Abstract
The activated alkaline materials constitute a group of eco-efficient binders. For materials with a low calcium content, excess free sodium in the alkaline activation process results in efflorescences that weaken the matrix. The excess of free sodium occurs due to failures in the quantification of the reactive fraction consumed by the alkaline activation reactions. The present work compares the conventional dosage methods with the method used by the Rietveld refinement, based on the application of the external standard (EP). To determine the amorphous phase content in the materials, chemical (XRF) and mineralogical (XRD) analyzes were performed on metakaolin and silica fume. The formulations were then dosed using both methods, the molar ratios of Na2O/Al2O3 and SiO2/Al2O3 varying between 0.8 and 1.4. and 3.3–3.6, respectively. The activated alkaline matrix dosed by the EP method exhibited mechanical resistance approximately twice as high as that dosed by the conventional method. The formulation EP-3.6–1.0 showed greater mechanical strength, in addition to high resistance to dissolution in hydrochloric acid (52% of the material remained indissoluble). The optimal SiO2/Al2O3 and Na2O/Al2O3 molar ratios were equal to 3.6 and 1.0, respectively, approaching works that used precursors with a high degree of amorphism.
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