Physical Properties

There can be considerable variability in the physical properties of blast furnace slag, depending on the slag generation method. Table 4.8 lists some typical physical properties of air-cooled, expanded, and pelletized blast furnace iron slags. Crushed air-cooled blast furnace slag is angular, roughly cubical, and has textures ranging from rough, vesicular (porous) surfaces to glassy (smooth) surfaces with fractures. Some air-cooled blast furnace slag has been reported to have a compacted unit weight as high as 1940kg/m3 (120lb/ft3). The water absorption of air-cooled blast furnace slag can be as high as 6%.

Crushed expanded slag is angular, roughly cubical in shape, and has a texture that is rougher than that of air-cooled slag. Its porosity is higher than that of air-cooled blast furnace slag aggregates. The bulk relative density of expanded slag is difficult to determine accurately, but it is ~70% that of air-cooled slag. Typical compacted unit weights for expanded blast furnace slag aggregates range from 800kg/m3 (50lb/ft3) to 1040kg/m3 (65 lb/ft3).19

Unlike air-cooled and expanded blast furnace slag, pelletized blast furnace slag has a smooth texture and rounded shape. Consequently, its porosity and water absorption are much lower than those of air-cooled blast furnace slag or expanded blast furnace slag. Pellet sizes range from 13 mm (1/2 in.) to 0.1 mm (No. 140 sieve size), with the bulk of the product in the 9.5 mm (3/8 in.) to +1.0 mm (No. 18 sieve size) range. Pelletized blast furnace slag has a unit weight of about 840 kg/m3 (52 lb/ft3).20

Granulated blast furnace slag is a glassy granular material that varies, depending upon its chemical composition and mode of generation, from a coarse, popcorn-like friable structure greater than 4.75 mm (No. 4 sieve) in diameter to dense, sand-sized grains passing a 4.75 mm (No. 4) sieve. Grinding reduces the particle size to cement fineness, allowing its use as a supplementary cementi-tious material in portland cement concrete.

Steel slag aggregates are highly angular in shape and have a rough surface texture. They have high bulk specific gravity and moderate water absorption (<3%). Table 4.9 lists some typical physical properties of steel slag.

Table 4.10 lists some typical physical properties for nonferrous slags. Because they have similar properties, lead, lead-zinc, and zinc slags are grouped together.

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