Development and characterization of eco-friendly cement-free composites activated by different sulfate-activators

Abstract Portland cement production accounts for nearly 8% of global CO 2 emissions, driving the search for sustainable alternatives. In this study, ground granulated blast-furnace slag (GGBFS) was chemically activated with four sulfate activators (Na 2 SO 4 , K 2 SO 4 , MgSO 4 , and CaSO 4 ) to produce cement-free composites (CFC). Prior research has primarily focused on individual sulfate activators, whereas direct comparison under standardized mixture conditions remains limited. Accordingly, this study was designed to systematically evaluate the influence of different sulfate-associated cations on hydration behavior, mechanical performance, and durability-related properties using a fixed mixture design (water-to-binder = 0.30 and activator dosage = 4.5% by mass of GGBFS). A series of fresh, mechanical, transport-related, and volumetric tests was conducted, complemented by scanning electron microscopy (SEM) and x-ray diffraction (XRD) analyses at 28 days to examine microstructural development. Rather than enumerating individual test results, the comparative analysis reveals clear performance trends governed by activator chemistry. CaSO 4 activation consistently promotes matrix densification and strength development, while MgSO 4 markedly suppresses drying shrinkage due to inhibited GGBFS dissolution. Sodium and potassium sulfates exhibit intermediate behavior, balancing workability, strength evolution, and durability-related indicators. The systematic comparative analysis conducted in this study identified CaSO 4 as the most effective activator among those investigated for eco-friendly cement-free composites. These findings demonstrate that sulfate activation can be effectively tailored through cation selection, offering a practical and safer pathway for the design of one-part, low-carbon GGBFS-based binders suitable for construction applications.