Probe into the pore structure of carbonated calcium silicate cement compacts by proton nuclear magnetic resonance...

Proton nuclear magnetic resonance relaxometry (¹H NMR) has been widely used for characterizing the pore structure of Portland cement materials; however, its applicability to carbonated calcium silicate cement materials, an important CO₂ capture technique applied in cementitious materials production, remains unresolved. This study systematically investigates the pore structures of carbonated calcium silicate cement compacts prepared from wollastonite, pseudowollastonite, γ-C₂S and C₃S using ¹H NMR. It is observed that surface relaxivity and the relationship between magnetization signal intensity and sample mass differ significantly among carbonated samples and between situations when the samples are saturated with water and isopropanol (IPA). When fitting the curves of magnetization signal intensity versus sample mass, consistent slopes are observed for carbonated wollastonite and pseudowollastonite under both saturation situations. However, the slopes observed in carbonated γ-C₂S and C₃S under water-saturated conditions decrease with increasing carbonation time, whereas those under IPA-saturated conditions remain stable. ¹H NMR can resolve nanopores (<10 nm) and capillary pores (10-1000 nm) in carbonated calcium silicate cements. The distributions of relaxation time evoluted during sample drying demonstrate that solvent removal occurs preferentially in capillary pores. Exchange of water by IPA treatment cannot remove all solvents from the samples. The findings contribute to elucidating the reliability of ¹H NMR data-processing methods and provide a foundation for characterizing the pore structure of carbonated calcium silicate cement materials.