Nature of Interatomic Bonding in Controlling the Mechanical Properties of Calcium Silicate Hydrates

Abstract

Calcium silicate hydrate (C-S-H) is the most important phase of hydrated cement gel which is the key material in construction industry. It is well accepted that hardened cement paste consists of either poorly crystalline or completely disordered phases. Although a myriad of speculative atomistic models of disordered C-S-H have been proposed, the fundamental basis of structure-property relationships remain elusive. This study focuses upon the correlations between mechanical properties and electronic structure based on well-defined quantum mechanical parameters. We use 20 CSH minerals with known structure to gain fundamental understanding of structure-property relationship. The results indicate Si-O bond order density, which represents the cumulative bond strength of SiO bonds, has no direct correlation with bulk mechanical properties which is counterintuitive and against conventional wisdom. The variations are determined more precisely by the overall atomic and electronic structure dictated by bond order density of the Ca-O and hydrogen bonds (HB). Most importantly, there is a multifaceted balance between different types of interatomic bonds including the HBs in controlling mechanical properties. HBs categorized in relation to next nearest neighbor (NNN) enable us to identify specific types of HBs that are prevalent in CSH. In certain crystals such as suolunite, the HB network is organized in such a unique way that enhances its mechanical properties. The approach and findings presented in this paper points to a broad roadmap for the developing next-generation cements.

Mesoscopic packing of disk-like building blocks in calcium silicate hydrate

“…At nanoscale (smaller than 10 nm), the structural water is found to be a scaffolding component enhancing mechanical properties of C-S-H nanoparticles13. On the contrary, the sub-micron mechanical properties (characterized by nanoindentation with a detecting window of around 500 nm) are lower when water content increases24.…”

“…By performing molecular dynamics simulation and further numerical analysis, one can measure material properties of C-S-H nanocrystals and adhesion strength between C-S-H layers101112. The internal structural water is found to be a scaffolding component that enhances the mechanical properties of C-S-H13. The Young’s modulus of C-S-H nanoparticles is around 70 GPa14, higher than that of conventional concrete.…”

Ab initiocalculations of thermomechanical properties and electronic structure of vitreloyZr41.2Ti13.8CHunca1, Dharmawardhana2, Sakidja3 et al. 2016Phys. Rev. BSelf Cite160130View full textAdd to dashboardCite

“…In fact, the BO is a single well-defined descriptor irrespective of the nature of the bonding, be it ionic, covalent, metallic, H-bonding, or non-directional bonding as in BMGs. The use of BO and TBOD in different materials systems has been demonstrated in several recent publications[62][63][64][65][66][67][68][69][70][71][72]. Results and Discussion3.1 Structure and topology of Vit-1 modelsThe total pair distribution function (PDF) G(r) of our model for Zr 41.2 Ti 13.8 C 12.5 Ni 10 Be 22.5 is shown inFigure 2(a).…”

“…The plot of BO vs BL is shown in Figure 6(a) From the BO values for all interatomic pairs, we can obtain the total bond order for that pair of atoms by adding them together and normalize by the volume of the cell, we have the bond order density (BOD). When the BOD of all pairs are added, we have the total BOD (TBOD) which is a single quantum mechanical metric best describe the interatomic cohesion of a crystal or a glass in the present case [67,69]. The use of TBOD in characterizing different type of materials is a novel concept that we advocate since the volume of the system is part of the metric.…”

Constitutive response of calcium‐silicate‐hydrate layers under combined loading

“…Due to the complexity of cementitious materials, the behavior of C‐S‐H at these length scales cannot be easily probed through experiments and requires atomistic simulations. Models are typically based on either idealized crystalline analogs of C‐S‐H or by manipulating an initially crystalline structure to obtain a defective C‐S‐H model . Simulations have found that under pure shear loading, the composite interface allows for strain localization that controls the strength of the atomistic structure .…”