Functionalised geopolymers against microbial corrosion

Abstract

Microbially induced concrete corrosion (MICC) is the primary deterioration mechanism in the urban wastewater infrastructure, which rises significant expenditure for restoration and upkeep. As an alternative to ordinary Portland cement, geopolymer is a potential solution to the issue of MICC in wastewater infrastructure. However, one of the major challenges hindering the industrial acceptance and practical application of geopolymers in sewerage facilities is the uncertain long-term durability performance of geopolymers under microbial attack, as well as their formulation techniques against microbial corrosion. This research aims to advance our understanding of the degradation pathways and mechanisms underlying geopolymer under microbial corrosion, and to develop novel functionalised geopolymers to maximise their anti-MICC capacities, organised in three parts. The first part of this thesis explores a newly designed benzoate (BZ)-modified alkali-activated slag (AAS) with the in-situ formation of antimicrobial layered double hydroxides (LDHs). The benzoate anions are spontaneously intercalated in a bilayer manner in the interlayers of LDHs to form antibacterial benzoate-intercalated LDHs during the alkali-activation process. The antibacterial performance and biodegradation mechanisms of newly designed BZ-modified AAS are examined, confirming that this functional AAS is effective in inhibiting the bacterial activity and the generation of biogenic sulfuric acid. The second part of the thesis focuses on tailoring the gel composition of calcium-aluminosilicate-hydrate (C-A-S-H) and sodium-aluminosilicate-hydrate (N-A-S-H) with antibacterial cations (e.g., Cu2+ and Zn2+) through metal cation exchange. Their chemical composition, micro- and nanostructure are investigated. The findings reveal that Cu and Zn perform dual functions in the structure of C-A-S-H and N-A-S-H, serving as a structure former that occupies the Ca-O polyhedral or SiO4 tetrahedra positions in the aluminosilicate chains or network and a modifier of charge compensation. Furthermore, their antibacterial performance and bio-deterioration mechanisms are systematically studied. The third part of the thesis investigates a long-lasting antibacterial fly ash/slag-based geopolymer by introducing seeding zeolite nuclei, which are treated by loading antibacterial ion (e.g., sorbate). The impacts of seeding zeolite nuclei on the reaction mechanisms, microstructural formation, and gel composition of geopolymers, coupled with the potential improvement against microbial corrosion are examined. The findings indicate that zeolite enhances the dissolution of fly ash and slag and the formation of reaction products through seeding effect by providing nucleation sites and the altered geopolymers significantly inhibit the adhesion of biofilm. The findings from this research provide valuable insights into the mechanisms of geopolymer-microorganism interactions and inform the development of novel antibacterial geopolymers for sustainable wastewater infrastructure. Ultimately, these new propositions promote widespread application of sustainable geopolymer in wastewater infrastructure by addressing current knowledge gaps surrounding bio-degradation processes and functional geopolymer with long-lasting antibacterial efficacy.