Tricalcium silicate, 1.25

The important compounds in Portland cement are dicalcium silicate (CazSi04) 26%, tricalcium silicate (CasSiOj) 51%. tricalcium aluminate (Ca3Al206) 11% and the tetracalcium species Ca4Al2Fe2 Oio (1%). The principal constituent of moistened cement paste is a tobermorite gel which can be represented schematically by the following idealized equations ... 

Tricalcium silicate 3CaO x Si02 Dicalcium silicate 2CaO x Si02 Tetracalcium aluminoferrite 4CaO X AI2O3 X Fe203... 

Portland cement refers to a class of hydraulic cements in which the two essential constituents are tricalcium silicate (3Ca0-Si02) and dicalcium silicate (2Ca0-Si02) with varying amounts of alumina, tricalcium aluminate, and... 

The percentage of dicalcium silicate, sometimes abbreviated as C2S in the industry, determines the final strength of the cement. The amount of tricalcium silicate, C3S, is related to the early strength (7-8 days) required of the cement. Tricalcium aluminate, C3A, relates to the set in the cement. 

Common (dry) cement consists of anhydrous crystalline calcium silicates (the major ones being tricalcium silicate, CasSiOs, and (3-dicalcium silicate, Ca2Si04), lime (CaO, 60%), and alumina (a complex aluminum silicate, 5%). While cement is widely used and has been studied in good detail, its structure and the process whereby it is formed are not completely known. This is due to at least two factors. First, its three-dimensional arrangement of various... 

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. 

Fig. 5.8 The rate of reaction of tricalcium silicate in the presence of calcium chloride and triethanolamine, measured by line production (Ramachandran).

Fig. 5.10 Degree of hydration of a tricalcium silicate paste in the presence of calcium chloride, measured by non-evaporable water content (Odier).

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). 

Omotoso, O. E., Ivey, D. G. Mikula, R. 1998a. Hexavalent chromium in tricalcium silicate Part 1 Quantitative X-ray diffraction analysis of crystalline hydration products. Journal of Materials Science, 33, 507-513. 

A shorthand notation is often nsed to designate the oxides (e.g., C for CaO and A for AI2O3 see Table 5.7), and it is also used to designate the compounds formed between the components during heating, such as calcium aluminate (CA) and tricalcium silicate (C3S) ... 

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. 

The lime is then added to silica, usually obtained as an aluminosilicate pozzolan (clay or shale), and the mixture is heated in a kiln to produce tricalcium silicate (called alite) ... 

Tricalcium silicate is the major component of Portland cement. A cement is produced when the tricalcium silicate is mixed with water (or hydrated ) ... 

Siegers, P. Rouxliet, P. Carbonation of the Hydration Products of Tricalcium Silicate. Cem. Conor. Res. 1976, 6, 381-388. 

Dicalcium silicate Tricalcium silicate Tetracalcium aluminate Tetracalcium aluminoferrite Magnesium oxide... 

The tobermorite obtained in the hydration of tricalcium silicate (Ca3Si02), / -dicalcium silicate (/ -Ca2Si04), portland cement, and concrete is a colloid, with a specific surface area of the order of 300 sq. meters per gram. To give an idea of how the elementary particles of tobermorite look, Figure 7 is an electron micrograph of a few particles (obtained by L. E. Copeland and Edith G. Schulz at the Portland Cement Association Research and Development Laboratories). These particles look like fibers, but if you watch them closely, you see that they are very thin sheets, rolled up as one would roll up a sheet of paper. At the lower end the sheets are partly unrolled. When one prepares tobermorite by the reaction of lime and silica, one usually obtains crumpled sheets, which are not rolled up. The electron microscopists tell us that the sheets are very thin, of the order of a single unit cell in thickness. 

The conclusion is that both the body structure and the surface structure of tobermorite are highly reproducible. Whether we use tricalcium silicate or fi-dicalcium silicate as starting solids, whether we use a water to solid ratio of 0.7 or 9.0, whether we use paste hydration or ball-mill hydration or a third type which I have not discussed (which gave the six other points on the curve), we wind up with a tobermorite having very nearly the same body structure and surface structure. 

Young, J. F., Capillary Porosity in Hydrated Tricalcium Silicate Pastes, ... 

Alite is the most important constituent of all normal Portland cement clinkers, of which it constitutes 50-70%. It is tricalcium silicate (CajSiOj) modified in composition and crystal structure by incorporation of foreign ions, especially Mg ", AP and Fe. It reacts relatively quickly with water, and in normal Portland cements is the most important of the constituent phases for strength development at ages up to 28 days, it is by far the most important. 

Chemical formulae in cement chemistry are often expressed as a sum of oxides thus tricalcium silicate, CajSiO, can be written as 3Ca0 Si02- This does not imply that the constituent oxides have any separate existence within the structure. It is usual to abbreviate the formulae of the commoner oxides to single letters, such as C for CaO or S for SiOj, CajSiOj thus becoming CjS. This system is often combined with orthodox chemical notation within a chemical equation, e.g. 

X-ray powder patterns and densities of tricalcium silicate and alites... 

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). 

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