Revisiting the Strength-Enhancement Mechanism of Graphene Oxide in Cementitious Materials

Although graphene oxide (GO) is widely reported to enhance the mechanical performance of cementitious materials, the results in the literature remain inconsistent. A primary reason for this variability is GO’s strong tendency to aggregate in alkaline and ion-rich environments, which limits its interaction with the cement matrix. This study revisits the fundamental mechanisms by which GO improves strength in cement pastes and reveals how ultrasonic treatment and polymer surfactants jointly control GO’s dispersion and reinforcing effectiveness. These insights arise from examining the dispersion state of GO in solution as well as the rheology and compressive strength of cement pastes containing GO. We show that ultrasonic treatment alone enhances GO dispersion, reducing the GO dosage required to activate its seeding effect, which yields early-age strength enhancement. In contrast, the addition of poly(carboxylate ether) (PCE) induces GO’s aggregation in DI water or pore solution, while the combination of ultrasonic treatment further amplifies this adverse influence of PCE. However, incorporating moderate dosages of PCE promotes the strength improvement of GO-modified cement pastes by improving the fluidity of fresh pastes and refining the pores at later ages. The results reveal that GO’s strengthening mechanism changes over time. At early stages, GO promotes strength by accelerating cement hydration, while at later stages, it enhances strength by reducing porosity and bridging microcracks within the cement matrix. Importantly, the extent of strength enhancement is not dictated by the GO dosage alone but by the exposed surface area of GO, which can be tuned through ultrasonic treatment and PCE additions. These findings provide practical guidelines for using GO to reliably achieve strength enhancement in cementitious composites.