Experimental Investigation on the Phase Evolution and Corrosion Resistance of a Graphene Oxide/Multiwalled Carbon Nanotubes-Doped Cementitious Matrix in a Coupled Chloride–Sulfate Attack

The durability of modern infrastructure in extreme environments faces critical challenges, particularly under a coupled chloride-sulfate attack. Unlike single-factor erosion, this coupled environment induces a complex synergistic deterioration mechanism involving chemical decalcification and physical crystallization pressure, which remains underexplored for nanomodified composites. To address this, this study systematically proposes a synergistic enhancement strategy for optimizing the dispersion of multiwalled carbon nanotubes (MWCNTs) by utilizing graphene oxide (GO) as a functional nanotemplate. The phase evolution and corrosion resistance of cementitious matrices incorporating varying dosages of GO (0-0.05 wt %) and MWCNTs (0-0.15 wt %) were rigorously investigated under this complex coupled chemical erosion. The results demonstrate that while the performance gains from single-doped MWCNTs are limited by agglomeration, the hybrid incorporation of GO and MWCNTs yields a robust synergistic effect. After 120 days of coupled erosion, the hybrid composites (e.g., C0.125-G0.05) maintained a compressive strength of 41.11 MPa and a flexural strength of 18.91 MPa, significantly outperforming both the control and single-doped groups. Microstructural analysis revealed that GO acts as an efficient nucleation template and dispersant, effectively debundling MWCNT aggregates and facilitating the formation of a uniform, interconnected collaborative nano-reinforcing framework. This framework not only provides multiscale crack bridging but also optimizes the pore structure, creating a highly tortuous, low-permeability path for ion transport. Crucially, this dual physical-chemical barrier significantly inhibits the synergistic intrusion of aggressive ions (SO₄²⁻, Cl⁻, and Mg²⁺) and retards the detrimental transformation of cementitious C-S-H into non-cementitious magnesium silicate hydrate (M-S-H) and brucite (Mg(OH)₂). By suppression of the formation of expansive products such as gypsum, this strategy effectively preserves the structural integrity of the C-S-H phase. This study provides essential theoretical guidance for the design of high-performance cement-based composites in extremely coupled corrosive environments.