Molecular Insight into the Fluidity of Cement Pastes: Nano-Boundary Lubrication of Cementitious Materials


The workability mechanism of fresh concrete at the molecular level remains essentially unexplored. To understand the molecular origin for cement fluidity, molecular dynamics and Density Function Theory (DFT) were utilized to construct a shear model of Calcium-Silicate-Hydrate (C-S-H) layers. The structure, dynamics, and reactivity of ultra-confined pore solution between C-S-H gels are systematically investigated. Under shear loading, periodic oscillation of friction force is observed as the typically Couette flow and the interfacial friction force is reduced from 35.2 Kcal/mol·Å to 3.3 Kcal/mol·Å with water content increasing. All of the systems contain breakage of noncovalent bonds of water-Ca and water-water in the lubrication process. But, the obvious breakage of covalent bonds is found in the low-water content system, in which a part of Ca atoms is separated from the C-S-H matrix for lubricating that does not occur in the high-water content system. Furthermore, DFT studies monitor the reaction pathway for the dissociation of water molecules and calcium ions from silicon oxide tetrahedrons. In the energetic respect, it distinguishes covalent-ionic bond transformation and H-bond breakage. The atomic-level mechanisms provide new insights on workability design for fresh concrete.


Civil, Architectural and Environmental Engineering


Financial support from the National Natural science foundation of China under Grant U2006224, 51978352, 51908308, 52178221, Natural science foundation of Shandong Province under Grant ZR2020QE253, ZR2020JQ25, ZR201910210098, Shandong Provincial Education Department under Grant 2019KJG010, Qingdao Research Program 16-5-1-96-jch.

Keywords and Phrases

Cement hydration; Fluidity of cement; Molecular dynamics; Nano interface; Quantum chemistry

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Article - Journal

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Publication Date

17 Jan 2022