Implementing the effect of geopolymer concrete pore solution pH in the standard rapid migration test NT Build 492 protocol

Abstract

This research investigates the impact of the pore solution pH values on chloride content at the colour change boundary determined according to the standard rapid migration test (NT Build 492), with a focus on alkali-activated materials, so-called geopolymer. The study investigates a range of geopolymer formulations using various proportions of ground granulated blast furnace slag (GGBFS), fly ash, and calcined clay, alongside different activator concentrations, to examine their influence on the pH value of the pore solution. Findings from this study suggest that the pH value of the pore solution greatly influence in the chloride ion concentration at the colour change boundary, which should be accounted for in the calculation of the non-steady-state migration coefficients (D_nssm). It is noted that mixtures with higher GGBFS content exhibit higher pH values than mixtures containing fly ash or calcined clay, impacting the D_nssm. The results advocate for modifications to the standard NT Build 492 protocol to enhance its applicability and accuracy for geopolymer materials, emphasizing the importance of using revised D_nssm values calculated considering the unique properties of geopolymer concrete for more durability assessment.