Ground Granulated Blast-furnace Slag (GGBS) powders, the massive by-products produced in the process of manufacturing cast iron are actively used as a substitute for cement, one of the major causes of greenhouse gas emissions. The purpose of this study was to investigate the proper mixing ratio of the activator, and to reduce the usage of cement in the production of high-strength steam cured concrete using GGBS. The cured products of various ratio were analyzed by XRD and TG/DTA, and the best ratio of the cured product were applied to the Pre-stressed high-strength concrete (PHC) Pile, and the performance was then evaluated. The results showed that the fluidity was improved by mixing with GGBS, and when an appropriate amount of activator was used, it was possible to produce high-strength cured products. In the PHC-Pile test, the replacement rate of 40% GGBS and combined 4% anhydrite gypsum and 2% Ca(OH) 2 as an activator was excellent. The compressive strength (2MPa more), shear strength (1.3MPa more), and Axial force strength (2.7Mpa more) were more improved than for the normal Portland cement PHC-Pile, and this GGBS pile can be manufactured more economically (the cost can be saved in the amount of 14.5%). This is caused by the activating agent destroying the glassy film of the GGBS, and actively inducing the pozzolanic reaction, so that the hydrate materials are generated, such as C–S–H. In addition, by positively utilizing the inexpensive industrial by-product, GGBS, it is possible to manufacture environmentally friendly concrete products, while reducing the amount of cement used.