An initial study on alkali activated limestone binders

Alkaline cements were studied using limestone as the only precursor activated with solutions of sodium hydroxide and waterglass; the activator was used at concentrations of 7 and 10%Na2O using modules of Ms = 0, 1 and 1.5. The compressive strength was followed on pastes and mortars for up to 360 days after an initial curing at 60 degrees C for 24 h. A paste with 7%Na2O and Ms = 1.5 and a mortar with 10%Na2O and Ms = 1 reached strength of 15-25 MPa after 360 days; the mortars showed trends towards higher strength with time. The characterization by SEM, EDS, XRD, FTIR indicated that the microstructure consisted of a mixture of silica gel, carbonates, C-S-H, N-C-S-H and N-S-H. Si-29 MAS-NMR showed the formation of calcium silicates possibly of long chains which contributed to the strength.