The Three Major Effects of Fly Ash
Release Time:
2021-01-08
Source:
The Three Major Effects of Fly Ash
Fly ash is a fine particulate material collected from the flue gases after coal combustion and constitutes the primary solid waste discharged by coal-fired power plants. The major oxide components of fly ash from Chinese thermal power plants include SiO2, Al2O3, FeO, Fe2O3, CaO, and TiO2. With the development of the power industry, the fly ash from coal-fired power plants
Emissions have been increasing year by year, making fly ash one of the major industrial waste residues in China today. If large quantities of fly ash are discharged without treatment, they can generate dust and pollute the atmosphere; if released into water bodies, they can lead to river siltation. However, fly ash can be recycled and utilized as a resource, for example as a mineral admixture in concrete.
Fly ash resembles cement in appearance, with a color ranging from off-white to grayish-black. The color of fly ash is an important quality indicator, reflecting the level and variability of its carbon content. To a certain extent, it also indicates the fineness of the fly ash: the darker the color, the finer the particle size and the higher the carbon content. Fly ash has
There is a distinction between low-calcium fly ash and high-calcium fly ash. Typically, high-calcium fly ash has a yellowish hue, whereas low-calcium fly ash tends to be grayish. Fly ash particles exhibit a porous, honeycomb-like structure with a large specific surface area, resulting in high adsorption activity; the particle size range is 0.5 to 300 μm. Moreover, the particle walls possess a porous structure, with pores
The water demand ratio can be as high as 50%–80%, indicating very strong water absorption. Low-quality fly ash exhibits a small glass bead content and requires a large amount of mixing water; after use, it readily causes bleeding or delayed bleeding in concrete, thereby reducing its workability and increasing the likelihood of insufficient 28-day strength and low late-age strength gain, which can result in substandard concrete quality. Therefore, selection...
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Fly ash exhibits three major effects:
(1) Surface effects: The surface of fly ash can adsorb certain ions in the cement paste, which facilitates the immobilization of harmful ions in fly-ash-stabilized concrete and serves as a nucleation site for the formation of hydration products.
(2) Filling effect: The difference in particle size between fly ash and cement particles allows the fly ash to fill the pores in the cement matrix and aggregate, thereby reducing the porosity of concrete and increasing its compactness.
(3) Pozzolanic activity of volcanic ash: The reactive SiO2 in fly ash undergoes a secondary reaction with the cement hydration product CH, forming C–S–H gel that fills the pores in the aggregate–cement paste interfacial transition zone, thereby improving the concrete’s interfacial microstructure and enhancing its strength and durability.
