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Slag Aggregates

Slag aggregates are obtained by crushing of smelter slag or by special treatment of fire-liquid slag melt (molten slag aggregates). Currently there are many types of concrete that are developed and used in construction that include metallurgical slags both as a binding component and as fillers. Slag, generally classed as a synthetic aggregate (also called artificial aggregate), is produced by altering both physical and chemical properties of a parent material, which may be produced and processed specifically for use as synthetic aggregate. A synthetic aggregate may also be the byproduct of manufacturing and a final burning process—blast furnace slag is an example of a synthetic aggregate. Briefly, blast furnace slag is formed when iron ore or iron pellets, coke, and a flux (such as limestone, CaCO3, or dolomite, CaCO3·MgCO3) are melted together in a blast furnace. When the metallurgical smelting process is complete, the lime in the flux has been chemically combined with the aluminates and silicates of the ore and coke ash to form the non-metallic blast furnace slag. During the period of cooling and hardening from its molten state, blast furnace slag can be cooled in several ways to form any of several types of ballast furnace products, including aggregate for the manufacture of road asphalt, construction or infrastructure development.

Fly Ash

Basic properties and influence of fly ash. Fly ash is the waste generated by coal-fired power plants after burning powdered carbon. It is the burning of volatile substances when pulverized coal passes through the high temperature area of ​​the furnace, and the mineral impurities such as clay and quartz in the pulverized coal are at high temperature. It is melted underneath and the hydrogen and nitrogen produced will bulge the melt to form a hollow body or a ruptured hollow body. These substances are finally sent to the low temperature area and after cooling, they become glass spherical particles. Most of the particles will follow the high temperature. It is discharged and collected by a dust collector, which is commonly used fly ash. The heavier particles will fall into the bottom of the furnace, called bottom ash. According to ASTM C618 and CNS 3036 standard specifications, the composition of fly ash can be divided into two types according to its calcium content. The first type is low calcium fly ash (F grade), in which the content of CaO is less than 10%, usually anthracite or the combustion products of bituminous coal. The second type is high calcium fly ash (grade C), where the content of CaO is less than 10 ~ 40%, usually the combustion products of lignite or sub-bituminous coal.

Fly ash can be a cost-effective substitute for Portland Cement in many markets. Fly ash is also known as an environmentally friendly material because it is a byproduct and has low energy, a measure of how much energy is consumed in producing and delivering building materials. In contrast, Portland Cement has very high energy content because its production requires a lot of heat. Flying ash requires less water than Portland Cement and is easier to use in cold weather. Other benefits include:
  1. Cold weather resistance,
  2. High strength gains,
  3. Can be used as a mixture
  4. Make solid concrete with smooth surfaces and sharp details
  5. Reduces cracking, permeability,and bleeding problems
  6. Reduces heat of hydration
  7. Reducing CO2 emissions