Effects of magnesia in semi-hydraulic and non-hydraulic calcium silicate binders during carbonation curing

This study presented an insight into the mechanical and microstructural properties of carbonated composites produced using slag, wollastonite, and magnesia. Paste batches containing various dosages of slag, wollastonite, and magnesia were subjected to carbonation curing regime at a concentration of 20% CO₂, 50 °C temperature, and 80% relative humidity. The microstructure of the samples was evaluated using scanning electron microscopy (SEM), dynamic vapor sorption (DVS), thermogravimetric analysis (TGA) coupled with mass spectroscopy (MS), Fourier transformed infrared spectroscopy (FTIR), and X-ray diffraction (XRD). It was observed that the formation of hydrated magnesium carbonates (HMCs) i.e., needle shape nesquehonite, Rosset-like hydromagnesite have increased the carbonated matrix density due to its expansive nature and by forming an interconnected network. The change in total and critical pore size distribution was observed with the addition of magnesia. The compressive strengths were also observed to increase by 44% and 126% when 25% magnesia was incorporated into wollastonite and slag composites, respectively. Furthermore, it was observed that under carbonation curing non-hydraulic wollastonite system performed better when compared to semi-hydraulic slag system.