Processing of Granulated Blast Furnace Slag and its applications
Granulated Blast Furnace Slag (GBFS) is the most used material in cement industry to make slag cement. How is GBFS made? What are the processing and its applications?
Process: water quenching
Generally speaking, GBFS is formed by water quenching. The glassy and granular material is generated when slag is rapidly chilled by immersion in water.
The most common process for granulating blast furnace slag involves the use of high water volume, high pressure water jets in direct contact with the molten blast furnace slag at a ratio of approximately 10 to 1 by mass. The molten blast furnace slag is quenched almost immediately to form a material generally smaller than a #4 sieve.
The efficiency, which the molten blast furnace slag is rapidly chilled, as well as the chemical composition of the slag source, largely determines its cementitious properties for use in concrete. After the granulated blast furnace slag is formed, it must be dewatered, dried and ground, using processes similar to those used with Portland cement clinker to make Portland cement.
Typically, granulated slag is ground to an air-permeability (blaine) fineness exceeding that of Portland cement to obtain increased hydraulic activity at early ages. As with Portland cement and pozzolans, the rate of reaction increases with the particle fineness.
Ground Granulated Blast Furnace Slag (GGBFS) is activated by alkalis or Ca(OH)2 etc.
GBFS has to be grind to get Ground Granulated Blast Furnace Slag (GGBFS) having large fineness. When GGBFS is mixed with water, initial hydration is much slower as compared with Portland cement. Therefore, Portland cement or alkali salts are used to increase the reaction rate. In the hydration process, GGBFS produces calcium silicate hydrate cement paste. This valuable contribution fromGGBFS improves the paste-to-aggregate bond in concrete. GGBFS mixtures with Portland cement typically result in greater strength and reduced permeability.
Color of GGBFS
GGBFS is considerably lighter in color than most Portland cements and will produce a lighter concrete end product. Occasionally, concrete containing GGBFS may exhibit a blue-green coloration. While this coloration effect seldom occurs, it is attributed to a complex reaction of the sulfide sulfur in the GGBFS with other compounds in the cement and will diminish with age.
General applications of GGBFS
- raw material for the manufacture of cement
- lightweight fill
- raw material for the manufacture of glass
Factors affecting cementitious properties of GGBFS
- chemical composition of GGBFS
- alkali concentration of the reacting system
- glass content of the GGBFS
- fineness of the GGBFS and Portland cement.
Added value of GBFS using in concrete applications
- reduced chloride permeability
- improved resistance to sulfate attack
- reduced heat of hydration in mass concrete
- improved compressive and flexural strength
- reduced alkali-silica reaction