Behaviors and influences of water confined within the C-S-H interlayer: A quenched solid density functional theory study

Abstract

Water confined within cement paste significantly influences the material's physical and chemical behaviors. Using quenched solid density functional theory (QSDFT), we investigate the complex behaviors of water confined within C-S-H interlayers. Confined water exists in forms of double layers (0–0.29 nm pores), three layers (0.32–0.59 nm pores), and multiple layers (≥0.65 nm pores). The adsorption isotherms reveal distinct adsorption behaviors depending on the pore size. For pores smaller than 0.59 nm, adsorption occurs as monolayer water adsorption and phase transition. In contrast, larger pores exhibit three stages: monolayer adsorption, multilayer adsorption, and phase transition. The pore pressure is positive for smaller pores (≤0.03 nm) and negative for larger pores; however, after the phase transition, the negative pressure is released with increasing relative humidity (RH). Additionally, temperature increase reduces the adsorption capacity, disrupts the water ordering, shortens the phase transition period, and affects the saturated pore pressure.