Blended limestone-Portland cements (LS-PC) were enhanced with two powdered sodium silicates (SiO₂/Na₂O = 3.26) and evaluated in mortars. In part 1, blends incorporating 10, 40 and 70%PC and 2, 11 and 20% of a commercial sodium silicate (CSS) were analyzed; in part 2, a sodium silicate synthesized from waste glass (PSWG) was compared with the CSS in LS-PC with 40%PC and 11% sodium silicate. The mortars were evaluated in terms of compressive strength, flowability and global warming potential; the formulations of part 2 also were analyzed by X-Ray diffraction and scanning electron microscopy. The CSS did not affect flowability and had a positive effect on mortars in LS-PC with 10 and 40%PC, while the PSWG had similar performance on strength and flowability relative to the reference. Mortars with PSWG achieved 50 MPa at 90 days and the global warming potential to MPa ratio was 50% lower than reference with 100%PC. The PSWG enhanced the reactions of the PC and densified the microstructures relative to the mortars with CSS. Waste glass in PSWG applied to the blended limestone-Portland cements appears as a more suitable route than as precursor in alkali activated cements.