Structure, Formation, Properties, and Application of Calcium and Magnesium Silicate Hydrates System—A Review

In order to expand the advantages of strong durability and high compressive strength of calcium silicate hydrates(C-S-H),at the same time to make up for the poor early mechanical strength of magnesium silicate hydrates (M-S-H),we present the features and advantages of C-S-H and M-S-H and a comprehensive review of the progress on CaO-MgO-SiO_(2)-H_(2)O.Moreover,we systematically describe natural calcium and magnesium silicate minerals and thermodynamic properties of CaO-MgO-SiO_(2)-H_(2)O.The effect of magnesium on C-S-H and calcium on M-S-H is summarized deeply;the formation and structural feature of CaO-MgO-SiO_(2)-H_(2)O is also explained in detail.Finally,the development of calcium and magnesium silicate hydrates in the future is pointed out,and the further research is discussed and estimated.

Effect of Hydrated Calcium Aluminate Cement on the Chloride Immobilization of Portland Cement Paste

To improve the efficiency and stability of chloride immobilization of portland cement paste,hydrated calcium aluminate cement(HCAC)prepared by wet grinding of CAC was added into portland cement paste as an additive.The immobilized chloride ratio(ICR)was evaluated,and the mechanism of chloride immobilization was researched by XRD,DTG,NMR,and MIP tests.The analysis results demonstrated that HCAC could improve the chloride immobilization capacity of portland cement paste.The mechanism was attributed to the following aspects:chemical binding capacity was enhanced via producing more Kuzel’s salt;physical adsorption capacity was reduced by decreasing the C-S-H gel;migration resistance was enhanced through refining the pore structure.

Hydration Behavior and Cementitious Properties of Calcium Carbonate-aluminate Minerals Composite

The purpose of this research is to investigate the hydration behavior and cementitious properties of the mixture of calcium carbonate and aluminate, and to explore whether it can be adopted as a new low-carbon cementitious material. The composite system of calcium carbonate and aluminate minerals is studied by measuring the component of hydration products, the hydration heat, setting time and compressive strength.The results prove that the composite system has certain cementitious properties and is feasible to prepare new low-carbon cement.

Study on Multi-Scale Tensile Strength and Tensile Strain of Calcium Silicate Hydrate Layered Nanocomposites Under External Physical Field

Calcium silicate hydrate(C-S-H)is the mainly strength source of cement-based materials,but there is little basic research.In this paper,molecular dynamics method is applied to analyze the multi-scale tensile strength and tensile strain of C-S-H layered materials under the condition of external physical fields(temperature and strain rate).The results show that the tensile strength and strain of C-S-H model decrease with temperature raises.The temperature(from 1 K to 600 K)has obvious influence on the tensile strain and strength of C-S-H layered materials.In addition,at(0.00025 ps^(-1)-0.001 ps^(-1)),the tensile strain and strength of C-S-H layered materials are less sensitive to strain rate.The whole model is closer to a 3-dimensional deformation.However,at(0.001 ps^(-1)-0.005 ps^(-1)),the dynamic load effect begins to increase,and the work done by the load per unit time increased.The tensile strain and strength of C-S-H layered materials indicates intensified by the change of strain rate.The energies are randomly distributed in the system,not concentrated in a certain area.

Early calcium monocarboaluminate hydrate formation in cement paste:effect of polycarboxylate type admixture

Effects of polycarboxylate type admixture（PCA）on calcium monocarboaluminate hydrate（AFmc）formation in hydrated cement paste containing limestone filler（LF）are investigated by the Fourier transform infrared spectroscopy（FTIR）,the scanning electron microscopy（SEM）,the derivative thermogravimetric（DTG）analysis and the adsorption amount measurement.Experimental results indicate that AFmc forms during the initial hydration period of cement as early as 15 min.It is found that PCA accelerates the early age AFmc formation and enhances cement hydration by promoting C4AF hydration at the early age,and,as a consequence,the iron associated AFmc phase forms more readily.The phenomenon is not observed when PCA is replaced by a naphthalene formaldehyde sulphonate condensate water reducer.Compatibility between PCA and cement is modified due to the presence of AFmc along with ettringite（AFt）,which results in a less adsorption amount of PCA on the surface of cement minerals.As a kind of high-range water reducer,PCA may be the preferred choice for concrete containing LF.

Fractionation and solubility of cadmium in paddy soils amended with porous hydrated calcium silicate

Previous studies have shown that porous hydrated calcium silicate （PS） is very effective in decreasing cadmium （Cd） content in brown rice. However, it is unclear whether the PS influences cadmium transformation in soil. The present study examined the effect of PS on pH, cadmium transformation and cadmium solubility in Andosol and Alluvial soil, and also compared its effects with CaCO3, acidic porous hydrated calcium silicate （APS） and silica gel. Soil cadmium was operationally fractionationed into exchangeable （Exch）, bound to carbonates （Carb）, bound to iron and manganese oxides （FeMnOx）, bound to organic matters （OM） and residual （Res） fraction. Application of PS and CaCO3 at hig rates enhanced soil pH, while APS and silica gel did not obviously change soil pH. PS and CaCO3 also increased the FeMnOx-Cd in Andosol and Carb-Cd in Alluvial soil, thus reducing the Exch-Cd in the tested soils. However, PS was less effective than CaCO3 at the same application rate. Cadmium fractions in the two soils were not changed by the treatments of APS and silica gel. There were no obvious differences in the solubility of cadmium in soils treated with PS, APS, silica gel and CaCO3 except Andosol treated 2.0% CaCO3 at the same pH of soil-CaC12 suspensions. These findings suggested that the decrease of cadmium availability in soil was mainly attributed to the increase of soil pH caused by PS.

Effect of C/S Ratio on Morphology and Structure of Hydrothermally Synthesized Calcium Silicate Hydrate

The samples of the C-S-H series were synthesized by hydrothermal reaction of fumed silica, CaO and deionized water at initial C/S ratios between 1.0-1.7. Phase composition and structural and morphology characteristics of C-S-H samples were analyzed by XRD, IR and SEM. The experimental results showed that the d-spacing of （002）, （110） and （020） decreased, the d-spacing of （200） increased, and the d-spacing of （310） varied randomly, the polymerization of silica tetrahedra of C-S-H decreased, and morphology of C-S-H samples varied from sheet shapes to long reticular fibers as C/S ratio increased.

Hydrothermal synthesis of zeolites-calcium silicate hydrate composite from coal fly ash with co-activation of Ca(OH)_(2)-NaOH for aqueous heavy metals removal

Coal fly ash is a typical secondary aluminum/silicon resource.The preparation of zeolite-type absorbent is a potential way for its value-added utilization,while the purity and adsorption property of zeolite are limited due to the occurrence of side reactions in the synthesis process.In this study,a designated composite consisted of crystalline zeolites and amorphous calcium silicate hydrate was selected,which was direct synthesized from fly ash under conditions of a Ca/Si molar ratio of 0.8,an initial NaOH concentration of 0.5 mol/L,a hydrothermal temperature of 170℃and a liquid–solid ratio of 15 mL/g.The results indicated that this composite had superior adsorption property for a variety of heavy metals,which was based on the exchange of calcium and sodium ions in zeolites and calcium silicate hydrate.Its adsorption capacities for Pb^(2+),Ni^(2+),Cd^(2+),Zn^(2+),Cu^(2+)and Cr^(3+)attained 409.4,222.4,147.5,93.2,101.1 and 157.0 mg/g,respectively,in single solution with a pH of 4.5.After regulating the synthesis conditions,the transformation of amorphous calcium silicate hydrate into crystallized tobermorite weakened the adsorption capacity of the composite.Besides,due to the competitive adsorption in a multiple ions solution,the adsorption capacities for these heavy metals had a reduction.

Effect of Calcium Silicate Hydrate Seeds on Hydration and Mechanical Properties of Cement

C-S-H series are synthesized at different temperatures and ages by pozzolanic reaction.The change of particle size distribution,phase composition,morphology and nanostructure of C-S-H with temperatures and ages,and the effects of C-S-H seeds and seeds parameters on the hydration behavior and mechanical properties development of cement were investigated by DLS,XRD,SEM,^(29)Si NMR,TAM-air isothermal calorimeter and mechanical properties test.The results show that the particle size,crystallinity,basal spacing and Q^(2)/Q^(1) ratio of C-S-H increases with the increase of synthesis temperature and age.The addition of synthesized C-S-H seeds to cement pastes results in the strong acceleration effect on cement hydration and significant improvement of the early strength of cement paste and mortar.The 1 day-C-S-H seeds synthesized at room temperature can increase the strength of cement paste by about 30 MPa at 12 h.The effect does not show a very regular change with the increase of the temperature and age of seeds synthesis.Considering the effect of C-S-H seeds on the hydration and mechanical properties of cement,and economy and short cycle of seeds synthesis,the C-S-H seeds synthesized at room temperature for 1 day or 55 ℃ water bath for 12 hours is recommended..

Optimizing the electrolyte salt of aqueous zinc-ion batteries based on a high-performance calcium vanadate hydrate cathode material

It is urgent to develop high-performance cathode materials for the emerging aqueous zinc-ion batteries with a facile strategy and optimize the related components.Herein,a Ca0.23V2O5·0.95 H2O nanobelt cathode material with a rather large interlayer spacing of 13.0 A is prepared via a one-step hydrothermal approach.The battery with this cathode material and 3 M Zn(CF3SO3)2 electrolyte displays high specific capacity(355.2 mAh g^(-1) at 0.2 A g^(-1)),great rate capability(240.8 mAh g^(-1) at 5 A g^(-1)),and excellent cyclability(97.7% capacity retention over 2000 cycles).Such superior performances are ascribed to fast electrochemical kinetics,outstanding electrode/electrolyte interface stability,and nearly dendrite-free characteristic.Instead,when ZnSO4 or Zn(ClO4)2 is used to replace Zn(CF3SO3)2,the electrochemical performances become much inferior,due to the slow electrochemical kinetics,inhomogeneous Zn stripping/plating process,and the formation of large dendrites and byproducts.This work not only discloses a high-performance cathode material for aqueous zinc-ion batteries but also offers a reference for the choice of electrolyte salt.

A molecular dynamics study of calcium silicate hydrates-aggregate interfacial interactions and influence of moisture

The interface properties between hydrated cement paste(hcp)and aggregates largely determine the various performances of concrete.In this work,molecular dynamics simulations were employed to explore the atomistic interaction mechanisms between the commonly used aggregate phase calcite/silica and calcium silicate hydrates(C-S-H),as well as the effect of moisture.The results suggest that the C-S-H/calcite interface is relatively strong and stable under both dry and moist conditions,which is caused by the high-strength interfacial connections formed between calcium ions from calcite and high-polarity non-bridging oxygen atoms from the C-S-H surface.Silica can be also adsorbed on the dry C-S-H surface by the H-bonds;however,the presence of water molecules on the interface may substantially decrease the affinities.Furthermore,the dynamics interface separation tests of C-S-H/aggregates were also implemented by molecular dynamics.The shape of the calculated stress-separation distance curves obeys the quasi-static cohesive law obtained experimentally.The moisture conditions and strain rates were found to affect the separation process of C-S-H/silica.A wetter interface and smaller loading rate may lead to a lower adhesion strength.The mechanisms interpreted here may shed new lights on the understandings of hcp/aggregate interactions at a nano-length scale and creation of high performance cementitious materials.

Preparation of MnO_2 and calcium silicate hydrate from electrolytic manganese residue and evaluation of adsorption properties

Electrolytic manganese residue(EMR), a high volume byproduct resulting from the electrolytic manganese industry, was used as a cheap and abundant chemical source for preparing MnO2 and EMR-made calcium silicate hydrate(EMR-CSH). The MnO2 is successfully synthesized from the metal cations extracted from EMR, which can effectively recycle the manganese in the EMR. By the combination of XRD, SEM and EDX analysis, the as-prepared MnO2 is found to exhibit a single-phase with the purity of 90.3%. Furthermore, EMR-CSH is synthesized from EMR via hydrothermal method. Based on the detailed analyses using XRD, FT-IR, FE-SEM, EDX and BET surface area measurement, the product synthesized under the optimum conditions(p H 12.0 and 100 °C) is identified to be a calcium silicate hydrate with a specific surface area of 205 m2/g incorporating the slag-derived metals(Al and Mg) in its structure. The as-synthesized material shows good adsorption properties for removal of Mn2+ and phosphate ions diluted in water, making it a promising candidate for efficient bulk wastewater treatment. This conversion process, which enables us to fabricate two different kinds of valuable materials from EMR at low cost and through convenient preparation steps, is surely beneficial from the viewpoint of the chemical and economical use of EMR.

Heterogeneous Nature of Calcium Silicate Hydrate(C-S-H) Gel:A Molecular Dynamics Study

Structure and mechanical properties of Calcium silicate hydrate (C-S-H) at a molecular level act as "DNA" of cement-based construction materials.In order to understand loading resistance capability of C-S-H gel,research on molecular dynamics (MD) was carried out to simulate the uniaxial tension test on C-S-H model along x,y,and z directions.Due to the structure and dynamic differences of the layered structure,the C-S-H model demonstrates heterogeneous mechanical behavior.On an XY plane,the cohesive force can reach 4 GPa,which is mainly provided by the Ca-O and Si-O ionic-covalent bonds.The good plasticity of calcium silicate sheet is attributed to the silicate branch structure formation and the recovery role of interlayer calcium atoms.However,in z direction,C-S-H layers connected by the unstable H-bonds network,have the weakest tensile strength 2.2 GPa.This results in the brittle failure mode in z direction.The relatively low tensile strength and poor plasticity in z direction provides molecular insights into the tensile weakness of cement materials at macro-level.

Synthesis of Calcium Silicate Hydrate based on Steel Slag with Various Alkalinities

This study aimed to improve the hydraulic potential properties of the slag. Therefore, a method of dynamic hydrothermal synthesis was applied to synthesize calcium silicate hydrate. The phases and nanostructures were characterized by XRD, FTIR, TEM, and BET nitrogen adsorption. The infl uence of alkalinity of steel slag on its structures and properties was discussed. The experimental results show that, the main product is amorphous calcium silicate hydrate gel with fl occulent or fi brous pattern with a BET specifi c surface area up to 77 m2/g and pore volume of 0.34 mL/g. Compared with low alkalinity steel slag, calcium silicate hydrate synthesized from higher alkalinity steel slag is prone to transform to tobermorite structure.

Influence of Hydrothermal Synthesis Conditions on the Formation of Calcium Silicate Hydrates:from Amorphous to Crystalline Phases

Hydrothermal treatment has been widely applied in the synthesis of well crystalline calcium silicate hydrate（CSH）, such as tobermorite and xonotlite. However, both morphology and crystallinity of CSH are greatly affected by the conditions of hydrothermal treatment including siliceous materials, temperature increase rate and isothermal periods. In this study, the influence of hydrothermal conditions on the growth of nano-crystalline CSH was investigated based on XRD analysis. Results showed that siliceous materials with amorphous nature（i e, nano silica powder） are beneficial to synthesize pure amorphous CSH, while the use of more crystallized siliceous materials（i e, diatomite and quartz powder） leads to producing crystalline CSH. Results also indicate that the formation of tobermorite and xonotlite is greatly affected by the temperature rise rate during hydrothermal treatment.

Geotechnical investigation of low-plasticity organic soil treated with nano-calcium carbonate

Soil stabilization using nanomaterials is an emerging research area although,to date,its investigation has mostly been laboratory-based and therefore requires extensive study for transfer to practical field ap-plications.The present study advocates nano-calcium carbonate(NCC)material,a relatively unexplored nanomaterial additive,for stabilization of low-plasticity fine-grained soil having moderate organic content.The plasticity index,compaction,unconfined compressive strength(UCS),compressibility and permeability characteristics of the 0.2%,0.4%,0.6%and 0.8%NCC-treated soil,and untreated soil(as control),were determined,including investigations of the effect of up to 90-d curing on the UCS and permeability properties.In terms of UCS improvement,0.4%NCC addition was identified as the optimum dosage,mobilizing a UCS at 90-d curing of almost twice that for the untreated soil.For treated soil,particle aggregation arising from NCC addition initially produced an increase in the permeability coef-ficient,but its magnitude decreased for increased curing owing to calcium silicate hydrate(CSH)gel formation,although still remaining higher compared to the untreated soil for all dosages and curing periods investigated.Compression index decreased for all NCC-treated soil investigated.SEM micro-graphs indicated the presence of gel patches along with particle aggregation.X-ray diffraction(XRD)results showed the presence of hydration products,such as CSH.Significant increases in UCS are initially attributed to void filling and then because of CSH gel formation with increased curing.

Influence of Associated Cations on the Transport and Adsorption of Chloride Ions in the Nano-channel of Calcium Aluminosilicate Hydrate Gel:A Molecular Dynamics Study

Molecular dynamics simulation was utilized to investigate the transport and adsorption of chloride in the nanopore of calcium aluminosilicate hydrate(C-A-S-H)with associated cation types of Ca,Mg,Na and K.The local ionic structure,atomic dynamics and bond stability were analyzed to elucidate the interaction between cations and chloride ions.The results show that interfacial chloride is absorbed through the ion pairing formation in the vicinity of C-A-S-H substrate.Interfacial cations can simultaneously interact aluminosilicate chains,water molecules and Cl^(-)ions,which restrict the motion of interfacial Cl^(-)ions.Pore solution chloride can be immobilized through the solvation effect of cations.Cations along with their hydration shell can connect to neighboring Cl^(-)ions to decrease their mobility.Owing to the varied ionic chemistry,cations show different interaction strength with neighboring water molecules and anions,which determines the chloride transport behavior in the nanopore of C-A-S-H.The chloride immobilization capacity of C-A-S-H nanopore with different associated cations is listed in following order:Mg^(2+)Ca^(2+)<Na^(+)≈K^(+),which agrees reasonably with previous experiments.

Unsaturated transport properties of water molecules and ions in graphene oxide/hydrated calcium silicate nanochannels:from basic principles to complex environmental performance effects

The problems of traditional concrete such as brittleness,poor toughness and short service life of concrete engineering under acid rain or marine environment need to be solved urgently.Hydrated calcium silicate(C-S-H)is a key component to improve the mechanical properties and durability of concrete.However,the traditional method of concrete material design based on empirical models or comparative tests has become a bottleneck restricting the sustainable development of concrete.The synthesis method,molecular structure and properties of C-S-H were systematically described in this paper;The interface structure and interaction of graphene oxide/calcium silicate hydrate(C-S-H/GO)were discussed.On this basis,the saturated and unsaturated transport characteristics of ions and water molecules in C-S-H/GO nanochannels under the environment of ocean and acid rain were introduced.The contents of this review provide the basis for improving the multi-scale transmission theory and microstructure design of concrete.It has important guiding significance for analyzing and improving the service life of concrete in complex environment.

Stress relaxation properties of calcium silicate hydrate:a molecular dynamics study

The time-dependent viscoelastic response of cement-based materials to applied deformation is far from fully understood at the atomic level.Calcium silicate hydrate(C-S-H),the main hydration product of Portland cement,is responsible for the viscoelastic mechanism of cement-based materials.In this study,a molecular model of C-S-H was developed to explain the stress relaxation characteristics of C-S-H at different initial deformation states,Ca/Si ratios,temperatures,and water contents,which cannot be accessed experimentally.The stress relaxation of C-S-H occurs regardless of whether it is subjected to initial shear,tensile,or compressive deformation,and shows a heterogeneous characteristic.Water plays a crucial role in the stress relaxation process.A large Ca/Si ratio and high temperature reduce the cohesion between the calcium-silicate layer and the interlayer region,and the viscosity of the interlayer region,thereby accelerating the stress relaxation of C-S-H.The effect of the hydrogen bond network and the morphology of C-S-H on the evolution of the stress relaxation characteristics of C-S-H at different water contents was elucidated by nonaffine mean squared displacement.Our results shed light on the stress relaxation characteristics of C-S-H from a microscopic perspective,bridging the gap between the microscopic phenomena and the underlying atomic-level mechanisms.

Effect of Calcium Aluminate Cement Variety on the Hydration of Portland Cement in Blended System

Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.