C-S-H/solution interface: Experimental and Monte Carlo studies

The surface charge density of C-S-H particles appears to be one of the key parameters for predicting the cohesion strength, understanding the ion retention, the pollutant leakage, and admixture adsorption in hydrated cement pastes. This paper presents a Monte Carlo simulation of the surface-ions interactions that permits the prediction of surface charge density (σ), electrokinetic potential (ζ) and ions adsorption of mineral surfaces in equilibrium with a given electrolyte solution. Simulated results are compared to experimental data obtained by titration, electrokinetic potential measurements and ions uptake in the case of C-S-H suspensions. An excellent agreement is found between simulated and experimental results. The wide spread idea that calcium is a potential determining ion in cement paste systems appears to be incorrect. Instead, the pH controls the charging behaviour of C-S-H nano-particles. This paper also shows to what extent the electrostatic interactions contribute to the measured Ca/Si ratio.