Carbonation Curing and Mechanical Properties of Alkali-Activated Composites Derived from Calcined Granite Waste and Waste Ceramic Powder

This study investigates the utilization of low-reactivity granite waste (GW) and waste ceramic powder (WCP), both rich in silica (SiO₂) and alumina (Al₂O₃), as sustainable precursors for producing high-performance alkali-activated pastes under accelerated carbonation curing. Both materials were first calcined at 700 °C for 2 h and subsequently blended at varying GW/WCP mass ratios of 50:50, 60:40, and 70:30, mixed with an alkaline activator consisting of 8 mol/L sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃), and then kept for 24 h before being removed from their molds. The resulting samples were then subjected to accelerated carbonation curing for 5 h at 55 °C under a CO₂ pressure of 0.4 MPa. The elemental compositions of GW and WCP were assessed through X-ray fluorescence (XRF) analysis. Furthermore, ICP-MS analysis revealed differences in Si and Ca dissolution behavior between GW and WCP, which may contribute to differences in reaction product development during alkali activation. Mechanical testing revealed that the mixture containing 70% GW and 30% WCP (GCP70) exhibited superior compressive strength, which was associated with differences in precursor composition, reaction product development, and microstructural characteristics. X-ray diffraction (XRD) confirmed calcite formation in all carbonated samples, with peak intensities following the order GCP50 > GCP60 > GCP70, corresponding to decreasing WCP content. Fourier transform infrared spectroscopy (FTIR) analysis showed Si-O-T stretching bands at 984 cm⁻¹ (GCP70), 983 cm⁻¹ (GCP60), and 991 cm⁻¹ (GCP50), indicating variations in aluminosilicate bonding environments with different GW/WCP ratios. Scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) image analysis estimated pore area fractions of 28.5%, 22.3%, and 18.7% for GCP50, GCP60, and GCP70, respectively, indicating a decreasing pore area fraction with increasing GW content. In addition, carbonate formation in carbon-cured samples was confirmed by XRD and FTIR analyses, while SEM–EDS observations further demonstrated a denser and less porous microstructure, particularly for GCP70, characterized by an improved interfacial transition zone (ITZ) and features associated with aluminosilicate-rich reaction products. To the best of our knowledge, this is the first study to systematically investigate the combined application of (i) calcination-induced amorphization of granite waste, (ii) alkali activation with 8 mol/L NaOH, and (iii) accelerated carbonation curing (0.4 MPa, 55 °C, 5 h) on GW-WCP blends. While individual aspects have been studied previously (e.g., calcination of granite waste, alkali activation of ceramic waste, or carbonation of OPC), the combined effects of these processes remain insufficiently explored. Specifically, the GW/WCP ratio modulates the competition between the formation of alkali-activated gels (sodium aluminosilicate hydrate, N-A-S-H; calcium aluminosilicate hydrate, C-(A)-S-H) and carbonate precipitation. This competition governs the mechanical–microstructural trade-off. Within the investigated carbonated systems, the different GW/WCP mixtures exhibited distinct mechanical and microstructural characteristics. Because no non-carbonated or non-calcined controls were included, the individual contributions of calcination and carbonation cannot be isolated in this study.