Page 186 - Handbook of Thermal Analysis of Construction Materials

Section 4.0 - Superplasticizers 169

Water-reducing–accelerating admixtures are particularly effective
in promoting early strength development, and should find application in
winter concreting. [74] For example, at 2, 5, and 18°C concrete with an
2
admixture shows 3-day strength of 3.6, 5.4, and 15.5 N/mm respectively,
but the corresponding concrete containing the admixture shows strength
2
values of 7.2, 8.0, and 19.2 N/mm .

4.0 SUPERPLASTICIZERS

Superplasticizing admixtures are capable of reducing water re-
quirements by about 30%, and also impart high fluidity characteristics to
concrete. They are variously known as superfluidizers, superfluidifiers,
super water reducers, or high range water reducers. They were first
introduced in Japan in 1964 and later in Germany in 1972. The basic
advantages derived from the use of superplasticizers are as follows:
production of concrete having high workability for easy placement without
a reduction in cement content or strength; production of high strength
concrete with normal workability, but with lower water content; the
possibility of making a mix having a combination of better than normal
workability and lower than normal amount of water; designing a concrete
mix with less cement, but having the normal strength and workability.
Because of the significant benefits that superplasticizers confer on con-
crete, an impressive number of patents have been taken on superplasticizers.
In eleven years, 1985–1995, more than three-hundred patents were filed
that refer to the development of a superplasticizer or it as an ingredient of
a multifunctional admixture.
A variety of organic water-soluble polymers can be used as
superplasticizers. The lignosulfonate compound may be considered as a
precursor to superplasticizers of today. Polynaphthalene sulfonate formal-
dehyde (SNF) has been used widely. Another superplasticizer that has been
used extensively is sulfonated melamine formaldehyde (SMF). Synthetic
organic polymer bearing carboxylic acid groups also act as high dispers-
ants. Polyacrylates are derivatives from a combination of anionic acrylic
and substituted acrylic polymers. With other anionic formation groups
(phosphonates, phosphates, sulfates) and polar functional groups (hydroxy,
ether, amide, amine, etc.), numerous types of polymers can be synthesized
for use as superplasticizers.
The mode of action of superplasticizers involves surface ad-
sorption, dispersion of the particles in the aqueous phase assisted by