Structure Of Calcium Silicate Hydrate Research Articles

Molecular Dynamics Simulation of Silane Inserted CSH Nanostructure.

Herein, the toughening mechanism and effects of 3-(aminopropyl)triethoxysilane (3-APTES) intercalation in calcium-silicate-hydrate (CSH) structures were investigated through molecular dynamics simulations. CSH established a model using 11 Å-tobermorite to simulate the tensile properties, toughness, adsorption energy, average orientation displacement and radial distribution function of 3-APTES intercalation at different Ca/Si ratios under conditions of a CVFF force field, an NVT system, and 298 K temperature. Simulation results demonstrate that 3-APTES alters the fracture process of CSH and effectively enhances its tensile properties and toughness. The presence of 3-APTES molecules increases the energy required to destroy CSH, thereby increasing the adsorption energy of CSH crystals. Furthermore, 3-APTES molecules effectively increase the atom density within the CSH structure. As the Ca/Si ratio increases, Ca-O bond formation is enhanced, with noticeable aggregation occurring because of modification by 3-APTES within the CSH structure. This study found that 3-APTES organic compounds can effectively improve the tensile, toughness, adsorption and other properties of the CSH structure, and further improve the microstructure of CSH.

Coarse-grained molecular dynamics study on submicron structuring of calcium silicate hydrate with enhanced tensile modulus and strength

Potential of cement-based materials for energy harvesting is encoded in their elusive mesoporous structure, and understanding the sub-micron structure of calcium silicate hydrate (C–S–H), a major binding phase of cement, is an important yet challenging task. Nanoscale C–S–H is ductile, while macroscopic performance is brittle, suggesting a gap in the transition of material properties from the nano-to the macro-scale, and a chance in finetuning the submicron (∼100 nm) structure to effectively deliver the atomistic properties to the bulk performance. The refined sub-micron structure of C–S–H can enhance the strength and modulus of concrete, thus providing a base material with better mechanical properties and durability. Here, two critical structural features of C–S–H, including agglomeration of globules and stacking of layers, are modeled by spherical and oblate ellipsoidal units, respectively. Coarse-grained modeling and peridynamics simulations find that the packing of ellipsoidal units is better than that of spherical units, from the perspectives of size distribution, morphology, fractality of pores and tensile properties. The analyses on the mesoporous structure shows that the ellipsoid-packing is more homogeneous than the sphere-packing model, and it yields a refined structure with enhancement in tensile modulus and strength. The submicron finetuning enhancement of C–S–H can be realized through different physical and chemical approaches, like inducing lateral growth of silicate chains by chemical additives, scaffolding materials, and conditioned hydration. This coarse-grained simulation work gives novel insights and fundamental strategies for toughening the cement matrix through delivering ductile nanoscale performance of C–S–H to macroscale cementitious materials, and provides superior performance for concrete in existing and new structures.

Effect of Modified Cellulose Nanocrystals on the Structure of Calcium Silicate Hydrate Studied by Molecular Dynamics Simulation and Experiment

Effect of Modified Cellulose Nanocrystals on the Structure of Calcium Silicate Hydrate Studied by Molecular Dynamics Simulation and Experiment

Effects of Hybrid Graphene Oxide-Nanosilica on Calcium Silicate Hydrate in the Simulation Environment and Cement.

This research aims to investigate the synergistic reinforcing mechanisms of chemically combined graphene oxide and nanosilica (GO-NS) in the structure of calcium silicate hydrate (C-S-H) gels compared with physically combined GO/NS. The results confirmed that the NS chemically deposited on the GO surface formed a coating to keep GO from aggregation, while the connection between GO and NS in GO/NS was too weak to prevent GO from clumping, making GO-NS better dispersed than GO/NS in pore solution. When applied to cement composites, the incorporation of GO-NS enhanced the compressive strength by 27.3% after 1-day hydration compared to that of the plain sample. This is because that GO-NS generated multiple nucleation sites at early hydration, reduced the orientation index of calcium hydroxide (CH), and increased the polymerization degree of C-S-H gels. GO-NS acted as the platforms for the growing process of C-S-H, enhancing its interface bonding strength with C-S-H and increasing the connection degree of the silica chain. Furthermore, the well-dispersed GO-NS was prone to insert in C-S-H and induced deeper cross-linking, thereby refining the microstructure of C-S-H. All these effects on hydration products resulted in the mechanical improvement of cement.

Influence of light radiation on performance-structure of tricalcium silicate (C3S) hydration products

In this work, high-power Xenon radiation is used to simulate real sunlight radiation and calcium silicate hydrate is prepared by hydration of tricalcium silicate (C3S) with two water-to-solids (w/s) ratios of 0.5 and 10. The absorbance, compositions, silicate chain structure, pore structure and micromorphology of C3S hydration products (C3S-H) after exposure to Xenon radiation were determined using XRD, TG, FITR, 29Si solid-stated NMR, BET and SEM. First of all, fibrous and needle-like calcium silicate hydrate is observed in C3S-H/10 while flaky and honeycomb-like shape is observed in C3S-H/0.5. Although there are remarkable differences in the micromorphology of calcium silicate hydrate in C3S-H with different w/s ratios, Xenon radiation reduces the amount of bound water, increases the polymerization of silicate chain and refines the nanopore structure of calcium silicate hydrate. The underlying mechanism for the re-organization of chemical structure is attributed to improved polymerization of silicate chains. In addition, the refinement on the nanopore structure is due to the coupling actions of shrinking and polymerization of calcium silicate hydrate sheets. The findings could provide basic knowledge regarding the durability of cement-based materials serviced in atmospheric environments especially with strong solar radiation.

Impact of chitin nanofibers and nanocrystals from waste shrimp shells on mechanical properties, setting time, and late-age hydration of mortar

Every year ~ 6–8 million tonnes of shrimp, crab, and lobster shell wastes are generated, requiring costly disposal procedures. In this study, the chitin content of shrimp shell waste was oxidized to produce chitin nanocrystals (ChNC) and mechanically fibrillated to obtain chitin nanofibers (ChNF) and evaluated as additives for mortar. ChNF (0.075 wt%) and ChNC (0.05 wt%) retarded the final setting time by 50 and 30 min, likely through cement dispersion by electrostatic repulsion. ChNF (0.05 wt%) with a larger aspect ratio than ChNC resulted in the greatest improved flexural strength and fracture energy by 24% and 28%. Elastic modulus increased by up to 91% and 43% with ChNC and ChNF. Solid-state nuclear magnetic resonance (NMR) showed ChNF (0.05 wt%) enhanced calcium–silicate–hydrate structure with a 41% higher degree of polymerization, 9% more silicate chain length, and a 15% higher degree of hydration at 28 days. Based on the findings, chitin seems a viable biomass source for powerful structural nanofibers and nanocrystals for cementitious systems to divert seafood waste from landfills or the sea.

Reutilization of oil and gas produced water in cement composite manufacturing

Fast-paced urbanism results in the growing demand for more infrastructure, leading to increased concrete production, further depleting freshwater sources. One sustainable solution to diminishing water resources is recycling and reusing non-potable waters and wastewaters in manufacturing operations. This study investigates the reutilization of produced water in cementitious systems. Produced water is the largest volume of waste stream from oil and gas production and usually contains various pollutants such as petroleum hydrocarbons, heavy metals, and toxic chemicals, which may result in unexpected environmental issues. The application of this type of water in a concrete system may not only aid the waste reduction but also yield sustainable concrete and mortar for the construction industry. The current study evaluates the performance of produced water cementitious systems at varying replacement concentration levels. The results indicate that the produced water cementitious system is significantly influenced by water replacement concentration levels. The long-term compressive strength and early age hydration peak heat flow both increase with increasing produced water replacement concentration up to approximately 60% concentration (60% compressive strength increase: 20.2 MPa–32.2 MPa; 120% peak heat flow increase: 2.67 mW/g to 5.92 mW/g). At higher produced water replacement concentrations, the long-term compressive strength and heat of hydration begin to decrease. The produced water leads to increased formation of Friedel's salts and bound calcite, and more polymerization in the calcium silicate hydrate structure. The produced water cementitious systems will increase the long-term compressive strength and early age heat of hydration more than comparable seawater cementitious systems reported in the literature.

Al uptake in calcium silicate hydrate and the effect of alkali hydroxide

The effect of Al and of pH on the structure of calcium silicate hydrate (C-S-H), the most important hydration product in Portland and blended cement, was studied at Ca/Si ~1.0. The presence of Al led to higher amounts of secondary phases, larger interlayer distances, longer silicate chains, higher concentrations of dissolved Al and Si, and lower Ca concentrations. The amount of secondary phases progressively decreased with increasing pH; that of strätlingite and Al(OH)3 dominated at low pH, and katoite at high pH values. High pH was also associated with increased Al and Si concentrations, lowered Ca concentrations, shortened silicate chain length and higher maximum Al/SiC-S-H ratios. The Al uptake in C-A-S-H increased with aqueous aluminium concentration. XANES analysis showed the presence of both Al(IV) and Al(VI) in different coordination environments in C-S-H.

Technological aspects of the preparation of polymer composites of building materials and coatings

In accordance with the principles of sustainable development, improving the quality and durability of structural elements and coatings, the construction industry requires the development and the implementation of resource- and energy-efficient building materials, as well as innovative technologies for their production. The use of complex modifiers for no-slump concrete mixtures and concrete is becoming increasingly widespread in modern materials science. The article presents the studies of influence of polymer additive structured carbon nanomaterials on physical and mechanical characteristics of no-slump concrete mixtures. The methods of infrared spectroscopy and thermogravimetric analysis showed that the use of carbon nanomaterials alters the structure of no-slump concrete mixtures significantly. As a result of the fact that the high-strength nanomaterial is the centre of crystallization of cement stone neo-formation, a denser reinforced microstructure is formed, which increases significantly the strength properties of no-slump concrete mixtures. The inclusion of a complex polymer additive in no-slump concrete mixtures leads to higher and longer plasticizing, which plays an important role in the production of monolithic products. It was determined that, in the presence of a complex modifier (a polymer additive structured by carbon nanotubes), the crystalline structure of calcium silicate hydrate is compacted, which determines high physical and mechanical characteristics of modified no-slump concrete mixtures. It was experimentally shown that the additive acted as an accelerator of a setting and hardening cement test and also increases its strength characteristics. In general, in this study, there is a water-reducing effect from the application of the additive for all no-slump concrete mixtures. Water consumption is reduced by 5% of the mass, while the strength is increased by 19%. No-slump concrete mixtures recipes modified by polymer additives, structured by carbon nanotubes, with high performance were developed.

Roles of CSH gel in the microstructure and piezoelectric properties variation of cement-based piezoelectric ceramic composite

The microstructures of cement-based piezoelectric composites with Portland cement (hydrated/fresh cement powder) as the matrix phase and lead zirconate titanate (PZT) particles as the functional phase are characterized to illustrate the effect of calcium-silicate-hydrate (CSH) on the binding behavior between two phases before and after polarization. Piezoelectric properties variation are traced to evaluate the aging effect. Results show the CSH structure change from nano-flocculent/fibrous to ellipsoid after polarization. The piezoelectric strain factor of the hydrated cement-based composite with low hydration capacity shows a decreasing trend with age due to the insufficient binding between the CSH and PZT particles, while that of the fresh cement-based composite shows an opposite tendency. This investigation also reveals the influence of polarization on the CSH gel structure, promoting the further understanding of binding behavior between the CSH and PZT for the piezoelectric performance variation during the non-polarization process.

Effects of soluble magnesium on the structure of calcium silicate hydrate

This paper aims to investigate the impact of soluble magnesium on the structure of C-S-H formed at elevated temperature. Magnesium chloride hexahydrate, calcium oxide and silica fume were used in the preparation of Mg2+ modified C-S-H. The obtained solid and liquid samples of synthetic C-S-H were characterized with XRD, FTIR, TGA, etc. to investigate the structural features of Mg2+ modified C-S-H. Results show that the mineralogical compositions of the synthesized C-S-H are highly related to the initial concentration of Mg2+. Large additions of Mg2+ lead to the instability of C-S-H. Meanwhile, magnesium can be incorporated into the structure of C-S-H. A heterogenous distribution of elemental Mg in C-S-H phase on nanoscale is observed.

Effect of relative humidity and porosity on the logarithmic creep of the layered C–S–H minerals tobermorite and jennite

Tobermorite is a natural mineral found in the microstructure of special concretes, such as autoclaved concrete and oil well cement, and along with jennite has been extensively studied for their analogy to the layered atomic structure of calcium silicate hydrate (C-S-H), which is the main product of the hydration of Portland cement. By means of creep microindentation, this work aims at further investigating the viscoelastic behavior of such C–S–H minerals at various levels of relative humidity (RH) and porosity.First, samples of 1.4 nm tobermorite and jennite were synthesized at different porosities. Then, the probed material volume was brought to the hygral equilibrium at various RH levels before carrying out a microindentation grid. Their microstructure was statistically characterized in terms of indentation modulus (M) and hardness (H), as well as the contact creep modulus (C), which was analyzed by a logarithmic contact creep compliance in time. The effects of RH and porosity on the microindentation parameters (M, H, and C) were then characterized and compared to those measured on synthetic C–S–H and a cement paste, which are available in the open literature. Finally, a simplified analysis showed that the creep rate is linearly dependent on RH, thus confirming the importance of the sliding of calcium silicate sheets structure on the long-term basic creep of layered C–S–H minerals.

Synthesis and structure of calcium silicate hydrate (C-S-H) modified by hydroxyl-terminated polydimethylsiloxane (PDMS)

Calcium silicate hydrate (C-S-H) is the main hydration product of cement, and its micro-nano-structure has an important influence on the properties of cement-based materials. The disadvantages of cement-based materials are related to the micro-nano-structure defects of C-S-H. The modification of the C-S-H structure by silane can make up the defects of C-S-H. Here, we studied the structure of C-S-H modified by a straight-chain silane containing silicon hydroxyl groups at both ends. Calcium silicate hydrate (C-S-H) gel particles modified by hydroxyl-terminated polydimethylsiloxane (PDMS) were synthesized by the sol–gel method. The influence of this organic modification on the structure of C-S-H was investigated by XRD, FTIR, NMR, SEM, TG-DTG and water contact angles techniques. The results show that various sizes of C-S-H gel particles are connected with PDMS via covalent bond. PDMS acts as a bridge between C-S-H particles. The introduction of PDMS changes the morphology of stacked spherical particles to cauliflower-like and increases water contact angle of C-S-H. In addition, various sizes of C-S-H gel particles are also coated by PDMS. This research explains the methods for affecting the stacking process of C-S-H gel particles.

Effects of asphalt emulsion on calcium silicate hydrate gel: Morphology and porosity

AbstractIn this paper, calcium silicate hydrate (CSH) gel and calcium silicate hydrate doped with asphalt emulsion (EACSH) were synthesised using Na2SiO3•9H2O, Ca (NO3)2•4H2O, NaOH, deionised water and anionic asphalt emulsion. N2 isothermal adsorption, X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the effect of asphalt emulsion on morphology and porosity of CSH. The Frenkel–Halsey–Hill (FHH) model was used to analyse the surface fractal characteristics. The results showed that the asphalt emulsion had little effects on the change of specific surface areas and the distribution of the micropores for CSH gel, which may be related to the absence of the intercalation reaction and the “opening” effect. The asphalt emulsion could promote the formation of mesoporous hydrated calcium silicate and decreased the number of mesopores in CSH gel but had little effects on the macroporous and microporous structure of CSH. The calculation results of the FHH model showed that the fractal characteristics between CSH and EACSH were different. The emulsifier may adsorb CSH gels result in globular accumulation state.

Determination of atomistic deformation of tricalcium silicate paste with high‐volume fly ash

AbstractWe examined the effect of incorporating high‐volume fly ash on the atomic arrangement and interatomic deformation behavior of calcium silicate hydrates in tricalcium silicate paste upon exposure to external forces. The interatomic structural changes and strains under compressive load were assessed using synchrotron in situ high‐energy X‐ray scattering‐based atomic pair distribution function analysis. Three different types of strains, which were (a) macroscopic strains from gauges on the surfaces of specimen, (b) strains in a reciprocal space (Bragg peak shift), and (c) strains in real space (PDF peak shift), were compared to each other. All monitored and calculated strains for tricalcium silicate‐fly ash (50 wt% fly ash) paste were compared with the counterparts of the pure tricalcium silicate paste. Pair distribution function analysis in the range of r < 10 Å indicated that the atomic arrangement of tricalcium silicate‐fly ash was similar to that of synthetic calcium silicate hydrates followed by that of pure tricalcium silicate paste. Moreover, the pair distribution function refinement results revealed that the calcium silicate hydrate structure in tricalcium silicate‐fly ash paste was similar to tobermorite 11 Å, unlike that in pure tricalcium silicate paste. The interatomic strain of tricalcium silicate‐fly ash in the real space (r < 20 Å) was smaller than that of tricalcium silicate under compression, which suggested that the incompressibility of calcium silicate hydrates at atomistic scale was enhanced by the incorporation of fly ash into it. This was likely to be caused by the increased silicate polymerization of calcium silicate hydrates, which was attributed to the increase in the amount of silicate in their structure via the addition of fly ash.

Structure evolution of the interface between graphene oxide-reinforced calcium silicate hydrate gel particles exposed to high temperature

Structure, reactivity, and dynamics of the interface between graphene oxide (GO)-reinforced calcium silicate hydrate (CSH) gel particles at the temperature from 900 to 1100 K are investigated by means of reactive molecular dynamics. The results show that, high temperature weakens the CSH structure, including the stretching of Si-O bonds, the decomposition of silicate chains, and the hydrolysis weakening caused by water molecules. The high kinetic energy and weakened structure result in the melting and diffusion of CSH gel. However, the incorporation of GO can effectively stabilize the CSH structure by following three factors. (1) GO prevents the diffusion of the gel, and the packing of gel on the GO nanosheet increases the compatibility between them. (2) Reduction reaction of GO creates the defects on the carbon plane, providing the space for silicate chains crossing GO sheet. (3) Frequency exchange of oxygen between GO and CSH promotes the formation of chemical bonding between them. The improvement of the stability of CSH gel can effectively reduce the ablation velocity under high temperature.

A comparison between fly ash- and basic oxygen furnace slag-modified gold mine tailings geopolymers

Fly ash (FA) and Basic oxygen furnace (BOF) slag were used to as additives in the geopolymerisation of gold mine tailings (GMT).The aim of the research was to determine the effects of the two additives on the strength formation and mechanism of metal immobilisation by modified GMT geopolymers. GMT, FA and BOF were mixed, respectively, and made into a paste with the addition of potassium hydroxide (KOH) before curing at various conditions. 50% replacement of GMT in the starting materials gave the highest unconfined compressive strength (UCS). The UCS for BOF-based geopolymer was 21.44 Mega Pascals (MPa), whilst the one for FA-based geopolymer was 12.98 MPa. The BOF-based geopolymer cured at lower temperature (70 °C) as compared to the FA-based geopolymer (90 °C). The optimum KOH concentration was 10 and 15 M for BOF- and FA-based geopolymers, respectively. BOF-based geopolymers resulted in the formation of calcium silicate hydrate (CSH) phases which contributed to higher strength; whereas in FA-based geopolymers, no new structures were formed. BOF-based geopolymers resulted in over 94% iron (Fe) immobilisation, whereas FA-based geopolymers had 76% Fe immobilisation. Fe immobilisation was via incorporation into the CSH or geopolymer structure, whilst other metal immobilisations were thought to be via encapsulation. 12-month static leaching tests showed that the synthesised geopolymers posed insignificant environmental pollution threat for long-term use.

Insights into structural characteristics and the mechanism of silicate-based calcium phosphates with phosphoric acid modulation

Si-containing calcium phosphate materials recently have attracted attention owning to their biomineral capability and benefit to the proliferation and differentiation of osteoblast-like cells. In this study, tri-calcium silicate (C3S), which can induce apatite layer deposition on its surface, and phosphoric acid are used to prepare silicate-based calcium phosphates via aqueous precipitation method. It's known that calcium phosphate undergoes phase transformation when the pH value changes. So, the different ratios of C3S and phosphoric acid are designed to study the phase transformation of calcium phosphate. The pH, ions release of solution, composition and structure are detected. The results show the phase transformation of calcium phosphate from hydroxyapatite to brushite with the increased content of phosphoric acid. The structure of calcium silicate hydrate (C–S–H) also undergoes a series of changes, including protonation and polymerization. Briefly, this study focuses primarily on the interaction between C–S–H and calcium phosphates. In addition, it may provide a new sight for the sustained delivery of bisphosphonates achieved by depositing on the surface of C3S for the treatment of osteoporosis.

Graphene oxide in ceramic-based layered structure: Nanosheet optimization

Using graphene oxide (GO) in ceramics can improve their performance on the molecular level. In this article, density functional theory was used to gain a better understanding of electron distribution in the composite consisting of GO inside a ceramic layered structure and its direct relation with the possible chemical bonds and bonding energy interactions. Moreover, with molecular dynamics calculations, the structure of calcium silicate hydrate (CSH) was considered as a ceramic perimeter and investigated to assess GO role. Extracted results revealed the calcium atoms in the CSH structure to be the most important species in the interaction between the CSH structure and GO. The aforementioned calcium ions have a high desire for electron, thus they are drawn to a distance from oxygen atoms residing on the functional groups to share their electron. With respect to this behavior and other factors, including the wrinkling phenomenon, an optimization study was conducted on the type, location and weight ratio of the concerned functional groups as well as the dimensions of the graphene oxide plane. Our findings expressed the complexity of GO behavior in ceramic composites as a function of several parameters. Here, results indicated that GO preserves its reinforcing quality under different scenarios concerning the combination of functional groups, their location and the optimal L/W ratio of the sheet. Best performance was achieved when hydroxyl, carboxyl and epoxy groups were presented on the surface and the edges of the GO platelet simultaneously. In this case, Young's modulus for the composite grows approximately 29%, which is not only a result of sustained mechanical properties of the GO itself, but also a product of powerful bonding between GO and CSH structures. The outcomes of this study could pave the way for applications of selectively functionalized graphene for efficient reinforcing of the GO-ceramics nanocomposites.

Microstructural and mechanical properties of (Ca, Na)-poly(sialate-siloxo) from metakaolin as aluminosilicate and calcium silicate from precipitated silica and calcined chicken eggshell

The aim of this work is to investigate the influence of the amorphous calcium silicate on the microstructural, physical and mechanical properties of (Ca, Na)-poly(sialate-siloxo) networks. The calcium silicate with molar ratio CaO/SiO2 equal to 1.0 was prepared from the precipitated silica and calcined chicken eggshell. The X-ray patterns and infrared spectra of the synthesized calcium silicate indicate that it mainly constitutes of the amorphous calcium silicate hydrate. The X-ray patterns of geopolymer cements indicate that the prepared amorphous calcium silicate hydrate does not include in the network. The compressive strengths of the geopolymer mortars decrease from 28.92 to 12.03 MPa with increasing the replacement level of metakaolin (from 0 to 25% by mass). Whereas, the values of the apparent densities increase with increasing the replacement level of metakaolin. It seems that the amorphous calcium silicate hydrate in the structure of calcium silicate affects negatively the mechanical properties of the (Ca, Na)-poly(sialate-siloxo) network. The heterogeneous structure of geopolymer mortars containing 25% of calcium silicate could be related to the higher calcium content and the amorphous structure of calcium silicate hydrate. It was typically found that in the absence of significant levels of dissolved calcium, the precursors such as silicate and aluminate condense to form (Ca, Na)-poly(sialate-siloxo) networks. This implies the homogenous structure and the higher values of the compressive strengths of geopolymer mortars containing 0, 5, 10 and 15% of calcium silicate. Whereas those from the replacement level of metakaolin by 20 or 25% of calcium silicate contain significant levels of dissolved calcium and amorphous calcium silicate hydrate in their structure which hinder the formation of the precursors and therefore impede the formation of the (Ca, Na)-poly(sialate-siloxo) networks.