Fly Ash Properties and Their Applications as a Soil Ameliorant

Fly Ash Properties and Their Applications as a Soil Ameliorant

Virendra Kumar Yadav (Central University of Gujarat, India) and Priti Raj Pandita (Central University of Gujarat, India)
Copyright: © 2019 |Pages: 31
DOI: 10.4018/978-1-5225-7940-3.ch005


Fly ash is one of the major global pollutants which is produced in millions of tons every year. The high content of heavy metals in fly ash categorizes them as hazardous materials. The presence of ferrous, alumina, and silica along with numerous macro- and micro-nutrients make them a suitable candidate for applications in agriculture, forestry, wasteland reclamation, soil stabilizer, etc. Fly ash has positive effects on the plant growth and crop yield. A numerous literature has reported the applications of fly ash as pesticides, herbicides, and insecticides. It has both alkaline and acidic pH which helps in maintaining the pH of the infertile soil. All these applications are cited with the previous work carried out by the investigators.
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Fly Ash

Fly ash is a fine-glass like, spherical shaped heterogeneous in nature whose size varies 0.01-100µ recovered from the gases of burning coal during the production of electricity in thermal power plants. Fly ash commonly resembles to volcanic ashes which were used for the production of earliest known hydraulic cements about 2,300 years ago. Fly ash is the best known, and one of the most commonly used, pozzolans, in the world.

Fly Ash Mineralogy and Composition

These micron-sized earth elements primarily consists of silica, alumina and ferrous. The mineralogy and composition of fly ash varies from one sample to next depending on the source of the coal; degree of coal preparation, cleaning and pulverization; design, type and operation of the power plant boiler unit; conditions during combustion; additives used to assist combustion or improve precipitation performance; efficiency of emission control devices; storage and handling of the by-products; and the prevailing climate (Adriano et al, 1988). The mineralogical characteristics determine the crystalline phases of the fly ash which is about 15-45% in the fly ash. The high calcium fly ash i.e. class C have larger amounts of crystalline contents i.e. 25-45% (ACI committee 226, 1987).

Different Classes of Fly Ash

There are two classes of fly ash namely: class C and class F depending on the source of coal used and compositions of fly ash. The primary difference between class C and class F fly ash is the amount of calcium, silica, alumina, and iron content in the ash. Besides these, the two types vary in their applications, mineralogy and content which have been summarized in the Table 1.

Table 1.
Major differences between class F and class C types of fly ash
S. No.Class F- Fly AshClass C-Fly Ash
1.Produced from burning harder, older anthracite and bituminous coalProduced from burning younger lignite and sub-bituminous coal
2.Contains less than 20% limeContains more than 20% lime
3.Calcium ranges from 1-12%, in the form of calcium hydroxide, calcium sulfate and glassy componentsCalcium content: 30-40%
4.Higher amount of alkali and sulfateLess amount of alkali and sulfate
5.Requires cementing agent like PC, quick lime, hydrated limeSelf-cementing properties
6.Addition of air entrainer neededDoes not require activator & air entrainer
7.Used in high sulfate exposure conditionsCan’t be used in high sulfate conditions
8.Useful in high fly ash content concrete mixesLimited to low fly ash content concrete mixes
9.Used for structural concretes, HP concretes, high sulfate exposure concretesPrimarily residential construction

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