Effect of the sequence and mixing time of the alkaline solution on the synthesis of metakaolin-based geopolymers

Abstract

Geopolymers are alternative binders produced from aluminosilicate precursors activated by alkaline solutions. To improve practicality, one-part systems replace liquid activators with solid components, requiring only water addition. However, the influence of mixing sequence and activator maturation on geopolymerization remains unclear. This study evaluates geopolymeric matrices prepared using different mixing procedures, varying the preparation time of the alkaline solution and mixture type. Fresh-state behavior was assessed through flow tests (mini-V funnel and mini-slump), while hardened properties included shrinkage, compressive strength, and capillary absorption. Complementary analyses using calorimetry and FTIR were also performed. Results indicate that pre-mixing the precursor with the alkaline base accelerates geopolymerization but increases heat release, reducing workability and increasing shrinkage. Conversely, mixing with a matured alkaline solution at room temperature provided improved performance, balancing reactivity and workability. These findings highlight the importance of processing conditions in optimizing geopolymer systems.