Theoretical and Experimental Strategy for the Control and Mitigation of Efflorescence in Metakaolin-Based Geopolymer

Abstract

Compared with portland-cement-based matrices, the high mechanical strength, satisfactory durability, and sustainable features of geopolymeric matrices have brought great interest in the civil construction sector. Excessive activator content in a geopolymer mixture can cause efflorescence, a phenomenon related to the unreacted alkalis that compromise the mechanical properties and aesthetics of the structures. This article proposes applying statistical mixture design (SMD), associated with simultaneous optimization for the dosage of geopolymeric matrices, to evaluate and mitigate efflorescence. Based on the extreme vertices screening design, the formulations were made using metakaolin as a precursor, NaOH and sodium silicate as the activator, and sand and superplasticizer. The formulation with the lowest efflorescence formation, highest compressive strength, and adequate workability was the one whose molarity of NaOH was equal to 9.02 M, and the ratios Na2O/Al2O3, SiO2/Al2O3, and H2O/Na2O were equivalent to 1.43, 2.65, and 8.36, respectively. In addition, the Na2O/Al2O3 ratio was the predominant factor for efflorescence occurrence. SMD associated with simultaneous optimization is a technically viable alternative for minimizing free sodium in geopolymeric matrices.