Composition, nanostructure and stability of Cu-modified C-A-S-H in antibacterial alkali-activated slag

Abstract

Antimicrobial alkali-activated slag (AAS) has been envisioned as a biologically resistant binder for potential application in sewer structures against biogenic sulfuric acid attacks. This work investigates the composition, phase assemblage, micro- and nano-structural alterations of AAS binders incorporating Cu-based antimicrobial agents (i.e., copper oxide and copper nitrate), as well as their antimicrobial properties and degradation mechanism under biological corrosion caused by sulphur-oxidising bacteria Acidithiobacillus thiooxidans. The results show that the incorporation of copper oxide or copper nitrate increases the degree of hydration of slag but reduces the mean chain length (MCL) of C-A-S-H as Cu preferably affects the bridging AlO4-tetrahedra over SiO4-tetrahedra. The substitution of Cu for the CaO polyhedral at the edges and corners of the C-A-S-H main chain makes the Al linkage blocked. Cu also possesses a charge-balancing role, resulting in a lower protonation of C-A-S-H in the Cu-doped AAS than that in the neat AAS, where C-A-S-H is a Tobermorite structure with MCL between 5 and 11. The Cu-doped AAS pastes show excellent antimicrobial efficiency, in particular, the CuO-doped AAS demonstrates 100 % effectiveness in inhibiting biofilm formation, with the corrosion depth significantly reduced by a factor of 10. The Cu ion is released initially from the outer surface of C-A-S-H due to its low bond dissociation energy, followed by the weak position, namely the AlO4-tetrahedra at the bridging position, rendering the rupturing of the C-A-S-H structure.