• 한국농공학회지
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• 제19권1호
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• pp.4312-4322
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• 1977

In order to investigate the effect of the water content and the accelerated curing on the strength of the soil-cement mixtures, laboratory test of soil cement mixtures was performed at five levels of water content, four levels of accelerated curing temperatures, three levels of normal curing periods, and six levels of accelerated curing time. Also this study was carried out to investigate the effect of grain size distribution of 21 types of soils on the strength of soil-cement mixtures at four levels of cement content and three levels of curing time. The results are summarized as follows: 1. Optimum moisture content increased with increase of the cement content, but maximum dry density was changed ununiformly with cement content. Water content corresponding to the maximum strength was a little higher than the optimum moisture content along the increase of cement content. 2. In molding the specimens with the optimum moisture content, the maximum strength appeared at the wet side of the optimum moisture content. 3. According to increase of curing temperature as 30, 40, 50, and 60$^{\circ}C$, unconiiend compressive strength of soil-cement mixtures increased, the rate of increase at the early curing period was large, and approximately 120 hours was suifficient to harden soil-cement mixtures completely. 4. The strength of soil-cement mixtures at the curing temperature of 10$^{\circ}C$ decreased at the rate of 30 to 50 percent than at the curing temperature of 20$^{\circ}C$, and the strength of soil-cement mixtures at the curing temperature of 0$^{\circ}C$ increased a little with increase of curing time. 5. Although the strength of soil-cement mixtures seemed to be a little affected by the temperature difference between day time and night, it was recommended that reasonable working period was the duration from July to August of which average maximum temperature of Korea was approximately 30$^{\circ}C$. 6. Accelerated curing time corresponding to the normal curing time of 28-day was shorten with increase of curing temperature, also it was a little affected by the cement. Accelerated curing time that the strength of soil-cement mixtures for the cement of 9 percent and the curing temperature of 60was shorten with increase of curing temperature, also it was a little affected by the cement. Accelerated curing time that the strength of soil-cement mix- tures for the cement of 9 percent and the curing temperature of 60$^{\circ}C$ was 45 hours at the KY sample, 50 hours at the MH, 40 hours at the SS, and 34 hours at the JJ respectively. 7. Accelerated curing time was depended upon the grain size distribution of soil, it decreased with increase the percent passing of No. 200 sieve. 8. Relationship between the normal curing times and the accelerated curing times showed that there was a linear relationship between them, its slope decreased with increase of curing temperature. 9. The most reasonable soil of the soil-cement mixtures was the sandy loam which was a well graded soil. Assuming the base of road requiring 7-day strength of 21 kg/$\textrm{cm}^2$ being used, the soil-cement mixtures could be obtained with adding 6 percent of cement in such a sails S-7, S-8, S-9, S-10, S-11, S-12, S-13. 10. The regression equation between the 28-day and the 7-day strength was obtained as follow; q28=1.12q7,+6.5(r=0.96).

• Current Research on Agriculture and Life Sciences
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• 제18권
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• pp.61-69
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• 2000

This study was conducted to investigate most effective the optimum lime content for lime-clay modification. To achieve the aim, characteristics of compaction and compressive strength were tested by adding of 0, 5, 10, 15 and 20% lime (Hydrated lime) of dry weight of the clay. Distilled water was added 10, 15, 20 and 25% of dry weight of lime-clay mixture. In this test, the compressive strength of the specimens was measured according to the following curing period : 7, 21, 28, 35 and 49 days. The results are as follows. (1) As lime additive increased, the optimum moisture content of lime-clay mixture was increased and the maximum dry density was decreased. (2) The soil mixture of 20% of the moisture content and 10% of lime additive was shown the maximum compressive strength. (3) As curing period longer, the compressive strength was increased but after 21 curing days, the increasing rate of compressive strength was low as compared with earlier its value. (4) In the range of 20% of the moisture content, compressive strength of mixture of 10% lime additive increased twice compared with that of mixture of 0% lime additive. (5) All of the lime-clay are possible to use for an sub-base material and 20% of moisture content of lime-clay mixture is possible to use for a base material.

• Geomechanics and Engineering
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• 제12권6호
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• pp.935-948
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• 2017

An experimental program was conducted to investigate the effects of the static compaction pressure, cement content, water/cement ratio, and curing time on unconfined compressive strength (UCS) of the cement treated sand. UCS were conducted on samples prepared with 4 different cement/sand ratios and were compacted under the lowest and highest static pressures (8 MPa and 40 MPa). Each sample was cured for 7 and 28 days to observe the impact of curing time on UCS of cement treated samples. Results of the study showed the unconfined compressive strength of sand increased as the cement content (5% to 10%) of the cement-sand mixture and compaction pressure (8 MPa to 40 MPa) increased. UCS of sand soil increased 30% to 800% when cement content was increased from 2.5% to 10%. Impact of compaction pressure on UCS decreased with a reduction in cement contents. On the other hand, it was observed that as the water content the cement-sand mixture increased, the unconfined compressive strength showed tendency to decrease regardless of compaction pressure and cement content. When the curing time was extended from 7 days to 28 days, the unconfined compressive strengths of almost all the samples increased approximately by 2 or 3 times.

• 한국건축시공학회지
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• 제6권3호
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• pp.107-114
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• 2006

In this study, the experiment was carried out to investigate and analyze the engineering properties of concrete using fine aggregate of PS bal slagl. The main experimental variables were water/cement ratio 30, 40, 50(%), water content $170kg/m^3$, replacement ratio of slag fine aggregate 0, 25, 50, 75(%) in experiment I and water/cement ratio 30, 40, 50(%), water content 165, 170, 175($kg/m^3$), replacement ratio of fine aggregate of PS ball 0, 50 in experiment II. According to the test results, the principle conclusions are summarized as follows (1) The workability of slag fine aggregate-mixed concrete tends to improve, as the replacement rate increases. (2) The air content of slag fine aggregate-mixed concrete tends to decrease, as the replacement rate increases. (3) The unit volume weight of slag fine aggregate-mixed concrete tends to significantly increase, as the replacement rate increases. (4) The compressive strength of slag fine aggregate-mixed concrete tends to show more increasing propensity, in case the curing period is relatively long, as the replacement rate increases.

• Geomechanics and Engineering
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• 제29권1호
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• pp.13-23
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• 2022

Peat soil has the characteristics of high moisture content, large void ratio and low shear strength. In this study, unconfined compressive strength and SEM tests are conducted to investigate the effects of ultrahigh moisture content, cement content, organic content and pH value on the strength of solidified peat. As an increase in the cement content and curing period, the failure mode of solidified peat soil changes from ductile failure to brittle failure. The influence of moisture content on the strength of solidified peat is greater than the cement content. As cement content increases from 10% to 30%, strength of solidified peat at a curing age of 28 days increases by 161%~485%. By increasing water content by 100%, decreases of solidified peat at a curing age of 28 days is 42%~79%. Compared with the strength of solidified peat with a pH value of 5.5, the strength of peat with a pH value of 3.5 reduces by 10% ~ 46%, while the strength of peat with a pH value of 7.0 increases by 8% ~ 38%. It is recommended to use filler materials for stabilizing peat soil with moisture content greater than 200%. Because of small size of clay particles, clay added in the cement solidified peat can improve much higher strength that that of sand.

• 대한토목학회논문집
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• 제34권2호
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• pp.529-536
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• 2014

점토-시멘트 혼합토의 물리적 특성인 함수비, 비중, 단위중량과 간극비 등은 혼합토의 강도, 압축성, 압밀거동 예측 등에 적용되는 주요한 인자이다. 기존에는 혼합토의 물리적 특성을 복잡한 실내시험 및 시공 후 확인조사를 통해 이루어 졌다. 본 연구는 점토 함수비 90~170%, 시멘트 함유율 5~25%와 재령기간은 3~90일 조건으로 실내시험을 수행하였으며, 양생 후 혼합토 함수비, 비중, 단위중량과 간극비 등에 대한 변화를 분석하였다. 시험결과를 이용하여 원지반 점토 함수비, 시멘트 함유율과 재령기간 등의 역학적 관계를 바탕으로 혼합토의 함수비, 비중과 단위중량에 관한 물성 예측식을 제안하였다. 혼합토의 물성 예측식을 지반공학 분야에서 일반적으로 사용하는 간극비 산출식에 대입하여 혼합토의 간극비 예측식을 도출하였으며, 방콕 점토를 대상으로 간극비에 대한 실험결과와 본 연구에서 제안한 예측식을 검증하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.132-135
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• 2004

High-performance concrete (HPC) may be expected to differ from usual concrete with respect to shrinkage behavior, and it shows high autogenous shrinkage due to the use of very low water-binder ratio (w/b) and various admixtures. Therefore, in order to minimize the shrinkage stress and to ensure the service life of concrete structure, volumetric change of HPC should be understood. In this study, small prisms made of HPC with w/b of 0.32 and blast-furnace slag content of $0\%,\;30\%,\;and\;50\%$ were prepared to measure the volumetric changes such as autogenous shrinkage, drying shrinkage, and swelling under three different curing conditions. It was observed that the concrete cured. sealed condition showed only autogenous shrinkage while the concrete let to dry condition at temperature of $20^{\circ}C$ and relative humidity of $60\%$ during the test period showed both autogenous and drying shrinkage. Moreover, the concrete exposed to dry condition after 2-day water curing swelled and then started to shrink with age. The total shrinkage (autogenous+drying) of this concrete was smaller than that of the concrete cured dry condition, especially at early-age. Therefore, the early-age moisture curing is very effective to control or minimize the volumetric change and its induced stress of HPC.

• 콘크리트학회논문집
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• 제12권4호
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• pp.41-48
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• 2000

This study is to investigate for the frost resistance of high-strength concrete using finely ground granulated blast-furnace slag with experimental parameters, such as water/binder ratio, replacement proportion of granulated blast-furnace slag, air content and methods of curing. The high-strength concrete using granulated blast-furnace slag is effective to resist frost and decrease scaling. The more increasable replacement proportion of granulated blast-furnace slag is, the better the effect is. The high-strength concrete using granulated blast-furnace slag needs hydrating adequately to prevent deterioration by drying in the early curing period. The micro structure of high-strength concrete, increased to the pore number with diameter of 0.03~0.1mm, is changed by using granulated blast-furnace slag, but is presented differently according to water/binder ration and replacement proportion of granulated blast-furnace slag.

• Restorative Dentistry and Endodontics
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• 제17권2호
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• pp.307-330
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• 1992

The aim of this study was to investigate the physical properties of visible light curing Glass Ionomer cement for restorative esthetic filling. The control group was the autopolymerizing GC Fuji II Glass Ionomer cement (2.2: 1 P/L ratio) and the experimental groups were made by following procedure. To induce the polymerization by visible light, the powder of GC Fuji II GI cement and the liquid of Vitrabond for base & liner were mixed in an amalgam capsule with 2.5:1, 3.0:1, 3.5:1 P/L ratio (% wt/wt). After fabrication of specimens, compressive strength, fracture toughness ($K_{IC}$) Scanning Electron Microscope and X-ray Diffraction, water-leachable content, marginal leakage and surface roughness were studied. The results were as follows: 1. Only experimental No. 1 group (visible light curing) showed less compressive strength than control group 1 hour after curing. Strength was increased with aging in all groups, so the compressive strength of light curing groups was no less than that of autopolymerizing group after 3 weeks. 2. Experimental No.3 group (visible light curing) was inferior to No.2 group (visible light curing) in fracture resistance but light curing groups were more resistant to fracture than autopolymerizing group and showed ductile fracture pattern as compared with the brittle fracture pattern of autopolymerizing group. 3. From scanning electron microscopic image, various sized unreacted powder particles, surrounded by silica gel, were embedded in polysalt matrix. Light curing groups showed little crack and more dense unreacted particles than autopolymerizing group. 4. From X-ray diffraction analysis, GC Fuji II Glass Ionomer cement powder and all groups showed glassy appearance but light curing groups seemed to be more intensive in crystaline than autopolymerizing group. S. The most significant dissolution was shown in early setting period in all group. Light curing groups were dissolved less than autopolymerizing group. 6. Marginal leakage was not different significantly in case of cavity margin composed of same tooth structure (ex. only enamel margin, only dentin margin) but much more leakage was shown in dentin/cementum margin than enamel margin. In only case of only enamel margin, light curing groups were superior to autopolymerizing group. 7. All groups showed relatively smooth surface, which irregularity was less than $1{\mu}m$. Light curing groups were smoother than autopolymerizing group.

• 한국건축시공학회지
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• 제10권5호
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• pp.121-128
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• 2010

본 연구에서는 한중 콘크리트의 단열보온양생 공법재료로 사용되고 있는 이중버블시트의 다양한 포설 시공조건 변화에 따른 단열보온성능을 검토하였는데, 그 결과는 다음과 같다. 먼저, 시공요인에 따른 콘크리트의 온도이력의 경우 4시간 이내의 버블시트 포설시기 변화 및 버블시트내 함수율 변화는 전체적으로 큰 차이없이 유사한 온도이력 및 적산온도를 나타냈으나, 구조체가 얇거나 여러 장의 버블시트를 포설할 경우 시트간 간격이 크게 발생하면 콘크리트 초기양생에 불리한 요건이 발생할 수 있음을 확인할 수 있었다. 콘크리트의 코어공시체 압축강도는 버블시트의 포설시기를 지연시키거나, 시트간 간격을 크게 유발시키거나, 버블시트내 함수율을 증가시키거나, 타설 콘크리트 구조체 두께가 얇게 되는 등 콘크리트 양생에 불리한 조건을 적용시킬수록 초기 압축강도는 저하하는 것으로 나타났으나, 재령이 경과할수록 그 차이는 작아지는 것으로 나타났다.