Query: calcium silicate

title: Experimental and molecular dynamics studies on the transport and adsorption of chloride ions in the nano pores of calcium silicate phase: The influence of calcium to silicate ratios
abstract: Chloride transport in the gel pore determines the durability of concrete material. In this paper, experiments and molecular dynamics (MD) simulation were utilized to systematically investigate chemical composition (calcium to silicate ratio C/S) influence on the transport and adsorption behavior of water, calcium and chloride ions confined in the nano pores of calcium silicate hydrate (C S H) The immersion experiments indicate C S H samples with higher C/S ratio have better chloride adsorption capability and the zeta potential measurements proved the calcium ions can determine the surface potential in the system and strongly affect the chloride adsorption. In the MD simulation, with increasing C/S ratio, the long surface silicate chains are broken to defective short chains that can provide more non bridging oxygen sites to accumulate surface water molecules and calcium atoms. There existed strong spatial correlation between surface calcium and chloride ions in the radial distribution function patterns, which confirms that the surface calcium plays critical role in chloride adsorption. Furthermore, the interaction mechanism between calcium and chloride ions can be categorized into two parts, the stronger one caused by the formation of ionic pairs Ca Cl (within 3 A) and the weaker interaction at larger distance (around 4 6A) Therefore, high calcium concentration in the vicinity of surface contributes to stronger chloride adsorption, more Ca Cl accumulation and longer resident time.

title: Nucleation seeding with calcium silicate hydrate A review
abstract: The development of green cements, with the aim of reducing CO2 emissions, often results in reduced hydration activity, especially during the first hours and days. Nucleation seeding with C S H has enormous potential to accelerate hydration, which can compensate for the above mentioned effect without compromising the long term strength of seeded cements. In this work, the effects of calcium silicate hydrate are reviewed in detail, with a focus on synthesis, as well as their influence on the hydration mechanism and the development of mechanical properties, such as early and long term compressive strength and porosity.

title: Magnesium and calcium silicate hydrates, Part I: Investigation of the possible magnesium incorporation in calcium silicate hydrate (C S H) and of the calcium in magnesium silicate hydrate (M S H)
abstract: Calcium silicate hydrate (C S H) and magnesium silicate hydrate (M S H) have been described as two separate phases. This work investigates their stability domains and the possible uptake of small amounts of magnesium by C S H or, reversely, the uptake of small amounts of calcium by M S H. The phases, synthesized by co precipitation, are characterized using a large panel of techniques (thermogravimetry analysis, X ray diffraction, X ray pair distribution function analysis, 29Si MAS NMR spectroscopy, measurement of zeta potential and cation exchange capacity) while the compositions of the solutions at equilibrium are determined by ion chromatography and pH measurements. Syntheses of C S H samples in the presence of magnesium (Ca Mg)/Si 0.80 and Mg/Si 0.05 or 0.10) yield two separate phases: C S H and M S H. There is no experimental evidence of any uptake of magnesium by C S H. On the contrary, when M S H samples are synthesized in the presence of calcium (Ca Mg)/Si 0.80 and Ca/Si 0.05 or 0.10) the low pH of the suspension (9 10) prevents the formation of C S H but favors the precipitation of M S H with small amounts of calcium. This latter may be sorbed onto the surface of M S H to outbalance its negative charges and/or incorporated into the interlayer, as suggested by small structural changes.

title: Nanoscale origins of creep in calcium silicate hydrates
abstract: The time dependent response of structural materials dominates our aging infrastructure's life expectancy and has important resilience implications. For calcium silicate hydrates, the glue of cement, nanoscale mechanisms underlying time dependent phenomena are complex and remain poorly understood. This complexity originates in part from the inherent difficulty in studying nanoscale longtime phenomena in atomistic simulations. Herein, we propose a three staged incremental stress marching technique to overcome such limitations. The first stage unravels a stretched exponential relaxation, which is ubiquitous in glassy systems. When fully relaxed, the material behaves viscoelastically upon further loading, which is described by the standard solid model. By progressively increasing the interlayer water, the time dependent response of calcium silicate hydrates exhibits a transition from viscoelastic to logarithmic creep. These findings bridge the gap between atomistic simulations and nanomechanical experimental measurements and pave the way for the design of reduced aging construction materials and other disordered systems such as metallic and oxide glasses.The nanoscale mechanisms behind the creep of calcium silicate hydrates remain difficult to model over long periods of time. Here, the authors use a three staged incremental stress marching technique to tie atomistic simulations and nanomechanical experimental measurements together.

title: The Atomic Level Structure of Cementitious Calcium Silicate Hydrate
abstract: Efforts to tune the bulk physical properties of concrete are hindered by a lack of knowledge related to the atomic level structure and growth of calcium silicate hydrate phases, which form about 50 60% by volume of cement paste. Here we describe the first synthesis of compositionally uniform calcium silicate hydrate phases with Ca:Si ratios tunable between 1.0 and 2.0. The calcium silicate hydrate synthesized here does not contain a secondary Ca(OH)2 phase, even in samples with Ca:Si ratios above 1.6, which is unprecedented for synthetic calcium silicate hydrate systems. We then solve the atomic level three dimensional structure of these materials using dynamic nuclear polarization enhanced 1H and 29Si nuclear magnetic resonance experiments in combination with atomistic simulations and density functional theory chemical shift calculations. We discover that bridging interlayer calcium ions are the defining structural characteristic of single phase cementitious calcium silicate hydrate, inducing the strong

title: Are Premixed Calcium Silicate based Endodontic Sealers Comparable to Conventional Materials? A Systematic Review of In Vitro Studies
abstract: This study aimed to compare the physicochemical and biological properties of premixed calcium silicate based endodontic sealers with other conventional root canal filling materials by systematically reviewing laboratory studies.  The search was conducted in 3 databases (Medline via PubMed, Scopus, and Web of Science) following the Preferred Reporting Items for Systematic Reviews and Meta Analyses. Two reviewers independently selected the studies and extracted the data. The properties of interest were bond strength, radiopacity, pH, solubility, setting and working time, dimensional change, flow, calcium ion release, antimicrobial activity, biocompatibility, and cytotoxicity.  From 2636 potentially eligible studies, 31 were selected for full text analysis, and 27 were included in the review. Premixed calcium silicate based endodontic sealers followed the ISO 6876:2012 requirements for most physicochemical properties except for solubility. The target sealers also presented favorable biological findings when compared with conventional sealers.  Despite the lack of well designed long term clinical trials, the target premixed calcium silicate based sealers show good physicochemical and biological properties in vitro. In general, the results were similar or better than conventional endodontic sealers as observed in in vitro and in vivo animal studies. HighlightsCalcium silicate based sealers showed proper physicochemical properties.Calcium silicate based sealers presented optimal biological properties.

title: Influence of calcium to silica ratio on aluminium uptake in calcium silicate hydrate
abstract: Aluminium uptake in calcium silicate hydrate (C S H) was studied at different Ca/Si ratios from 0.6 to 1.6 at 20 degC. Aluminium incorporation in C S H depends on the total amount of aluminium present in the sample. At low Al/Si ratio 0.05) the major part of the aluminium is taken up in C S H while at higher Al/Si ratio, the precipitation of stratlingite and/or katoite limits the Al/Si ratio in C S H to 0.15, regardless of the Ca/Si ratio. A strong correlation between the aqueous aluminium concentration and the aluminium uptake in the solid phase is observed. At high Ca/Si ratios, aluminium in C S H is observed mainly as octahedrally coordinated Al(VI) in TAH and the aluminium uptake increases with the aqueous aluminium concentration. At low Ca/Si ratio 0.8) aluminium is observed mainly as tetrahedrally coordinated Al(IV) and low aqueous aluminium concentrations (below detection limit) indicate a high affinity of aluminium towards C S H.

title: Sol gel synthesis and characterizations of hybrid chitosan PEG/calcium silicate nanocomposite modified with ZnO NPs and (E102) for optical and antibacterial applications.
abstract: Hybrid Chitosan/Poly ethylene glycol/calcium silicate (CS/PEG/calcium silicate) nanocomposite modified with different two types, zinc oxide nanoparticles (ZnO NPs) and tartrazine dye (E102) were prepared by sol gel method and the characterization of their structure and biological properties were carried out in order to evaluate the possible use in optical and biomedical fields. The hybrid CS/PEG/calcium silicate complex formations have been established by X ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic analysis. The spheres like chitosan PEG/calcium silicate and modified with both ZnO NPs and (E102) were obtained with optimum concentration of 11% ZnO NPs and 0.3gm (E102) dyes. Spheres like particle shape of these nanocomposites from SEM images, higher UV absorption in the region of 200 300nm by UV vis absorption spectrophotometer are recorded. The fabricate CS/PEG/calcium silicate nanocomposites and doped with ZnO NPs and tetrazine were studied contrary to gram positive (Staphylococcus aureus) gram negative (Pseudomonas aeruginosa) bacteria, fungi (Candidia albicans) and Aspargillus niger via the agar plate method. The obtained results indicated that the prepared CS PEG/calcium silicate nanocomposites have good antibacterial properties agnist G+ve, G ve bacteria and fungi, so that it could be a promised candidate in various optical and in biological applications as well as packaging application.

title: Influence of the Ca/Si ratio on the compressive strength of cementitious calcium silicate hydrate binders
abstract: The relation between the chemical composition of calcium silicate hydrate (C S H) phases and its influence on the compressive strength of cementitious materials is investigated by a new approach where prisms of C S H phases have been synthesized directly by the reaction of calcium hydroxide, amorphous SiO2 and water. The synthesized samples employ molar Ca/Si ratios of 0.83, 1.0, 1.25 and 1.50, and the compressive strengths and age depending changes of the pastes have been followed for up to three months of hydration, after which the microstructures were characterized. The model pastes feature most characteristics of hydrated cements, including zones of different density but similar chemical composition. The experimental data demonstrates that the compressive strengths of the C S H pastes increase for decreasing Ca/Si ratio for all synthesized samples and testing ages. The molar volumes of the C S H phases decrease with decreasing Ca/Si ratio, which along with the related higher surface areas may partly explain the differences in strength development.

title: Effect of magnesium on calcium silicate hydrate (C S H)
abstract: The addition of MgCl2 to synthetic calcium silicate hydrate (C S H) with Ca/Si 0.8 lowers the pH values below 10. Experimental observations and thermodynamic calculations show the destabilization of C S H and the precipitation of magnesium silicate hydrate (M S H) In contrast, the addition of MgO to C S H increases the pH values up to 11.5 and the Ca/Si in C S H from 0.8 to 1.0. At high pH, the formation of M S H and brucite is observed experimentally. Less brucite is present at 50 than at 20 degC indicating a slow dissolution kinetic of brucite at 20 degC. Thermodynamic modelling is in good agreement with the changes in C S H and M S H formation in the presence of MgO although no brucite is predicted. M S H is observed in the presence of both MgCl2 and MgO, is stable from pH 7.5 to 11.5 and has a structure comparable to the structure of M S H prepared from MgO and SiO2 only.