Roles of particle packing and water coating thickness in carbonation and strength of γ-dicalcium silicate-based low carbon materials

In this work, a low carbon material of γ-dicalcium silicate (γ-C₂S) was examined, with an emphasis on the properties influenced by its particle packing and water coating thickness (WCT). Differences in morphology and reactivity from that of cement particles render γ-C₂S particles have different particle packing behavior and water film surrounding each particle. However, limited research has been conducted on it to deepen the understanding of γ-C₂S-based materials. To fill this gap, the wet packing density of γ-C₂S particles was measured and the WCT was varied at different water to solid ratios. At each WCT, the carbonated γ-C₂S samples were characterized by techniques of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) consistently. Experimental results revealed little early strength gain when the WCT exceeded a certain value. Moreover, a critical carbonation depth was identified. Below the critical depth, the amounts and characteristics of carbonation products dominated, whilst above the critical depth, the strength gain was influenced by CO₂ diffusion rate. An optimal WCT exists for achieving the highest strength and CO₂ uptake. This work shall advance the development of low carbon γ-C₂S-based materials from the perspective of particle packing.