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.

As the construction industry seeks to reduce its carbon footprint, supplementary cementitious materials (SCMs) play a vital role in reducing the clinker content of concrete. This paper synthesizes and comparatively analyze the 365-day compressive strength development of six locally sourced SCMs to establish their long-term performance for use in the Nordic region. The locally sourced SCMs are calcined clay (CC), fly ash (FA), natural pozzolan (NP), electric arc furnace slag (EAFS), oil shale ash (OSA), and ground granulated blast furnace slag (GGBS). A total of 31 concrete mixes were evaluated, with SCMs replacing cement at levels from 15% to 60%. While all SCM mixes exhibited lower early-age strength than the Portland cement reference, long-term strength was significantly enhanced. The most promising results include 15% FA (102 MPa), 35% NP (99.5 MPa), and 45% GGBS (96.5 MPa) at 365 days. High-volume replacement was also proven viable, with 35% oil shale ash matching the reference strength. The findings demonstrate that these regionally available SCMs offer a viable pathway towards producing high-performance concrete with significantly reduced clinker content, suitable for a wide range of structural applications.