Cement microstructure

The picture of cement microstructure that now emerges is of particles of partially degraded glass embedded in a matrix of calcium and aluminium polyalkenoates and sheathed in a layer of siliceous gel probably formed just outside the particle boundary. This structure (shown in Figure 5.17) was first proposed by Wilson Prosser (1982, 1984) and has since been confirmed by recent electron microscopic studies by Swift Dogan (1990) and Hatton Brook (1992). The latter used transmission electron microscopy with high resolution to confirm this model without ambiguity. 

Gajewicz, A. M. (2014). Characterisation of Cement Microstructure and Pore-Water Interaction by IH Nuclear Magnetic Resonance Relaxometry . PhD thesis, Department of Physics, University of Surrey, Guildford, U.K. 

Etude et realisation de sondes pour la caracterisation non destructive par courants de Foucault de couches de cementation des aciers. Les proprietes electromagnetiques des aciers dependent de leur composition, de leurs microstructures et des contraintes appliquees. II est done naturel d essayer d utiliser les parametres electriques et magnetiques des aciers pour evaluer leur microstructure. 

Fig. 5. Microstructure of a cemented carbide alloy, 86%WC—8%(Ti,Ta,Nb)C—6%Co, with a cobalt-enriched periphery and a TiC—TiCN—TiN coating.

Wilson, A. D., Kent, B. E., Clinton, D. Miller, R. P. (1972). The formation and microstructure of dental silicate cement. Journal of Materials Science, 7, 220-38. 

Figure 5.14 The microstructure of the set cement is clearly revealed by Nomarski reflectance optical microscopy. Glass particles are distinguished from the matrix by the presence of etched circular areas at the site of the phase-separated droplets (Barry, Clinton Wilson, 1979).

Brune, D. Smith, D. (1982). Microstructure and strength properties of silicate and glass-ionomer cements. Acta Odontologica Scandinavica, 40, 389-96. 

Figure 6.11 Scanning electron micrographs showing the microstructure of a cement formed from magnesium oxide and ammonium hydrogenphosphate solutions (Sugama Kukacka, 1983b).

Figure 6.12 Microstructure of MgO-aluminium hydrogenphosphate cement (Finch Sharp, 1989).

Abdelrazig, B. E. I., Sharp, J. H. El-Jazairi, B. (1989). Microstructure and mechanical properties of mortars made from magnesia-phosphate cement. Cement Concrete Research, 19, 247-58. 

Unfortunately, although EBA cements have been subjected to a considerable amount of development, this work has not been matched by fundamental studies. Thus, the setting reactions, microstructures and molecular structures of these EBA cements are still largely unknown. In addition, the mechanism of adhesion to various substrates has yet to be explained. Such knowledge is a necessary basis for future developments. 

Concrete is a composite material composed of cement paste with interspersed coarse and fine aggregates. Cement paste is a porous material with pore sizes ranging from nanometers to micrometers in size. The large pores are known as capillary pores and the smaller pores are gel pores (i.e., pores within the hydrated cement gel). These pores contain water and within the water are a wide variety of dissolved ions. The most common pore solution ions are OH", K+ and Na+ with minor amounts of S042" and Ca2+. The microstructure of the cement paste is a controlling factor for durable concrete under set environmental exposure conditions. 

The essential step is the efficient grinding and blending of raw materials. The final properties of cement strongly depend on its mineral composition so that raw composition and firing conditions are adjusted, depending on the type of cement to be produced. The microstructure of the steel fiber-cement paste interface was studied by scanning electron microscopy (SEM). The interfacial zone surrounding the fiber was found to be substantially different from the bulk paste further away from the fiber surface. The interfacial zone consisted of... 

The most important characteristic of cement is its pore structure and aqueous phase hence, the microstructure of the hardened cement paste via the pore system. It is highly alkaline (pH >13) due to rapid and almost quantitative dissolution of Na and K salts from the cement clinker. The porosity of the paste comprises interconnected and isolated pores, the pore sizes of which are important to the strength and dimensional stability of cement products. Different types of cement are used to meet different performance criteria. Properties can be estimated from compositions and fineness (i.e., particle size and size distribution). In the past, additives... 

Fluorine is an essential element involved in several enzymatic reactions in various organs, it is present as a trace element in bone mineral, dentine and tooth enamel and is considered as one of the most efficient elements for the prophylaxis and treatment of dental caries. In addition to their direct effect on cell biology, fluoride ions can also modify the physico-chemical properties of materials (solubility, structure and microstructure, surface properties), resulting in indirect biological effects. The biological and physico-chemical roles of fluoride ions are the main reasons for their incorporation in biomaterials, with a pre-eminence for the biological role and often both in conjunction. This chapter focuses on fluoridated bioceramics and related materials, including cements. The specific role of fluorinated polymers and molecules will not be reviewed here. 

Glasser, F. P. 1993. Chemistry of cement-solidified waste forms. In Spence, R. D. (ed) Chemistry and Microstructure of Solidified Waste Forms. Lewis, Boca Raton, 1 -39. 

The properties and performance of cemented carbide tools depend not only on the type and amount of carbide but also on carbide grain size and the amount of binder metal. Information on porosity, grain size and distribution of WC, solid solution cubic carbides, and the metallic binder phase is obtained from metallographically polished samples. Optical microscopy and scanning and transmission electron microscopy are employed for microstructural evaluation. Typical microstructures of cemented carbides are shown in Figure 3. 

Fig. 3. Microstructures of cemented carbides, (a) 94%WC—6%Co alloy, coarse grain, (b) 85%WC—9%(Ta,TL>Nb)C—6%Co alloy, medium grain size. The gray angular particles are WC and the dark gray rounded particles are solid solution carbides. The white areas are cobalt binder.

The performance of cemented carbide tools is determined not only by chemical composition (amount of carbides and binder metal), but by the size and distribution of WC, solid solution carbides, and the binder in their microstructures. These in turn determine the physical and mechanical properties of the tools. 

Optical microscopy and scanning and transmission electron microscopy are employed for microstructural evaluation. Typical microstructures of cemented carbides are shown in Figure 2.4. Among the physical... 

Supercritical C02 treatment affects the microstructure of the cement paste. In the first stage of the sc C02 treatment, free water in the cement pores is extracted. As a consequence of this dehydration process, channels of about 50-pm diameter develop. Dissolved calcium in the free water reacts with the C02 and crystallizes with the C02 as calcite along the channel walls. In the second stage, the structural water of the hydrated cement phases is extracted. The carbonation of the portlandite to form more calcite takes place. Water, bound to the CSH surrounding the partially hydrated cement clinker particles, is partially replaced by a carbonate formation. The short fibers of the CSH-cement framework, which are responsible for the physical properties of the cement, are not affected (Hartmann et al., 1999). 

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