Tricalcium Silicate Phase Research Articles

Experimental Study on Calcination of Portland Cement Clinker Using Different Contents of Stainless Steel Slag.

In order to increase the utilization rate of stainless steel slag, reduce storage needs, and mitigate environmental impacts, this study replaces a portion of limestone with varying amounts of stainless steel slag in the calcination of Portland cement clinker. The study primarily examines the influence of stainless steel slag on the phase composition, microstructure, compressive strength, and free calcium oxide (ƒ-CaO) content of Portland cement clinker. The results show the following: (1) Using stainless steel slag to calcine Portland cement clinker can lower the calcination temperature, reducing industrial production costs and energy consumption. (2) With an increase in the amount of stainless steel slag, the dicalcium silicate (C2S) and tricalcium silicate (C3S) phases in Portland cement clinker initially increase and then decrease; the C3S crystals gradually transform into continuous hexagonal plate-shaped distributions, while the tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) crystal structures become denser. When the stainless steel slag content is 15%, the dicalcium silicate and tricalcium silicate phases are at their peak; the C3S crystals are continuously distributed with a relatively dense structure, and C3A and C4AF crystals melt and sinter together, becoming distributed around C3S. (3) As stainless steel slag content increases, the compressive strength of Portland cement clinker at 3 days, 7 days, and 28 days increases and then decreases, while ƒ-CaO content decreases and then increases. When the stainless steel slag content is 15%, the compressive strength at 28 days is at its highest, 64.4 MPa, with the lowest ƒ-CaO content, 0.78%. The test results provide a basis for the utilization of stainless steel slag in the calcination of Portland cement clinker.

Hydration behavior of an experimental tricalcium silicate/tetracalcium phosphate bio-cement in Streptococcus thermophiles bacterial solution in comparison with distilled water used as a root canal furcation perforation repair material

BackgroundThe aim of this study is to evaluate an experimental tricalcium silicate phase (C3S) and tetracalcium phosphate (TTCP) material to be used as a root canal furcation perforation repair. C3S and TTCP phases were synthesized in nano-size particles by firing the required molar ratios of chemically pure reactants by solid-state reactions at elevated temperatures. The influence of Streptococcus thermophilus bacterial medium on the hydration reaction characteristics and morphology of 1:1 composite material of C3S and TTCP in comparison with distilled water was studied. Setting time, micro-hardness, pH of immersion solution, calcium ion concentration, phosphorous ion concentration, XRD, FTIR, scanning electron microscopy and cytotoxicity of the synthesized composite were investigated, and also, its sealing ability in bacterial media and in distilled water was evaluated.ResultsThe results showed that curing of pastes in the bacterial medium did not inhibit the hydration process of the synthesized composite but surface softening due to the great acceleration and encapsulation effects of the highly ionized curing medium resulting in lower micro-hardness values. The dissolution of TTCP phase was also increased in the bacterial medium resulting in precipitation of more hydroxyapatite inside the more porous system of pastes cured in the bacterial solution which was also evident by a non-significant decrease in the sealing ability in bacterial medium.ConclusionsMixing of tricalcium silicate (C3S) and tetracalcium phosphate (TTCP) resulted in a mix that was stable in bacterial medium and could be used for root canal perforation repair.

Preparation and characterization of Portland cement clinker from sulfuric acid leaching residue of coal fly ash

This work reported a process for the preparation of Portland cement clinker from sulfuric acid leaching residue of coal fly ash. Aluminum and iron in fly ash were effectively leached by sulfuric acid leaching, and the silica was all concentrated in the acid leaching residue. The chemical analysis showed that the content of SiO2 in the leaching residue was 79.1% and the leaching residue contained a small amount of Al2O3, CaO and Fe2O3, which could replace clay as the raw material for the preparation of Portland cement clinker. The effects of main process conditions on the quality of prepared cement clinker were studied. The results showed that the burnability of the raw material with clinker rate value KH = 0.92, SM = 2.1, IM = 1.2 and leaching residue content of 26.98% was excellent and good. The mineralogical analysis and microscopic examination showed that the good quality clinker was obtained under the conditions of sintering temperature of 1450 °C and holding time of 60 min, and the tricalcium silicate phase was well developed. Based on this study, acid leaching residue of coal fly ash was viable as an effective, alternative raw material in Portland cement production.

Replacement of lime with industrial wastes in hot metal desulfurization mixtures

The steel production enhancement in recent decades has increased the solid waste generation in the steel plants. Due to the increase in the environmental policies stringency, efforts have been made to give them a more appropriate destination. In this context, the internal reuse of these materials is a solution often applied by the industry to reduce production costs and to decrease slag generation. Therefore, the aim of this research is to replace calcitic lime by limestone waste and KR slag in hot metal desulfurization, which are wastes from steel production. The KR slag is the waste generated by the desulfurization process in Kambara Reactor. Experimental desulfurization tests were carried out in a resistance furnace at a temperature of 1350?C, in an inert atmosphere with constant stirring of 500 rpm. Along with the tests, simulations were carried out with FactSage 7.0 software in order to obtain the phases present in each mixture at the working temperature and compare them with the practical results. It was found that the tricalcium silicate phase (3CaO?SiO2) was present in mixtures with lower desulfurization efficiency, which shows its kinetic limitation. The use of limestone waste proved to be more efficient than the use of KR slag.

Rheology and microstructure development of hydrating tricalcium silicate - implications for additive manufacturing in construction

Dielectric RheoSANS measurements are conducted on hydrating triclinic and monoclinic tricalcium silicate pastes with and without a sucrose admixture to simultaneously probe the changing microstructure by small angle neutron scattering (SANS), rheology, and electrical conductivity. The average total surface area of nanoscale calcium silicate hydrate (C-S-H), determined from fractal models fitted to SANS data, at the setting time is estimated to be (17.1(56)) m2 cm−3, independent of C-S-H polymorph or retardation of the hydration reactions. The growth rate of C-S-H with respect to the degree of hydration of the triclinic tricalcium phase is approximately 48 % less than the monoclinic tricalcium silicate phase, a result that may be attributed to the increased number of fine grains in the monoclinic C3S paste. Developing an understanding between the microstructural changes of cement paste and engineering material properties is a critical first step toward engineering cement phase compositions.

Development of Crystallinity of Triclinic Polymorph of Tricalcium Silicate.

Tricalcium silicate phase is one of the main components of modern Portland cements. One of the major industrial challenges in the field of cement production is mapping the influence of individual clinker minerals and their polymorphs on the properties of industrially produced clinkers. The primary goal of this work is to improve the fundamental knowledge of understanding the process of alite formation and development from a crystallographic point of view. This study focuses on the observation of the crystallization process of triclinic alite during the firing process, which to date has not been thoroughly described. The effects of a wide range of temperatures and sintering periods on crystallinity were assessed on samples fired in platinum crucibles in a laboratory furnace. X-ray analysis—together with calculation of crystallinity using Scherrer’s equation—was used for observing the crystallite size changes of T1 alite polymorph. According to the acquired results, among the most technologically and economically advantageous regimes of production of a high-quality triclinic alite is the temperature of 1450 °C and sintering time of two hours. The most significant changes in the crystallite size occurred within the first hour of sintering for the whole investigated temperature range.

The Application of 29Si NMR Spectroscopy to the Analysis of Calcium Silicate-Based Cement using Biodentine™ as an Example.

Biodentine is one of the most successful and widely studied among the second generation of calcium silicate-based endodontic cements. Despite its popularity, the setting reactions of this cement system are not currently well understood. In particular, very little is known about the formation and structure of the major calcium silicate hydrate (C-S-H) gel phase, as it is difficult to obtain information on this poorly crystalline material by the traditional techniques of powder X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy (FTIR). In this study, the hydration reactions of Biodentine are monitored by XRD, FTIR, isothermal conduction calorimetry and, for the first time, 29Si magic angle spinning nuclear magnetic resonance spectroscopy (29Si MAS NMR) is used to investigate the structures of the anhydrous calcium silicate phases and the early C-S-H gel product. XRD analysis indicated that the anhydrous powder comprises 73.8 wt% triclinic tricalcium silicate, 4.45 wt% monoclinic β-dicalcium silicate, 16.6 wt% calcite and 5.15 wt% zirconium oxide. Calorimetry confirmed that the induction period for hydration is short, and that the setting reactions are rapid with a maximum heat evolution of 28.4 mW g−1 at 42 min. A progressive shift in the FTIR peak maximum from 905 to 995 cm−1 for the O-Si-O stretching vibrations accompanies the formation of the C-S-H gel during 1 week. The extent of hydration was determined by 29Si MAS NMR to be 87.0%, 88.8% and 93.7% at 6 h, 1 day and 1 week, respectively, which is significantly higher than that of MTA. The mean silicate chain length (MCL) of the C-S-H gel was also estimated by this technique to be 3.7 at 6 h and 1 day, and to have increased to 4.1 after 1 week. The rapid hydration kinetics of Biodentine, arising from the predominance of the tricalcium silicate phase, small particle size, and ‘filler effect’ of calcite and zirconium oxide, is a favorable characteristic of an endodontic cement, and the high values of MCL are thought to promote the durability of the cement matrix.

Hydration and Physico-mechanical Properties of Blended Calcium Sulfoaluminate-belite Cement Made of Industrial By-products

Portland cement blended Calcium Sulfoaluminate-belite (CŜAB) cements were studied in order to improve its binding properties and workability for specific applications. The binders consisted of calcium sulfoaluminatebelite, Flue Gas Desulfurization-gypsum and Ordinary Portland Cement (OPC). In this research, effects of OPC contents (25, 50, 75 wt%) as a CŜAB replacement on hydration behaviors and physico-mechanical properties of the binders were observed. Used CŜAB cement was synthesized using industrial by-products viz., fly ash, Flue Gas Desulfurization-gypsum, Al-rich sludge as starting materials via hydrothermal-calcination method. The results revealed that the replacement of CŜAB cement with OPC extended the setting times of pastes. The reduction of hydration rate with higher OPC content was due to dilution of fast setting phases such calcium sulfoaluminate and mayenite. Hydration products of calcium sulfoaluminate cement were ettringite responsible for high early strength together with Al(OH)3. From 6 h onwards, hydration of tricalcium silicate phase from the OPC generated calcium silicate hydrate. Stratlingite was also found in low OPC content mix resulting from the reaction between the Al(OH)3 and either alite phase in OPC or belite phase in CŜAB cement. Ettringite could also react with Al(OH)3 to generate monosulfate at later ages. The calcium sulfoaluminate phase was mainly responsible for the early mechanical properties, while OPC played an important role to improve strength at later ages.

Electronic Origin of Doping-Induced Enhancements of Reactivity: Case Study of Tricalcium Silicate

Systematic manipulation of the reactivity of silicate materials in aqueous environment remains a challenging topic. Herein, by combining first-principles and reactive molecular dynamics simulations, we present a complete picture of the influence of impurity species on hydration reactivity, using the reactive triclinic tricalcium silicate phase as an example. We show that although initial hydration is influenced by the surface’s chemistry and structure, longer-term hydration is primarily controlled by proton transport through the bulk solid. Both shorter- and longer-term hydration processes are noted as being intrinsically correlated with electronic features. These outcomes provide the first direct evidence of the linkages between electronic structure and the longer-term (i.e., on the order of several nanoseconds) hydration behavior and sensitivity of hydrophilic crystalline materials and also offer a pathway to efficient compositional design for similar materials.

Effect of autoclaving and sintering on the formation of β-wollastonite

β-wollastonite (β-CaSiO3) was synthesized from rice husk ash and calcium carbonate, and a study of the effects of the autoclaving and sintering steps is presented here. Autoclaving and sintering at 8h and 2h yielded the β-wollastonite phase in full, with improved crystallinity. Nucleation between rice husk ash and calcium oxide occurred around 135°C, pressure 0.24MPa, and growth proved to be more crystalline after the ripening period. For shorter processing times, and for both unsintered and unautoclaved samples, cristobalite and unstable tricalcium silicate phases were present. Crystallite size was increased by longer sintering times but reduced by longer autoclaving times. The β-wollastonite obtained had a random branch-like structure. In conclusion, the introduction of the autoclaving step successfully obtained β-wollastonite from a reaction between rice husk ash and calcium oxide.

Predicting Electronic Structure in Tricalcium Silicate Phases with Impurities Using First-Principles

Tricalcium silicate (Ca3SiO5) is heavily used in industry as it is the most predominant constituent in Portland cement clinkers. In this work, using ab-initio calculations, we assess the ability of a large selection of substitutions to modify the electronic structure in the M3 polymorph of tricalcium silicate. We demonstrate the relation between electronic structure, hybridization of the impurity orbitals, and charge transfer from impurity atoms to the bulk material. Our work suggests that charge localization upon introducing impurities can passivate the reactive sites and several such substitutions are identified.

Microscopic investigation of modified hydration kinetics in tricalcium silicate paste and mortar strength caused by dicalcium silicate addition

It was recently revealed that some processes of hydrating tricalcium silicate are altered by the addition of dicalcium silicate. Previous neutron scattering results revealed two critical tri/dicalcium silicate compositions. At one composition, changes in the early time hydration kinetics were observed that result in the formation of more products (reflected in increased 28 day strength), despite dicalcium silicate being essentially unreactive at early times. At the other composition, changes in the early-time hydration kinetics were observed that correspond to reduced strength. The current work uses scanning electron microscope analysis with backscattered electron imaging of 50 day hydrated tri- and dicalcium silicate mortars to reveal that at the former critical composition increased hydration of the tricalcium silicate phase occurs, and at the latter critical composition, the amount of dicalcium silicate reacted is decreased.

Effect of TiO 2 on the hydration of tricalcium silicate

The hydration kinetics of titania-bearing tricalcium silicate phase have been studied. TiO 2-doped tricalcium silicate (C 3S) was obtained by repeated firing of calcium carbonate and quartz in the stoichiometric ratio of 3:1 in the presence of varying amounts of titanium dioxide from 0.5 to 6% by weight. The study revealed that the presence of up to 2% TiO 2 has an inhibiting effect on the rate of hydration of C 3S. One percent TiO 2 in C 3S marginally slows down the rate of hydration of tricalcium silicate up to approximately 2 days and then increases sharply to overtake the hydration rate of pure C 3S. Higher percentages of TiO 2 (>2%) in C 3S have a higher hydration rate than C 3S containing up to 2% TiO 2 from 1 h to 28 days. This is achieved by modification of the polymorphic form of C 3S and by the formation of CaOTiO 2 in the CaO-SiO 2-TiO 2 system.

Influence of titania on the formation of tricalcium silicate

The effect of titania on clinker formation has been studied by many researchers [1–5]. Its effect on the formation of pure tricalcium silicate phase and the formation of titanium compounds at 1450°C, has rarely been investigated. The present work relates to the investigation of the formation of titanium compounds in the C 3S-TiO 2, system and to find the polymorphic forms of C 3S. The study also attempts to establish the limit of incorporation of TiO 2 in C 3S at 1450°C, at different levels of TiO 2 in the concentration range of 0.5–6% of TiO 2. It is found that TiO 2 affects the polymorphic form differently at different concentrations. Up to 2% TiO 2, triclinic form, 4–5% TiO 2 monoclinic, and with 6% rhombohedral form is stabilized. TiO 2 is incorporated into C 3S up to 4.5% at 1450°C and beyond this limit a compound CaOTiO 2 is formed. Techniques used for the investigations are X-ray diffraction, optical microscopy (OM), scanning electron microscopy, with energy dispersive analysis of X-rays (EDAX) and chemical analysis.

Solid solution and hydration behaviour of magnesium-bearing tricalcium silicate phase

Saturation solubility of MgO in tricalcium silicate (C 3S) and the hydration kinetics of magnesia-bearing tricalcium silicate phase have been studied. MgO-doped C 3S was obtained by repeated firing of calcium carbonate and quartz in the stoichiometric ratio of 3:1 in the presence of varying amounts of MgO from 0.5 to 5% by weight. Elemental analysis and X-ray diffraction studies have revealed that up to 1.5% MgO goes in solid solution at 1450°C and the rest precipitates as periclase. Presence of 1% MgO marginally slows down the rate of hydration of tricalcium silicate up to about 20 h and then increases sharply to overtake the hydration rate of pure C 3S. Complete hydration could be achieved in 28 days for the doped sample, against 83% for the undoped C 3S in the same period. The study has been found useful in understanding the relationship between modified chemical/mineral composition and the hydration behaviour of magnesia-doped C 3S phase.

Effect of Fluorine and Magnesium on the Polymorphism of Tricalcium Silicate: A New Fluorine-Containing Tricalcium Silicate Superlattice

There is evidence both by XRPD and by TEM electron diffraction of the presence of a new tricalcium silicate phase containing fluorine with triclinic cell parameters a= 2.32(7), b= 0.71(3), c= 1.28(3) nm, α= 106.5(3), β= 90(1), γ= 118(1)°. It is a superlattice of the rhombohedral C3S, whose structure is probably deformed by the fluorine/oxygen substitution plus some calcium vacancies, the deformation being nevertheless smaller than that found in the triclinic polymorph of pure C3S. Magnesium proves to have an effect additional to that observed for fluorine probably because it fixes the fluorine to the silicate lattice.