Interfacial nano-engineering by graphene oxide to enable better utilization of silica fume in cementitious composite

As an industrial by-product, silica fume (SF) has been widely employed as supplementary cementitious material to develop high-performance concrete, and contribute to the sustainability goals of the concrete industry. However, with the typical size in the range of 50-300 nm, SF particles tend to form agglomerations when mixed with water and quickly become covered by a gel-like layer, thus retarding hydration. In this study, SF was coated with graphene oxide (GO) to nano-engineer the interface between SF and cement, aimed to allow better utilization of SF in cementitious composites. We report the concept of a nano/microhybrid via the electrostatic adsorption of negatively charged GO on positively charged modified SF (termed as MSF@GO), which aims to improve the dispersion quality of SF as well as the SF-cement interaction. The addition of 5 wt% modified SF (MSF) and 0.04 wt% GO (by mass of binder) result in a significant improvement of 3-d and 28-d compressive strengths of a cement paste by 56% and 29%, respectively, as compared to the sample incorporating 5 wt% SF. Additionally, the 5MSF@GO paste exhibits a greatly reduced initial sorptivity, by 33% (from 1.56 mm to 1.05 mm), along with the lowest secondary sorptivity. The noticeably higher strengths and lower water transport are primarily attributable to the increased polymerization of calcium silicate hydrates and the refinement of pore structure. This study demonstrates the great potential to improve the utilization efficiency of SF by interfacial nano-engineering with GO nanocoating and provide a new strategy to develop low-carbon cementitious composites for practical applications.