Blast furnace slag cement concrete

The degree of the attack by pure water depends to a large extent on the perme-abihty of the concrete, but its Ca(OH)2 content also plays an important role. Concrete types with a low level of Ca(OH)2, Hke blast furnace slag cement concrete, have improved resistance with regard to this type of degradation. In addition to... 

Several techniques, including TG, chemical analysis, and pore size distribution, were utilized to determine the extent of carbonation of granulated blast furnace slag cement concrete which was exposed for twenty years The weight loss at 450-550°C was attributed to the loss of water from Ca(OH)2, and that at 780°C, to CaC03 decomposition. The amount of calcium carbonate formed at different depths from the interior of the building and from the exposed surface is compared in Fig. 43. The extent of carbonation is maximum at the surface which decreases to a low level from a distance of 40 mm from the surface. 

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

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

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. 

The rate of reaction of blast furnace slag and fly ash differs strongly To show this. Figure 1.8 compares electrical resistivity measurements of wet cured concrete with a water/cement ratio of 0.45 made with Portland, Portland fly ash and blast furnace slag cements. The development of resistivity of concrete at an early age... 

Table 2.3 Resistivity [Cl m) of concrete made with Portland cement (OPC), blast furnace slag cement (GGBS), and Portland cement with addition of 5% silica fume (SF) iv/c = 0.45. lues were determined after 1.5—2.5 y exposure in a fog room or 20°C 80% R.H. climate [37]...

With regard to protection against sulfate attack, the quality of the concrete is a crucial factor a low permeability is the best defence against this type of attack, since it reduces sulfate penetration. This can be obtained by decreasing the w/c ratio and using blended cement (i. e. pozzolanic or blast furnace slag cement that reduce the calcium hydroxide content and refine the pore stracture of the matrix). Finally, the severity of the attack depends on the content of CjA and, to a lesser extent, of C4AF in the cement. Standards in different countries provide for sulfate resistant cements with a C3A content below 3-5 %. 

CO2 (molecular weight 44) that can react with a concrete produced with 300 kg/m Portland cement that we can suppose is composed by 64% of CaO (molecular weight 56) is 300 X 0.64 X 44/56 150 kg/m. In the case of blast furnace slag cement with 70 % of GGBS, the percentage of CaO is only 44%. For other blended cements, the quantity of CaO is somewhere between these two values [3]. For blended cement, hydration of pozzolanic materials or GGBS also leads to a lower Ca(OH)2 content in the hardened cement paste which may increase the carbonation... 

Table 12.5 Initiation time for chloride-induced corrosion estimated for different concrete cover thicknesses, utilising apparent diffusion coefficients of chlorides (D,pp) evaluated on specimens submerged in the North Sea for 16 y (concrete of 420 kg/m of Portland cement, OPC, or blast furnace slag cement with 70% GGBS and identical curing procedures) [18]...

With a few of the products that complied with all requirements described above, further investigations were carried out [23,24]. The conclusions apply to concrete of reasonable quality (wjc = 0.50) made with Portland or blast furnace slag cement, which was thought to be representative for the upper parts of bridge decks. They can be summarised as follows ... 

De Schutter, G. (1999) Hydration and temperature development of concrete made with blast-furnace slag cement. Cement and Concrete Research 29,143-149. 

Majumdar, A.J., Singh, B., and Edmonds, R.N. (1990) Hydration of mixtures of ciment fondue aluminous cement and granulated blast furnace slag. Cement and Concrete... 

The use of plasterboard gypsum (PG) combined in mixtures with blast furnace slag, cement kiln dust (CKD), cement bypass dust (BPD) and power station mn-of-station ash (ROSA) was investigated to form a novel blended binder with pozzolanic properties. This novel binder had potential use to stabilise soils and to produce semi-dry roller compacted paste and roller-compacted concrete (RCC) for road foundation construction. 

The porous concretes are preferably composed with blast-furnace slag cements, gap graded crushed aggregate with grain size above 5 mm and without fines or minimizing sand volume fraction with superplasticizers and fly ash. Pavements with increased porosity are built in a few layers with different tasks. A minimum required permeability between 7-10 m/s and 3-10 m/s was proposed by Beeldens and Brishant (2004). 

Concretes prepared with blast furnace slag cement and pozzolanic cement have lower Ca(OH)2 content and pH of the pore solution, thus in principle providing less protection against carbonation or chloride induced corrosion with time. However, the pozzolanic reaction leads to a filling and refining of the pore system and thus to a less or much less permeable concrete. Due to the slow hydration reaction curing (keeping wet the concrete in its early age) is much more important to achieve low porosity. 

Litvan, G. G., Carbonation in Slag Cements, Int. Workshop on Granulated Blast Furnace Slag in Concrete, pp. 301-327, Toronto (1987)... 

Schutter, G. D., Hydration and Temperature Development in Concrete Made with Blast-Furnace Slag Cement, Cement Conor. Res., 29 143-149 (1999)... 

The manufacture of Portland concrete consists of three basic steps—crushing, burning, and finish grinding. As noted earlier, Portland cement contains about 60% lime, 25% silicates, and 5% alumina with the remainder being iron oxides and gypsum. Most cement plants are located near limestone (CaCOs) quarries since this is the major source of lime. Lime may also come from oyster shells, chalk, and a type of clay called marl. The silicates and alumina are derived from clay, silicon sand, shale, and blast-furnace slag. 

Previous work on superplasticized Portland cement concrete containing fly ash or blast furnace slag has shown that such mixes require 10% less admixture than reference Portland cement concrete to attain the same workability. Therefore, a given dosage may produce higher water reduction. The reason for the reduced admixture requirement has not been determined. It is probably due to the lowering (dilution) of the C3A content... 

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