INDIVIDUAL CEMENT COMPOUNDS

Knowledge of the hydration behavior of individual cement compounds and their mixtures forms a basis for interpreting the complex reactions that occur when portland cement is hydrated under various conditions. For a given particle size distribution and water solid ratio, tricalcium silicate and alite harden in a manner similar to that of a typical Portland cement. 

The variation in the rate of strength development in individual cement compounds was determined by Bogue and Lerch in 1934.t The comparison of reactivities and strength development of these compounds... 

Quantitative x-ray diffraction has been used to determine the degree of reaction of individual cement compounds present in cement. Some errors in these estimations are recognized. Figure 5 shows the fractional amounts of alite, belite, aluminate, and ferrite phases that hydrate in cement when hydrated for different times.These rates are not the same when the individual compounds are hydrated. 

The lignosulfonate-based admixtures have been used more widely than other water redueers. They are capable of redueing water requirements and retarding the setting times of concrete. They influenee the dispersion and the hydration rate of the individual cement compounds, and, thus, the cement itself. Techniques such as XRD, DTA, DSC, TG, DTG, and conduction calorimetry have been used extensively to follow the hydration of cement and cement compounds containing different t5q)es and amounts of lignosulfonates (LS). 

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. 

One of the limitations to the wider use of calcium chloride in reinforced concrete is that, if present in larger amounts, it promotes corrosion of the reinforcement unless suitable precautions are taken. The use of calcium chloride is banned in many countries. There is, hence, a continuing attempt to find an alternative to calcium chloride, one equally effective and economical, but without its limitations. A number of organic and inorganic compoimds including aluminates, sulfates, formates, thiosulfates, nitrates, silicates, alkali hydroxides, carbonates, halides, nitrites, calcium salts of acetic acid, propionic acid, butyric acid, oxalic acid and lactic acid, urea, glyoxal, triethanolamine, and formaldehyde have been suggested. However, practical experience and research on these admixtures are limited. The effect of these compounds on the hydration of individual cement compoimds and cement has been widely studied by thermal analysis techniques. 

A number of other studies of AB cements have used X-ray diffraction. For example, Sorrell (1977) and Sorrell Armstrong (1976) employed the technique in the study of oxychloride cements formed in aqueous solution by interaction of oxides and chlorides of either zinc or magnesium. Individual phases were identified, again using Cu K radiation, this time comparing results with those previously obtained for pure compounds. Results from these two studies are described in detail in Sections 7.2 and 7.3 respectively. 

Costa cl al. (C58) showed that superplasticizers increase the fluidity of C,S pastes much as they do that of cement pastes. Studies on individual anhydrous and hydrated compounds in aqueous and non-aqueous media indicate that calcium lignosulphonate and superplasticizers are adsorbed by C -S-H, AFm phases or CH but not by C,S, C,A or C,AH (R54, R55,R56,C58,M 105), though they appear to be taken up by unhydrated P-CiS (C59). The admixtures also enter interlayer sites of C4AF1. and perhaps also of C -S--H (R55). Intercalation of organic molecules in C4AH, is a well-established effect (Section 6.1.1),... 

Fisher AA (1979) Paresthesia of the fingers accompanying dermatitis due to methylmethacrylate bone cement. Contact Dermatitis 5 56-57 Fisher AA, Dooms-Goossens A (1976) The effect of perfume ageing on the allergenecity of individual perfume ingredients. Contact Dermatitis 2 155-159 Fisher AA, Tobin L (1953) Sensitivity to compound G4 ( dichlorophene ) in dentifrices. JAMA 15 998... 

Extensive work has been carried out on the effect of lignosulfonate on the hydration of individual compounds as well as on cement itself. The effects are similar to what has already been described under the previous section on Retarders. ... 

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