Search Results (17)

γ-dicalcium silicate (γ-C₂S) is a carbonatable binder with excellent carbonation reactivity. However, its extremely low hydration activity prevents the paste from setting and hardening properly, making it difficult to be directly cast and molded. This study introduces β-hemihydrate gypsum as an early-strength regulating agent, which utilizes its rapid hydration to form dihydrate gypsum, thereby imparting early-age strength to the composite system and enabling subsequent carbonation curing after demolding. The experimental investigation examined the effects of β-hemihydrate gypsum content on the fluidity, setting time, and carbonation performance of γ-C₂S paste. The results indicate that when the β-hemihydrate gypsum content is not less than 10%, the paste can obtain sufficient early-age strength to achieve smooth demolding. At a β-hemihydrate gypsum content of 10%, after pre-drying treatment, samples subjected to carbonation curing for 24 h under a CO₂ partial pressure of 0.3 MPa achieved a peak absolute dry compressive strength of 117.29 MPa with a softening coefficient of 0.92. Further increases in β-hemihydrate gypsum content lead to reductions in both strength and water resistance. Microstructural analysis reveals that at a gypsum content of 10%, the crystalline network of dihydrate gypsum interlocks and coexists with calcium carbonate and silica gel generated from γ-C₂S carbonation, forming a compact structure. In contrast, the framework formed by excessive gypsum before carbonation restricts the continuous interlocking and overall development of calcium carbonate products generated from γ-C₂S, resulting in deterioration of structural integrity and mechanical properties. This study provides theoretical foundation and technical support for the engineering application of γ-C₂S-based carbon mineralization materials. Full article

This study investigates the impact of different temperatures and initial Mg²⁺/Ca²⁺ molar ratios in the solution on the wet-accelerated carbonation of β-dicalcium silicate (β-C₂S). The x-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), thermogravimetric analyzer (TGA), and field emission scanning electron microscopy (FE-SEM) analysis results indicated that temperature and the Mg²⁺/Ca²⁺ molar ratio are key factors in the nucleation of aragonite. Aragonite formed at a temperature above 60 °C, and the high temperature promoted the crystallinity of needle-like aragonite with a length of 1–6 μm and a diameter of ~1 μm. Moreover, 80 °C was the most favorable temperature for the formation of aragonite with a large aspect ratio in the carbonation system of β-C₂S. Mg²⁺ had a significant effect on inhibiting the transformation of aragonite to calcite and promoting the stability of aragonite. Aragonite became the dominant CaCO₃ polymorph instead of calcite when the Mg²⁺/Ca²⁺ molar ratio was above 1.0, and pure aragonite-style calcium carbonate was formed at a Mg²⁺/Ca²⁺ molar ratio of 1.5. Full article

This paper investigates the structural transformation of dicalcium silicate (C₂S) crystals brought about through boron doping. Both qualitative and quantitative analyses were conducted to explore the correspondence between boron content and the structure of dicalcium silicate. The results show that boron doping can stabilize β-C₂S and the high-temperature phase α′_H-C₂S, and the structural transformation does not involve the modulation of α′_L-C₂S. There is a corresponding relationship between the unit cells of β-C₂S and α′_H-C₂S, which can be transformed using a transformation matrix. The relationship between boron content and the content of different C₂S structures, as well as the structural expressions for β-C₂S and α′_H-C₂S, is determined using linear fitting and multivariable linear regression analysis. Full article

In order to high-value utilize the secondary solid waste calcium silicate slag (CSS) generated in the process of the extraction of alumina from fly ash, in this paper, tobermorite was synthesized using CSS and silica fume (SF) at different hydrothermal synthesis times. The hydrothermal synthesis was evaluated by means of XRD, SEM, EDS, and micropore analysis, and the results discussed. The results indicate that β-dicalcium silicate, the primary phase in the CSS, partially hydrates at the beginning of hydrothermal synthesis conditions to form mesh-like crystal C-S-H (calcium-rich) and calcium hydroxide. It then reacts with SF to form yarn-like crystal C-S-H (silicon-rich) and then furtherly grows into large flake-like crystal C-S-H (silicon-rich) at 3 h. When the synthesis time is 4 h, β-dicalcium silicate completely hydrates, and crystal C-S-H (calcium-rich) and calcium hydroxide further reacts with large flake-like crystal C-S-H (silicon-rich) to generate medium flake-like tobermorite. With the increase in time, the crystal of hydrothermal synthesis grows in the order of medium flake-like tobermorite, small flake-like tobermorite, strip flake-like tobermorite, fibrous-like tobermorite, and spindle-like tobermorite, and the APV, APD, and SSA show a trend of decreasing first, then increasing, and then decreasing. Meanwhile, strip flake-like tobermorite with a higher average pore volume (APV), average pore diameter (APD), and specific surface area (SSA) can be synthesized at 6 h. Full article

It is still a challenge to overcome the extended setting process of pure Ca-silicate as root canal fillers. We investigated the effects of attapulgite (a basic hydrous silicate of magnesium and aluminum) and ball-milling liquid medium on the self-curing properties of conventional β-dicalcium silicate (C2Si)-based cements. It was shown that a minor amount of attapulgite nanofibers (1–4%) had only a slight influence on setting time but caused a large increase in compressive resistance and structural stability. In particular, the ball milling media with different acetone/water ratios (3:0, 2:1, 1:2, 0:3) could directly influence the particle size distribution of C2Si powders, and the co-existence of liquid media (2:1 or 1:2) may be beneficial for shortening the setting time, enhancing early-stage compressive strength, and significantly improving the anti-microleakage ability of cement. Moreover, the composite cements also exhibited appreciable antibacterial efficacy in vitro. These findings demonstrated that the physicochemical properties of the Ca-silicate powders could be tuned by adding a minor amount of inorganic silicate nanofibers and a simple ball milling condition, and such a facile strategy is favorable for developing novel (pre-mixed) Ca silicate-based cements as root canal sealers. Full article

Considering the recent eco-friendly and efficient utilization of three kinds of solid waste, including calcium silicate slag (CSS), fly ash (FA), and blast-furnace slag (BFS), alkali-activated cementitious composite materials using these three waste products were prepared with varying content of sodium silicate solution. The hydration mechanisms of the cementitious materials were analyzed by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the composite is a binary cementitious system composed of C(N)-A-S-H and C-S-H. Si and Al minerals in FA and BFS are depolymerized to form the Q⁰ structure of SiO₄ and AlO₄. Meanwhile, β-dicalcium silicate in CSS hydrates to form C-S-H and Ca(OH)₂. Part of Ca(OH)₂ reacts with the Q⁰ structure of AlO₄ and SiO₄ to produce lawsonite and wairakite with a low polymerization degree of the Si-O and Al-O bonds. With the participation of Na⁺, part of Ca(OH)₂ reacts with the Q⁰ structure of AlO₄ and the Q³ structure of SiO₄, which comes from the sodium silicate solution. When the sodium silicate content is 9.2%, the macro properties of the composites effectively reach saturation. The compressive strength for composites with 9.2% sodium silicate was 23.7 and 35.9 MPa after curing for 7 and 28 days, respectively. Full article

Increasing attention is focused on developing biomaterials as temporary scaffolds that provide a specific environment and microstructure for bone tissue regeneration. The aim of the present work was to synthesize silicon-doped biomimetic multi-phase composite scaffolds based on bioactive inorganic phases and biocompatible polymers (poly(ε-caprolactone), PCL) using simple and inexpensive methods. Porous multi-phase composite scaffolds from cuttlefish bone were synthesized using a hydrothermal method and were further impregnated with (3-aminopropyl)triethoxysilane 1–4 times, heat-treated (1000 °C) and coated with PCL. The effect of silicon doping and the PCL coating on the microstructure and mechanical and biological properties of the scaffolds has been investigated. Multi-phase scaffolds based on calcium phosphate (hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate) and calcium silicate (wollastonite, larnite, dicalcium silicate) phases were obtained. Elemental mapping revealed homogeneously dispersed silicon throughout the scaffolds, whereas silicon doping increased bovine serum albumin protein adsorption. The highly porous structure of cuttlefish bone was preserved with a composite scaffold porosity of ~78%. A compressive strength of ~1.4 MPa makes the obtained composite scaffolds appropriate for non-load-bearing applications. Cytocompatibility assessment by an MTT assay of human mesenchymal stem cells revealed the non-cytotoxicity of the obtained scaffolds. Full article

The kinetics and mechanism of ternesite formation (calcium sulfosilicate, Ca₅(SiO₄)₂SO₄, C₅S₂$) were investigated by studying the reaction between beta-dicalcium silicate (β-C₂S) and calcium sulfate dihydrate (CaSO₄∙2H₂O). Mineralogical composition development was monitored using X-ray diffraction (XRD) and backscattered scanning electron microscopy (BSEM) coupled to energy-dispersive X-ray spectroscopy (EDS). Ternesite can form in the 1100 to 1200 °C range by the solid-phase reaction of β-C₂S and CaSO₄. The formation of ternesite is favored by increasing the sintering temperature or extending the sintering time. The solid-phase reaction is carried out by diffusion of CaSO₄ to β-C₂S. The kinetics equation of ternesite is consistent with three-dimensional diffusion models (3-D model, D3 model or Jander model). The equation of the D3 model is 1 − 2α/3 − (1 − α)^2/3 = kt. On the basis of the Arrhenius equation, the activation energy of ternesite is 239.8 kJ/mol. Full article

In order to realize high-value utilization of calcium silicon slag (CSS) and silica fume (SF), the dynamic hydrothermal synthesis experiments of CSS and SF were carried out under different hydrothermal synthesis temperatures. In addition, phase category, microstructure, and micropore parameters of the synthesis product were analyzed through testing methods of XRD, SEM, EDS and micropore analysis. The results show that the main mechanism of synthesis reaction is that firstly β-Dicalcium silicate, the main mineral in CSS, hydrates to produce amorphous C–S–H and Ca(OH)₂, and the environment of system is induced to strong alkaline. Therefore, the highly polymerized Si-O bond of SF is broken under the polarization of OH⁻ to form (SiO₄) of Q⁰. Next, amorphous C–S–H, Ca(OH)₂ and (SiO₄) of Q⁰ react each other to gradually produce various of calcium silicate minerals. With an increase of synthesis temperature, the crystal evolution order for calcium silicate minerals is cocoon-like C–S–H, mesh-like C–S–H, large flake-like gyrolite, small flake-like gyrolite, petal-like gyrolite, square flake-like calcium silicate hydroxide hydrate, and strip-like tobermorite. In addition, petal-like calcium silicate with high average pore volume (APV), specific surface area (SSA) and low average pore diameter (APD) can be prepared under the 230 °C synthesis condition. Full article

Dicalcium silicate is one of the main mineral phases of steel slag. Ascribed to the characteristics of hydration and carbonation, the application of slag in cement production and carbon dioxide sequestration has been confirmed as feasible. In the current study, the precipitation process of the dicalcium silicate phase in steel slag was discussed. Meanwhile, the study put emphasis on the influence of different crystal forms of dicalcium silicate on the hydration activity and carbonation characteristics of steel slag. It indicates that most of the dicalcium silicate phase in steel slag is the γ phase with the weakest hydration activity. The hydration activity of γ-C₂S is improved to a certain extent by means of mechanical, high temperature, and chemical activation. However, the carbonation activity of γ-C₂S is about two times higher than that of β-C₂S. Direct and indirect carbonation can effectively capture carbon dioxide. This paper also summarizes the research status of the application of steel slag in cement production and carbon dioxide sequestration. Further development of the potential of dicalcium silicate hydration activity and simplifying the carbonation process are important focuses for the future. Full article

The study mainly aims at the potential of Argon Oxygen Decarburization Slag (AODS) as a supplementary cementitious material and explores the mechanisms of stabilization/solidification (S/S) of chromium in cement-based composite pastes. The basic cementitious parameters, such as water requirement, setting time, soundness, hydration characteristics, and strength indexes of composite binders, were examined through standard methods. The results showed that the most beneficial mineral phase in AODS for cementitious behavior was beta dicalcium silicate (β-C₂S). The utilization of a higher AODS dosage in composite binders increased the water requirement and the setting time, while it decreased the hydration heat and the strength indexes. Although the AODS possessed limited cementitious properties, it conformed the Grade II steel slag powder qualified for concrete and cement. Sequential leaching tests were conducted targeting the leachability of chromium in the pastes with different AODS dosage and curing time. Results showed that with the lower AODS dosage and the longer curing time, the S/S efficiency for chromium leaching from the composite paste was better. Utilization of AODS as a cement substitute not only can recycle this solid waste and decrease the emission of CO₂ concerning cement production, but also helps to effectively reduce the chromium leaching risk. Full article

Calcium silicates are the most predominant phases in ordinary Portland cement, inside which magnesium is one of the momentous impurities. In this work, using the first-principles density functional theory (DFT), the impurity formation energy (E_for) of Mg substituting Ca was calculated. The adsorption energy (E_ad) and configuration of the single water molecule over Mg-doped β-dicalcium silicate (β-C₂S) and M3-tricalcium silicate (M3-C₃S) surfaces were investigated. The obtained Mg-doped results were compared with the pristine results to reveal the impact of Mg doping. The results show that the E_for was positive for all but one of the calcium silicates surfaces (ranged from −0.02 eV to 1.58 eV), indicating the Mg substituting for Ca was not energetically favorable. The E_ad of a water molecule on Mg-doped β-C₂S surfaces ranged from –0.598 eV to −1.249 eV with the molecular adsorption being the energetically favorable form. In contrast, the E_ad on M3-C₃S surfaces ranged from −0.699 eV to −4.008 eV and the more energetically favorable adsorption on M3-C₃S surfaces was dissociative adsorption. The influence of Mg doping was important since it affected the reactivity of surface Ca/Mg sites, the E_ad of the single water adsorption, as well as the adsorption configuration compared with the water adsorption on pristine surfaces. Full article

Vascularization is a crucial factor when approaching any engineered tissue. Vascular wall–mesenchymal stem cells are an excellent in vitro model to study vascular remodeling due to their strong angiogenic attitude. This study aimed to demonstrate the angiogenic potential of experimental highly porous scaffolds based on polylactic acid (PLA) or poly-e-caprolactone (PCL) doped with calcium silicates (CaSi) and dicalcium phosphate dihydrate (DCPD), namely PLA-10CaSi-10DCPD and PCL-10CaSi-10DCPD, designed for the regeneration of bone defects. Vascular wall–mesenchymal stem cells (VW-MSCs) derived from pig thoracic aorta were seeded on the scaffolds and the expression of angiogenic markers, i.e. CD90 (mesenchymal stem/stromal cell surface marker), pericyte genes α-SMA (alpha smooth muscle actin), PDGFR-β (platelet-derived growth factor receptor-β), and NG2 (neuron-glial antigen 2) was evaluated. Pure PLA and pure PCL scaffolds and cell culture plastic were used as controls (3D in vitro model vs. 2D in vitro model). The results clearly demonstrated that the vascular wall mesenchymal cells colonized the scaffolds and were metabolically active. Cells, grown in these 3D systems, showed the typical gene expression profile they have in control 2D culture, although with some main quantitative differences. DNA staining and immunofluorescence assay for alpha-tubulin confirmed a cellular presence on both scaffolds. However, VW-MSCs cultured on PLA-10CaSi-10DCPD showed an individual cells growth, whilst on PCL-10CaSi-10DCPD scaffolds VW-MSCs grew in spherical clusters. In conclusion, vascular wall mesenchymal stem cells demonstrated the ability to colonize PLA and PCL scaffolds doped with CaSi-DCPD for new vessels formation and a potential for tissue regeneration. Full article

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. Full article

β-dicalcium silicate (β-C₂S) minerals were prepared. The compositions, microstructures, and distributions of the carbonation products of hardened β-C₂S paste were revealed by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, and backscattered electron (BSE) image analysis. The results show that a dense hardened paste of β-C₂S can be obtained after 24 h of carbonation curing. The hardened pastes are composed of pores, silica gel, calcium carbonate, and unreacted dicalcium silicate, with relative volume fractions of 1.3%, 42.1%, 44.9%, and 11.7%, respectively. The unreacted dicalcium silicate is encapsulated with a silica gel rim, and the pores between the original dicalcium silicate particles are filled with calcium carbonate. The sufficient carbonation products that rapidly formed during the carbonation curing process, forming a dense microstructure, are responsible for the carbonation hardening of the β-C₂S mineral. Full article