Hydrated cement components

Because of the complexity of hydrated cement pastes and the variety of possibilities for binding, a study of the binding of metal and metalloid ions to specific cement minerals is advantageous. The binding to single components of the hydrated cement paste can be compared to the teachability of an ion bound in a hydrated cement paste and deductions made as to the dominant mechanism that limits the solubility in the porewater. 

In the first effective studies of hydrated cements by DTA, Kalousek and co-workers (K27,K32,K33) observed the early formation of ettringite and its subsequent replacement by what was termed a solid solution, but which was probably a mixture of AFm phases. They found no CjAHg or other hydrogarnet phases. Quantitative or semiquantitative determinations of gypsum and ettringite indicated that less than half the total SO3 present could be accounted for by these phases. The authors concluded that the solid solution was eventually replaced by a product which they termed Phase X , and which was possibly a gel containing all the oxide components of the original cement. 

The cement-in-polymer dispersions under investigation consist of two components, namely a finegrained, non-hydrated cement and a polymer. To investigate the influence of the polymer on the reactivity and performance of the mixture, two polymers with contrasting chemical and physical properties namely poly(vinyl acetate) and poly(vinyl alcohol) have been chosen (Fig. 2). 

Parallel with cement production development the significant progress in cement chemistry was achieved. The real revolution we owe to French scientist Le Chat-eher. This great chemist determined the phase composition of Portland cement clinker and the hypothesis of hydration process. Le Chatelier stated that, similarly as in the case of gypsum, the anhydrite cement components dissolve, the solution became oversaturated in relation to hydrates, which causes their crystallization [3],... 

The XRD studies of the interfacial transition zone (material produced by abrasion of paste layers) [16], as well as the SEM observations with EDS analysis [16] revealed the presence of transition zone surrounding the aggregate grains, determined by Maso as an aureole [ 10]. This relates to the former water film around the aggregate. This area shows higher w/c ratio and subsequently cement components can readily dissolve, as well as the hydration products crystallize from the solution. Calcium hydroxide crystallizes in this interfacial transition zone and the crystals are oriented in such a way that their (001) axis is perpendicular to the surface of aggregate, as it was reported by Barnes et al. [17]. The C-S-H is then formed and the two products occur together as a duplex film about 1 pm thick (Fig. 6.7). 

Outside this duplex film there is a porous zone where the following components are observed primary—coarse and secondary— fine crystalline CatOH), C-S-H particles and hydrated cement grains the latter ones are present often in the forms... 

The construction of interfacial transition zone aroiuid the reinforcement in concrete is very similar to the aggregate paste interface. This is presumably the consequence of locally occurring higher w/c ratio, promoting dissolution of cement components and crystallization of cement hydration products from the liquid phase. This interfacial transition zone reveals also higher porosity and lower strength than the bulk cement matrix. 

Concrete is well known to be made up of two primary components stone and sand aggregates surrounded by a hydrated cement paste matrix. It is the latter which acts as the glue that hinds the aggregates together. It is also the hydrated cement paste that is the dominant factor when it comes to permeahihty, since the aggregates typically used in concrete tend to be far less permeable than the surroimding matrix. 

The mechanical behavior of concrete should be viewed from the point of view of a composite material. A composite material is a three dimensional combination of at least two chemically and mechanically distinct materials with a definite interface separating the components. This multiphase material will have different properties from the original components. Concrete qualifies as such a multiphase material. Concrete is composed of hydrated cement paste (C-S-H, CH, aluminate, and ferrite-based compounds) and imhydrated cement, containing a network of a mixture of different materials. In dealing with cement paste behavior, basically it is considered that the paste consists of C-S-H and CH with a capillary system. The model of concrete is simplified by treating it as a matrix containing aggregate embedded in a matrix of cement paste. This model provides information on the mechanical properties of concrete. 

Ramachandran, V. S., Seeley, R. C., and Polomark, G. M., Free and Combined Chloride in Hydrating Cement and Cement Components,Mater. Struct., 17 285-289 (1984)... 

Ramachandran, V. S., Thermal Analysis of Cement Components Hydrated in the Presence of Calcium Carbonate, ThermochimicaActa, 127 385-394 (1988)... 

Thermal analysis techniques have been applied widely for the investigation of the role of admixtures, espeeially that related to the hydration of cement and cement components. AppUcation of thermal analysis permits determination of the heat of reaction, mechanism of reaction, kinetics of reactions, compatibility of admixtures with cements, prediction of some properties, durability problems, material characterization and selection, development of new admixtures, quick assessment of some physical properties, etc. In some instances, they 5deld results that are not possible to obtain with the use of other teehniques. 

Many inorganic and organic salts have been examined for their action on the hydration of cement and cement compounds utilizing thermal techniques. They include sodium and calcium salts of chloride, bromide, nitrite, thiosulfate, thiocyanate, iodide, nitrate, hydroxide, carbonate, hydroxide, etc. A few typical examples are given illustrating the application of thermal techniques in the investigation of these compounds on cements and cement components. 

The physicochemical characteristics of concrete depend on the behavior of the individual components of portland cement as well as on the cement itself. The second chapter provides essential information on cement and cement components so that the informationpresented in subsequent chapters can easily be followed. In this chapter, the formation of cement, the hydration of individual cement compounds and cement itself, physicochemical processes during the formation ofthe pastes, the properties ofthe cement paste, and the durability aspects of concrete are discussed. 

This chapter describes the basic features and common practise of solid-state NMR in studies of portland cement systems and illustrates how this tool can be used to derive structural and quantitative information about cement components and cement hydration for both pure portland cement and Portland cements, including admixtures or supplementary cementitious materials (SCMs). Particular emphasis is given on the NMR techniques generally used in solid-state NMR studies of portland cement systems. However, a comprehensive overview of the NMR studies that have been performed so far or of the new chemical and physical knowledge derived from these studies will not be given. 

The expansive component C A SI in Type K expansive cements hydrates in the presence of excess sulfate and lime to form ettringite is... 

ASTM C845 Type E-I (K) expansive cement manufactured ia the United States usually depends on aluminate and sulfate phases that result ia more ettriagite formation duriag hydration than ia normal Portland cements. Type K contains an anhydrous calcium sulfoaluminate, C A SI. This cement can be made either by iategraHy burning to produce the desired phase composition, or by intergrinding a special component with ordinary Portland cement clinkers and calcium sulfate. 

The ionic bond is the most obvious sort of electrostatic attraction between positive and negative charges. It is typified by cohesion in sodium chloride. Other alkali halides (such as lithium fluoride), oxides (magnesia, alumina) and components of cement (hydrated carbonates and oxides) are wholly or partly held together by ionic bonds. 

In addition to the four compounds discussed above, the final Portland cement may contain gypsum, alkali sulfates, magnesia, free lime and other components. These do not significantly affect the properties of the set cement, but they can influence rates of hydration, resistance to chemical attack and slurry properties. 

Water is also a component of set AB cements. In glass-ionomer cements, for example, it may serve to coordinate to certain sites around the metal ions. It also hydrates the siliceous hydrogel that is formed from the glass after add attack has liberated the various metal ions (Wilson McLean, 1988). Such reactions continue long after the initial hardening of the cement is complete, and for this reason water must be retained as far as possible during the first hours and days after formation of the cement. If water is lost from the cement and desiccation occurs, these post-hardening... 

Portland cement is a fine, soft, powdery substance that acts as a critical component in producing Portland cement concrete. When mixed in contact with water, the cement will hydrate and generate complex chemicals that eventually bind the sand and gravel into a hard, solid mass, known as concrete. 

For solid wastes to be suitable as a full or partial replacement for components in other applications, it should be free of objectionable material such as wood, garbage, and metal that can be introduced at the foundry. It should be free of foreign material and thick coatings of burnt carbon, binders, and mold additives that could inhibit product manufacture, such as cement hydration. It may be necessary to crush the solid waste to reduce the size of oversized core butts or unclasped molds. Magnetic separation is a good solution to producing a suitable coarse or fine aggregate product. 

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