Reactive alumina, Al2O3r-, is a constituent of natural and artificial pozzolans (thermally activated clays, natural pozzolans of volcanic origin, fly ash, diatomite, silica fume), used as mineral additions to Portland cement (PC) based materials due to environmental (1 t of conventional PC releases 1 t of CO2), technological (higher mechanical strength of the resultant PC blends) and economic reasons (energy savings) [1][2]. Performance of this hydraulic factor in building materials, if present, is related directly to the chemical durability against their exposure to chlorides and/or sulphates. Ergo, thaw salts and marine environments contribute to hindering and preventing electrochemical corrosion of steel reinforcement of reinforced concrete due to rapid forming Friedel's salt [3][4][5]. In return, gypsum-bearing water and/or soils promote degradation of concrete and mortar quality due to expansion, shrinkage and decomposition of PC hydration products caused by rapid forming ettringite [6][7]. Qualitative and quantitative assessment of the reactive alumina, Al2O3r-, content in pozzolans is addressed pioneeringly in this research as all the tetra– or penta–coordinated alumina [8][9] capable to react chemically in form of Friedel’s salt compound. Saline hydration natural and artificial pozzolans are here subjected to, is studied maximally up to 28 days-age using TGA (TG/DTG/DTA) techniques (TA Instruments). The resultant amorphous and/or vitreous Al2O3rcontents are contrasted with the Florentin reference method [10] up to 1 year-age, giving a satisfactory convergence between both data sets. Finally, the precision and repeatability of the newly proposed analytical method is validated conforming obligatory requirements of ISO/IEC 17025 standard for quality and reliability of new analytical trials [11], namely its standardization is resultatively recommended to be considered in a future.