| Supplementary Cementing Materials
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Supplementary cementing materials, also called mineral admixtures,
contribute to the properties of hardened concrete through hydraulic
or pozzolanic activity. Typical examples are natural pozzolans,
fly ash, ground granulated blast-furnace slag, and silica fume,
which can be used individually with portland or blended cement or
in different combinations. These materials react chemically with
calcium hydroxide released from the hydration of portland cement
to form cement compounds. These materials are often added to concrete
to make concrete mixtures more economical, reduce permeability,
increase strength, or influence other concrete properties.
Fly ash, the most commonly used pozzolan in concrete,
is a finely divided residue that results from the combustion of
pulverized coal and is carried from the combustion chamber of the
furnace by exhaust gases. Commercially available fly ash is a by-product
of thermal power generating stations.
Blast-furnace slag, or iron blast-furnace slag,
is a nonmetallic product consisting essentially of silicates, aluminosilicates
of calcium, and other compounds that are developed in a molten condition
simultaneously with the iron in the blast-furnace.
Silica fume, also called condensed silica fume
and microsilica, is a finely divided residue resulting from the
production of elemental silicon or ferro-silicon alloys that is
carried from the furnace by the exhaust gases. Silica fume, with
or without fly ash or slag, is often used to make high-strength
concrete.
Below is a summary of the specifications and classes of supplementary
cementing materials:
- Ground granulated iron blast-furnace slag-ASTM C989
- Grade 80-Slags with a low activity index
- Grade 100-Slags with a moderate activity index
- Grade 120-Slags with a high activity index
- Fly ash and natural pozzolans — ASTM C618
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Related Topics:
How Cement is Made
Aggregrate
Chemical
Admixtures
Placing
& Finishing Concrete
Curing Concrete
Air
Entrained Concrete
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