Composition, silicate anion structure and morphology of calcium silicate hydrates (C-S-H) synthesized by silica-lime reaction and by the controlled hydration of tricalcium silicate (C3S)

The main product of Portland cement hydration is C-S-H. Despite constituting more than half of the volume of hydrated pastes and having an important role in strength development, very little is known about the factors that determine its morphology. To investigate the relationship between the chemical composition, silicate anion structure and morphology of C-S-H, samples were synthesized via silica-lime reactions and by the hydration of C3S under controlled lime concentrations and with/ without accelerators. The silicate anion structure of the samples was studied by 29Si MAS NMR and the morphology and chemical composition by TEM and SEM. All samples prepared via silica-lime reactions with bulk Ca/Si up to 1.5 were foil-like. The hydration of C3S at fixed lime concentration yielded foil-like C-S-H for [CaO]22mmol/L. A relationship between the silicate anion structure and the morphology of C-S-H was found for the samples fabricated with accelerators

Luminescent Ruthenium(II) Polypyridyl Functionalized Gold Nanoparticles; Their DNA Binding Abilities and Application As Cellular Imaging Agents

The synthesis and photophysical and biological investigation of Ru(II)-polypyridyl stabilized watersoluble, luminescent gold nanoparticles (AuNPs) are described. These structures bind to DNA and undergo rapid cellular uptake, being localized within the cell cytoplasm and nucleus within 4 h

Appearance of dark neurons following anodal polarization in the rat brain.

An anodal direct current of 3.0 microA or 30.0 microA was unilaterally applied for 30 min or 3 h to the surface of the sensorimotor cortex of rats, and the effects of polarization on the morphology of brain cells were examined by light microscopy. After five repeated anodal polarization trials, dark neurons appeared mainly in the polarized neocortex regardless of the intensity and duration of the polarizing currents. Such dark neurons were scarce in the control animals or the animals receiving only one trial of polarization. The dark neurons were most abundant in the second to fourth layers of the ipsilateral superior-lateral convexity of the frontal cortex, but a few were present in the contralateral cortex. The dark neurons began to appear 24 h after the last polarization; thereafter almost all of these neurons gradually reverted to their normal morphological profiles through a transitory state within 1 month of the last trial of repeated polarization. No morphological changes were apparent in any of the brain structures other than the cerebral cortex. These findings indicate that repeated anodal polarization has reversible morphological effects on the cortical neurons, suggesting that the appearance of dark neurons after anodal polarization is an important index for evaluation of cortical plastic change induced by polarization.</p

Hydration of cementitious materials, present and future

This paper is a keynote presentation from the 13th International Congress on the Chemistry of Cement. It discusses the underlying principles of hydration and recent evidence for the mechanisms governing this process in both Portland cements and other cementitious materials. Given the overriding imperative to improve the sustainability of cementitious materials, routes to reducing CO2 emissions are discussed and the impact of supplementary materials on hydration considered. (C) 2011 Elsevier Ltd. All rights reserved

Mechanisms and parameters controlling the tricalcium aluminate reactivity in the presence of gypsum.

International audienceTo understand the mechanisms and the parameters controlling the reactivity of tricalcium aluminate in the presence of gypsum at an early age, a study of the hydration of the “C3A–sulphate” system by isothermal microcalorimetry, conductimetry and a monitoring of the ionic concentrations of diluted system suspensions have been carried out with various gypsum quantities. The role of C3A source and its fineness were also studied. This work shows the fast initial formation of AFm phase followed by ettringite formation during the period when the sulphate is consumed. It has been highlighted that the time necessary to consume all the gypsum varies with the type of C3A and it has been attributed to the intrinsic reactivity of each one and mainly to the change of fineness from one C3A to another. Results are discussed alongside hypothesis from the literature to explain the slowing down of C3A hydration process in the presence of calcium sulphate

Influence of PC superplasticizers on tricalcium silicate hydration.

International audienceThe influence of polycarboxylate superplasticizers with variations of content of anionic groups was studied on pure tricalcium silicate hydration. The hydration in diluted suspension has been investigated by conductimetry, calorimetry, and ionic and total organic carbon analysis of the liquid phase. The tricalcium silicate hydration is always delayed in presence of polycarboxylate superplasticizer. Moreover, the delay can be correlated with the number of carboxylate groups which are on the adsorbed superplasticizer molecules. This effect seems to be due to a decrease of the C3S dissolution rate. Namely the pure C3S dissolution was studied by ICP with or without a carboxylate functionalized latex. A drastic decrease of the C3S dissolution rate was observed in presence of the polycarboxylate functionalized latex and this effect increased with higher hydroxyde calcium concentrations

Influence of the slag content on the hydration of blended cement

International audienceSlag is increasingly used for replacing a part of clinker. The addition of slag modifies the hydration process and so the physico-chemical properties (such as porosity, transport properties) of cementitious materials. Indeed the evolution of the physico-chemical properties are determined by the hydration kinetics of the anhydrous phases and the composition of the hydrated phases. The hydration process of slag blended cement is still under investigation due to the complex interactions between clinker and slag. The aim of this work is to link the evolution of slag blended cement properties (such as bound water, chemical shrinkage, mineralogy, porosity) to the hydration state. The latter was defined by the degree of hydration of the cementitious material.For this study, three commercial cements with variable amounts of the same slag (0%; 61%; 80%) were considered. Cement paste samples hydrated from one week to one year were characterized. $^{29}$Si MAS NMR experiments were performed in order to quantify the consumption of the anhydrous phases. A degree of hydration of clinker, slag and cement could be deduced from these experiments. The results are compared with the evolution of the bound water content (measure by thermogravimetric analysis which is strongly correlated to the global degree of hydration). For each measurement of the degree of hydration, the porosity was determined (total free water porosity measurement) and the mineralogy was described (thermogravimetric analysis (TGA) and X-ray diffraction (XRD)).Measurement of the degree of hydration shows that the slag used in this study is less reactive than other slags which are characterized in the literature. On the one hand the low reactivity of slag explains why the chemical shrinkage and bound water are much more important for a Portland cement than for slag blended cement. On the other hand, for fully hydrated cement, the chemical shrinkage and bound water are more important for slag blended cement than for Portland cement. The consumption of portlandite by the hydration of slag is less important than its production by the clinker even after one year of hydration. The slag degree of hydration is too low to underline an impact of the slag hydration on the porosity and the bound water content.A simplified hydration model, based on mass balance, was applied to determine the mineralogical composition of hydrated slag blended cement according to a specific degree of hydration. Stoichiometric equations used in this model were based on the hydrates compositions as detected by XRD or available in the literature. The model considers the consumption of portlandite by the hydration of slag and the incorporation of aluminum in the C-S-H. The results are used to estimate a volume of chemical shrinkage and bound water. The model has given promising results concerning the porosity and chemical shrinkage estimation. However the portlandite content predicted by the model is too low when it is compared to experimental measurements

Hydration of a CEM V Blended Cement: Characterization of PFA and BFS Reactivity and Evolution of the Porosity

The long term behaviour of cement based materials is strongly influenced by the internal chemistry and the paste microstructure. The industrial byproduct additives like pulverised fly ash (PFA) or blastfurnace slag (BFS) used in blended cement influence together the paste microstructures and the chemistry. A blended cement, designated CEM V in the European standard, containing PFA and BFS has been studied in order to understand processes involved during hydration. Several techniques as Xrays diffraction (XRD), solid-state NMR, thermogravimetry analysis (TGA) have been used to characterize the hydration of the PFA, BFS and the components (C2S, C3S) of the clinker. Such types of characterization have been performed both on old (10 years) and recent samples (from 28 days to 2 years old). Microstructure characterisations, mainly by mercury intrusion porosimetry (MIP), have been also done. Interpretations of all these characterizations allow to build a sketch for the hydration of CEM V cement