Civil Engineering Reference
In-Depth Information
7.1
Expansion Producers
These admixtures control settlement and provide expansion in the
plastic state. In the plastic state, metallic Al, Mg, or Zn produce gases.
Admixtures that produce expansion both in plastic and hardened states are
calcium sulfoaluminate and lime based materials. Those which produce
expansion only in the hardened state are granulated iron filings and
chemicals that promote the oxidation of iron and offset volume changes due
to shrinkage.
7.2
Pigments
Concrete may be colored by integral addition or by the application
of color in the hardened state. Integral colored compounds include natural
and synthetic products, for example, chromium oxides, cobalt oxide, and
organic pigments based on Cu complexes of phthalocyanine.
7.3
Dampproofing and Waterproofing Admixtures
They are applied on roofs, slabs on ground, basements, water-
retaining structures, concrete blocks, and clay bricks. Waterproofing ad-
mixtures reduce the permeability of concrete. The dampproofing admix-
tures impart water repellency and reduce moisture migration by a capillary
action. Examples of these admixtures are soaps and fatty acids which react
with cement, conventional water reducers, methyl siliconates, etc.
7.4
Pumping Aids
They are used to pump marginally pumpable concrete. Materials
that are used for this purpose are water-soluble synthetic and natural
organic compounds such a cellulose ether, polyethylene oxide, alginates,
organic water-soluble flocculants, emulsion of organic materials, fine
clays, kaolin, diatomaceous earth, and calcined pozzolans.
7.5
Flocculating Admixtures
The chief function of these admixtures is to reduce the destructive
type of bleeding to a more gradual seepage in mixes. The materials include
