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Atomic density profile along z direction for the C–S–H gel with interlayer distance a 13 Å, b 15 Å and c 20 Å
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Water molecules confined in the interlayer region of calcium silicate hydrate (C–S–H) are closely related to the cohesion in the cementitious materials. In this research, molecular dynamics is employed to investigate the structure, dynamics and mechanical properties of water molecules in the nanopore of C–S–H gels at ambient temperature. In order t...
Citations
... Hydrophobic materials can change the surface of concrete from hydrophilic to hydrophobic, thereby improving its oil absorption performance [10,11]. Hydrophobic materials are usually based on silanes and siloxanes, and hydrophobic nanosilica exhibits a hydrophobic and oil absorbent capacity through photocatalysis [12][13][14]. Studies have shown that hydrophobic materials, such as isooctyltriethoxysilane, can form silicon-hydrogen oxide bonds after hydrolysis. ...
The aim of this study is to improve the compressive strength of oil absorbent concrete (OAC) and to encourage its use in slope protection projects. This study used fly ash and slag produced in thermal power plants to substitute cement in significant amounts to prepare oil absorbent concrete (OAC). The water–cement ratios were set at 0.4, 0.5, and 0.6 and the sand rates were set at 30%, 35%, and 40% to investigate the effects of these factors on the oil absorption properties of the concrete, the variation of the oil absorption rate over time, and the compressive strengths at 28 days, 60 days, and 90 days. The compressive strength of oil absorbent concrete was improved by incorporating seashell powder (SC), alkali-modified seashell powder (SSC), and acid–base-modified seashell powder (CSC). The results showed that the optimal water–cement ratio for comprehensive oil absorption performance and compressive strength was 0.5, while the optimal sand ratio was 0.35. Compared with ordinary concrete, the oil absorption performance improved by 58.69%. The oil absorption rate decreased gradually over time. However, the oil absorption time could be effectively extended and the oil absorption performance could be improved by the addition of a silane modifier. The best method for seashell modification was acid–base modification. The compressive strength reached 14.32 Mpa at 28 days and 17.45 Mpa at 90 days, which was 19.62% higher than that of OAC. Scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) were used to analyze the microstructure of OAC. It was discovered that the inclusion of CSC caused a reaction with hydrocalumite in the concrete, resulting in the formation of alumohydrocalcite. Additionally, Ca(OH)2 in CSC facilitated the hydration reaction of mineral admixtures like fly ash and slag. At 28 days, more amorphous gels (C-S-H, C-(A)-S-H) and Aft were produced. The three components were combined to enhance the bonding between the cementitious materials and the aggregates, resulting in a denser internal structure of the OAC and improving its strength. This study promotes the use of OAC in slope protection projects.
... That means that the reaction with water molecules comes from the weakening of Al-O bond, since most of bridging oxygen in silicate tetrahedron did not react with water molecules. 77 Aluminate tetrahedron having a weak ionic-covalent bond has the ability to interact with neighboring water molecules to form H-bond and aluminate hydroxyls. This induces a reduction of the attractive electrostatic interaction between Al and their bonding O, which increases the bond distance. ...
Nowadays, geopolymers are advanced alternatives to cementitious materials, where their excellent chemical and fire resistance are some of its most appealing properties. Fly ash geopolymers enable the use of industrial waste materials while converting them into a novel binding material. Their production is accompanied by a much lower CO 2 emission when compared to Portland cement. Reinforcing fly ash geopolymers with carbon nanotubes would significantly strengthen its microstructure and with this enhancing the long‐term mechanical and durability performance. The aim of this work is to use reactive molecular dynamics simulation method to optimize the mechanical properties of fly ash geopolymers with nano‐reinforced carbon nanotubes (CNTs). During this study, the impact of humidity and interfacial bonding strength between carbon nanotube and geopolymer is investigated. Our findings show that structural transformations under hydration process comes from the weakening of AlO bond, leading to the elongation of AlO and NaOH bonds, forming aluminum and sodium hydroxyls. Conversely, silicate is not sensitive to water and exhibits hydrophobic behavior. In addition, our results show that there is an optimal value of water content (7.17 wt.%) that makes the geopolymer nanostructure strengthen. The related elastic modulus rises by 21.56%, 20.60%, and 18.41% for Si/Al ratio of 1, 2, and 3, respectively. Inserting carbon nanofillers to fly ash nanostructure has remarkably shown an interesting strength enhancement. More precisely, when interfacial bonding concentration is around 19.36%, it is observed a positively increasing of the compressive strength, shear, indentation and elastic modulus with 39%, 65.2%, 72.3%, and 144.85%, respectively. Reduced density gradient supports that the interaction between carbon nanotube and fly ash geopolymer is dominated by a van der Waals one.
... It is remarkably noticed that the lowest adsorption energy is obtained for the highest silicon content sample (Si/Al = 3) due to the hydrophobic character of silicon and the weakening of Al -O bond in aluminate tetrahedron. Previous studies [60] report that in the reaction of the aluminosilicate with water molecules, most of bridging oxygen in silicate tetrahedron did not react with water molecules. ...
Enhancement of metakaolin graphene coated geopolymer wettability. • A decrease of surface energies of gra-phene/geopolymer with MD and DFT methods. • The contact angle between water nano-droplet and geopolymer surface rises to 79 •. • The diffusion coefficient of water drops and is equal to 0.131 10 − 10 m 2 /s. • The interfacial chemical bonding has a great effect on the mechanical behavior. Improving the durability of metakaolin aluminosilicate materials (named geopolymer) is a key challenge in the building industry. One approach to enhancing these materials resistance to water infiltration and other aggressive agents is to modify their surface properties. This study investigates the atomic-level interfacial interactions between a nanodroplet of water and a graphene-coated geopolymer surface. Using molecular dynamics and density functional theory methods, we computed the surface adsorption and free energies for metakaolin geopolymer surfaces, varying the chemical composition content between Si and Al atoms. Our MD results demonstrate that graphene-coating increases the geopolymer surface's stability, reducing its surface energy from 151 meV/ Å 2 to 7.71 meV/ Å 2. Moreover, the graphene-coated surface's contact angle with a water nanodroplet increased remarkedly from 31 • to 79 • , significantly reducing water permeability. We also found that the mobility of water molecules on the coated surface was twenty times lower, with a diffusion coefficient of 0.131 × 10 − 10 m 2 .s − 1. Importantly, our study revealed the crucial role of interfacial chemical bonding, with the evaluated elastic and indentation moduli increasing 70 and 39 times, respectively, when the interfacial bonding 2 concentration was 14.15%. Our findings provide fundamental insights into the interactions between graphene-coated geopolymer surfaces and water nanodroplets, representing a crucial step towards the development of superhydrophobic geopolymer materials.
... It is remarkably noticed that the lowest adsorption energy is obtained for the highest silicon content sample (Si/Al = 3) due to the hydrophobic character of silicon and the weakening of Al -O bond in aluminate tetrahedron. Previous studies [60] report that in the reaction of the aluminosilicate with water molecules, most of bridging oxygen in silicate tetrahedron did not react with water molecules. ...
Improving the durability of metakaolin aluminosilicate materials (named geopolymer) is a key challenge in the building industry. One approach to enhancing these materials resistance to water infiltration and other aggressive agents is to modify their surface properties. This study investigates the atomic-level interfacial interactions between a nanodroplet of water and a graphene-coated geopolymer surface. Using molecular dynamics and density functional theory methods, we computed the surface adsorption and free energies for metakaolin geopolymer surfaces, varying the chemical composition content between Si and Al atoms. Our MD results demonstrate that graphene-coating increases the geopolymer surface's stability, reducing its surface energy from 151 meV/ Å2 to 7.71 meV/ Å2. Moreover, the graphene-coated surface's contact angle with a water nanodroplet increased remarkedly from 31° to 79°, significantly reducing water permeability. We also found that the mobility of water molecules on the coated surface was twenty times lower, with a diffusion coefficient of 0.131 × 10−10 m2.s−1. Importantly, our study revealed the crucial role of interfacial chemical bonding, with the evaluated elastic and indentation moduli increasing 70 and 39 times, respectively, when the interfacial bonding concentration was 14.15%. Our findings provide fundamental insights into the interactions between graphene-coated geopolymer surfaces and water nanodroplets, representing a crucial step towards the development of superhydrophobic geopolymer materials.
... It is remarkably noticed that the lowest adsorption energy is obtained for the highest silicon content sample (Si/Al = 3) due to the hydrophobic character of silicon and the weakening of Al -O bond in aluminate tetrahedron. Previous studies [60] report that in the reaction of the aluminosilicate with water molecules, most of bridging oxygen in silicate tetrahedron did not react with water molecules. ...
... This line of research, which explores the molecular perspective and thus provides a theoretical basis for verification at the macroscopic level, is also reflected in the study of Mutisya et al [15,16].Molecular dynamics simulations (MD) can be used to study phenomena and mechanisms at the nanoscale that are not easily studied by direct experimental means [17][18][19]. For example, the transport and adsorption properties of water molecules and ions in hydration product nanopore channels were studied by molecular simulations by Hou et al. [20,21]. In addition, Kalinichev simulated the adsorption of ions at the surface of various cement hydration products. ...
The aluminum-based flameless ration heaters (FRHs) in self-heating food packaging are the heating elements, while water is the activator. Inevitable inadequate reactions can lead to reduced heating capacity and material waste. The transport behavior of activators (water and ions) in the main components of FRHs was investigated with molecular dynamics to study the mechanism of low exothermic efficiency. This paper transported a mixed solution composed of calcium ions, sodium ions, chloride ions, and water in the nanopores with three pore sizes 1.0, 1.5, and 2.5 nm. Results demonstrate that the formation of hydrogen bonds at the surface of tricalcium aluminate (C3A) with water can slow the movement of water molecules. Sodium, calcium ions, and oxygen atoms on the surface of C3A combine competitively through surface chemical bonding, forming Ca-O and Na-O bonds. In addition, as the pore size becomes smaller, the hindering effect of the nano-pore channel becomes stronger. Calcium ions and chloride ions form ion pairs through ionic bonding, which can continuously aggregate to hinder the transport of water molecules and ions. This work provides a basis for understanding the study of the transport and adsorption behavior of liquids in C3A pores and provides a viable idea for subsequent experimental studies.
... CO 2 adsorption in anhydrous grains is of much interest, but it is not well studied in the literature. Most literature studies on the C-S-H structure are related to the mechanical properties assessment and mechanical strength [18,[23][24][25][26][27][28][29][30][31]. We note that the C-S-H structure is mainly studied and considered as a defective version of Tobermorite 11 Å in the literature [32]. ...
... In the unit cell (cell size: 8.13 × 6.69 × 6.85 Å), there are 26, 28, 30, 32 and 34 atoms in S.1, S.2, S.3, S.4 and S.5, respectively. 7 The interlayer distances for different CaO/SiO 2 ratio have been studied [39] and shown to vary from 13 to 22 Å for dried C-S-H as reported elsewhere [30] making it difficult to provide a precise estimation of the interlayer distances in dried C-S-H. Consequently, we take it as 13.50 Å (Table 3). ...
... Clearly, this does not apply to the realistic globulous structure of C-S-H and we are far away from the perfect crystalline atomic network as mentioned earlier. This implies that C-S-H structure is more likely semi-amorphous rather than perfect crystalline in structure as assumed in the present work and similar studies dealing with the C-S-H structure in the literature [27,29,30,40,85]. ...
The paper deals with the understanding of the CO2 capacity of adsorption through the anhydrite cement compound, i.e., CaO⋅SiO2 structure. The Wollastonite structure is prepared with various CaO/SiO2 ratios for the atomistic simulations. Subsequently, simulations of binary adsorption of H2O and CO2 have been performed to arrive at C–S–H structure. The CaO/SiO2 ratio is varied from 0.66 to less than 1.5 in the present study. The interlayer spacing between CaO sheets is considered as 13.5 Å. The impact of the electrostatic charges has been explored using available CLAY_FF and CSH_FF potentials. The outcomes have been successfully examined and compared with experimental results. To understand the capacity adsorption of CO2 and selectivity effect on C–S–H forming, numerical experiments have been performed using CO2 concentrations from 10 ppm up to1,000,000 ppm at 20°C. These numerical experiments allow understanding of the selectivity of H2O and CO2 in binary mixture adsorption, and the capacity of CO2 adsorption in the Wollastonite atomic structure. According to the physisorption simulations, the CO2 adsorption capacity depends not only on CO 2 concentration but also the Wollastonite structure. The possible CaCO3 precipitation and C–S–H structure are addressed.
... As shown in Fig. 6(a), the vector perpendicular to the substrate is normal vector V n , the angle bisector of the two hydrogen atoms in the water molecule is dipolar vector V d , the angle between the two vectors is dened as the dipole angle. 46 The dipole angle distribution and local molecular conguration of water molecules in the MKP[001], MKP[010] and MKP[100] models are shown in Fig. 6(b), (c) and (d), respectively. It can be seen from Fig. 6(b) that the MKP[001] model has two peaks in the dipole angle distribution of water molecules in the range of 1.5Å from the solid matrix, which are located at 70-100 and 140-180 , respectively. ...
The sustainable green building material magnesium phosphate cement (MPC) is widely used in the fields of solidifying heavy metals and nuclear waste and repair and reinforcement. Magnesium potassium phosphate hexahydrate (MKP) is the main hydration product of MPC. The transport of water and ions in MKP nanochannels determines the mechanical properties and durability of MPC materials. Herein, the interface models of MKP crystals with sodium chloride solution in the [001], [010] and [100] direction were established by molecular dynamics. The interaction of the MKP interface with water and ions was studied and the durability of MPC in sodium chloride solution was explained at the molecular level. The results show that a large number of water molecules are adsorbed on the MKP crystal surface through hydrogen bonds and Coulomb interactions; the surface water molecules have the bigger dipole moment and the dipole vector of most of the water molecules points to the solid matrix, when the crystal surfaces of the three models all show hydrophilicity. In addition, plenty of sodium ions are adsorbed at the MKP interface, and some potassium ions are desorbed from the matrix. In the MKP[001] model, the amount of potassium ions separated from the matrix and diffused into the solution is the highest and the interface crystal is the most disordered. Due to the attack of water and ions, the K–Os bond loses its chemical stability and the order of the MKP crystal is destroyed, which explains the decline of MPC performance after the erosion of sodium chloride solution at the molecular level. Besides, in the three models, the Na–Cl ion bond is more unstable than the K–Cl ion bond due to the smaller radius of the sodium atom. The stability of ionic bonds in the models is as follows: MKP[010] > MKP[100] > MKP[001].
... Calcium counterions act an dominant role of electrostatic force in the interface adhesion between C-S-H gel and GO sheet. Such a behaviour is manifested in many other materials with charged surface, such as the cohesion between C-S-H colloids and the interaction between polyelectrolyte [54][55][56][57][58]. ...
The incorporation of graphene oxide (GO) into ultra-high performance concrete (UHPC) can solve the problems of brittle fracture and low tensile strength of UHPC to some extent. By means of molecular dynamics simulation, this paper provided an insight into the interfacial bonding between GO and calcium silicate hydrate (C-S-H) gel, the dominant component of bonding phase in cement-based materials, in the chemical environment of UHPC in terms of C-S-H/GO interfacial structure, energies, and mechanical properties and gave the comparison with the case of ordinary Portland cement (OPC) materials. The results show that, as compared with the case of OPC, the C-S-H produced in UHPC has more calcium and hydroxyls distributed in the interlayer, leading to larger interlayer spacing with more water molecules absorbed. Water and hydroxyls occupy the sites of interfacial chemical bonds and weakens the C-S-H/GO interfacial Ca–O ionic bonds and H-bond network, but serve as bridges connecting C-S-H gel and GO sheet. More interlayer calcium for the UHPC case leads to larger interfacial interaction energies, which results in the higher tensile strength of the C-S-H/GO interface of UHPC sample. During tensile process, water molecules in the interface deforms with the structure and forms H-bond network serving to C-S-H/GO adhesion, which improves ductility of the structure. Furthermore, the configuration during elongation that the edge of GO sheet is tightly attached to C-S-H indicates the strong strength of Ca–Ocoo− bonds.
... The parametrization and performance of the ReaxFF for Si, Al, Na, O, H were obtained directly from ref. 26. The ReaxFF has been successfully used to simulate silicate glass, 15 calcium silicate hydrate gel, 27,28 and nano-crystals. 29 ...
Sodium aluminosilicate hydrate (NASH) gel is the primary adhesive constituent in environmentally friendly geopolymer. In this study, to understand the thermal behavior of the material, molecular dynamics was utilized to investigate the molecular structure, dynamic property, and mechanical behavior of NASH gel subjected to temperature elevation from 300 K to 1500 K. The aluminosilicate skeleton in NASH gel provides plenty of oxygen sites to accept H-bond from the invading water molecules. Upon heating, around 18.2% of water molecules are decomposed and produce silicate and aluminate hydroxyls. About 87% of hydroxyls are associated with the aluminate skeleton, which weakens the Al–O bonds and disturbs the O–Al–O angle and the local structure, transforming it from an aluminate tetrahedron to a pentahedron and octahedron. With increasing temperature, both Al–O–Si and Si–O–Si bonds are stretched to be broken and the network structure of the NASH gel is gradually transformed into a branch and chain structure. Furthermore, the self-diffusivity of water molecules and sodium dramatically increases with the elevation of temperature, because the decrease in connectivity of the aluminosilicate network reduces the chemical and geometric restriction on the water and ions in NASH gel under higher temperatures. The high temperature also contributes to around 63% of the water molecules further dissociating and hydroxyl groups forming; meanwhile proton exchange between the water molecules and aluminosilicate network frequently takes place. In addition, a uniaxial tensile test was utilized to study the mechanical behavior of the NASH gel at different temperatures. During the tensile test, the aluminosilicate network was found to depolymerize into a branch or chain structure which plays a critical role in resisting the tensile loading. In this process, the breakage of the aluminosilicate skeleton is accompanied with hydrolytic reactions that further deteriorate the structure. Due to the reduction of the chemical bond stability at elevated temperature, both the tensile strength and stiffness of the NASH gel are weakened significantly. However, the ductility of the NASH gel is improved because of the higher extent of structural rrangement at the yield stage and partly due to the lower water attack. Hopefully, the present study can provide valuable molecular insights on the design of alkali-activated materials with high sustainability and durability
