Tricalcium silicate hydrate

Addition of dampproofers based on caprylic, capric or stearic acids, stearates or wax emulsions do not have any effect on the setting characteristics of hydration products of Portland cement. However, the unsaturated fatty acid salts, such as oleates, although not affecting the tricalcium silicate hydration, have a marked effect on the ettringite and monosulfate reaction [12] and this is illustrated in the isothermal calorimetry results in Fig. 4.4. It is possible that a calcium oleoaluminate hydrate complex is formed involving the double bond of the oleic acid. 

F/g. The lime-silica ratio of hydration products of tricalcium silicate hydrating in the presence of 0 and 2% calcium chloride as a function of the degree of hydration (Odier). 

The properties of cured Pordand cement are affected by these four constituents of the manufactured Pordand cement. Tricalcium silicate hydrates and hardens rapidly, giving rise to the initial set and eady strength. Increased concentrations of tricalcium silicate causes an increase in the early strength of Pordand cement concretes. Dicalcium silicate hydrates and hardens more slowly, giving the cured concrete its strength increases beyond one week. 

Ft is doubtful whether XRD can distinguish a mixture of tobermorite and C-S-H from a uniform material of intermediate crystallinity the situation may lie between these extremes (A30). This question is discussed further in Section 11.7.4. Crystallization is probably favoured by low bulk density its extent is apparently minimal in calcium silicate bricks (P49), but considerable in aerated concretes (A30). In cement-silica materials, substantially all the AljOj appears to enter the C-S-H, which as its Ca/Si ratio decreases can accommodate increasing amounts of tetrahedrally coordinated aluminium (S70). NMR results (K34) support an early conclusion (K62) that 1.1-nm tobermorite, too, can accommodate aluminium in tetrahedral sites. Small amounts of hydrogarnet have sometimes been detected, especially in products made from raw materials high in AljOj, such as pfa or slag. Minor amounts of tricalcium silicate hydrate (jaffeite C, S2H,) have sometimes been detected (A29,K61). 

M.C.G. Juenger, P.J.M. Monteiro, E.M. Gartner, G.P. Denbeaux, A soft X-ray microscope investigation into the effects of calcium chloride on tricalcium silicate hydration. Cement Concrete Res. 35 (2005) 19-25. 

The tricalcium silicate hydration, and as a matter of fact, the tricalcirrm silicate hydrolysis is of special importance, because this phase is a dominant component of Portland cement clinker, constitnting more than 60 %. Moreover, the tricalcium silicate hydration is often considered as a good model of cement reaction with water. 

Portland cement is made from limestone or other natural sources of calcium carbonate, clay (a source of silica), alumina, ferric oxide, and minor impurities. After grinding, the mixture is fired in a kiln at approximately 2500°F/1137°C. The final product is ground to a fineness of about 10 pm, and mixed with gypsum to control setting. When mixed with water, the portland cement forms a hydrated phase and hardens. As the cement hardens, chemical reactions take place. The two most important reactions are the generation of calcium hydroxide and of tricalcium silicate hydrate. The calcium hydroxide generated could theoretically... 

As discussed in Chapter 17 under portland cement coating, when water is added to portland cement a chemical reaction takes place during the hardening. This reaction produces calcium hydroxide and tricalcium silicate hydrate. The alkalinity of concrete is provided by the presence of calcium oxide from the cement. Consequently, concrete attack can be due to chemicals that react with the Portland cement binder and form conditions that physically deteriorate the material. Any material that will cause the calcium oxide or hydroxide to be removed, lowering the pH of the cement mix, will cause instability and solution of the cement hydrates. 

Tricalcium silicate hydrate (tobermorite gel) is the compound most responsible for the mechanical strength and dimensional stability of the hardened concrete. The pore space within the hardened concrete leading to its adsorption, porosity, and drying shrinkage is the result of the tobermorite gel structure. 

In the manufacture of autoclave products, cement, lime, or both, and silica-bearing materials form the raw mix. Various hydration products are identified when cement or calcium silicate is autoclaved. The compounds include C-S-H gel, a-C2SH, tricalcium silicate hydrate, CH, C3AHg, and a modified form of 7-C2S hydrate. In the cement-aggregate system,products that may form are C-S-H(I), C-S-H(II), 11 Atobermorite,... 

The retarding effect on tricalcium silicate hydration is almost completely eliminated in the presence of C3A or NC3A + gypsum. Adsorption of TEA on ettringite may remove the admixture to facilitate the hydration of tricalcium silicate. Figure 4 shows that the amount of TEA in solution in contact with ettringite decreases with time, Another possibil-... 

The rate of hydration of tricalcium silicate in the presence of different amounts of calcium formate (0.5%-6.0%) has been reported by Singh and Abha.i Calcium formate accelerates the tricalcium silicate hydration at 2% addition. It is speculated that in the presence of formate the protective layer on the silicate surface is ruptured, resulting in an acceleratory effect. 

Figure 5. Possible states of chloride in tricalcium silicate hydrated for different periods.

Kantro, D. L., Tricalcium Silicate Hydration in the Presence of Various... 

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