Behavior of organic compounds in the pore solution of cement-experimental and molecular dynamics study

This study summarizes molecular dynamics (MD) simulations and experiments using four ester-based cement shrinkage reducing agents in pure water and simulated cement pore solution. The esters were found to completely dissociate in the alkaline pore solution to form acid and alcohol analogue compounds. The alcohol analogues were further found to be entirely responsible for the surface tension reduction capacity of the parent compounds. In addition, the surface tension reduction capacity of the alcohol analogues are not affected by relevant counterions present in the pore solution. The MD-based analysis show that water molecules form stable hydrogen bonds with head groups of the alcohol analogues and that relevant dissolved ions, K+ and Na+, have virtually no effect on hydrogen bond stability. Furthermore, the higher the self-diffusion coefficient of water molecules in the neighborhood of the head groups the lower the resulting surface tension at the air-water interface.