This study demonstrates how polycarboxylate ether-based superplasticizers (PCE) enable graphene oxide (GO) to improve the early hydration and mechanical performance of a low-clinker ternary cement, while also revealing an unexpected trade-off in carbonation behaviour. The ternary system consisted of ordinary Portland cement, slag, and limestone powder. The dispersion state of GO was evaluated through visual observation, ultraviolet-visible spectroscopy (UV-Vis) and dynamic light scattering (DLS), which confirmed that a PCE/GO mass ratio of 10 provided optimal stabilization. Isothermal calorimetry showed that 0.2 wt% GO accelerated hydration most effectively, while mortar testing demonstrated that 0.1 wt% GO increased 1-day compressive strength by 26 %. In-situ X-ray diffraction (XRD) further verified the promotion of early hydration phases. Under accelerated carbonation, however, 0.1 wt% GO increased the initial carbonation rate by 83.7 % without a corresponding increase in the total carbon dioxide (CO₂) uptake, as determined by thermogravimetric analysis (TGA). This paradox suggests that GO may act as a nucleation agent for rapid surface precipitation of calcium carbonate (CaCO₃), producing a dense outer layer that restricts further CO₂ ingress. The finding that GO accelerates carbonation kinetics without enhancing total sequestration challenges prevailing assumptions in the literature and provides new guidance for the design of sustainable, nano-engineered, low-clinker binders, requiring a careful balance between early-age performance and long-term durability.