The supply of aggregates with good quality has been a significant issue under the situation that requires high quality and high durability in recent domestic construction field. The low-grade aggregates have been alternatively used for a part of natural aggregates by using simply the mixed low-grade aggregates that were barely used in the past as a solution for this issue of aggregate supply and environment, but this may cause a problem that deteriorates the quality of aggregate and concrete and the real situation is that there are many difficulties in manufacturing and using mixed aggregates since KS standard on the mixed aggregate is not established properly.
Therefore, this study is ultimately intended to utilized the mixed aggregates with more than 2 kinds of aggregates for KS standardization and business field by comparatively analyzing the features of concrete in case of using fine?coarse aggregate independently with different components and fineness distribution and in case of mixing 2 kinds and 3 kinds of aggregates with a certain ratio in order to improve utilization of low-grade fine?coarse aggregates, and the results can be summarized as follows.

1) As for the flow characteristics according to mixing of fine aggregates, the case of using mixed 2 kinds of aggregates showed the overall increase in fluidity compared to the case of using only fine aggregates, and among them, it was found that it was effective in improving the fluidity in case of mixing and using RFA and EFA. Besides, in case of air content, the case of mixing 2 kinds of aggregates showed slightly higher air content compared to the sole use.
2) In case of compressive strength, the case of mixing and using 2 kinds of aggregates showed high compressive strength, and among them, the case of EFA showed generally high strength, but it is judged that the rise of expenses according to the separate aging and processing should be considered. It was found that the ratio of length change of drying shrinkage did not make a big influence according to the mixed use of aggregates.
3) It could be known that the case of mixing 3 kinds of aggregates showed th e increase in fluidity compared to the mixing of 2 kinds of aggregates in flowing characteristics according to the mixing of coarse aggregates. Especially, in case that BCA is mixed, it showed remarkable increase of slump. Meanwhile, in case of air content, it was found that air content generally deviated from the standard range according to mixing different kinds of aggregates. As for the characteristics of compressive strength, the case of mixing 3 kinds of aggregates was found to increase compressive strength compared to the case of mixing and using 2 kinds of aggregates. Meanwhile, in case of drying shrinkage, it was found that regardless of changes of aggregate types, it did not affect drying shrinkage significantly.

To synthesize above, using mixed low-grade fine aggregates does not affect the quality of concrete significantly, and it is judged that the caution is required to use aggregates mixed with defected ones such as WFA, RFA and GFA. Besides, in case of coarse aggregates, it is judged that the mixing with 3 kinds of aggregates would be possible to compensate with effective quality rather than 2 kinds of aggregates. Therefore, in case of using aggregates mixed with low-grade ones, it generally does not affect the quality of concrete, and it is judged that it could be widely utilized as an alternative material to be proper for the current situation that the supply of natural aggregates is difficult.