Effect of Preconditioning on Carbonated Reactive MgO-Based Concrete Samples

This study investigated the influence of preconditioning on the strength and microstructural development of carbonated reactive MgO cement (RMC)-based concrete mixes. The hydration mechanisms of the prepared formulations were studied via isothermal calorimetry. Compressive strength and porosity measurements were conducted to assess sample performance. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used for the microstructural analysis and quantifications of phases within each sample. Subjecting RMC samples to moderately elevated temperatures (50°C–60°C) for 1–2 days before the start of the curing process enhanced the hydration process. This increase in the degree and rate of the hydration reaction increased the amount of phases available for the subsequent carbonation reaction. The increase in the content and size of hydromagnesite [4MgCO₃⋅Mg(OH)₂⋅4  H₂O] crystals led to denser microstructures, thereby facilitating higher strengths in samples subjected to preconditioning. The obtained results showed that the application of this practical approach to the preparation of RMC-based samples can not only present a more efficient use of the binder component, but also enable the increased sequestration of CO2 within these samples.