• First-principles DFT study reveals that multiple water molecule adsorption on M3-C3S(001) exhibits anticooperative behavior, with total adsorption energy becoming more negative but average adsorption energy per molecule becoming more positive as coverage increases.
• Water–water interactions weaken water–surface interactions, highlighting the need to consider coverage effects in modeling cement hydration.
• Dissociative adsorption, forming Ca–OH bonds, facilitates calcium detachment from covalent oxygen, providing atomic-level insights into the initial hydration mechanism.
• The findings extend understanding from single to multiple water molecule adsorption, crucial for optimizing cement strength development and sustainable construction materials.