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Inorganic Polymers 427

It is believe that these diseases are caused by asbestos particles (whether asbestos or other sharp
particles) about 5–20 μm in length corresponding to the approximate sizes of the mucous openings
in the lungs. Thus, they become caught in the mucous openings. Because they are sharp, they cut
the lining when people cough. Scar tissue and the repeated healing process cause scar tissue buildup
and the opportunity for cancerous mutations to begin.
12.15 FLY ASH AND ALUMINOSILICATES

Aluminosilicates or aluminum silicates include industrial waste materials such as fly ash and ground

granulated blast-furnace slag (GGBFS), and natural materials such as metakaolin, kaolin, microsil-
ica, and volcanic ash. All are inorganic polymers derived from aluminum oxide and silicon oxide.
Fly ash is one residue created from the combustion of coal. Because there are different sources
of coal, fly ash has a variable composition. Table 12.7 contains the general chemical composition as

a function of the three major varieties of coal.
Fly ash consists of a variable mixture of somewhat spherical glasses ranging in size from 0.5–100
microns in diameter. It also contains minute amounts of many other elements, including arsenic,
beryllium, boron, barium, copper, cadmium, chromium, thallium, vanadium, zinc, strontium, lead,
and nickel. Fly ash is further divided by ASTM C618 standards into two general groupings, Class
F and Class C. Class F typically comes from the combustion of older anthracite and bituminous
coal that contains less than 10% lime (CaO). Pozzolanic materials combine with calcium hydrox-

ide forming a cement-like material. Class F fly ash is pozzolanic with the glassy silica and alumina
requiring a cementing agent such as Portland cement and water to produce a cement. Class C fl y ash
generally comes from younger lignite and subbituminous coal. Along with being pozzolanic, it is

more self-cementing in comparison to Class F fly ash containing more lime, alkali, and sulfates.
Fly ash used to be simply land filled but recycling is increasing. Coal burning power plants pro-

duce about 80 million tons of fly ash yearly in the United States. About 30 million tons are currently

recycled. Recycling of fly ash also reduces the need to quarry and the energy related to preparing
concretes such as Portland cement. Fly ash is used with Portland cement allowing the amount
of Portland cement to be reduced by up to 30% by mass. The resulting concrete is often greater

in strength compared to employing only Portland cement. The use of fly ash to replace Portland
cement is considered green-friendly since the production of 1 ton of Portland cement produces
about 1 ton of carbon dioxide in comparison to zero carbon dioxide for fl y ash.

Unlike soils, fly ash is more uniform in particle size so its addition to soil gives the mixture some

interesting properties. Fly ash is used in the production of fl owable fill or controlled low-strength
material. It is used as a self-leveling, self-compacting backfi ll.
Asphalt concrete is a composite of asphalt and a mineral aggregate. Fly ash is used to fi ll voids
between larger aggregates. Fly ash—containing asphalt concrete is stiffer resisting rutting.
Fly ash is a source of what is referred to as geopolymer. This term covers a group of inorganic
synthetic aluminosilicate materials. Other major sources of geopolymer are volcanic materials and

TABLE 12.7
Percentage Average Chemical Composition of Fly
Ash Derived from Different Coals
Composition Bituminous Subbituminous Lignite
20–60 40–60 15–45
SiO 2
5–35 20–30 20–25
Al 2 O 3
10–40 5–10 5–15
FeO, Fe 2 O 3
CaO 1–12 5–30 15–40

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