Portland-slag cement

Notation of cement indicates the cement type (Table 1.3) and the strength class (Table 1.4). For instance, CEM II/A-S 42.5N indicates Portland-slag cement with addition of blast furnace slag in the range of 6-20% and strength class 42.5 with normal early strength. 

Portland-slag cement 11/A-S 80-94 Granulated blast furnace slag 6-20... 

In most instances the constituents of Portland-slag cement are ground together in an... 

Table 8.1 Hydration of alite and slag in Portland-slag cements with different contents of granulated blast-furnace slag.

Table 8.2 Free lime content in Portland-slag cements.

The microstmcture of Portland-slag cement pastes is not too different from that of plain Portland cement. The main difference consists in a reduced amount of free Ca(OH) 2- Just as with clinker grains, layers of reaction products formed in situ are also present at the boimdaries of the slag grains, in addition to the hydrated material formed within the space originally filled with water. 

Portland-slag cements may be employed in most applications in which plain Portland cement is also used, as long as a high short-term strength is not required. The main areas of their use are applications in which a high corrosion resistance or a slow hydration heat liberation of the binder are required. 

Roy, S. et al. (1998) Investigation of Portland slag cement activated by water glass. Cement and Concrete Research 28,1049-1056. 

Portland-slag cements tend to exhibit improved resistance to sulfate attack compared with plain Portland cement at high slag contents (60% and more), whereas the resistance is scarcely affected or even made worse at low substitution levels (below 25%) (Mehta, 1992 Gollop and Taylor, 1992-1996 Giergiczny, 1997 Krizan and Zivanovic, 1997 Sersale et al, 1997). The improved response to sulfate attack appears to be due mainly to a dilution effect, rather than to aity special mechanism. An increase of the slag content at the expense of clinker results in a lower amount of C3A in the system, which is the phase mainly responsible for the susceptibility of Portland cement to sulfate attack. 

The mechanism of the sulfate attack on Portland-slag cement is broadly similar to that observed in pure Portland cement pastes. In an attack by alkali sulfates the dominant reactions are the partial decalcification of the C-S-H phase and the conversion of the existing monosulfate to ettringite. The amount of ettringite formed is lower than in the case of Portland cement, as monosulfate is the only phase that can serve as a direct source for ettringite formation, whereas neither Al incorporated in the C-S-H phase nor that present in hydrotalcite are available for such a reaction, jnst like Al in ettringite already formed independently of snUate attack (Gollop and Taylor, 1992-1996). 

Because in Portland-slag cement, unlike in Portland cement, the decomposition of the C-S-H phase is the main feature of sulfate attack rather than the formation of ettringite, disintegration and softening rather than expansion and cracking are the main visible characteristics of the process. 

Galvanized steel is susceptible to chloride-induced corrosion in highly alkaline environments, as exist in mixes made with ordinaiy Portland, Portland-pozzolana, or Portland-slag cements. The corrosion may be reduced significantly by the use of supersulfate cement (Dass et al, 1992). 

In Portland slag cements the electrical conductivity was foimd to decline with increasing slag content. The following are average values [in (fl.m)" ] found in cements with different slag contents (w/c=0.50, water-saturated pastes) (Hinrichs 1987) ... 

For high slag contents with respect to neat Portland cement concrete the carbonation was significantly enhanced and these results confirmed earlier publications, e.g. Portland slag cements with substantial fraction (25-85%) of ground blast-furnace slag show increased resistance against chemical corrosion, but durability may be decreased when exposed to outdoor conditions. 

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