Search Results
Abstract
Calcium sulfoaluminate (CSA) cements, which represent a CO2-friendly alternative to conventional Portland cements, are produced by blending CSA clinker with gypsum and/or anhydrite. The hydration kinetics and the hydrated phase assemblages of the main hydraulic phase ye’elimite (calcium sulfoaluminate) with calcium sulfate were studied by isothermal conduction calorimetry, thermogravimetric analysis, X-ray diffraction analysis and thermodynamic modelling. Two calcium sulfates with different reactivities (gypsum and anhydrite) were applied. It was found that the pure phase without any calcium sulfate addition exhibits very slow hydration kinetics during the first 10 h. The hydration can be accelerated by the addition of calcium sulfate or (less effective) by increasing the pH of the aqueous phase. The amount of the calcium sulfate determines the ratio between the hydration products ettringite, monosulfate and amorphous aluminium hydroxide. The reactivity of the added calcium sulfate determines the early hydration kinetics. It was found that the more reactive gypsum was better suited to control the hydration behaviour of ye’elimite.
Introduction Fly ash, a by-product from coal power plants, has been recognized as an important construction material due to its environmental benefits and engineering benefits (produce less heat of hydration, increase
1 Introduction Natural gas hydrates are crystalline solids composed of water and gas. The gas molecules are trapped in water cavities that are composed of hydrogen-bonded water molecules [ 1 ]. Typical natural gas composition includes methane
Early stages hydration of high initial strength Portland cement
Part I. thermogravimetric analysis on calcined mass basis
Introduction Thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis have helped to understand and to study the behavior of cementitious materials during their hydration stages. Among these applications, there
distribution [ 3 ], which mainly depend on packing density of fresh paste and filling effect of hydration products. Water requirement for normal consistency, which consists of filling water, chemically combined water, absorption water, and free water, has a
Hydrophobic hydration
Ecological aspects
Abstract
The problem of interaction between organic and water moieties (neutral or ionized water molecular species) is of particular interest in chemistry in view of its implications to physico-chemical behavior of chemical and biological systems. Hydration patterns which result from interaction between hydrophilic and hydrophobic species are non trivial in chemistry. The key issue is that water molecules are able to aggregate in extremely large variety of structural modes. Tetrahedral geometry of intermolecular bonding around water molecule is analogous in geometrical terms to that of intramolecular geometry of carbon atom, known as a source of infinite number of organic structures. In general, space filling with hydrogen bonded water molecules is rather low. It may be illustrated in the following way: volume of neonium atoms is comparable to that of water molecules whilst having atomic mass just 10% higher than molecular mass of water. Thus, liquid neonium and liquid water would have similar densities if molecular packing is of comparable efficiency. The real values are much different, however. Liquid neonium at its boiling temperature has density of 1.20 g cm–3 , thus displaying significantly denser packing that that of water molecules. It certainly means that solid or liquid water has a ‘porous’ structure and may lead to molecular inclusion of foreign (guest) species in the intermolecular space of water framework. This property is not that simple, however, since inclusion of foreign (guest) species is, as a rule, associated with rearrangement of the host framework structure [1]. Anyway, inefficient packing of the mono-component host solid phases may be considered as a prerequisite for its pronounced clathration ability.
Introduction The cement hydration begins around the cement clinker particles interacting with dissolved ions in solution and the properties of cement paste, such as heat generation, strength development and shrinkage, are the
α-A III: 110 °C A II-E: >700 °C During the hydration of β-phases of gypsum sulfates in calcined gypsum, β-anhydrite III changes to β-hemihydrate with a fast
Hydrated goethite nanorodS
Vibration spectral properties, thermal stability, and their potential application in removing cadmium ions
Abstract
Vibration spectral properties and dehydration behaviors of goethite nanorods with diameters ranging from 13 to 32 nm were investigated using infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. All goethite nanorods were highly hydrated with physisorbed and chemisorbed water. As the diameters of goethite nanorods increased, the hydroxyl deformation vibration in the a-b plane showed a significant blue shift, while the Fe-O vibration in the a-b plane shifted to lower frequencies, indicating an enhancement of O-H bond and the ionicity of Fe-O in a-b plane. The hydrated goethite nanorods are also proved to be useful in environmental remedy because of their excellent removal ability of heavy metal ions.
, researchers have rarely investigated the hydration heat of fly ash and fluorgypsum co-doped cement. The hydration of cement is an exothermic reaction, which can result in serious problem for mass concrete: The interior of the concrete could reach very
