Effect of Different Superplasticizers on Carbonation Behavior of C2S and C4A3S¯ in Calcium Sulfoaluminate Cement

The demand for the development of low-carbon and energy-saving technologies in the cement industry is extremely urgent, and calcium sulfoaluminate (CSA) cement has attracted much attention because of the low-carbon and energy-saving advantages for cement production. However, the disadvantage of CSA cement is that the hydration products are susceptible to carbonization, which may cause a decrease in the mechanical properties and durability of the cement matrix. To address this issue, this work focused on the primary minerals of CSA cement, and explored the effects of different superplasticizers on C2S and C4A3S¯. The study employed three types of superplasticizers: sodium lignosulfonate superplasticizer (CMN), naphthalene series superplasticizer (FDN), and polycarboxylate superplasticizer (PCE). The adsorption degree of these superplasticizers on C2S and C4A3S¯ was analyzed using ultraviolet spectroscopy (UV-Vis). Zeta potential measurements were conducted to assess the effect of superplasticizers on the surface potential of C2S and C4A3S¯, thereby studying their dispersion properties. Furthermore, the study examined the phase, composition, and morphology of different carbonation products under the action of superplasticizer by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, asynchronous thermal analyzer thermogravimetry coupled with differential scanning calorimeter (TG-DSC), and scanning electron microscopy (SEM), and then their carbonation activity was analyzed. The results indicated that the adsorption capacity of C4A3S¯ was higher for CMN and FDN compared to C2S, while C2S showed a higher adsorption capacity for PCE than C4A3S¯. This difference in adsorption was attributed to the distinct charging properties and main functional groups of the superplasticizers. Specifically, FDN formed a robust electrostatic repulsion layer when adsorbed on the surface of hydration particles, while PCE exhibited steric hindrance during adsorption. These actions affect the carbonation process of the minerals, resulting in the compressive strength and durability of CSA cement being affected as well.