Search

Salt lakes are major sources of dust. Formation of natural evaporitic salt crusts can reduce the dust efflux, but protection is dependent on environmental conditions and the mineralogical composition of lakebed deposits. Chemical stabilization with conventional additives can benefit in further reducing the dust efflux. These however disrupt the soils’ biogeochemical cycles which are reliant on intertwining pore networks—a perspective commonly overlooked by engineers. In making provision for an engineered thin, porous, and lightweight crust that limits the dust deflation and preserves the soil’s open structure, this work examines prospects of administrating a mixture of ground rubber (GR) from the waste tire and five grades of mediated colloidal nanosilica (NS) hydrosol to calcareous lake sand. This research presents evidence for interaction between carbonates in the sand and the added NS that yields a matrix of calcium silicate hydrates (C–S–H). It also presents SEM micrographs of novel honeycomb sand-GR open structures bonded with C–S–H units. The resulting sand-GR-NS mat offers reasonable unconfined compressive strength equal to levels seen in sand-NS systems, following a 28-day of curing. The preserved open network of pores functions as an ideal air and water conveyance system. Overall, a NS content in 15–25% mixed with 5% by weight of GR seems to have offered optimal strength and post-peak response.

To promote the engineering applications of high water backfill materials (HWBM) in mining, a series of experiments are performed to investigate the effects of the direct current (DC) electric field on the mechanic properties and electrical resistivity of HWBMs. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations, the influence of electrochemical treatment on the hydration products and the microstructure of the HWBM was studied. The results show that the peak strength, elastic modulus, deformation modulus and electrical resistivity of the HWBM samples all first increased and then decreased with the increasing of the potential gradient, and the peak points appeared when the potential gradient was 0.2 V/cm. The anisotropy of content of ettringite and calcium silicate hydrates (C–S–H) increased betweent the anodic and cathodic regions of samples. Meanwhile, microstructure in the anodic region of the samples was more stable after electrochemical treatment, which indicates that the different variation of mineralogical compositions and microstructures in different regions of the samples are the primary factors affecting the mechanic properties and electrical resistivity of the HWBM. Therefore, the electrochemical method is a potential technology to modify the engineering properties of the HWBM.

Alkali-activated materials (AAMs) are considered as promising alternatives to ordinary Portland cement (OPC). In order to obtain the further potentiality of AAMs in marine environments, calcium silicate slag (CSS)-based AAMs with tapwater and seawater as mixing water were synthesized, respectively. Then the effects of seawater on the mechanical properties, mineralogy and microstructure were investigated. The reaction between liquid sodium silicate and seawater was observed and analysed. The results show that the main reaction products of CSS-based AAMs are amorphous C-(A)-S-H gels no matter whether the mixing water is tapwater or seawater. However, the ion exchange reaction of Mg2+ in seawater and silicate anions in alkaline solution produced M-S-H gels and SiO2 gels. The concomitant decrease of the pH value and the soluble silica content of alkaline solution, as well as the coating effect of gel products on the unreacted particles partly hindered the further alkali-activation and strength development. The findings of this study indicated the possibility of using seawater as mixing water of AAMs in marine environments.

We carried out a series of silicate fractional crystallization experiments at lower mantle pressures using the laser‐heated diamond anvil cell. Phase relations and the compositional evolution of the cotectic melt and equilibrium solids along the liquid line of descent were determined and used to assemble the melting phase diagram. In a pyrolitic magma ocean, the first mineral to crystallize in the deep mantle is iron‐depleted calcium‐bearing bridgmanite. From the phase diagram, we estimate that the initial 33%–36% of the magma ocean will crystallize to form such a buoyant bridgmanite. Substantial calcium solubility in bridgmanite is observed up to 129 GPa, and significantly delays the crystallization of the calcium silicate perovskite phase during magma ocean solidification. Residual melts are strongly iron‐enriched as crystallization proceeds, making them denser than any of the coexisting solids at deep mantle conditions, thus supporting the terrestrial basal magma ocean hypothesis (Labrosse et al., 2007)., Key Points Experimental determination of lower mantle melting reltaions and phase diagram by laser‐heated diamond anvil cellOne third of a pyrolitic magma ocean would first crystallize iron‐depleted bridgmanite, than contains a substantial amounts of calciumCalcium concentration in liquidus bridgmanite is constant from 52 to 129 GPa, and delays the crystallization of calcium‐silicate perovskite

This study reports the first analytical study conducted on samples of fired bricks, bedding mortar and plaster layers collected from the catacombs of Ptolemy IV Philopator at Karnak temples, Upper Egypt. These unique constructions comprise three-level rectangular vaulted brick shrines that lined up in three passages. The microscopic particularities of the samples were assessed by digitalized optical handheld microscope, while the petrographic analysis was depicted by polarized light microscope. X-ray diffractometer was used to analyse some brick, mortar and plaster samples. The morphological description and microchemical analysis, on various points in the samples, were attained via the field-emission scanning electron microscope with an energy-dispersive X-ray spectrometer. Further, the molecular and vibrational attributions of some fragments and pigment grains were recognized using Fourier transform infrared spectrometer and Raman microspectrometer (µ-Raman). Results showed that the studied bricks were fired at low temperature using poor-calcium clays. The cross-sectional observation on the plaster layers defined three layers, which are mainly made up of calcium carbonate (calcite). Minerals of quartz, rutile, plagioclase feldspars and calcium silicate were identified, in varying proportions, in the studied plasters. Pigments as Egyptian blue, yellow ochre and red ochre were characterized along the plaster layers. Likely, the microscopic examination and the molecular analysis of the samples disclosed that “fresco” technique was used to decorate the catacombs.

We investigate the impact of minor iron content on the crystallization behavior and thermal stability of hydrothermally treated calcium silicates for insulation at high temperatures. The impurity content of the raw materials (micro silica and quicklime), particularly iron, varies greatly with the production site and method. In this work the porous calcium silicate is synthesized with a Ca/Si molar ratio of 1. To systematically study the iron impact on crystallization during synthesis of calcium silicates, we introduce different amounts of iron (Fe/Si = 0 to 0.013) into the reactants. Using Fourier transform infrared spectroscopy we find a pronounced decrease in the number of 3-bridging oxygen coordinated Si sites in the calcium silicate with increasing iron content. The X-ray diffraction results revealed that the fractions of tobermorite, calcite, and amorphous phases increase with iron content, whereas the fraction of xonotlite phase decreases. These phase changes affect the compressive strength and thermal shrinkage of the calcium silicates. The compressive strength decreases with increasing iron content until amorphous phase becomes dominant, and then it increases again. The shrinkage increases from 1.3% at 1050 °C for the reference sample, to 30.4% for the sample with Fe/Si = 0.01. We discuss why such a small amount of iron can greatly affect the crystal structure of calcium silicates and deteriorate the physical performances of final products. Therefore, the iron contamination of raw materials should be avoided to ensure high temperature stability of porous calcium silicates.

Trivalent dysprosium (Dy 3+ ) ions -doped calcium silicate (Ca 2 SiO 4 ) phosphors have been synthesized by utilizing agricultural waste of egg shell and rice husk through solid-state reaction method. The synthesized Ca 2 SiO 4 powders thus obtained are crystallized in monoclinic structure with unit cell parameters of a = 5.53 A; b = 6.67 A; c = 9.13 A; β = 87.43° and irregular shape morphology. Luminescent properties of Dy 3+ :Ca 2 SiO 4 phosphors were studied by varying active ion concentration. The phosphors emit characteristic blue and yellow emissions of Dy 3+ ions corresponding to the 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 transitions, respectively. Color coordinates evaluated from emission spectra are found to fall in the white light region. Decay curves for the 4 F 9/2 level of Dy 3+ ions exhibit single exponential nature and turn into non-exponential with shortening of lifetime from 739 µs to 510 µs when Dy 3+ ion concentration is increased from 0.001 to 0.5 mol%. All these results confirm that Ca 2 SiO 4 :Dy 3+ phosphors are suitable for the use as low cost white light emitting phosphors.

In recent years, cement composites based on calcium silicate have been more generally considered for medical applications. Calcium silicate Cement are among the categories that are used in dental root canal treatment. The aim of this study is to make new calcium silicate cement with dicalcium phosphate and chitosan additives to preserve and strengthen desirable properties of this type of cements. In this study, composite dental cement based on calcium silicate was prepared. Then effect of adding biodegradable and biocompatible polymer such as chitosan on setting properties and its structure were studied. In this study, a combination of calcium silicate, dicalcium phosphate (DCP) and bismuth oxide (Bi2O3) as powder phase and 2% solution of the chitosan dissolved in 1% acetic acid solution as liquid phase, was used. As well as control sample was obtained by mixing the powder with distilled water as the liquid phase. Based on the obtained results, setting time of composite cement was changed from 51 to 67 minutes by adding chitosan polymer. Presence of chitosan also reduced the compressive strength a little. The bioactivity of the cement were studied in a solution of simulated body fluid (SBF) for 14 days. The samples were analyzed by SEM to identify the microstructure and by XRD to determine crystal structure. The composition of cement before incubation in SBF was included early phases (phase calcium silicate and calcium phosphate) that after 14 days of immersion in SBF, they were converted to layer-shaped hydroxy apatite and the presence of chitosan had not any influence on the final phase of hydroxy apatite.

A series of 5, 10 and 20 mol% zinc substituted for calcium bioceramics with composition of CaO–ZnO–SiO 2 –P 2 O 5 were successfully prepared by sintering the sol–gel-derived powders. The effects of zinc on samples structure, dissolution behavior and apatite-forming ability were comprehensively investigated by means of X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray technique (SEM/EDX) and in vitro tests. The results indicated that with more zinc substitution, calcium silicate phases of Ca 3 (Si 3 O 9 ) and β-Ca(SiO 3 ) gradually disappeared, whereas new phases of Ca 2 ZnSi 2 O 7 , SiO 2 and ZnSiO 4 were induced. Moreover, the samples dissolution rate decreased and the apatite-forming ability was delayed, suggesting that a controlled rate of dissolution and apatite formation of CaSiO 3 –Ca 2 ZnSi 2 O 7 -based bioceramics can be achieved.

Hydration of minerals, playing fundamental role in many technological applications, involves multi-stage chemical reactions, morphology changes and compositional variations. For the first time, the hydration mechanism for the tricalcium silicate was investigated by the combination of C3S hydration experimentally and polymerization of silicate monomers via molecular dynamics simulation. Tricalcium silicate was self-synthesized and utilized to hydrate with water at the water/solid ratio of 50. Samples hydrated from one day to one year were obtained and characterized by XRD, IR, SEM, NMR and TEM techniques. Based on SEM observation, the morphology of hydrated C3S transformed from small localized to foil-like wrinkled clusters with fibrillar-like wrinkles distributed randomly. Wrinkled product of C-S-H possessed poor-crystallined or amorphous feature based on XRD and TEM analysis. Such was also evidenced by the fact that no layered crystal phase was observed in simulated calcium silicate gel clusters. Besides, the simulated pair distribution function of C-S-H gel demonstrating the structure feature of short range order and long range disorder, also confirmed glassy structural nature for the C-S-H gel. Furthermore, based on NMR and SEM results C/S ratio changed to 1.2 and the mean silicate chain length in C-S-H was obtained at around 4 after hydration for one year with Q1 and Q2 species representing linear silicate chain structure present dominantly. The molecular dynamics helped illuminate the hydration mechanism that the morphology of C-S-H gel was closely related with C/S ratio. At C/S ratio of 1, solid branched 3-dimmensional cluster was segregated from the solution while ellipsoid colloid particle with the size of 4 nm × 4 nm × 8 nm was formed at C/S ratio of 1.75. It was also found that calcium ions prevented the polymerization reaction of silicate monomers and silicate chains were shortened significantly at high Ca/Si ratio, amplifying the predominate percentage of Q1 species in the C-S-H gel.

In Na2O–CaO–SiO2–H2O system, systematic investigations of phase and morphology of calcium silicate in hydrothermal conditions were concisely conducted for high-value utilization of silicon resource in high-alumina fly ash (HAFA). The results show that crystal composition and phase may be affected by relatively low concentration of NaOH, and sodium ions are rearranged into the structure to form NaCaHSiO4 and Na2Ca3H8Si2O12 with different C/S ratio at high concentration of NaOH. In addition, phases in wollastonite group possess the morphology of nanofiber. Formation of nanofiber is attributed to the difference of surface energies between axial and radial direction, and higher temperatures lead to easier growth along radial direction. The preparation of C–S–H with different phases and morphologies can guide for the application of silicate solution with high alkalinity with different purposes.

Honey powder is a hygroscopic powder due to its composition and structure. The addition of anti-caking agent was aimed to increase the stability of honey powder. The present study aimed to study the influence of anti-caking agent on the water sorption isotherm and flow-ability properties of vacuum dried honey powder. Anti-caking agents, calcium silicate and calcium stearate, were added in honey powder. The addition of anti-caking agent influenced water sorption and flow-ability properties of honey powder. Calcium silicate addition seemed not to affect water sorption isotherm properties of honey powder, however, calcium stearate showed more inhibiting effect of recrystallization and collapse of structure of amorphous honey powder. Addition of anti-caking agent to honey powder increase flow-ability of honey powder and calcium stearate seemed to increase flow-ability better than calcium silicate.

In the course of an exploratory study on the quaternary system Na2O-K2O-CaO-SiO2 single crystals of the first anhydrous sodium potassium calcium silicate have been obtained from slow cooling of a melt in the range between 1250 and 1050 °C. Electron probe micro analysis suggested the following idealized molar ratios of the oxides for the novel compound: K2O:Na2O:CaO:SiO2 = 1:1:12:8 (or KNaCa6Si4O15). Single-crystal diffraction measurements on a crystal with chemical composition K1.08Na0.92Ca6Si4O15 resulted in the following basic crystallographic data: monoclinic symmetry, space group P 21/c, a = 8.9618(9) A, b = 7.3594(6) A, c = 11.2453(11) A, β= 107.54(1)°, V = 707.2(1) A3, Z = 2. Structure solution was performed using direct methods. The final least-squares refinement converged at a residual of R(|F|) = 0.0346 for 1288 independent reflections and 125 parameters. From a structural point of view, K1.08Na0.92Ca6Si4O15 belongs to the group of mixed-anion silicates containing [Si2O7]- and [SiO4]-units in the ratio 1:2. The mono- and divalent cations occupy a total of four crystallographically independent positions located in voids between the tetrahedra. Three of these sites are exclusively occupied by calcium. The fourth site is occupied by 54(1)% K and 46%(1) Na, respectively. Alternatively, the structure can be described as a heteropolyhedral framework based on corner-sharing silicate tetrahedra and [CaO6]-octahedra. The network can build up from krohnkite-like [Ca(SiO4)2O2]-chains running along [001]. A detailed comparison with other A2B6Si4O15-compounds including topological and group-theoretical aspects is presented.

Background/Purpose Calcium silicate (CS) cements have excellent bioactivity and can induce the bone-like apatite formation. They are good biomaterials for bone tissue engineering and bone regenerative medicine. However, they have degradability and the dissolved CS can cause the inflammatory response at the early post-implantation stage. The purpose of this study was to design and prepare the curcumin-loaded mesoporous CS (MesoCS/curcumin) cements as a strategy to reduce the inflammatory reaction after implantation. Methods The MesoCS/curcumin cements were designed and prepared. The characteristics of MesoCS/curcumin specimens were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their physical properties, biocompatibility, and anti-inflammatory ability were also evaluated. Results The MesoCS/curcumin cements displayed excellent biocompatibility and physical properties. Their crystalline characterizations were very similar with MesoCS cements. After soaking in simulated body fluid, the bone-like apatite layer of the MesoCS/curcumin cements could be formed. In addition, it could inhibit the expression of tumor necrosis factor-α (TNF-α) and interleukin-1 (IL-1) after inflammation reaction induced by lipopolysaccharides and had good anti-inflammatory ability. Conclusion Adding curcumin in MesoCS cements can reduce the inflammatory reaction, but does not affect the original biological activity and properties of MesoCS cements. It can provide a good strategy to inhibit the inflammatory reaction after implantation for bone tissue engineering and bone regenerative medicine.

The mineral carbonation (MC) curing of cement-based materials could be employed to obtain both CO2 sequestration and accelerated strength gain. But there is still absence of understanding on the gas-solid reaction kinetics and mechanisms. This study aims to improve the understanding of gas-solid reaction between CO2 and cement-based materials during the MC curing, and evaluate the feasibility of blending calcium silicate (CS) as intensified addition. Based on the accelerated carbonation experiments, the impact of different factors (pressure, temperature and water-to-binder rate) on the reaction rate and the CO2 uptake were systematically investigated. The MC curing showed significant diffusion-controlled kinetics and the reaction gradually turned into the stable product-layer diffusion controlling process. The evolution process of kinetics indicated the increasingly dense structure of cement matrix, as verified by SEM analysis. The blended CS was found to significantly enhance the reaction rate and CO2 uptake capacity, accompanied with the intensified carbonation conversion of cement components. The increased Klinkenberg permeability of blended CS paste after MC curing demonstrated the diluted effect of CS. In terms of the practical feasibility, MC curing also contributed remarkably to the compressive performance improvement of cement paste with blended CS.

Chemical comparisons of powder and hydrated forms of calcium silicate cements (CSCs) and calculation of alterations in tricalcium silicate (Ca3SiO5) calcium hydroxide (Ca(OH)2) are essential for understanding their hydration processes. This study aimed to evaluate and compare these changes in ProRoot MTA, Biodentine and CEM cement. Powder and hydrated forms of tooth coloured ProRoot MTA, Biodentine and CEM cement were subjected to X-ray diffraction (XRD) analysis with Rietveld refinement to semi-quantitatively identify and quantify the main phases involved in their hydration process. Data were reported descriptively. Reduction in Ca3SiO5 and formation of Ca(OH)2 were seen after the hydration of ProRoot MTA and Biodentine; however, in the case of CEM cement, no reduction of Ca3SiO5 and no formation of Ca(OH)2 were detected. The highest percentages of amorphous phases were seen in Biodentine samples. Ettringite was detected in the hydrated forms of ProRoot MTA and CEM cement but not in Biodentine.

High-temperature annealing of hydrated forms of calcium silicate produced in the multicomponent system CaCl 2 Na 2 SiO 3 H 2 O yields the formation of a heterophase structure containing high-temperature phases of pseudo-wollastonite and silica. Under these conditions, it is observed that there is an increase in the calcium silicate crystal lattice energy, particle size, reflection coefficient in the visible and near-IR spectral ranges, and radiation stability of the synthesized powders. The improved characters make the work useful, interesting and important.

Aim To evaluate the abilities of three calcium silicate-based pulp-capping materials (ProRoot MTA, TheraCal LC, and a prototype tricalcium silicate cement) to produce apatite-like precipitates after being subcutaneously implanted into rats. Methodology Polytetrafluoroethylene tubes containing each material were subcutaneously implanted into the backs of Wistar rats. At 7, 14, and 28 days post-implantation, the implants were removed together with the surrounding connective tissue, and fixed in 2.5% glutaraldehyde in cacodylate buffer. The chemical compositions of the surface precipitates formed on the implants were analyzed with scanning electron microscopy-electron probe microanalysis (SEM-EPMA). The distributions of calcium (Ca) and phosphorus (P) at the material-tissue interface were also analyzed with SEM-EPMA. Comparisons of the thicknesses of the Ca- and P-rich areas were performed using Friedman test followed by Scheffe's test at a significant level of 5%. Results All three materials produced apatite-like surface precipitates containing Ca and P. For each material, elemental mapping detected a region of connective tissue in which the concentrations of Ca and P were higher than those seen in the surrounding connective tissue. The thickness of this Ca- and P-rich region exhibited the following pattern: ProRoot MTA > prototype tricalcium silicate cement ≥ TheraCal LC. ProRoot MTA had a significantly thicker layer of Ca and P than the other materials at all time points (P < 0.05), and a significant difference was detected between the prototype cement and TheraCal LC at 28 days (P < 0.05). Conclusions After being subcutaneously implanted, all of the materials produced Ca- and P-containing surface precipitates and a Ca- and P-rich layer within the surrounding tissue. The thickness of the Ca- and P-rich layer of ProRoot MTA was significantly thicker than that of the other materials. This article is protected by copyright. All rights reserved.

Compared with the traditional partition board, the superior properties of calcium silicate board are attributed to the generation of tobermorite, which can be influenced by many preparation conditions. The purpose of this study is to investigate the effect of Ca/Si ratio, and some others factors on the preparation and formation of tobermorite in calcium silicate board. The results reveal that the optimal cement content is 72%, at this time, Ca/Si ratio in calcium silicate board reaches 1.22. The tobermorite will gradually fade away when Ca/Si ratio continues to increase. XRD and mercury intrusion porosimetry after compression molding demonstrate that the molding pressure has mainly no effect on the hydration production and only has improvement on the structure of specimens. Due to the transformation of hydration production, autoclaved curing time and curing temperature should be controlled in specific range of 4–8 h and 190–195 °C, respectively. Additionally, the strength tests in different preparation factors present that the synthesis conditions confirmed in this paper are very promising to be applied in calcium silicate board.

There are a variety of applications for glasses in alkaline environments, including glass fibers and glass-coated steel to reinforce concrete structures. To understand how a simple glass reacts in such environments, the dissolution behavior of a 25Na2O-25B2O3-50SiO2 (mole%) glass, doped with and without 3 mole% P2O5, in pH 12 KOH and pH 12 KOH saturated with Ca2+ ions was studied. Ca2+ ions in the solution significantly reduce the glass dissolution rate by forming a passivating calcium silicate hydrate (C-S-H) gel layer on the glass surface. When these corroded glasses were then exposed to Ca-free KOH, the C-S-H layer re-dissolves into the undersaturated solution and the glass dissolution rate increases. For phosphate-doped borosilicate glass, PO43- units released from the dissolving glass react with Ca2+ ions in saturated solutions to form crystalline hydroxylapatite on the glass surface, but this layer does not protect the glass from corrosion as well as the C-S-H does. The nature of the C-S-H layer was characterized by Raman spectroscopy, which reveals a gel layer constituted mainly of silicate anions. This article is protected by copyright. All rights reserved.

The structural stability and anti-deforming capability of borophene and graphene-filled calcium silicate (C 2 S) for cement-based materials are studied by employing molecular dynamic simulations. By analyzing and comparing their various potential energies, it is found that the introduction of borophene or graphene into C 2 S can effectively improve its structural stability, make the complex nanosheets cling tightly together, and enhance the ability to resist deformation of the configuration at high temperature, especially for borophene-filled calcium silicate (C 2 S-B). Structural analyses on the above complexes at a high compression strain (14.06%) and a high temperature (1000 K) indicate that the graphene-filled calcium silicate (C 2 S-G) has the best pressure resistance and the C 2 S-B has the greatest high temperature tolerance, while C 2 S is always the worst. The results indicate that filling graphene and borophene in calcium silicate can significantly improve the structural stability and enhance the resistance to compressive and high temperature.

Three kinds of novel diatomite/ground calcium carbonate composite humidity control materials were prepared with different calcination temperatures using diatomite and ground calcium carbonate (GCC) as raw materials. The microstructure and morphology properties of samples were studied by nitrogen gas adsorption, mercury intrusion porosimetry (MIP) and fractal dimensions on the basis of gas adsorption isotherms with FHH methods. Fourier transform infrared spectroscope (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the mineral composition and surface properties. Furthermore, X-ray diffraction (XRD), thermo-gravimetry and differential scanning calorimetry (TG-DSC) were used to analyze the formation mechanism of composite material. It was indicated that DG750 showed the better moisture adsorption performance. The 72 h moisture adsorbed amount of DG750 reached 11.66%, 8.81% and 8.00% at 98%RH, 85%RH and 75%RH, respectively, which improved about 0.46, 0.54 and 0.53-fold as those of diatomite. The hydrophilic calcium silicate, calcium oxide and calcium hydroxide were formed in the DG750 during the calcinations process. As compared with the raw materials, the content of mesoporous component increases in the DG750, which is in favor of capillary condensation and improving moisture adsorption ability.

This work focuses on the synthesis of calcium silicate insulating material via solid state reaction using avian eggshell waste as alternative calcium source. The calcium silicate formulations were mixed in a molar ratio SiO2:CaO (1:1) and fired at 1100 °C for 24 h. The calcium silicate formulations were characterized by XRD, TG-DTA, dilatometry, SEM/EDS, and thermophysical properties (thermal diffusivity, heat capacity per unit volume, and thermal conductivity). The synthesized calcium silicate materials are composed mainly of wollastonite with minor amounts of larnite and rankinite. It was found that a processing of the avian eggshell waste (raw eggshell waste and calcined eggshell waste) had an influence on the thermophysical properties. Calcium silicate pieces were prepared by uniaxial pressing at 82 MPa, curing, and then testing to determine their use as thermal insulating material. The microstructure was evaluated by SEM. The results showed that both raw and calcined avian eggshell wastes could be used as an alternative calcium source in the calcium silicate formulation. It was found that the calcium silicate pieces reached low thermal conductivity values (0.252–0.293 W/mK). Thus, the developed calcium silicate materials using avian eggshell waste act as a good thermal insulation ceramic material.

The influence of aluminum additive on the thermal stability and hydration peculiarities of calcium silicate hydrates were determined. Calcium silicate hydrates were synthesized in the primary mixtures with the molar ratios of CaO/(SiO2 + Al2O3) = 1.5 and Al2O3/(SiO2 + Al2O3) = 0 or 0.05. The hydrothermal synthesis has been carried out in unstirred suspensions under saturated steam pressure in argon atmosphere at 175 °C temperature for 24 h by applying extra argon gas (10 bar). It was estimated that after 24 h of synthesis, the intensities of diffraction peaks and the quantity of α-C2SH were close, suggesting that Al2O3 additive have no influence on the quantity of formed α-C2SH. It was determined that Al2O3 additive changes not only the sequence of the formed compounds, but also their stability during the calcination in the temperature range 100–1000 °C. It was estimated that pure sample and sample with Al2O3 additive are stable till 400 °C. Meanwhile, in the higher temperature of calcination (450 °C), both samples fully recrystallized to anhydrous C2S phases: x-C2S and calcium olivine; at the same time, the crystallinity of sample with Al2O3 additive was 1.37 times higher. The microcalorimetry and the crystallinity studies show strong direct dependence of α-C2SH samples reactivity on the level of its amorphization. The best results were obtained after calcination at 450 °C, intensive exothermic effect with the maximum (~4.25 mW g–1), appeared after ~4.5 h, and cumulative heat after 70 h–188.92 J g–1. The addition of Al2O3 during synthesis did not influence significantly the initial hydration stage: the first exothermic peak was found to be analogous to that of pure system. However, in further heat flow evolution, the two-step hydration process was observed: The first weak peak (~1.0 W g–1) appeared after ~4 h of hydration and was followed by second acceleration of reaction rate after ~5.5 h. The obtained results were confirmed by the simultaneous thermal analysis, microcalorimetry, and X-ray diffraction analysis.

In this work, an artificially tunable luminescence emitting Ca2SiO4 based Eu2+ ions doped phosphor was successfully developed using differently aged propylene glycol modified silane (PGMS) as the silica source. The powder XRD patterns of all the prepared samples confirm the presence of three different crystal phases namely αL′, β & γ, which afford for the variable site accommodation of Eu2+ dopant in the host. Prototype phosphor converted LEDs (pc-LEDs) have also been fabricated using all the prepared phosphors. Photoluminescent and electroluminescent properties were investigated for the synthesized phosphors and prototype pc-LEDs, respectively. Colorimetric properties such as CIE coordinates, CCT and CRI values calculated to compare the effects of differently aged PGMS on the Eu2+ doped Ca2SiO4 phosphor, which confirmed the ability to produce color tuning with ageing of silicate source. The results indicate that these phosphors are potential candidates to use in solid state lighting applications.

Development of 3D porous scaffolds with proper mechanical strength is crucial in bone tissue engineering. In this study, calcium sulfate hemihydrate (CSH) cement was functionally incorporated into mesoporous calcium silicate (MCS) through a 3D printing technique in order to improve the scaffold strength. Compared to printed MCS scaffolds, the characterizations revealed that 20% CSH incorporation had enhanced their compressive strength by 2 times via 4 weeks' hydration. Furthermore, CSH incorporation prevented the fast pH value rise and achieved a balanced degradation rate. SEM observations showed a good apatite formation on the surfaces of both MCS and MCS/CSH scaffolds. Cellular experiments demonstrated no significant differences between MCS and MCS/CSH scaffolds in promoting osteoblast-like cell (OCT-1) adhesion, alkaline phosphatase (ALP) activity, proliferation and bone-related gene expressions. Furthermore, MCS component in the composite scaffolds exhibited sustained release behavior of dexamethasone drugs to assist bone regeneration.

International audience; Climate changes are inducing a modification of environmental loads on historical sites, requiring new actions towards their conservation. In the paper, the results of an experimental work on sustainable improvement of a pyroclastic soil belonging to the Orvieto cliff (Central Italy) have been investigated in the perspective of its preservation from degradation. The slightly coherent facies of Orvieto Ignimbrite (pozzolana) was treated with hydrated lime and the subsequent chemo-physical evolution was investigated by means of a multi-scale analysis. The beneficial effects obtained from the improvement in terms of mechanical behaviour were interpreted and correlated to the chemo-physical evolution of the system. Microstructural analyses, X-ray diffractometry, thermo-gravimetric analyses (DTG), SEM observations, mercury intrusion porosimetry performed on raw and treated samples, showed that the pozzolanic reactions develop since the very beginning in the system and that the observed mechanical improvement of the treated soil is mainly due to the formation of calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH). In the paper, the mechanical improvement is put in evidence by comparing the results of oedometer tests performed on both raw and treated samples.

Radon generated in the earth’s crust enters the pore spaces and transported by diffusion, then released into the surrounding atmosphere. Grain size is one of the important factors that effect on the radon exhalation rate from the soil. Radon emanates through the soil grains into air and diffuses to the atmosphere. The variation in radon concentration and exhalation rate from calcium silicate rock samples with different grain size were measured using Alpha Track Detector. The high value of radon exhalation rate was 43.05 ± 2.17 at gravel size and the lowest value was 8.98 ± 0.85 at mud size. The results indicate that the exhalation rate was increased with increase the grain size of the studied samples. The obtained values of radon exhalation rate for all the samples are found to be under the radon exhalation rate limit reported worldwide, and UNSCEAR. The present study is important to radiological impact assessment of requiring information on the exposure due to natural radiation to protect the environment.

Scientific reports 9(1), 7898 (2019). doi:10.1038/s41598-019-44326-9, Calcium carbonate is a relevant constituent of the Earth’s crust that is transferred into the deep Earth through the subduction process. Its chemical interaction with calcium-rich silicates at high temperatures give rise to the formation of mixed silicate-carbonate minerals, but the structural behavior of these phases under compression is not known. Here we report the existence of a dense polymorph of Ca$_5$(Si$_2$O$_7$)(CO$_3$)$_2$ tilleyite above 8 GPa. We have structurally characterized the two phases at high pressures and temperatures, determined their equations of state and analyzed the evolution of the polyhedral units under compression. This has been possible thanks to the agreement between our powder and single-crystal XRD experiments, Raman spectroscopy measurements and ab-initio simulations. The presence of multiple cation sites, with variable volume and coordination number (6–9) and different polyhedral compressibilities, together with the observation of significant amounts of alumina in compositions of some natural tilleyite assemblages, suggests that post-tilleyite structure has the potential to accommodate cations with different sizes and valencies, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

This work focuses on the thermal characterization of a calcium silicate-based material synthesized with different solid wastes (chamotte and marble) for use as thermal insulation material. Thermal and structural changes occurring during heating were accompanied by differential thermal analysis, thermogravimetric analysis, dilatometric analysis, open photoacoustic cell technique, X-ray diffraction (XRD), and scanning electron microscopy. An endothermic event at 823.2 °C was interpreted as decomposition of carbonates. An exothermic event around 900 °C is associated with the crystallization of calcium silicate phases mainly wollastonite. The themophysical properties of the calcium silicate-based material (thermal diffusivity, thermal conductivity, specific thermal capacity, and thermal effusivity) are influenced by the synthesis temperature. The thermal analysis results agree well with the XRD. The calcium silicate pieces presented low thermal conductivity values (0.227−0.376 W m−1 K−1). These results suggest that the calcium silicate-based materials produced essentially with chamotte and marble wastes has high potential to be used as thermal insulation construction material.

Marly clay was treated with calcitic and Mg-rich lime in order to determine the influence of the clay's high carbonate content on the stabilization effectiveness. The evolution of mineralogical and physical properties over the course of the treatment were studied using XRD, TEM, SEM, elemental analysis, TG, granulometry, and nitrogen sorption and correlated with the marly clay's improved geotechnical behaviour. Only a small portion of smectites and other clay minerals dissolved upon lime treatment. Changes in clay mineralogy had, thus, only very limited influence in the improvement of the material's plasticity and swelling behaviour, which was rather modified by an increase in particle size. This increase was primarily caused by aggregation induced by calcium silicate aluminium hydrate (C-(A)-S-H) formation, whereas flocculation had an only minor effect. After the initial improvement, disaggregation of clay particles occurred which resulted in a particle size decrease, most likely, caused by carbonation of C-(A)-S-H phases. These findings question the effectiveness of lime stabilization for marl using currently applied standard treatment protocols.

Chloride is known to volatilize from silicate glass melts and until now, only a limited number of studies on oxychloride silicate glasses have been reported. In this paper we have synthesized silicate glasses that retain large amounts of CaCl2. The CaCl2 has been added to the calcium metasilicate composition (CaO·SiO2). Glasses were produced via a melt quench route and an average of 70% of the chloride was retained after melting. Up to 31.6 mol% CaCl2 has been successfully incorporated into these silicate glasses without the occurrence of crystallization. 29Si MAS-NMR spectra showed the silicon being present mainly as a Q2 silicate species. This suggests that chloride formed Cl-Ca(n) species, rather than Si-Cl bonds. Upon increasing the CaCl2 content, the Tg reduced markedly from 782 °C to 370 °C. Glass density and glass crystallization temperature decreased linearly with an increase in the CaCl2 content. However, both linear regressions revealed a breakpoint at a CaCl2 content just below 20 mol%. This might be attributed to a significant change in the structure and is also correlated with the nature of the crystallizing phases formed upon heat treatment. The glasses with less than 19.2 mol% CaCl2 crystallized to wollastonite, whilst the compositions with CaCl2 content equal to or greater than 19.2 mol% are thought to crystallize to CaCl2. In practice, the crystallization of CaCl2 could not occur until the crystallization temperature fell below the melting point of CaCl2. The implications of the results along with the high chloride retention are discussed.

We study calcium silicate glass of composition (CaO)X(SiO2)(1−X), where X = 40–70 mol%, by means of molecular dynamics for different cooling rates between 1011–1013 K s−1. The thermodynamic and kinetic properties of calcium silicate materials are determined, discussed, and correlated to local structures at short and intermediate range orders and to the potential energies of the oxygen atoms. We show that the amount of non-bridging oxygens and the appearance of free oxygens are related to the increase of the glass transition temperature for an increasing CaO content. Our results are analyzed and discussed in connection with the available experimental data.

Aim: Calcium silicate cements are widely used in endodontics. Novel fast-setting calcium silicate cement with fluoride (Protooth) has been developed for potential applications in teeth crowns including cavity lining and cementation. Objective: To evaluate the surface apatite-forming ability of Protooth compositions as a function of fluoride content and immersion time in phosphate-buffered saline (PBS). Material and methods: Three cement compositions were tested: Protooth (3.5% fluoride and 10% radiocontrast), ultrafast Protooth (3.5% fluoride and 20% radiocontrast), and high fluoride Protooth (15% fluoride and 25% radiocontrast). Powders were cap-mixed with liquid, filled to the molds and immersed in PBS. Scanning electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy were used to characterize the precipitations morphology and composition after 1, 7, 28, and 56 days. Apatite/belite Raman peak height indicated the apatite thickness. Results: Spherical calcium phosphate precipitations with acicular crystallites were formed after 1-day immersion in PBS and Raman spectra disclosed the phosphate band at 965 cm−1, supporting the apatite formation over Protooth compositions. The apatite deposition continued and more voluminous precipitations were observed after 56 days over the surface of all cements. Raman bands suggested the formation of β-type carbonated apatite over Protooth compositions. High fluoride Protooth showed the most compact deposition with significantly higher apatite/belite ratio compared to Protooth and ultrafast Protooth after 28 and 56 days. Conclusions: Calcium phosphate precipitations (apatite) were formed over Protooth compositions after immersion in PBS with increasing apatite formation as a function of time. High fluoride Protooth exhibited thicker apatite deposition.

Although lime is one of the most suitable binders in soil improvement projects, the associated environmental impact and some accompanying mechanical deficiencies should not be ignored. Partial substitution of lime with other binders is one of the ways of reducing the associated harm and improving the engineering properties of lime. This study investigated the effect of the partial substitution of lime with ground granulated blast furnace slag (GGBFS) on the strength and mechanical properties of lime stabilised clay by performing a total of 246 volumetric shrinkage strain (VSS), unconfined compressive strength (UCS) and ring shear (RS) tests. The VSS results demonstrated that the addition of GGBFS to lime is very effective in reducing the volumetric shrinkage of lime stabilised clay, and that the reduction in volumetric shrinkage behaviour is linearly related to curing period. The UCS results revealed that the partial replacement of lime with GGBFS led to significantly higher compressive strength for all ageing periods. The ring shear results also demonstrated that the partial replacement of lime with GGBFS led to a greater shear strength. Moreover, microstructural studies were performed to better understand the reactions of the mixtures. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) carried on selected specimens revealed that the addition of GGBFS in a lime stabilised clay results in production of the cementitious products in a faster rate. X-ray powder diffraction (XRD) test results revealed that the main hydration products are cementitious products such as calcium silicate hydrates (CSH), calcium aluminates (CAH).

In this study the possibility of using alternative waste materials with cementitious properties was studied. Lime rich sludge (LRS) (solid waste of acetylene industry), ground granulated blastfurnace slag (GGBFS) and fine kaolinite sand (FKS) (by-product during kaolin mineralization) were used in the production of cementitious building materials. Different mixes were prepared using percentage weight ratios 80/20, 75/25, 70/30 of GGBFS and LRS, respectively, at water/cement ratio of 0.20 by weight. Fine kaolinite sand (5 wt%) was used as addition in these mixes. The mechanical and hydration characteristics of the prepared pastes were studied at various time intervals up to 90 days. The results showed that LRS acts as an alkaline activator for GGBFS and the optimum mix composition for activation was 75% GGBFS and 25% LRS. Addition of fine kaolinite sand (FKS) to these mixes resulted in a marked improvement in the hydraulic properties especially in the early hydration ages; this is related to the higher rate of pazzolanic interaction between the lime in LRS and the aluminosilicate constituents in fine kaolinite sand leading to formation of excessive amounts of calcium silicate hydrates (CSH) which act as binding centers between the remaining unhydrated parts of GGBFS and FKS. XRD patterns and DSC thermograms obtained for all pastes showed that the main hydration products are nearly amorphous and microcrystalline calcium silicate hydrates as well as minor amounts of calcium aluminosilicate hydrates.

Red mud, the Bayer process residue, is generated from alumina industry and causes environmental problem. In this paper, a novel calcification-carbonation method that utilized a large amount of the Bayer process residue is proposed. Using this method, the red mud was calcified with lime to transform the silicon phase into hydrogarnet, and the alkali in red mud was recovered. Then, the resulting hydrogarnet was decomposed by CO2 carbonation, affording calcium silicate, calcium carbonate, and aluminum hydroxide. Alumina was recovered using an alkaline solution at a low temperature. The effects of the new process were analyzed by thermodynamics analysis and experiments. The extraction efficiency of the alumina and soda obtained from the red mud reached 49.4% and 96.8%, respectively. The new red mud with

Magnesium silicate hydrate (M-S-H) gel can be fabricated via the reaction of MgO with silica fume in the presence of sodium hexametaphosphate (Na-HMP). In this study, in effort to reduce the cost of the M-S-H gel system, pulverized fuel ash (PFA) was utilized as a silica source to replace silica fume. The influence of various PFA quantities on the compression strength and other properties of the M-S-H system were investigated via XRD, SEM, and TG-RTG analysis. Compressive strength was optimal when 35 wt% of silica fume was replaced. The hydration products were relatively more complex when PFA was used, containing hydrated calcium silicate, hydrated magnesium silicate, and carbonate gel, among other products. Magnesium carbonate participated in the hydration reaction process, which generated carbonated gel to form a grid structure and promoted the initial strength of the material. Taken together, the results showed that PFA can be feasibly and effectively used to form M-S-H gel cement systems at low cost.

New amorphous calcium silicate binders, hydraulically active, were produced by a process consisting in fully melting and rapid cooling of a mixture of typical raw materials (limestone, sand, fly-ash and electric furnace slag) with overall CaO/SiO2 molar ratios (C/S) comprised between 1.1 and 1.25. Pastes were produced from these materials by mixing them with water in a water/binder ratio of 0.375. Compressive strength was determined at the ages of 7, 28 and 90 days and the hydration of these pastes was followed during this period by XRD, FTIR and 29Si MAS-NMR. Tobermorite-like structures with low C/S and semi-crystalline character were observed to develop upon hydration of these new amorphous calcium silicate hydraulic binders. Moreover, no Portlandite was formed during hydration of these materials. The maximum compressive strength after 90 days is above 40 MPa. TGA was performed in order to determine the amount of structural water present in the pastes and their content related to the amount of hydrated products obtained. The relation between compressive strength and the amount of hydration products was investigated and some considerations about the mechanical properties of the hydration products and paste microstructure were inferred.

The composite cement mixtures were prepared by mixing brushite (B) with, the amorphous hydrated calcium silicate phosphate (CSPH) or annealed calcium silicate phosphate (CSP composed of Si-saturated hydroxyapatite, wollastonite and silica) phases and water as liquid component. The contents of the silicate-phosphate phase in composites were 10.30 and 50 wt%. The significant effect of both the Ca/P ratio and different solubility of calcium silicate phosphate component in starting cement systems on setting time and phase composition of the final composite cements was demonstrated. The compressive strength of the set cements increased with the filler addition and the highest value (~ 48 MPa) exhibited the 50CSP/B cement composite. The final setting times of the composite cements decreased with the CSPH addition from about 25 to 17 min in 50CSHP/B and setting time of CSP/B composites was around 30 min. The higher content of silica in cements caused the precipitation of fine hydroxyapatite particles in the form of nanoneedles or thin plates perpendicularly oriented to sample surface. The analysis of in vitro cement cytotoxicity demonstrated the strong reduction in cytotoxicity of 10CSPH/B composite with time of cultivation (a low cytotoxicity after 9 days of culture) contrary to cements with higher calcium silicate-phosphate content. These results were attributed to the different surface topography of composite substrates and possible stimulation of cell proliferation by the slow continuously release of ions from 10CSPH/B cement.

The hydration of ternary blended cements comprising Portland cement, metakaolin and blast-furnace slag was studied at different temperatures of 30, 40, 50 and 60 °C by isothermal calorimetry. Phase composition of hydration products was determined by thermal analysis and X-ray diffraction for sample hydrated at 60 °C. Hydration involves different sequential and successive reactions in which mechanism, kinetics and products are strongly influenced by temperature. Activation energy for each exothermic reaction was determined. The linear trend of heat flow maxima for 2nd, 3rd and 4th exotherm versus temperature was revealed. The first peak is related to formation of mostly amorphous aluminate hydrates with no evidence of crystalline ettringite. Formation of first crystalline ettringite detected by X-ray diffraction was correlated with the distinct 3rd peak that occurs after 2nd “silicate” peak that corresponds to formation of calcium silicate hydrates and calcium hydroxide. The 4th peak recognizable at temperatures above 40 °C is related to the conversion of ettringite to hemicarbonate.

In the present report, a bioactive glass was synthesized from silica sand as economic substitute to alkoxy silane reagents. Sodium metasilicate (Na2SiO3) obtained from the sand was hydrolyzed and gelled using appropriate reagents before sintering at 950 °C for 3 h to produce glass in the system SiO2Na2OCaOP2O5. Compression test was conducted to investigate the mechanical strength of the glass, while immersion studies in simulated body fluid (SBF) was used to evaluate reactivity, bioactivity and degradability. Furthermore, the glass samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDX) to evaluate the microstructure and confirm apatite formation on the glass surface. The glass, dominated by bioactive sodium calcium silicate, Na2Ca2Si3O9 (combeite) crystals, had mechanical strength of 0.37 MPa and showed potentials for application as scaffold in bone repair.

This study aims to investigate the effect of modifying tricalcium silicate (TCS) cements on three key properties by adding ZrO2. TCS powders were prepared by adding ZrO2 at six different concentrations. The powders were mixed with 1 M CaCl2 solution at a 3:1 weight ratio. Biodentine (contains 5 wt.% ZrO2) served as control. To evaluate the potential effect on mechanical properties, the mini-fracture toughness (mini-FT) was measured. Regarding bioactivity, Ca release was assessed using ICP-AES. The component distribution within the cement matrix was evaluated by Feg-SEM/EPMA. Cytotoxicity was assessed using an XTT assay. Adding ZrO2 to TCS did not alter the mini-FT (p = 0.52), which remained in range of that of Biodentine (p = 0.31). Ca release from TSC cements was slightly lower than that from Biodentine at 1 day (p > 0.05). After 1 week, Ca release from TCS 30 and TCS 50 increased to a level that was significantly higher than that from Biodentine (p 0.05). EPMA revealed a more even distribution of ZrO2 within the TCS cements. Particles with an un-reacted core were surrounded by a hydration zone. The 24-, 48-, and 72-h extracts of TCS 50 were the least cytotoxic. ZrO2 can be added to TCS without affecting the mini-FT; Ca release was reduced initially, to reach a prolonged release thereafter; adding ZrO2 made TCS cements more biocompatible. TCS 50 is a promising cement formulation to serve as a biocompatible hydraulic calcium silicate cement.

Calcium silicate materials have attracted a great deal of interest because of their osteogenesis. The purpose of this study was to use the hydrothermal method without the use of ethanol and an acidic medium to synthesize calcium silicate powder. After mixing the powder with water, the in vitro bioactivity and osteogenesis of calcium silicate cements were examined in comparison with the cement prepared by the sol–gel route. The morphology, phase composition, weight loss, and diametral tensile strength of the cement after soaking in a simulated body fluid (SBF) for different time periods were assayed. Human fetal osteoblasts (hFOBs) cultured on the cement surfaces were used to evaluate the in vitro osteogenesis. The results indicated that after 1 day of soaking in SBF, a precipitated apatite layer was found on the two cement surfaces. Notably, although the two cements were derived from the different powder technologies, there were no significant differences (P>0.05) in bioactivity including phase evolution, morphology change, strength variation, and degradation between cements during soaking in SBF. The hydrothermally-derived calcium silicate cement showed similar cell attachment, proliferation, differentiation, and mineralization expressions compared to the sol–gel-derived cement, but being higher than those obtained in the tissue culture plate. The present results suggest that the calcium silicate cements prepared by a hydrothermal method had an excellent bioactivity and osteogenesis and may be suitable for bone repair.

Density functional theory (DFT) simulations are carried out to systemically investigate doping in dicalcium silicate (Ca2SiO4: C2S), a major phase in calcium silicate cements. By evaluating the energetics of defect formation mechanisms for species involving Na+, K+, Mg2+, Sr2+, Al3+, Fe3+, B3+, and Ge4+, we find a strong site preference for all cationic substitutions. As a result, distinct defects form at low dopant concentrations (i.e., ≤ 0.52 atom %), in which, expectedly, larger dopants prefer (larger) Ca2+ sites, while smaller dopants favor (smaller) Si4+ sites, with charge balance being ensured by the formation of vacancies. Such site preferences arise due to local atomic distortions, which are induced when doping occurs at unfavorable substitution sites. Interestingly, we note that the formation enthalpy of each substitutional defect is proportional to the size mismatch between the dopant and the native cations. This indicates that the destabilization of the C2S structure has its origins in an “atom...

Pure β-dicalcium silicate and monocalcium aluminate powder were prepared by Pechini method. A series of calcium silicate/calcium aluminate cements (CSC/CAC) were prepared. The setting time, crystal...

Calcium silicate slag is an alkali leaching waste generated during the process of extracting Al2O3 from high-alumina fly ash. In this research, a cementitious material composed of calcium silicate slag was developed, and its mechanical and physical properties, hydration characteristics and environmental friendly performance were investigated. The results show that an optimal design for the cementitious material composed of calcium silicate slag was determined by the specimen CFSC7 containing 30% calcium silicate slag, 5% high-alumina fly ash, 24% blast furnace slag, 35% clinker and 6% FGD gypsum. This blended system yields excellent physical and mechanical properties, confirming the usefulness of CFSC7. The hydration products of CFSC7 are mostly amorphous C-A-S-H gel, rod-like ettringite and hexagonal-sheet Ca(OH)2 with small amount of zeolite-like minerals such as CaAl2Si2O8·4H2O and Na2Al2Si2O8·H2O. As the predominant hydration products, rod-like ettringite and amorphous C-A-S-H gel play a positive role in promoting densification of the paste structure, resulting in strength development of CFSC7 in the early hydration process. The leaching toxicity and radioactivity tests results indicate that the developed cementitious material composed of calcium silicate slag is environmentally acceptable. This study points out a promising direction for the proper utilization of calcium silicate slag in large quantities.

Road construction is one of the most material-intensive industrial production. In this context, the urgent task for this branch is the maximum reduction in consumption of materials through usage of effective local materials, decrease energy intensity of processes by using new materials. The developed network of local roads require constant care and maintenance, thus it is advisable to consider the use of protective coatings for such roads on the basis of contactcondensation hardening, which can be obtained on the basis of local raw materials. One of the representatives of such material is disperse hydrated calcium silicate, which found wide practical application as the main components in the production of building materials, glass, glass ceramics and ceramic products. For example, relatively cheap highly dispersed crystalline material is intermediate product of hydrochemical synthesis of wollastonite xonotlite Ca 6 (Si 6 O 17 )(OH) 2 . A variety of calcium and silicon-containing raw materials, suitable to obtain various types hydrated calcium silicate, as well as increasing requirements for physical and chemical properties, caused by actuality of problems of search and study the best ways of synthesis hydrated calcium silicate from man-made and natural materials. The theoretical basis of the proposed technology for material production for road pavement lower categories is the ability of silicate dispersed materials transferred in an unstable state, forming a rock-like waterproof body at the time of application of mechanical load. Disperse hydrated calcium silicate are the most typical representatives of contactcondensation hardening binders. It should be noted that the technology of obtaining these binders is not related to high-temperature processes and the synthesis of HCS realized when wet treatment of available cheap raw materials on the standard equipment, what determines their practical significance.

In this work, the influence of the mineral composition of the synthesized calcium silicate hydrates on their hydraulic activity after thermal treatment was determined. Primary mixture, consisting of quartz sand and burnt limestone (CaO/SiO2 = 2), was treated hydrothermally with NaOH additive at 200 °C. It was determined that α-C2SH prevailed in the product after 4 h of the synthesis. The results of DSC and XRD analysis revealed that α-C2SH was partially decomposed after 12 h of the synthesis and newly formed compounds were identified—killalaite, portlandite and C–S–H. The products of 4 and 12 h synthesis were treated thermally at temperatures between 450 and 1000 °C. It was determined that dellaite and x-C2S formed already at 450 °C, β-C2S at 600 °C and α′L-C2S at 800 °C when the 4 h synthesis product, in which α-C2SH prevailed, was treated thermally. On the other hand, killalaite remained stable up to 600 °C, and the temperature values, at which mentioned calcium silicates formed, increased in case of a 12 h synthesis product. Heat flow values of the main hydration reaction and total heat release exceeded 3.1 mW g−1 and 140 J g−1 accordingly in case of the samples in which α-C2SH prevailed. However, increase in the thermal treatment temperature resulted in a decrease in the mixtures hydraulic activity. It was proved that killalaite formation in the product of the 12 h hydrothermal synthesis vividly decreases its hydraulic activity after the thermal treatment in the temperature range of 450–1000 °C. No increment in the heat flow values that could be attributed to the main hydration reaction (acceleration period) was witnessed in all the curves of the heat flow analysis in this case.