• Journal of the Korean Society of Industry Convergence
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• v.2 no.1
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• pp.45-52
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• 1999

It is difficult to keep the balance of supply and demand for natural aggregates in recent years, because natural resources have become to be almost exhausted. Crushed stone is already used for coarse aggregate instead of river gravel at present. Now, crushed sand or sea sand should be used for fine aggregate, because natural sand also has been exhausted with a few exceptions around Nakdong River. The sea sand has a lot of problems which are the corrosion of reinforcement bars, the investment of facility for cleansing salt and the cost increase due to the insufficiency of industrial water. Therefore, it is necessary to produce and to utilize the crushed sand very actively, but some material properties which are related to water absorption, strength and chemical durability, prevent from determining the generalized criteria because its rocks make much differences in its physical and chemical characteristics. In this paper, fundamental physical properties of crushed sand, which comes from Daegu Subway construction fields, have been investigated for the usability on basic material of concrete. The optimum replacement ratio and the strength estimation method of crushed sand replacing natural sand also have been presented here through the compressive strength test of ready-mixed concrete cylinders.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.463-466
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• 2005

This study examined the effects of comparatively widely used fine aggregates in the domestic construction fields on the quality of concrete through the analysis of the effects of such fine aggregates on the physical properties of fresh concrete and strength of hardened concrete. Results revealed that crushed sand degrades the fluidity and air entraining of concrete compared to natural aggregates like sea sand and river sand. Especially, the use of crushed sand exhibiting low grain shape and grade was seen to have larger adverse effect on the physical properties of concrete.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.108-112
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• 2005

In this research, the physical properties of fresh concrete using lime stone powder as a part of cement were investigated. Fresh concrete using lime stone powder was prepared with various lime stone powder replacement($5{\sim}12$ volume %) for cement and the quantities of sand aggregate ratio in concrete were 47.3%, 48.5% and 49.4% of ratio of sand aggregate. The workability, flowing characteristics, air content and bleeding of concrete using lime stone powder were tested and the results were compared with those of ordinary portland cement concrete. In the experiment, we acquired satisfactory results at the point of fresh concrete characteristics using lime stone powder within the replacement ratio of $8{\sim}12%$ and the optimum quantity of sand aggregate ratio in concrete was found to be $48.5%{\sim}50%$ of ratio of sand aggregate.

• Proceedings of the Korean Institute of Building Construction Conference
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• v.y2004m10
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• pp.55-58
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• 2004

This paper investigated the results of quality of concrete using mixed sand with grading adjustment in order to find out the applicability of fine aggregate with bad grading, According to test results, fluidity of concrete with fine level grading river sand was decreased while with coarse level grading crushed sand increased compared with that with medium level grading crushed sand. Use of mixed sand with grading adjustment(MSG) resulted in an improvement in fluidity. Increase in fineness modulus led to an increase in bleeding, For compressive strength, use of MSG increased compressive strength. For drying shrinkage, use of fine level grading river sand resulted in an increasing drying shrinkage due to the larger presence of fine particles, while use of MSG led to a reduction in drying shrinkage

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.84-88
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• 1995

The results of an experimental study on manufacture and mechanical properties of concrete utilizing crushed sand and fly ash for construction materials are presented in theis paper. As the results show, the workability, compressive strength and freezing-thaw resistance were improved by proper contents of fly ash, replaced crushed sand, and air entraining agent. And the drying shinkage was decreased by proper contents of those. Also, the suitable weight contents of replacing ratio of crushed sand and weight ratio fly ash in concrete using crushed sand were in range of 30% and 15% respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.597-600
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• 1999

Recitly, the use of sea-sand is increasing in the construction due to the rapid reduction of river-sand. In that case, one of the major problem is that a sand salt in sea-sand induce the corrosion of embedded reinforcing bar in concrete. In addition, the deterioration of concrete quality arises a social problem in the durability of reinforced concrete. This research is aimed at providing the data for the control of design method of repair and rehabilitation in the reinforced concrete structure by means of the evaluation of structural performance due to corrosion.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.118-123
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• 1995

Evaluating the moisture content for sand is useful for quality cotnrol of concrete. If water content of evaluate instantly and apply for mix proportion sand of concrete, in mixing propertion of concrete, it can makes to improve of concrete quality. In this study, the evaluating method for moisture content of sand, using the electric velocity and dielectric constant was proposed as a study of quality control of concrete. The obtained results are summarized as follow. The resistance ratio was decreased as the increase of moisture content The dielectric constant was decreased as the sand of the moisture content increase.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.153-159
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• 1999

The objective of this study was to investigate the bond strength properties of antiwashout underwater concrete. The fine aggregate(river sand, blended sand (river sand : sea sand = 1 : 1), condition of cast and cure(sea water, fresh water), and compressive strength of proportion(210kgf/$\textrm{cm}^2$ ~ 330kgf/$\textrm{cm}^2$) were chosen as the experimental parameters. The experimental results show that the underwater segregation resistance was increased, but flowability (slump flow) and air contents were decreased as the compressive strength of proportion increased. Bond strength of antiwashout underwater concrete was similar to plain concrete. From this study, rational analytic formula for the modulus of rupture and bond stress are to be from compressive strength of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.81-84
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• 2006

Currently, natural aggregates of good quality are hard to use because of continuous decrease of internal aggregate resource and regulation of gathering. So, use of crushed sand was being increased. On the other hand, skyscraper projects with 100 stories are being planned within the country and high strength concrete must be used to construct a skyscraper with 100 stories. High strength concrete is necessary to use crushed sand too because we are still unable to secure natural aggregates of good quality. So, This study indicated basic data necessary for mix design of high strength concrete through valuation of concrete property by quality variation of crushed sand.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.249-255
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• 2006

Recently, interest grew on the quality of aggregates following the diminution of primary resources from river as to grow construction demand and the low grade of nature sand like sea sand. following, need is to diversify the supply sources of fine aggregates which are excessively relying on sea sand and urgency is to find as soon as possible aggregate resources that can substitute sea sand. On the other hand, various fine aggregates we utilized to produce concrete in the domestic construction fields. However, few studies have been systematically investigated on the effects of such fine aggregates on concrete properties. Therefore, this study examined the effects of comparatively widely used fine aggregates in the domestic construction fields on the shrinkage, durability and watertightness of concrete. Results revealed that drying shrinkage increases, and durability and watertightness degrades for concrete using crushed sand than natural fine aggregates like sea sand and river sand. Especially, the use of crushed sand exhibiting bad grain shape and grade was larger adverse effect on the quality of concrete. In addition, appropriate adjustment of the grain shape and grade during the blending of crushed sand exhibiting bad grain shape and grade with natural aggregates appeared to enhance the shrinkage and durability of concrete.