Enhancing the sulfate resistance of modified fly ash-based cementitious materials in marine environments using a graphene oxide–silane emulsion

Concrete structures in marine environments are highly vulnerable to sulfate attack, which leads to microstructural degradation and severe durability loss. Modified fly ash (MFA), obtained by flotation to reduce unburned carbon, has shown promise as a supplementary cementitious material due to its pozzolanic reactivity and ability to refine pore structures. However, its performance remains limited under aggressive sulfate exposure. To address this challenge, this study evaluates the combined use of MFA and a graphene oxide-isobutyltriethoxysilane (GO/IBTS) composite emulsion as an internal modifier for improving hydration behavior and long-term durability. Comprehensive experimental analyses, including calorimetry, compressive strength testing, thermogravimetric analysis (TG), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM), were conducted to assess hydration kinetics, microstructural evolution, and resistance to sulfate attack. The results reveal that low dosages of GO/IBTS emulsion (≤ 2 %) promote secondary hydration of MFA and refine the pore network, thereby enhancing structural stability during prolonged erosion. In contrast, higher dosages (> 2 %) significantly suppress cement hydration, increase total porosity, and lead to marked strength loss. Under sulfate exposure, the incorporation of GO/IBTS reduces the formation of expansive phases such as gypsum and calcium aluminate hydrates, effectively limiting internal cracking and ensuring long-term stability. This study demonstrates a novel and reliable strategy for enhancing the durability of MFA-based cementitious systems in marine environments. The findings provide both theoretical insights and practical guidance for the design of eco-friendly, sulfate-resistant construction materials.