The corrosion potential of geomaterials must be investigated before their use in geotechnical applications. Soils with unfavorable corrosivity characteristics can accelerate the degradation of surrounding pipes and metal structures. Steel slag with high CaO may be advantageous when stabilization and strength-gain characteristics of geo-materials are considered. However, the high alkalinity may also lead to metal corrosion. In addition, some chemical and mineralogical components of steel slag resemble cement, but steel slags, unlike cement, do not necessarily show self-cementing characteristics, with increasing strength gain over time. Cement, lime, or class C fly ash can be used to activate cementitious reactions in steel slag. Activated mixtures of steel slag can be utilized in pavement layers when high strength is required or, in other applications, as controlled-low strength materials. This study focuses on corrosivity and strength-gain characteristics of steel slag. The corrosive nature of steel slag was investigated in the laboratory using electrical resistivity and pH measurements. Additionally, the self-cementing characteristics of two types of steel slag were investigated through unconfined compressive strength tests. Steel slag samples were activated by class C fly ash replacement, and the strength-gain characteristics of the mixtures were evaluated over time. Results of this study showed that steel slag samples were mildly corrosive to very corrosive, depending on their moisture content. A high corrosion potential indicates that proper precautions should be taken to protect pipes and other metallic components in contact with steel slag. The unconfined compressive strength test results indicated that steel slag samples do not possess strong self-cementing characteristics. On the other hand, when activated with class C fly ash, the activated mixtures of steel slag show superior strength-gain properties that are favorable when used in stabilized pavement layers.