Concrete slag cement effect

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

The water requirement of alkali-activated slag cements is relatively low, owing to the plasticizing effect of the alkali compounds that are present, resulting in a lower total porosity of the hardened material, as compared with Portland cement mixes. The produced fresh AAS cement based concrete mixes exhibit a distinct thixotropy and require continuous mixing, to prevent a quick slump loss and setting. Owing to their thixotropic properties even stiff mixes may be compacted if vibration is applied. 

The replacement of cement clinker by GGBS may vary from 10% up to 70% or even more for pure slag cements, and different kinds of blended cements are available. The use of GGBS as a partial replacement of Portland cement has a significant ecological effect. The deposits of industrial waste are transformed into a constituent of concrete. The emissions of dusts and gases into the atmosphere from cement production are limited and the need of natural raw materials is proportionally reduced (Bijen 1996). 

Tomisawa, T, Fujii, M. (1995) Effects of high fineness and large amounts of GGBFS on properties and microstructure of slag cement, in Proc. 5th CANMET/ACI Int. Conf. Fly Ash, Silica Fume and Natural Pozzolans in Concrete, V. M. Malhotra ed., Milwaukee, WI 951-73. 

Concrete, made from cement, aggregates, chemical admixtures, mineral admixtures, and water, comprises in quantity the largest of all synthesized materials. The active constituent of concrete is cement paste and the performance of concrete is largely determined by the nature of the cement paste. Admixtures are chemicals that are added to concrete for obtaining some beneficial effects such as better workability, strength, durability, acceleration, retardation, air entrainment, water reduction, plasticity, etc. Mineral admixtures, such as blast furnace slag, fly ash, silica fume, and others, are also incorporated into concrete to improve its quality. 

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. 

Studies in the early 1970s [16,17] demonstrated that the addition of natural poz-zolana to Portland cement could reduce the chloride diffusion coefficient of concrete by three times. Additions of ground granulated blast furnace slag (GGBS) and fly ash (PFA) have an even more marked effect on the diffusion coefficient... 

The effect of mineral additions (slag, fly ash, pozzolanic materials) on the same properties of concrete has been also determined. However, there are still some problems to be resolved as yet. Amongst them, the role of cement phases as concrete corrosion resistance controlUng factors has been pointed out by Bombled [3], though... 

Many research were focused on the effect of fly ash, siUca fume and granulated blast furnace slag addition on the concrete freeze-thaw resistance. All these additions improve the freeze-thaw resistance, as compared with the concrete from Portland cement, however, on condition that all these eoncretes are air entrainment [80], Freeze-thaw resistance of concrete with fly ash ean be lowered in the case when it has high coal content. The limit value, increased recently to 9% (according to the European standard EN 197-1 2002/A3 2007), is too high and the 5% level should be maintained, as it was reeommended by the elder directives (previous standard EN 197-1 2002). The effeet of non-eombusted coal on the appUcabilily of fly ash is diseussed in details in Seet 7.4. 

As aforementioned, the efflorescence is not harmful for the durability of concrete. When the mechanism involved in efflorescence formation is known, the remedies of effective preventing its occurrence are also possible. For example cements with mineral additions can be used in the production of concrete elements. Silica fume has particularly beneficial effect, which prevents efflorescence already from 5 % addition. The groimd granulated blastfurnace slag or siliceous fly ash are good additives too. The latter one should be groimd when added to concrete or taken from the last section of electrical precipitator, where the finest fractions are collected. 

The other fine powder components, added to control the workability of concrete mixture are fly ash, limestone flour and ground granulated blastfurnace slag. The content of these mineral additions can be substantially high when cement type CEM 1 is used they substitute up to 50% cement, particularly that of class 42.5. One can conclude that the Portland cements with mineral additions can be also applied. The effect of limestone flour on the properties of concrete mixture was studied, among the others, by Gizeszczyk [32],... 

Tan, K., and Pu, X. (1998) Strengthening effect of finely ground fly ash, granulated blast furnace slag, and their combination. Cement and Concrete Research 28, 1819-1825. 

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