Blast furnace cement composition

Generally, concrete used for water treatment plant pipes, water tanks, and filters is made using (ordinary) Portland cement, whereas cement-mortar linings can be made of diflerent types of cements, such as Portland cements, blast furnace cement or the non-Portland calcium aluminate cement. Each type of cement has a typical composition. Table 4.14 gives the typical composition of the primary cements used for manufacturing pipe. 

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.

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. 

Mineral composition of calcium aluminate cements can be assessed based on the three component Ca0-Al203-Si02 system and the following phases can occur CA, CA2, C,2A, C2S, C2AS (Fig. 9.1) [5]. However, the mineral composition is variable and depends primarily on the chemical composition, in which iron plays the main role and the atmosphere oxidizing (rotary kilns) or reducing one (blast furnaces, L furnaces), thus the Fe +/Fe + ratio. It should be also remembered that the calcium aluminate cements composition is rather closer to the C-A-F system. 

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. 

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,... 

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). 

Wo = wollastonite. AC, PC, and BFS indicate the compositional areas of aluminate cement, Portland cement, and blast furnace slags, respectively. 

Four super sulfated cement compositions were realized, hi order to limit the number of variables, the amount of blast furnace slag was set at 85%, in accordance with the best results available in the literature [4,5,6], Initially, only OPC and heat-activated gypsum levels change ... 

R.H. Mills, Age embrittlement of glass-reinforced concrete containing blast furnace slag , in D.M. Roy, A.J. Majumdar, S.P. Shah and J.A. Manson (eds) Advances in Cement-Matrix Composites, Proc. Materials Research Society Syrnp., Materials Research Society, Bagneux, France, 1980, pp. 201-208. 

Scholei A., B. Lothenbach, E Winnefeld and M. Zajac (2015). Hydration of quaternary Portland cement blends containing blast-furnace slag, siliceous fly ash and limestone powder . Cement and Concrete Composites 55 374—382. 

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