This study was intended to evaluate the applicability(availability) of melted slag as concrete aggregate. With the objective, first of all, cement mortar was manufactured to measure the basic properties such as flow, compression strength and bending strength, and the durability through accelerated carbonation test, freezing & thawing test and change in length test, to verify the appropriate availability as aggregate, from which it was proven the availability as cement concrete aggregate. In the result of accelerated carbonation test of concrete, it was not initially different with plain one but the degree of carbonation was getting increased as concrete age and replacement rate are increased. It was shown that in the reduction rate in compression strength after freezing & thawing, 100% replacement concrete was the largest value, 34% but the freezing resistant degrees after 300 cycles were all over 60%. From the above results, it could be concluded that using air-cooled slag for alternative of thick aggregate should be based on the results in compression strength, accelerated carbonation test and freezing & thawing test and that the appropriate replacement rate of air-cooled slag would be preferably 50% and lower, considering the fluidity.