Abstract—The effect of water-binder ratio and Blaine fineness on the carbon dioxide activation of a cement-free binder was studied. An electric-arc furnace slag from the national steel industry in Portugal was used. The slag’s chemical composition was determined by energy dispersive spectroscopy analysis, it was rich in calcium oxide, iron oxide and silicon oxide with some minor contents of other oxides. The slag was turned into powder and mixed with water in three different ratios from 0.10, 0.125 and 0.15. Two different sieve ranges of powder were used, 45μm and 125μm, each powder had its own density and Blaine number which were respectively 3.7712g/cm3 and 529m2/kg; and 3.7033g/cm3 and 136m2/kg for the 45μm and the 125μm. The temperature and the gas pressure were controlled aiming to improve its activation. Compressive strength up to 71MPa was achieved on the samples. Thermogravimetric analysis and x-ray diffraction were done to see the formed products, mineralogical phases and compare the activation between the different situations.