• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 연약지반처리위원회 학술세미나
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• pp.84-95
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• 1999

Laboratory experiments were performed to evaluate the strength characteristics of solidified sandy soils by portland cement with mixing conditions. Factors considered in the experiments were the fine content(<#200, %), cement content(%) and water-cement ratio and unconfined compressive strength tests were performed on samples at 7 and 28 cured day. Results of tests showed that for a low cement content(7%∼10%) the fine content was very important while for a high cement content the water-cement ratio was very important. For 7%∼10% cement content, the optimum fine content which gained maximum strength was about 30%. But for 13% cement content, low fine content and water-cement ratio were more useful than others. In the multi regression analysis, significant equation was gained.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.85-88
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• 2006

This study describes the optimum mix proportion of the high strength and self-compacting concrete placed in main structures of LNG above tank. This concrete requires high strength level about $60{\sim}80MPa$, low hydration heat, balance between workability and consistency without vibrating in the actual work. For this purpose, low heat portland cement and fly ash are selected and design factors including water-binder ratio, replacement ratio of fly ash are tested. As experimental results, low heat portland cement shows lower the confined water ratio than another cement type and the optimum replacement ratio of fly ash in order to improve properties of the binder-paste shows 10% by cement weight considering test results of the confined water ratio$({\beta}p)$. Also, flowability of the high strength and self-compacting concrete by using fly ash about $10{\sim}20%$ is improved. The replacement ratio of fly ash 10% and water-binder ratio $25{\sim}27%$ are suitable to the design strength 80MPa and cost, In case of the design strength 60MPa, the replacement ratio of fly ash and water-binder ratio show 20% and $25{\sim}30%$ separately. Based on the results of this study, the optimum mix proportions of the high strength and self-compacting concrete will be applied to the construction of LNG above tank as a new type.

• 한국건축시공학회지
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• 제8권5호
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• pp.59-65
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• 2008

In the evaluation method of KS on the activity factor of fly ash, same amount of cement should be replaced with fly ash. Therefore, contradictory effects on concrete strength exist, i. e. strength decease due to low content of cement and strength increase of strength due to filling-pore-function of fly ash. European Committee for Standardization (CEN) specifies the method 1 to 4. adding fly ash without reducing the content of cement, for the evaluation method on activity factor of fly ash. This study investigates the applicability of the method 2 of CEN to mix design of concrete. The followings are derived ; There is a key ratio of f)y ash mixing which enhances the incremental ratio of mixing water to improve fluidity of mortar. The incremental ratio of mixing water is maximized about 11% ratio of fly ash mixing. Compressive strength most slightly increases at that ratio of fly ash mixing. Activity factor of fly ash increases as water-cement ratio becomes low and contents of fly ash becomes high. Moreover, quality of fly ash and condition of mix design affect the applicable amount of fly ash and available range of water-cement ratio. However, this method has some problems for practical purpose because activity factors of fly ash for some cases are over 1.0. Further research should be conducted to develop more useful method of evaluating activity factor of fly ash.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.527-532
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• 2003

When fresh concrete is exposed to sufficiently low temperature, the free water in the concrete is cooled below its freezing point and transforms into ice, which causes decrease in compressive strength of concrete. Of the many influencing factors on the loss of compressive strength, the age of concrete at the beginning of freezing, water-cement ratio, and cement-type are significantly important. The objective of this study is to examine how the these factors affect the compressive strength of concrete frozen at early ages. The results from the tests showed that as age at the beginning of freezing is delayed and water-cement ratio is low, the loss of compressive strength decreases. In addition, concrete made with high-early-strength cement is less susceptible to frost damage than concrete made with ordinary portland cement.

• Journal of Construction Engineering and Project Management
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• 제7권1호
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• pp.26-29
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• 2017

This paper represents the experimental investigation of chloride penetration into plain concretes and reinforced concretes. The main objective of this work is to study the main influencing parameters affecting corrosion of steel in concrete. Plain cement concrete and reinforced cement concrete with different water-cement ratios and different cover depth were subjected to ponding test. Ponding of specimens were done for different periods into 10% NaCl solution. Depth of penetration of chloride solution into specimens was measured after ponding. Specimens were crushed and reinforcements were washed using $HNO_3$ solution and weight loss due to corrosion was calculated accordingly. There was a linear relationship between depth of penetration and water-cement ratio. It was also observed that, corrosion of reinforcing steel increases with chloride ponding period and with water-cement ratio. Corrosion of steel in concrete can be minimized by providing good quality concrete and sufficient concrete cover over the reinforcing bars. Water-cement ratio has to be low enough to slow down the penetration of chloride salts into concrete.

• 산업기술연구
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• 제22권A호
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• pp.193-200
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• 2002

Drying shrinkage cracking which may be caused by the relatively large specific surface IS a matter of grave concern for latex modified concrete(LMC) overlay and rapid-setting cement latex modified concrete(RSLMC) overlay. LMC and RSLMC were studied for field applications very actively in terms of strength and durability in Korea. However, there were no considerations in drying shrinkage. Therefore, the purpose of this dissertation was to study the drying shrinkage properties of LMC and RSLMC with the main experimental variables such as cement types(ordinary portland cement, rapid setting cement), water-cement ratios and curing days at a same controlled environment of 60% of relative humidity and $20^{\circ}C$ of temperature The drying shrinkage for specimens was measured with a digital dial gauge of Demec. The test results showed that the drying shrinkage of LMC and RSLMC were considerably lower with low water-cement ratio, respectively This might be attributed to the interlocking of hydrated cement and aggregates by a film of latex particles, water retention due to hydrophobic, and colloidal properties of the latexes resulting in reduced water evaporation.

• 한국농공학회지
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• 제43권6호
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• pp.135-142
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• 2001

Laboratory experiment was performed to evaluate the influence of mixing conditions to the strength of solidified sandy soils with cement. The major physical factors considered in this experiment were the fine particles content(<$\sharp200%$), cement content(%) and water-cement ratio, and unconfined compressive strength test was performed on the samples at 7 and 28 cured day. The results of tests shows that when the cement content is relatively low (7~10 percents) the fine content in the sandy soils is very important, but when cement content is high the water-cement ratio became more important. It was appeared that in the range of the cement content of 7~10 percents, about 20~30 percents of fine content to the total sample weight is the optimum condition to get the maximum strength. In the case of the cement content of 13 percents, the strength of sample was considerably affected by the water-cement ratio rather than the fine content. In this paper, empirical equations were also developed and evaluated to verify the relationship among three factors by the multi-regression analysis.

• 한국건설순환자원학회논문집
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• 제3권2호
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• pp.132-139
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• 2015

본 연구는 파쇄처리 순환골재를 사용한 콘크리트의 특성을 검토하기 위하여 순환골재의 흡수율별 단위시멘트량 및 물시멘트비를 변화시켜 콘크리트의 특성에 미치는 영향을 검토하였다. 실험결과 물시멘트비가 높은 저강도 배합에서는 파쇄처리 순환골재를 사용한 콘크리트와 쇄석 콘크리트의 압축강도가 동등한 수준으로 나타나 순환골재의 부착모르타르 영향이 작은 것으로 나타났다. 그러나, 물시멘트비가 낮은 고강도 배합에서는 파쇄처리 순환골재를 사용한 콘크리트가 부착모르타르의 영향으로 쇄석을 사용한 콘크리트보다 약 40%의 압축강도저하를 나타내었다. 한편, 흡수율 7%인 순환골재의 건조수축량은 재령 10주에서 흡수율 1%인 쇄석의 $-310{\times}10^{-6}$보다 2배 증가된 $-700{\times}10^{-6}$을 나타내어 콘크리트용 골재로의 재활용시 건조수축에 대한 검토가 선행되어야 할 것으로 사료된다. 또한 단위시멘트량 $450kg/m^3$인 부배합 콘크리트의 압축강도는 흡수율 3%인 순환골재 사용시 쇄석 사용 콘크리트와 동등하게 나타난 반면, 흡수율 7%인 순환골재를 사용한 경우에는 쇄석 사용 콘크리트에 비해 약 7%정도 낮게 나타났다. 그러나, 단위시멘트량 $350kg/m^3$인 일반배합 콘크리트의 압축강도는 쇄석 사용 콘크리트에 비해 압축강도 저하가 현저하게 나타났다.

• 콘크리트학회논문집
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• 제17권2호
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• pp.293-302
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• 2005

This study describes data from determination of the optimum mix proportion and site application of the mass concrete placed in bottom slab and side wall having a large depth and section as main structures of LNG in-ground tank. This concrete requires low heat hydration, excellent balance between workability and consistency because concreting work of LNG in-ground tank is usually classified by under-pumping, adaptation of longer vertical and horizontal pumping line than ordinary pumping condition. For this purpose, low heat Portland cement and lime stone powder as cementitious materials are selected and design factors including unit cement and water content, water-binder ratio, fine aggregate ratio and adiabatic temperature rising are tested in the laboratory and batch plant. As experimental results, the optimum unit cement and water content are selected under $270kg/m^3$ and $l55{\~}l60 kg/m^3$ separately to control adiabatic temperature rising below $30^{\circ}C$ and to improve properties of the fresh and hardened concrete. Also, considering test results of the confined water ratio($\beta$p) and deformable coefficient(Ep), $30\%$ of lime stone powder by cement weight is selected as the optimum replacement ratio. After mix proportions of 5cases are tested and compared the adiabatic temperature rising($Q^{\infty}$, r), tensile and compressive strength, modulus of elasticity, teases satisfied with the required performances are chosen as the optimum mix design proportions of the side wall and bottom slab concrete. $Q^{\infty}$ and r are proved smaller than those of another project. Before application in the site, properties of the fresh concrete and actual mixing time by its ampere load are checked in the batch plant. Based on the results of this study, the optimum mix proportions of the massive concrete are applied successfully to the bottom slab and side wall in LNG in-ground tank.

• 한국세라믹학회지
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• 제25권5호
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• pp.532-540
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• 1988

Even the finest cement as having a specific surface area of 6.000~8.500$\textrm{cm}^2$/g (Blaine) is to convert into low-porosity hardened cement paste by the use of appropriate plasticizer. In this study, tests were carried out on such a special cement mix(fineness of 6.000$\textrm{cm}^2$/g, Ca-lignosulfonate plus k2CO3 as plasticizer and W/C=0.25) in comparison with ordinary Portland cement. Owing mainly to the high fineness of the cement powder and the low water-to-cement ratio, the hardened low-porosity cement paste showed a very tight microstructure, the pore texture of which consisted of micropores and wide pores only of small radii. The consequence of such mix was hence that the low-porosity special cement had excellent properties of early-high and very high strengths as compared to ordinary Portland cement. Its volume change when dried in the air or re-wetted, exhibited superor behaviour as well.