Slag cements

Activation of the latent hydraulic properties of foundry sand can also be achieved with gypsum (sulfate activation). Mixtures of foundry sand with a high aluminum oxide and lime content with ca. 15% calcium sulfate (as raw gypsum or natural anhydrite) are known as supersulfated cement. 

Blast-furnace slag cements with high slag contents have lower heats of hydration than pure Portland cement, which is advantageous for large scale concrete structures (e.g. dams). The lower calcium hydroxide content results in their being somewhat more chemically stable than Portland cement. Blast-furnace slag cements are used in similar applications to Portland cement. 

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Type IS Pordand cement and blast furnace slag cement... 

Little information is available about the corrosion of metals in concrete, although it seems likely that all Portland cements, slag cement and high-alumina cement behave similarly Concrete provides an alkaline environment and, under damp conditions, the metals behave generally as would be expected e.g. zinc, aluminium and lead will react, copper is unaffected, while iron is passivated by concrete. 

Furnace slag cement High service temperatures [1128]... 

A furnace slag cement slurry can have a density of 1500 to 1600 kg/m. A combination of silica flour and furnace slag may be used to achieve service temperatures exceeding 200° C [670]. A gas may be suitable as a foaming agent [358]. 

Hogan, F.J., The effect of blast furnace slag cement on alkali aggregate reactivity a literature review, Cement Concrete and Aggregates, 7, 2, 1985. 

Reference ASTM 114—00, Standard Test Method for Chemical Analysis of Hydraulic Cement. As suggested in this document, the sample should not be a slag cement sample. Your instructor may choose to dispense... 

Jiang, W Wu, X. Roy, D. M. 1993. Alkali activated fly ash - slag cement based nuclear waste forms. Materials Research Society Symposium Proceedings, 294, 255-260. 

Mascolo, G. 1973. Hydration products of synthetic glasses similar to blast furnace slag. Cement and Concrete Research, 3, 207-213. 

Mascolo, G. Marino, O. 1980. MgO-bearing phases in the hydration products of slag cement. 

Gypsum cement is used in plasters and plasterboards. Slag cement made with slag of blast furnaces, can resist erosion by chemicals. 

Table 9.3 Percentages of slag reacted in slag cements... 

Table 9.4 Calculated mass balance and compositions by weight and by volume for a 14-month-old slag cement paste Percentages on the ignited weight for material equilibrated at 11% RH... 

As with the slag cement discussed in Section 9.2.7, the calculated water contents for different humidity states are lower, and the porosities higher than for comparable Portland cement pastes. The water contents are lower because replacement of CH by C-S-H or hydrated aluminate phases causes relatively little change in the HjO/Ca ratio, so that the water content tends to fall towards the value which would be given by the Portland cement constituent alone. Diamond and Lopez-Flores (D39) found that, for two 90-day-old pastes similar to that under discussion (30% pfa, w/s = 0.5), the non-evaporable water contents were l2.5 /o and 13.0%, while that of a Portland cement paste was l5.4 /o. The porosities are discussed in Section 9.7. 

Fig. 9.6 Pore size distributions for pastes of Portland and composite cements (vv/s = 0.45. curing temperature 21 C), determined using mercury intrusion porosi-metry. CID. CIY Portland cement pastes cured for 1 day and 1 year. S2D. SIY Portland-blastfurnace slag cement (70% slag) pastes, cured for 2 days and I year. F.3D, FI Y pfa cement pastes (13% CaO in fly ash) cured for 3 days and 1 year.. After Feldman (F34).

Fig. 9.6 compares curves obtained on first intrusion for pastes of Portland and composite cements. At early ages, pfa or slag cement pastes are more porous than comparable Portland cement pastes because of the relatively slow reactions of the mineral additions, but the pore size distribution curves indicated by MIP are essentially similar in shape. For mature pastes, the apparent distributions for the composite cements indicate that there is a greater proportion of fine porosity. For the pfa cement paste, the mercury porosity obtained at maximum pressure are greater than that of the Portland cement paste. Day and Marsh (D32) agreed with Feldman that discontinuity... 

Under some circumstances, the Mg enters sparingly soluble phases other than brucite. Roy et al. (R70) observed the formation of a hydro-talcite-type phase in a slag cement paste that had been treated with MgS04 solution. Its formation was possibly favoured by the enhanced availability of A1(0H)4 provided by the slag. Cole (C70) reported the formation of a hydrated magnesium silicate in a deteriorated concrete seawall. 

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