Mechanical properties of colloidal calcium-silicate-hydrate gel with different gel-pore ionic solutions: A mesoscale study

The mechanical properties of hydrated cement paste are largely influenced by the interaction of nano-scale calcium-silicate-hydrate (C–S–H) particles that reside in the gel-pore aqueous ionic solution of colloidal C–S–H gel (C–S-H_gel). The ionic species and ionic concentration of the gel-pore solution can fluctuate – due to the hydration process of cement, the use of various admixtures, and ion exchange with the surrounding environment – and influence the dielectric constant (ε_r) of the gel-pore solution and the Debye length (κ⁻¹). Mesoscale simulations were employed to investigate the mechanical properties of C–S-H_gel with gel-pore ionic solutions of different ε_r and κ⁻¹. The results showed that ε_r and κ⁻¹ influenced the packing density and cohesion of C–S-H_gel, and, in turn, its compressive stiffness, hardness, and strength. The lowest values of ε_r and κ⁻¹ (i.e., highest ionic concentrations) resulted in higher stiffness, hardness, and strength. The information obtained in this study provided insight into the mechanism by which the gel-pore ionic solution affects the mechanical properties of C–S-H_gel and demonstrated that ε_r and κ⁻¹ are useful parameters to consider when engineering design strategies for cementitious materials.