Sulfuric acid degradation of alkali-activated metakaolin cements supplemented with brucite

Juan Pablo Gevaudan, Zoey Craun, Wil V. Srubar

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Abstract

This study investigated the effect of alkali content (Na:Al = 0.86 and 1.39) and brucite (i.e., Mg(OH)2) mineral addition on the sulfuric acid resistance of alkali-activated metakaolin (i.e., geopolymers). Geopolymers consist primarily of a sodium-stabilized aluminosilicate hydrate (N-A-S-H) framework. Results demonstrate that higher alkali contents and brucite addition improve the acid resistance of N-A-S-H, as evidenced by reduced dealumination and Si and Na leaching upon exposure to acid. These results are mechanistically explained by increased retention of Mg+2 within the microstructure and increased Mg–Al interaction upon acid exposure. Higher Mg+2 retention and increased Mg–Al coupling together provide empirical evidence of polyvalent cationic stabilization—a mechanism involving polyvalent cations (e.g., Mg+2) that stabilize the N-A-S-H binder by arresting acid-induced electrophilic attack. Results further illustrate that brucite addition, especially at high-alkali content formulations, reduces micro-scale porosity while increasing the proportion of gel pores (<5 nm), which suggests that increased tortuosity of gel pores may aid in Mg+2 retention and promote the increased Mg–Al coupling observed herein.

Original languageEnglish (US)
Article number104063
JournalCement and Concrete Composites
Volume121
DOIs
StatePublished - Aug 2021

All Science Journal Classification (ASJC) codes

  • Building and Construction
  • Materials Science(all)

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