• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.347-354
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• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.63-72
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• 2012

The high-flowing concrete requires additionally or excessively more expensive admixture than conventional concrete. So, the concrete has not to be widely used in practical field due to the increase of production price, need of additional facilities, and excessive development of concrete strength in associate with addition of too much cementitious material even though it has more significant advantages than conventional concrete. Thus, this study aims at developing high-flowing concrete with general strength unlike high strength which has been carried out in conventional study. To observe the role of aggregate in the concrete quantitatively and to increase the performance of high-flowing concrete effectively, parametric studies were carried out such as W/C, s/a, fineness modulus of aggregate, contribution degree of particle sizes, and the effect of 13mm aggregate and fine stone powder as a partial replacement of aggregates. And the effect of these factors on performance of the concrete was evaluated by measuring slump-flow and gap of penetration height in U-typed instrument. As a result, it was found that flowability of high-flowing concrete depends upon grading of fine aggregate more significantly than that of coarse aggregate and is enhanced greatly as fineness modulus of fine aggregate decreases and the value of s/a increases. In addition, the application of 13mm aggregate and fine stone powder are expected as a partial replacement of aggregate in order to increase the performance of high-flowing concrete more effectively.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.90-91
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• 2014

In this study, the effect of very fine sand on drying shrinkage cracking of concrete was experimentally evaluated. As a result of the study, the time-to-cracking of concrete used very fine sand was shorter than plain concrete. Also, the stress rate of concrete used very fine sand was higher than plain concrete. It was due to the increase of water content when very fine sand was used in concrete. In conclusion, the use of very fine sand can lead the increase of water content to meet the target slump and higher potential of cracking of concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.10a
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• pp.121-122
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• 2016

Recently in the domestic construction industry, source depletion has resulted in instances of ready-mixed concrete companies using river sand or crushed sand with high fine particle content. But the use of such low-quality fine aggregate is known to cause concrete quality to decline and have negative effects. So this study analyzed how much of an impact changes in fine particle content have on cement mortar's engineering characteristics. As a result, the flow rate and air quantity, which are characteristics of unhardened mortar, were shown to decrease as fine particle content increased, and compression strength, a characteristic of light mortar, was shown to subtly increase as fine particle content decreased.

• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.561-567
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• 2001

It is reported that a lot of sludge powder is produced during the process of manufacturing crushed fine aggregate in mines. However, there is a limitation on the its use that most of them are disposed and wasted, which cause environmental pollution. Therefore, in this paper, tests are carried out in order to recycle sludge powder as filler for cement mortar products. Kinds of aggregates and mix proportion of mortar are varied under various contents of sludge powder. According to test results, it is found that cement mortar products using sludge powder as substitution of fine aggregate about 10% have better qualities than those without sludge powder.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.2
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• pp.93-100
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• 2019

In this study, the mechanical properties of early-age concrete were evaluated by mixing the electric arc furnace oxidizing slag fine aggregate with 30% and 50% replacement ratio. Slump test, air content test and unit volume weight test were performed for fresh concrete, and compressive strength test and chloride penetration experiments were carried out in hardened concrete. The compressive strength increased up to 7 days of curing age with increasing replacement ratio of the electric furnace oxidizing slag, but the strength decreased to 90% level of OPC concrete at 28 days of age. Regarding the result of chloride penetration test, no significant differences from OPC concrete were evaluated, which shows a feasibility of application to concrete aggregate.

• Journal of the Korea Institute of Building Construction
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• v.18 no.3
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• pp.219-225
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• 2018

The aim of the research is improving the quality of concrete by using the alternative aggregate resources and recycling wastes. To make a combined aggregate fitted in standard particle size distribution curve, crushed sand from blasted rock debris was used as a base aggregate. Additionally, to increase the portion of fine particles, sea sand was mixed. Although these aggregate combination fit the standard particle size distribution curve, in this research, raw coal ash was replaced as a microfine. According to the experiment, by replacing 5% raw coal ash, the most favorable results were achieved in aggregate gradation and cement mortar quality.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.1
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• pp.53-64
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• 1983

It was investigated by experimental method whether fine powder and coarse particle obtained by briquet cinders crushing could be used in the place of cement and fine aggregate or coarse aggregate for concrete. Except these experiments, further study, containing the fundamental physical properties of briquet cinders and the mechanical properties of concrete using briquet cinders, is needed for practical use, but these experimental results suggest the possibility for using briquet cinders as materials for mortar or concrete.

• Journal of the Korea Institute of Building Construction
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• v.20 no.4
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• pp.331-338
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• 2020

The aim of the research is to evaluate the possibility of using coal gasification slag (CGS) as a combined aggregate for concrete mixture. To achieve this goal, the fundamental properties and the durability of concrete were analyzed depending on various combining ratio of CGS into both fine aggregate with favorable gradation and relatively coarse particles. According to the results of the experiment, slump and slump flow were increased with content of CGS regardless of crushed fine aggregate with good and poor gradations while the air content was decreased. For the compressive strength of the concrete, in the case of using the crushed aggregate with good gradation, increasing CGS content decreased compressive strength of the concrete, while when the concrete used crushed aggregate with poor gradation, the compressive strength was the maximum at 50% of CGS content. As a durability assessment, drying shrinkage was decreased and carbonation resistance was improved by increasing CGS content. On the other hand, for freeze-thawing resistance, CGS influenced adverse effect on freeze-thawing resistance. Therefore, it is known that an additional air entrainer is needed to increase the freeze-thawing resistance when CGS was used as a combined aggregate for concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.299-306
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• 2016

In this research, influence of low quality aggregate on engineering properties of concrete was evaluated experimentally. From the experiment, the fresh properties of slump and air content were controlled with unit water and AE dosage and all mixture were designed to have similar fresh properties of slump and air content with various quality of aggregate. Under this conditions, comparing with the mixture with high quality aggregate, the mixture with low quality aggregate showed the unit water and AE dosage were increased about 18 and 98%, respectively, because of poor grading and quantity of fines. For compressive strength, the low quality aggregate, specifically, exploded debris, clay sand, and sea sand contributed on decreasing compressive strength about 20~35%. Additionally, the concrete mixture including low quality fine and coarse aggregate showed adverse quality in not only compressive strength but also durability of freeze-thawing resistance, drying shrinkage, carbonation, and chloride ingression. Therefore, it is considered that for low quality aggregate, extra treatment processes such as washing or controlling gradation, and regulation to limit the use of low quality aggregate are needed.