The development of new cementitious materials from industrial waste has allowed the constitution of supplementary alternative cementitious materials. However, traditional cement production generates large quantities of greenhouse gases such as CO2. Therefore, the study of supplementary alternative cementitious materials like alkaline activated blast furnace slag has become a viable option for the development of alternative cements, especially in the region of Boyacá, Colombia, where there are industries that produce these materials. Therefore, the present research generated mortars made of granulated blast furnace slag, alkaline activated with Na2SiO3/Na2CO3 in 3.5 M solution, dosed at 40%, 50% and 60% addition. Subsequently, the mortars were characterized by studying their crystalline structure by X-ray diffraction, thermogravimetric analysis, microstructural changes by scanning electron microscopy and the influence of the activator concentration was evaluated. The results obtained showed higher strengths in mortars dosed with 60% addition of the activator and up to 15% higher than traditional Portland cements. Therefore, this supplementary alternative cementitious agent is viable for various engineering applications and its implementation will mitigate the environmental impact generated by the consumption of raw materials and the manufacture of traditional cements.