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This study investigates the influence of the replacing method and kinds of mineral and chemical admixtures on early strength development of concrete. According to the results, compressive strength of concrete at early age incorporating fly-ash(FA) and blast-furnace(BS), is lower than that of plain concrete in the case of replacement of admixture for cement, but higher than that of plain concrete in the case of replacement of admixture for sand and combination. As BS is used, and replacing ratio for fine aggregate, compressive strength at early age gains higher than that of plain concrete. Compressive strength development at early age is higher in the case of melamine and polycarbonic type superplasticizer(SP) than in the case of naphthalene type SP, and higher in the case of accelerating type than standard type. The rebound value of P type schmidt hammer shows similar tendency to early strength development. When the rebound value of P type schmidt is more than 25, compressive strength of 5MPa, which the side form can be removed, is gained. Strength development of concrete at early age shorten removable time of side form can be achieved by using melamine based SP and replacing 20% of BS by cement weight, of which combination is 1:3(by cement:by sand), in order to attain economical advantage and usefulness.