Shale is a sedimentary rock formed in shallow seas and lakes.
 | Distinctive features: Splits easily into thin plates along well-defined planes parallel to the original stratification. |
| Colour: Buff, red, and various shades of gray or green.. |
| Texture and granularity: Fine-grained. |
| Composition: Complex mixture of microscopic clay minerals, plus mica and quartz. |
Most of shale used for construction is used in the manufacture of bricks. Not all shale is suitable for brick, and even fewer deposits are suitable for expanded shale production. The shale must contain minerals (mostly carbonates) that will produce gas at the same temperature as the shale begins to sinter (soften prior to melting). This allows the mass to expand. Rapid cooling preserves expanded voids.
Slate is metamorphosed shale; the expansive properties of slate likewise depend on its mineralogy and bulk chemistry.
The process of producing expanded aggregate from shale is outlined below:
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The shale is mined in open pits and delivered to the crusher by truck. It is crushed to the proper size and conveyed into storage silos. |
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Shale Delivery to Crusher |
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The shale is introduced to the rotary kiln at the cold end. The kiln is fired at the discharge end with natural gas. The material is retained in the kiln approximately one (1) hour. During this time, minerals which are subject to decomposition at high temperatures, are evolving gases. |
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Rotary Kilns |
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The shale is simultaneously being softened by the flame temperature of approximately 2200 Deg. F. The resulting vitreous material contains a large number of tiny nonconnecting cells or pockets formed from the gas. The expanded material is discharged from the kiln into a grate cooler. It is moistened prior to crushing to eliminate dust and to minimize segregation. |
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Fired @ 2200 Deg. F. |
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The clinker is crushed and screened to achieve properly balanced gradations for different end uses. The various sizes of expanded shale are stored in bins or in a stocking yard for loading into trucks and railroad cars |
