Nanoscale insight into fluidity improvement of supplementary cementitious materials on concrete: The nano-lubrication process

The workability of concrete is a fundamental property that is frequently influenced by chemical admixtures. In this paper, we provide an interesting perspective to understand the effect of silica fume on the fluidity of cement slurries. By employing molecular dynamics techniques, a nanoscale boundary friction model is proposed to evaluate the flow of cement slurries resulting from cement hydration. According to conventional experimental data, interfacial friction decreases as the water content rises. And additional lubrication of the silica surface is possible. The investigation into the microscopic mechanisms behind interfacial lubrication reveals that water lubricates SiO2 and CSH sheets in various ways at low and high water levels. Throughout the system, non-covalent water-water and water-calcium bonds break down during the lubricating process. It appears that some calcium atoms are split out of the CSH matrix, a sign of a covalent break. In the high water content system, this separation did not happen despite the lubricating ac-tion in the low water content system. It is also possible to visually evaluate the impact of additional cementitious materials on the cement paste's fluidity by using the recently discovered mechanism.