This study is to investigate the effect of the use of electric arc furnace oxidizing slag as aggregate replacement on the engineering properties of the ultra high strength concrete with 80 MPa. The physical and chemical properties of aggregates such as limestone aggregate and electric arc furnace oxidizing slag aggregate(EFA) were investigated firstty. Then, the limestone fine aggregate and the electric arc furnace oxidizing slag fine aggregate were applied to ultra high strength mortar to analyze their usability for ultra high strength concrete. Based on these analyses, EFA was used for the ultra high strength concrete mixture, and its effect on engineering properties and summarized as follows.

1) The quality test for the aggregates used in this study showed the following results. The limestone fine and coarse aggregates showed excellent results which sufficiently satisfies all the KS standards in both physical and particle properties. The granite fine and coarse aggregates had a higher absorption rate and a higher fineness modulus than other aautogenous shrinkage was analyzed. EFA did not have a good grain size and showed a higher density than other aggregates.

2) The table flow of fresh mortar satisfied every target value. However, as the replacement ratio of EFA increased, the fluidity decreased only a little. The air content and the unit volume weight increased with the increasing replacement ratio of EFA, and the setting time was shortened to the range of 1~2 hours.

3) The compressive strength decreased with the increasing of replacement ratio of EFA at an early age, but 25% replacement ratio resulted in the same or higher strength than when only limestone aggregate at later ages. More than 50% replacement ratio of EFA resulted in the decrease of strength. The autogenous shrinkage was reduced by EFA replacement. In particular, 50% replacement ratio resulted in about 17% decrease in autogenous shrinkage, which was the highest level. Consequently, when EFA was mixed at 25% or 50% replacement ratio, it was found that the appropriate reduction of autogenous shrinkage was produced without harmful effect on fluidity and strength.

4) The slump flow, 500 mm reaching time and U-Box filling test for fresh concrete showed that the use of limestone aggregate along with EFA produced an overall improvement in performance than the use of granite aggregate. Especially, when granite aggregate is used, more high-range water-reducing agent needs to be applied to achieve target performance than when using limestone aggregate. Accordingly, it seems that the use of limestone aggregate would be a cost-efficient alternative to manufacture ultra high strength concrete.

5) The use of limestone aggregate also resulted in the highest compressive strength. When EFA was used, the initial compressive strength was high, but the development of the strength decreased after 28 days. Young''s modulus had the same trend as the compressive strength. The splitting tensile strength increased along with the increase in the replacement ratio of EFA.

6) The autogenous shrinkage was much more reduced by limestone aggregate than by granite aggregate. Also, as more EFA were used as aggregate replacement, the autogenous shrinkage was further reduced. Like in the case of mortar, the replacement ratio of 50% resulted in the largest autogenous shrinkage.

Consequently, as for the autogenous shrinkage of ultra high strength concrete with 80 MPa, limestone fine aggregate with 50% replacement ratio of EFA seems to be the optimal mixture that can reduce autogenous shrinkage without decreasing fluidity and strength.