Dicalcium 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 ... 

Dicalcium silicate (2CaO SiO ) is very important in the final strength of the cement. This compound hydrates very slowly. The average dicalcium silicate content is 25% to 35%. 

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... 

In the Pidgeon process discussed above, a secondary side reaction occurs between the CaO and Si02 forming dicalcium silicate ... 

Fig. 2. Pseudotemary diagram showing projected compositions in mol% of coal combustion fly ashes and of phases present in ash. Polymorphs of dicalcium silicate include lamite. Bulk composition of fly ash lies within the field bounded by the shaded thick line.

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. 

FURNACES, FUEL-FIRED] (Vol 12) a (A) Dicalcium silicate hydrate [15630-58-7]... 

INSECT CONTROL TECHNOLOGY] (Vol 14) d (D) Dicalcium silicate hydrate [54694-02-9]... 

The term Celite is also applied to a soln of dicalcium silicate dicalcium aluminate used in Portland cement industry(Ref 1)... 

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. 

Figure 7. Electron micrograph of tohermorite obtained from hydration of ff-dicalcium silicate...

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. 

Dicalcium Silicate at Room Temperature, Proc. Int. Symp. Chem. Cem.9 3rd (1960) 1, 135-165. 

Table 1.4 Crystal data for the dicalcium silicate polymorphs... 

Name l.l-nm tobermorite" l.l-nm tobermorite a-Dicalcium silicate hydrate... 

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