Reactive Molecular Simulation on Water Confined in the Nanopores of the Calcium Silicate Hydrate Gel: Structure, Reactivity, and Mechanical Properties

Abstract

Calcium silicate hydrate (C−S−H) is a mesoporous amorphous material with water confined in the gel pores, which provides the medium for investigating the structure, dynamics, and mechanical properties of the ultraconfined interlayer water molecules. In this study, C−S−H gels with different compositions expressed in terms of the Ca/Si ratio are characterized in the light of molecular dynamics. It is found that with increasing Ca/Si ratio, the molecular structure of the silicate skeleton progressively transforms from an ordered to an amorphous structure. The calcium silicate skeleton, representative of the substrate, significantly influences the adsorption capability, reactivity, H-bond network, and mobility of the interlayer water molecules. The structures were tested for mechanical properties by simulated uniaxial tension, and the mechanical tests associated with structural analysis reveal that the stiffness and cohesive force of C−S−H gel is weakened by both breakage of silicate chains and penetration of water molecules. In addition, the reactive force field is coupled with both the mechanical response and chemical response during the large tensile deformation process. On the one hand, the silicate chains, acting in a skeletal role in the layered structure, depolymerize to enhance the loading resistance. On the other hand, water molecules, attacking the Si−O and Ca−O bonds, dissociate into hydroxyls, which are detrimental to the cohesive force development.

Atomistic computer simulations of water interactions and dissolution of inorganic glasses

“…It was found that the increase of water content transforms C-S-H gel into a layered structure. Hou et al 74 also studied the water confinement in nanoporous C-S-H gel using the ReaxFF potential. It was found that the calcium silicate skeleton significantly influence the adsorption, reactivity, hydrogen-bond network and diffusivity of water molecules.…”

Synthesis of Calcium Silicate Hydrate in Highly Alkaline System

“…8,9 In this regard, the composition and crystal structure of C-S-H synthesized in the CaO-SiO 2 -H 2 O system must be investigated. [10][11][12][13][14] Various C-S-H structural models, especially those obtained from portland cement hydration, have been established; these models confirmed the existence of fragments similar to structural elements in jennite and 14 A tobermorite. 12,[15][16][17][18][19] The Ca/Si ratio strongly affects the crystallinity of C-S-H.…”

“…Nevertheless, C‐S‐H exhibits variable and poorly ordered microstructure, which affects its application performance . In this regard, the composition and crystal structure of C‐S‐H synthesized in the CaO–SiO 2 –H 2 O system must be investigated . Various C‐S‐H structural models, especially those obtained from portland cement hydration, have been established; these models confirmed the existence of fragments similar to structural elements in jennite and 14 Å tobermorite .…”

Effect of Chloride‐Based Accelerator in the Presence of Water‐Reducing and Retarding Admixture on Autogenous Shrinkage

“…Figure 9 shows a plot of autogenous shrinkage versus tensile strength. [45][46][47] (4) X-ray Diffraction Measurements Figure 11 shows XRD scans of CHA and CDA mixtures at 3 d. The two extreme accelerator dosages were selected to evaluate the effect of accelerator dosage on cement hydration products. The same was observed for elastic modulus (Fig.…”