Alkali-activated cements based on limestone-fly ash: Effect of the MgO-NaOH activation, compressive strength and reaction products

This study investigates the effects of alkaline activation with MgO-NaOH on the compressive strength and reaction products of alkali activated cements of limestone powder (PClz) and Class C fly ash (CV). Results showed that substitutions of 25%<PClz<75% allowed 25-76 MPa at 360 days of curing, obtaining the highest strength with 25%PClz-75%CV and 50%PClz-50%CV with 10 and 12% NaOH-MgO, respectively. The results suggest that PCLz participates in hydration reactions as filler and nucleating agent while CV is the main contributor to the advance of the chemical reactions. X-ray diffraction (XRD), Thermal analysis (TA) and Scanning Electron Microscopy (SEM) indicated the formation of M-S-H, and C, N-A-S-H-type products, in addition to carbonate phases such as hydrotalcite, gaylussite, and pirssonite. Traces of unreacted MgO were not observed indicating its whole incorporation into the reaction products.