Industrial processes often release by-products during the refining of raw materials, combustion, filtering, cleaning of effluents, etc. Materials such as smelting slag and combustion ash are also by-products.
By-products can have several interesting properties when considered as raw materials:
• They are abundant without necessarily being in demand.
• Chemically speaking, they can be relatively pure in composition.
• It is usually difficult to dispose of them.
• Other raw materials are saved by using them.
• They will often cause environmental pollution if released to air, earth or water.
The planned use of industrial by-products is a relatively new phenomenon in building, and is now primarily a consideration of substances, which can be used as constituents in cement and concrete products (Table 12.1). Increased use of by-products, which have properties similar to pozzolana, for example, will drastically reduce energy consumption within the cement industry, as well as save other raw material resources.
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