Quality control and assessment of geopolymer cements based on reacted and free alkalis

In this paper, new parameters based on reacted and free alkalis are introduced to assess and control the qualitative properties of geopolymer cements. For this, Fly ash-based geopolymer paste were prepared to study the correlation between compressive strength and reacted alkali at different curing time and temperatures. Since the properties of geopolymers strongly depend on the reactive oxides content (Al2O3 + SiO2)reactive and composition [Al2O3/(Al2O3 + SiO2)]reactive of the precursors, variation of this ratio on the relationship between compressive strength and reacted alkali and between efflorescence intensity and free alkali were also investigated using by blended natural pozzolan/calcium aluminate cement and fly ash/calcium aluminate cement geopolymer pastes. The results confirm the existence of strong correlations between compressive strength and reacted alkali and between efflorescence intensity and free alkali. The findings, therefore, prove the suitability of the reacted and free alkali contents as proper quality control parameters in geopolymer cements.