Effects of highly dispersed LDH nano-platelets on chloride binding and corrosion protection of cementitious materials

Abstract

The chemical binding of free chloride ions in cementitious materials, crucial for prolonging their lifespan, relies heavily on aluminate hydrates and can be modulated by incorporating the layered double hydroxides (LDHs). Yet, the currently synthesized LDHs in field of cement and concrete usually suffer from nano crystallites aggregation, limiting their potential as nanofillers and hindering the chloride-capturing efficiency. This study compares the cementitious materials containing highly dispersed LDH nano-platelets (HDLNPs) with those using conventional LDH powder (LP) to unveil the ion-exchange-efficiency-dependent aluminates regulation and particle-size-related pores refinement of LDHs. HDLNPs regulate the sulfate to aluminate balance at a concurrent rate with early-age hydration of tricalcium aluminate (C₃A) to promote the conversion from ettringite (AFt) to alumino-ferrite-mono (AFm) phases. Furthermore, due to their high dispersion, HDLNPs mitigate the interlayer inertness toward chloride binding induced by carbonation. However, HDLNPs primarily occupy micropores around outer C-S-H, failing to refine capillary pore, which is amplified by the concomitant AFt shortage, leads to higher capillary adsorption rates. Nevertheless, HDLNPs outperform LP in terms of corrosion protection at equivalent dosage, evoking the LDHs’ unsung ion-exchange capacity in delaying chloride ingress. This advancement in the dispersion of incorporated LDHs underscores their valuable roles in designing durable and sustainable cementitious materials.