Effects of sodium/calcium cation exchange on the mechanical properties of calcium silicate hydrate (C-S-H)

Role of nanofillers for high mechanical performance cementitious composites

“…where 𝑔(𝑟) is the RDF; 𝜌 𝑏𝑢𝑙𝑘 is the bulk density of NF around C-S-H; 𝑟 is the distance between the C-S-H and mineral NF atoms, and 𝑑𝑛(𝑟) is a function that computes the number of NF atoms within a shell thickness of 𝑑𝑟 (0.1nm) Apart from the interphase, the interfacial interaction can also modify the structure of C-S-H that is adjacent to the nanofiller [15,47]. Because the weakest part of C-S-H is the connection between silicate and interlayer water [18,48], the 𝜌(𝑟) of the silicate chain (Ob: bridging oxygen atoms, Onb: non-bridging oxygen atoms) and water molecules (Hw: hydrogen atoms) was calculated to quantify this modification on the mechanical properties of C-S-H [49]. As shown in Figure 2(e), the general 𝜌(𝑟) values of the Ob-Hw pairs and Onb-Hw pairs in SCSH were about 10-fold higher than those in ACSH and FCSH, which demonstrates a much stronger spatial correlation between the silicate chain and water molecules [50].…”

Nanoscale Insights into the Influence of Seawater (NaCl) on the Behavior of Calcium Silicate Hydrate

“…To represent water, CSH-FF employs the flexible single-point charge (SPC) water model, which considers the bond stretch term and angle bend term to be harmonic. Since CSH-FF does not include the parameters for Na + and Cl – ions, the parameters from ClayFF for these two types of ions were added to CSH-FF to describe their interactions with other atoms, as done in the literature. ,, The force field parameters employed in this study have been widely proven to be able to accurately study the performance of various aspects of C-S-H based systems, including the mechanical properties of C-S-H structure influenced by sodium/calcium cation exchange, the diffusive behavior of solutions in porous C-S-H structures, and alkali (Na + , K + , and Cs + ) adsorption on C-S-H surfaces. , Different from the reactive force field (e.g., ReaxFF), CSH-FF is a nonreactive force field, which does not consider the potential chemical events as well as any charge transfer in a system.…”

“…The results demonstrated that there existed an Na−Ca cation exchange between the C-S-H layers and the NaCl solutions, which is a common phenomenon observed in experiments. 43,48 In conclusion, the Na + ions showed a strong adsorption capacity on the calcium silicate layers, which can cause the partial release of Ca 2+ ions from the surface (termed as "Na−Ca cation exchange"). Increasing NaCl concentrations led to more Na−Ca cation exchange as well as the loss of H-bond at the solid−solution interface.…”

The missing link in the bottom-up theory of mechanical properties of calcium silicate hydrate

“…Ab-initio [22,77], hardness [23,24,61,64], shear strength [78], tensile strength [79], compressive strength [24,80,81], fracture [82,83], modulus [25][26][27]84] Nanoscale or microscale Potential mean force Surface forces [49,77,85] MC simulation Surface forces [86,87] FEM Modulus, hardness [35,36] Coarse-grained model (Discrete element model) Modulus, hardness [37][38][39][40], creep [88] Figure 2 Multiscale mechanical models of C-S-H. Images are adopted from [18,36,37,[47][48][49][50][51].…”