Hydration of slag cement

Battagin, A.F. (1992) Influence of degree of hydration of slag cement, in Proceedings 9th ICCC New Delhi, Vol. 3, pp. 166-172. 

The rate of hydration of slag cements has been followed by conduction calorimetry, TG, and The temperature of curing... 

Superplasticizing admixtures are used widely in high performance concrete production. Not only do they influence the rheological parameters, but also the setting characteristics. These effects depend on the type and dosage of the admixture. In Fig. 17, the role ofthree types of superplasticizers, viz., 0.5% Ca-SNF, commercial SMF, or Na-SNF on the hydration of slag cements is examined. Addition of the superplasticizer results in the retardation in terms of the time of appearance of the exothermal peak and also a decrease of the peak intensity. Na-SNF retards most of the superplasticizers studied. 

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

Figure 1.7 Microstructure of hydration of Portiand cement [a), and cements with addition of fiy ash (fa) and blast furnace slag (c) (Bakker from [5])...

The resistivity of concrete is an important parameter used to describe, for example, the degree of water saturation, the resistance to chloride penetration or the corrosion rate. The resistivity of concrete may have values from a few tens to many thousands of n m (Table 2.3) as a function of the water content in the concrete (relative humidity), the type of cement used (Portland or blended cements), the iv/c, the presence of chloride ions or whether the concrete is carbonated or not At early ages, the resistivity of concrete is low and considerable increases occur due to hydration of the cement AU of these factors can be rationalised on the basis of ion migration in the porous and tortuous concrete microstructure a high relative humidity increases the amount of water-filled pores (decrease of resistivity), the iv/c ratio and type of cement determine the pore volume and pore-size distribution (less but more coarse pores with pure Portland cement more but finer pores and less interconnectivity of pores with blast furnace slag or fly ash) chloride ions increase the conductivity of the pore solution and carbonation decreases it. An increased resistivity is accompanied by a reduced corrosion rate [38]. Table 2.4 shows resistivities determined for mature concrete in various chmates [39-41]. 

The examination of chemical composition of slag glass surface at the early age of hydration has shown that it is modified immediately after the contact with the Uquid phase [6]. As the result of incongment dissolution of slag grains on their surface the l er of C-S-H is formed, with, however, lower C/S ratio than in the Portland cement paste. When the hydration of slag is activated by alkalis, this phase contains the Na+ orK+ ions. 

Fig. 8.4 Hydration process of slag cement (w/e = 0.4) (according to [10]), preinduction period is omitted...

Hardtl, R. (1992) Chemical bonding of water during the hydration of Portland cements and blastfurnace slag cements blended with fly ash, in Proceedings 9th ICCC, New Delhi, Vol. 4, pp. 678-690. 

This reaction - in contrast to OPC - is slow and slag cement needs an activator, usually NaOH, KOH or sulfates. In blast furnace slag cement, a mixture of OPC and up to 70% slag, these activators are present. The hydration of slag does not produce Ca(OH)2 but rather consumes it, incorporating the reaction products into the cement gel. The quantity of free lime in hydrated... 

The prineiple hydration produets of slag cements are essentially similar to those found in pordand eement pastes. The microstructure of slag cement pastes is also similar to that of portland cement pastes. X-ray microanalysis has, however, shown that the C/S ratio of C-S-H product in hydrated slag cement is lower than that found in portland cement paste. 

Figure 15. Conduction calorimetric curves of slag cements hydrated at different temperatures and dosages of slag.

The relative effects of 10% of fly ash, limestone, or sludge on the hydration of portland cement have been investigated by DTA/DTG/TG and XRD. Based on Ca(OH)2 estimation, it has been concluded that lime sludge and limestone enhance hydration of cement compared to that by slag or fly ash.l ]... 

The significant increase in the use of supplementary cementing materials (such as fly ash and slag) in the last decade has dictated the need for an admixture that can offset the slowed hydration that results when such materials are incorporated in concrete. Strong basic salts such as sodium aluminate, alkali hydroxides, silicates, sulfates and thiosulfates have shown some promise. A number of proprietary admixtures which claim to catalyze the pozzalanic and thereby increase the rate of hydration are now marketed. 

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

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). 

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