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13 mm이하 순환 굵은골재 치환사용에 의한 연속입도 콘크리트의 공학적 특성
In this research, as a solution of environmental load and exhaust of natural resources due to the increased construction wastes, the recycled aggregate extracted from building waste is sieved for 13 mm size aggregate and replaced to 13 to 25 mm manufactured coarse aggregate to obtain well-graded aggregate conditions. Using this aggregate, the method for securing favorable properties of concrete is suggested. The result of a series of the experiment is as follow. (1) The plain concrete without replacement of 5-13 mm recycled coarse aggregate used the aggregate with less fines although it could be passed KS standard gradation. Hence, it was known that replacing 5 to 13 mm of recycled aggregate is necessary to supply fines and achieve good gradation. (2) For the workability of the concrete, when the concrete contained the aggregate replaced 5 to 13 mm of recycled coarse aggregate, the workability was improved. Especially, about 30 % of 5 to 13 mm recycled coarse aggregate replacement showed better workability than the concrete without replacement of 5 to 13 mm recycled coarse aggregate. Although the gradation of aggregate used was well-graded, over the threshold of 30 % of replacement, decreased workability was observed. (3) For the air content of the concrete mixtures, regardless of water-to-cement ratio, as the replacement ratio of 5 to 13 mm recycled coarse aggregate is increased, the air content of the concrete mixture was decreased. It is considered that the decreased the volume of voids due to the well-graded aggregate with replacement. On the other hand, over 50 % of replacement of 5 to 13 mm recycled coarse aggregate caused increased air content of the concrete mixture because of increased air voids. In the case of unit weight, regardless of water-to-cement ratio, the values were changed related with the amount of air in the concrete mixtures. In the case of 100 % replacement of 5 to 13 mm of recycled coarse aggregate, however, decreased unit weight was obtained because of lighter density of recycled aggregate than the density of manufactured aggregate. (4) The compressive strength of the concrete mixture replaced 5 to 13 mm recycled coarse aggregate was increased due to the well-graded aggregate and thus densely filled microstructure. Especually, when the 5 to 13 mm of recycled coarse aggregate was replaced 30 %, the highest compressive strength was achieved and this value was similar to the concrete replaced with 5 to 13 mm of manufactured coarse aggregate. In the case of drying shrinkage, although there was no significant difference, recycled aggregate replacement contributed decreasing drying shrinkage. In summary, replacing the recycled coarse aggregate of 5 to 13 mm of size for 30 %, a good grade of aggregate was achieved and thus general quality improvement and financial advantages were obtained. Additionally, as increasing the utilization of recycled aggregate, it is expected to contribute on providing the solution of reducing environmental load and the method of preferred quality of concrete with low cost.
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