-700{\times}10^{-6}$. Thus, the dry shrinkage should be prior to any other conditions in recycling waste concrete for the aggregate for concrete. When the recycled aggregate with 3% of the ratio of water absorption is used, the compressive strength of the rich mix concrete ($450kg/m^3$ of the unit cement content) is equivalent to that of the concrete using broken stones, while in using the recycled aggregate with 7% of the ratio of water absorption, the rich mix concrete has 7% lower compressive strength than the concrete using broken stones. But, the compressive strength of the ordinary mix concrete ($350kg/m^3$ of the unit cement content) is far lower than that using broken stones.

• Journal of the Korean GEO-environmental Society
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• v.10 no.2
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• pp.51-59
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• 2009

This study is based on field data obtained from rock grouting such as RQD value, Unit cement grout volume, Lugeon value(Lu), and Maximum grout pressure in four different dam sites. The relationship were analyzed and compared as follow. The cut-off effect after rock grouting in dam-foundation which are mostly consist of metamorphic rock is better than that of Sedimentary rock. And the impermeable effect after consolidation grouting is more efficiency than the impermeable effect after curtain grouting. The unit cement grout volume are increased as RQD value is higher in rock mass. But there is no relationship between RQD value and Lugeon value. In the sedimentary rock, which is more permeable than metamorphic rock, Lugeon value (Lu) is a linear function (Lu=0.22Vc) of unit cement grout volume (Vc). Cut-off effect of curtain grouting is less influential at each near holes which are already grouted than that of consolidation grouting. And the behavior characteristics of Lugeon value vs. the unit cement grout volume as the order of installations are almost the same.

• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.165-173
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• 1998

투수성 콘크리트포장은 우천시 도로포장 노면의 배수, 차량 주행 안전성의 향상 및 소음의 저감등을 목적으로 개발된 포장이지만 주행환경 및 도로주변과의 환경조화에도 기여한다. 일반적인 배수성 아스팔트 콘크리트포장에서는 투수계수 1$\times$10-2cm/sec를 목표로 정하고 있으나 본 연구에서는 투수성 콘크리트포장의 실용화를 위한 연구의 일환으로 투수계수1$\times$10-1cm/sec를 목표로 정하여 골재의 최대치수, 잔골재율 및 단위시멘트량을 변화시킨 투수성 콘크리트의 공극률, 연속공극률 및 투수계수와 제강도를 측정한 결과에 대하여 고찰하였다. 투수성 콘크리트의 목표투수계수 1$\times$10-1cm/sec 일 때 공극률 및 연속공극률은 각각 15 %와 12%정도이며, 압축강도는 240kg/$\textrm{cm}^2$정도의값을 나타내었으며, 골재의 최대치수가 10~13mm일 경우, 잔골재율 10~20%, 단위시멘트량 380 kg/$\textrm{cm}^2$정도가 적절한 배합으로 생각된다.