Blastfurnace slag

Blastfurnace slag Iron smelting Nearly all used As roadstone, railway ballast, filter medium, aggregate for concrete, fertilizer and in manufacture of cement... 

Blastfurnace slag Iron smelting Nearly all used As roadstone, railway... 

Various types of cement and pozzolanas (e.g., coal burning fly ash, lime, blastfurnace slag and similar materials) are mostly used as the stabilizing matrix. That stabilization technique is used for the immobilization of inorganic or organic waste. 

Due to the increasing cost of energy, the need to preserve the environment, and the non-existence or exhaustion of suitable natural raw materials in some areas, industrial and other waste materials are of interest as possible raw materials or supplementary fuels or both. Energy can be saved if even a part of the CaO can be provided by a material, such as blastfurnace slag, that does not require decarbonation. Supplementary fuels include such materials as used or reject tyres and pulverized household refuse, which can be introduced into the system in various ways. Some materials, such as pulverized fuel ash (pfa fly ash) can serve as raw materials that also possess some fuel content. Other wastes that have been used include calcium silicate residues from aluminium extraction, mining residues, and precipitated calcium carbonate from various industries. 

Table 9.1 Chemical compositions of some blastfurnace slags" (D35) ...

Table 9.2 Atom ratios in a typical ground granulated blastfurnace slag...

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).

Major Portland cement clinker Granulated blastfurnace slag Natural pozzolanas Thermally activated clays and shales Siliceous fly ash Calcareous fly ash Unslaked calcareous fly ash Burnt shale Limestone Limes... 

BS 1047 Specification for air-cooled blastfurnace slag aggregate for use in construction , 1983. 

BSI (1983) British standard specification for air-cooled blastfurnace slag aggregate for use in construction (BS 1047). British Standards Institution, London, p 96... 

First of all the C/S molar ratio changes depending on the saturation of the liquid phase in concrete, in relation to Ca(OH)2 (Fig. 3.17). Especially in the case of cements with mineral additions, particularly siliceous fly ash or ground granulated blastfurnace slag, this ratio decreases and the sections of chains composed of [SiO ] " tetrahedra become longer [32]. 

Fig. 3.20 C-S-H honeycomb constitution in the pastes produced from the ground granulated blastfurnace slag activated with NUjSiOj, the cracked slag grain is visible. (By the courtesy of B. Trybalska)...

The shrinkage of mortars produced from different cements increases with then-strength class (higher fineness) but decreases in the case of cements with mineral additions, particularly at high granulated blastfurnace slag and siliceous fly ash content. 

The granulated blastfurnace slag and siliceous fly ash addition will have a similar effect on the ability of chloride ions binding in cement pastes, because they will also decrease the C/S ratio in C-S-H gel. Uchikawa and Okamura [210] report the following C/S ratio 1.7 for Portland cement, 1.6 in case of 40% slag addition and 1.2 at 40% of sihceous fly ash addition. Simultaneously, these additions will cause the aluminates content decrease in favor of calcium silicate hydrates. 

The opinion of favourable effect of pozzolanic additions, particularly blastfurnace slag and siliceous fly ash against the srrlphate corrosion, is maintained to the present days and has the universal, rich documentation [251], However, some authors are of the opinion, that the physical effect of reduced porosity and capillary adsorption (permeability), in the case of high performance concrete with superplasticizers addition is more important than the influence of pozzolanic additions [252]. Analogous opinion was supported by Skalny and Pierce [65]. 

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. 

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