The wide use of ox)'gen converter steel-making, coll/)Ied with the much illl/Hoved blast furnace process, and recent abundance of rich iron ore supplies have altered the whole steelmaking situation. Progress in the chemical indust./y did, for a time, spur the develo/)lI1ent of , direct reduction' processes, as the various methods of making iron withollt a blast furnace were called. However, blast furnace has become so e.Dicient that direct redllctioll processes are now aimed less at replacing the conventional /JI'ocess than at supplementing it. This sllp/Jlemenlmy /JI'ocess has come to be kllown as , pre-reduction,' since its product is to be subsequently treated by the conventional /Jrocess. Yawata Iron & Steel Co., Ltd. carried out a series of tests on olle /y/Je of IHe-reduced material, slJonge iron, and /Ha ctically confirmed that its lise reduced coke rate and increased iron output. Pre-reduction at mines ""D' be economical. BlIt , for the /Hesen t, although technically feasible , (He-redllction at j a/Janese steelworks has not yet /) roved economical.

In this research, we have carried out the fundamental research on development of high strength concrete using the powder combining three industrial by-products as substitute of cement. The by-products used were fly ash of type II, ground granulated blast-furnace slag and gypsum. As a result,-it was possible to make a high strength paste, using vibrating compaction, with a water-powder ratio of 25%, The paste had compressive strength greater than 60 N/mm2 after curing for 91 days. Further we found it was possible to make high strength concrete of varying sand-aggregate ratios which all had a compressive strength of about 30 N/mm2 after curing for 28 days and 40 N/mm2 after curing for 91 days. Finally we obtained the optimum mixture proportion of concrete is unit water content = 170 kg/m3, water-powder ratio = 25%, and sand-aggregate ratio = 40%, For each of these results no cement was used.

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For enlarging and promoting usage of blast furnace slag sand and improving construction performance of concrete with it, the behavior of the mortar under both static and dynamic, using vibrator, conditions were confirmed from the viewpoint of plastic viscosity, filling property and bleeding rate. As the results, within the scope of this experiment, by investigating the mixing ratio at which the plastic viscosity changes from the vibration plasticity viscosity obtained by the feather penetration type viscosity measurement test, it was considered that the appropriate fine aggregate mixing ratio can be estimated. Furthermore, the pore water pressure was measured for a sample in which the mixing ratio of the fine aggregate was changed, and the possibility of evaluating the fresh properties from the tendency of disappearance of pore water pressure after stopping the vibration was indicated.