Blast furnace slag composition

The composition of blast furnace coke with respect to its Ume, silica and alumina contents also needs to be taken into account when calculating the required sinter composition and corresponding flux additives to give the required blast furnace slag composition. 

Fig. 2. Cement 2ones in the CaO—AI2O2—Si02 system (5) where B represents basic blast-furnace slag D, cement compositions which dust on cooling E, compositions showing no tendency to set G, aluminous cement and PC, Pordand cement.

Table 4.11 depicts the typical chemical composition of blast furnace iron slag. It is suggested that the chemical composition of blast furnace slags produced in North America has remained relatively consistent over the years. 

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. 

C-S-H = poorly crystalline or amorphous calcium silicate hydrate of unspecified composition. Ggbfs = ground granulated blast furnace slag. Hep = hardened cement paste. Pfa = pulverised fuel ash (fly ash). 

Some compositional features also have a strong influence on the mechanical strength of the concrete, in particular the wjc ratio. However, in particular in chloride-contaminated environments, the cement type is even more important. In previous chapters, the microstructure of the cement paste and the beneficial role of blast furnace slag and pozzolana such as fly ash have been outlined. The other most important factor is of course the thickness of the concrete cover, which will be discussed in Section 11.4. 

Dining manufacturing of cement-based pipeline products, the silicates and alumi-nates present in the cement react with water to form products of hydration and, in time, these set to a hard mass. The various solid phases formed come into thermodynamic equilibrium with the interstitial water (pore water), which is rich in calcium, sodium, and potassium hydroxide phases. The presence of these hydroxides raises the pH of the pore water solution to about 13 or 13.5. Table 4.15 gives typical compositions of pore solution for two types of cement Portland and blast furnace slag cement. 

Table 7.1 summarizes the typical composition and properties of a representative series of mineral additions used in blended cements. Binders based on granulated blast furnace slag and related materials are discussed in mote detail in Chapter 8, and those based on natural and artificial pozzolanas in Chapter 9. Cements containing calcium caibonate ate discussed in section 2.2.14. 

The oxide composition of blast furnace slags may differ considerably between individual steel mills, but usually varies little in a given plant, as long as the source of the ore stays the same. Typically, the content of the individual oxides may vary in the following ranges ... 

Richardson, I.G., and Groves, G.W. (1992) The composition and stincture of C-SH gel in cement pastes containing blast furnace slags, in Proceedings 9th ICCC, New Delhi,... 

Falling Slag. Blast-furnace slag that contains sufficient calcium orthosilicate (q.v.) to render it liable to fall to a powder when cold. Such a slag is precluded from use as a concrete aggregate by the limits of composition specified in B.S. 1047. 

The typical chemical composition of pozzolanic materials such as pulverised fuel ash (PFA) and ground granulated blast furnace slag (GGBS) is well understood and their use as cement replacements is well-established in construction and concrete technology. Figure 15 compares the chemical composition of the waste materials used in this project and commonly used cementitious materials (OPC, GGBS and PFA). 

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