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The molecular-scale mechanical properties of calcium silicate hydrates are crucial to the macro performance of cementitious materials, while achieving coincidence between accuracy and efficiency in computational simulations still remains a challenge. This study utilizes a deep-learning potential, specifically developed for calcium silicate hydrates based on artificial neural network, to achieve molecular dynamics simulations with accuracy comparable to first-principle methods. With this potential, the elastic properties and uniaxial mechanical behaviors are explored, wherein the anisotropy and impact mechanism of calcium ratios are analyzed. The results add to evidence that the deep-learning potential possess a higher accuracy than common force fields. The anisotropy of elastic modulus is mainly attributed to different atomic interactions in various directions, while the anisotropy of strength is additionally affected by the form of failure. This study may advance the accurate molecular-scale simulation and deepen the understanding of the strength source and cohesion mechanism of cement-based materials. [ABSTRACT FROM AUTHOR]

• A dense plate-like C-S-H was fabricated based on Layer-by-layer method and H-cell penetration method. • The novel C-S-H platelets own significantly higher elastic modulus than traditional C-S-H. • The growth mechanism of the compacted hierarchical C-S-H platelets was proposed combined with molecular dynamics simulation. An ordered structure and high mechanical property of calcium silicate hydrate (C-S-H) gel has been always pursued in the field of cementitious materials. In this paper, compacted and layer-by-layer stacking C-S-H plates were fabricated based on Layer-by-Layer (LBL) method and H-cell penetration (HCP) method through cation exchange membrane templating. This new way changed the randomly packing structure of traditional C-S-H, and synthesized a high-orderly C-S-H platelets with denser structure. Based on molecular dynamics simulations, it can be attributed to the strong adsorption and nucleation sites contributed by sulfonic acid groups on the cation exchange membrane. Besides, AFM indentation experiments indicate this C-S-H owns significantly higher elastic modulus than traditional C-S-H, while the mechanical properties can be further increased by the addition of PVA and the regulation of reaction time. This new type C-S-H may pave the way to the preparation of high-performance concrete in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reactive functional groups on GO and FGO contribute to the nucleation of C-S-H. • Bulk C-S-H particles are packed on the surface of GO and FGO, with diameters 3~5 nm. • The ranking with regards to the interfacial bonding strength is FGO > GO≫G. • Interfacial Ca-O and Si-O connections cause the strong adsorption of C-S-H on FGO. It has been proved that the incorporation of graphene (G) -based two-dimensional (2D) materials can improve the mechanical and durability performance of cementitious matrix to varying degrees. However, there is not a clear understanding of the nano-scale interaction mechanism between the matrix and 2D materials, as well as its correlations with the improvement efficiency. By the molecular dynamics simulation, this work simulated the growth process of C-S-H gel on 2D matrix with different functional groups, investigated interfacial interaction between C-S-H gel and 2D materials, and revealed the underlying reinforcement mechanism. The results show that C-S-H gel tend to nucleate on the surface of graphene oxide (GO) and functionalized graphene oxide (FGO) due to strong attractions of hydroxyl and silanol groups. As a consequence, C-S-H particles are regularly packed on the surface of GO and FGO, with diameters ranging from 3 nm to 5 nm, consistent with the CM-II model. Furthermore, the ranking with regards to the interfacial bonding strength is FGO > GO≫G. It is attributed to the high-strength Ca-O and Si-O connections formed on the C-S-H/FGO interface, which can contribute to a greater enhancement efficiency of 2D materials. The mechanism interpreted here may optimize the application of graphene-based materials on the cementitious matrix. [ABSTRACT FROM AUTHOR]

Supersulfated cement (SSC) is recognized as a cementitious material with low CO 2 emissions, consisting predominantly of ground granulated blast-furnace slag (GGBS) and a minor activator content. The production of GGBS production constitutes the primary source of CO 2 emissions in SSC. In contrast, carbon emissions from the production of basic oxygen furnace slag (BOFS) are lower, and BOFS inherently exhibits substantial carbonization potential. Therefore, in this study, BOFS is employed as a replacement for GGBS in formulating an innovative low-emissions binder denoted as BOFS-modified supersulfated cement (BMSC). This study investigates the influence patterns of BOFS substitution for GGBS on the strength properties of BMSC. Furthermore, a series of experiments involving QXRD, TGA, SEM, and MIP were conducted to systematically investigate the mechanistic impact of BOFS on the hydration microstructure of BMSC. The findings reveal that substituting 10 % of GGBS with BOFS contributes to an enhancement in both flexural and compressive strength of specimens at 7 and 28 days. BOFS exerts a positive influence on the formation of ettringite in BMSC. The C 2 S and C 4 AF within BOFS also demonstrate distinct hydration activity. Additionally, BOFS can reduce large pores in the early hydration paste and contribute to narrowing the average pore size. Moreover, the evaluation of the Global Warming Potential (GWP) demonstrates that the replacement of slag with BOFS can lead to a further reduction of up to 30 % in the carbon emissions of SSC. • Utilizing BOF slag as a substitute in supersulfated cement for eco-friendly materials. • Small amounts of BOF slag enhance 7-day and 28-day strength in supersulfated cement. • BOF slag promotes ettringite formation and optimizes pore structure in supersulfated cement. [ABSTRACT FROM AUTHOR]

The directional migration of ions was induced by the external electric field, which generated the current in the nano-pores of ettringite. • The directional migration of ions was induced by the external electric field, which generated the current in the nano-pores of ettringite. • The magnitude of the current is proportional to the electric field intensity. • The chlorides account for about 80% of the total ion current intensity. In this research, molecular dynamics simulations were employed to unravel the transmission mechanisms of chloride ions and sodium ions throughout ettringite nanopores as exposed to an external electric field 0–0.04 V/Å. The current was generated by the directional migration of cations and anions, proportional to the intensity of electric field, among which chlorides account for 80% while sodium contributes little. The migration of sodium ions was limited as a result of the attraction from the oxygen atoms in the sulfate ions on the ettringite surface. This effect weakened due to the increase in the electric field intensity. Furthermore, the relocation rate of ions may obey in the following ranking: Cl− > Ow > Na+. The development of this work can reveal the mechanism of ion migration and diffusion inside the pores of concrete during the application of the electrochemical desalination method, which has a guiding significance for the durability design of concrete structures. [ABSTRACT FROM AUTHOR]