Chemical admixtures are water soluble ingredients (other than cement, water, and
aggregate) added to concrete in small quantities before or during mixing to
obtain some desired performance in the fresh and hardened state. They should
improve workability of the fresh mixture and strength or durability of the
hardened concrete. Chemical admixtures can be classified into five major
categories depending on the effectiveness; superplasticizers, air-entraining,
water-reducers, retarders, and accelerators. There are also other admixtures
that have functions such as corrosion inhibition, shrinkage reduction,
alkali-silica reaction inhibition, workability enhancement, damp proofing, and
coloring. Mineral admixtures are hydraulic or pozzolanic supplementary fine
powder materials to increase additional strength and durability of hardened
concrete.
- Superplasticizers
- Sulphonated naphthalene formaldehyde polymer
- Sulphonated melamine formaldehyde
polymer
- Lignosulfonates,
modified
- Polycarboxylates
- Mineral
admixtures
- Blast-furnace slag
- Fly ash
- Condensed silica fume
Sulfonated naphthalene formaldehyde
polymer is a major ingredient of superplasticizers. It
takes role in neutralizing the surface charges
on the cement particles and enhancing water tied up
in the cement agglomerations and thereafter reducing the viscosity of
the paste and concrete. It
promote dispersing of
cement particles and reduce water requirements without
affecting the workability, thus resulting high-strength concrete
and lower permeability. Superplasticizers
are linear polymers containing sulfonic acid groups
or carboxylic groups attached to the polymer backbone at regular intervals.
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