Civil Engineering Reference
In-Depth Information
maleic anhydride copolymer, Na salt of styrene, polyacrylamide,
polymethacrylic acid, etc.
7.6
Bacterial, Fungicidal, and Insecticidal Admixtures
Many organisms contribute to concrete degradation by establish-
ing and maintaining large colonies on or within concrete. Bactericidal
admixtures consist of polyhalogenated phenols, Na benzoate, benzalko-
nium chloride, and copper compounds. Fungicidal admixtures include
polyhalogenated phenols, copper acetoarsenite, and copper arsenate. Ter-
mite-proofing admixtures contain emulsion of the chemical dieldrin and is
used at a dosage of 0.5% by weight.
7.7
Shotcreting Admixtures
The shotcreting process involves quick setting (3-12 minutes) of
the mix on a surface and should also provide a thick layer without sloughing
off, and a rapid strength of the order of 500-1000 psi. Materials such as air-
entraining agents, strong alkalis, accelerators, organic bases, and sodium
aluminate are used for this purpose.
7.8
Antiwashout Admixtures
These are cohesion-inducing admixtures that render concrete co-
hesive enough to allow limited exposure to water with little loss of cement.
Such admixtures allow placement of concrete under water without the use
of conventional tremies. The active ingredient in such admixtures is a
water-soluble cellulose ether or water-soluble acrylic type polymer. Other
auxiliary agents are also added.
7.9
Corrosion Inhibiting Admixtures
The use of de-icing salts on concrete pavements has a deleterious
effect on reinforced concrete. Many bridges and parking garages with cast-
in-place concrete and reinforced steel develop cracks by allowing corrosive
chemicals to react with the steel. In normal concrete, the water in the pores
is highly alkaline and a protective iron oxide layer forms on the steel. This
