perature range by simply varying the TCT catalyst concentration while holding all of the
other constituents constant.
Polyurethanes
Technically, polyurethanes are the reaction products of molecules containing two or
more isocyanate groups (polyisocyanates) with molecules containing two or more hydroxyl
groups (glycols, polyols, glycerine, etc.) and water and phenols, to form the chain, making
a series of interconnected isocyanates and hydroxy-containing molecules. Since the con-
figurations of the ingredients can be varied to produce macromolecular polyurethanes, many
different types of polyurethane chains and spatial configurations can be designed for any
specific purposes, with one's curiosity limited only by one's imagination. However, the
commercial availability of raw materials and toxicity problems may limit the free design of
molecular structures.
Polyurethanes are commonly used for concrete sealing during new construction periods.
Chemical grouts are also available for nonstructural crack repairs. Polyurethanes are gener-
ally applied at temperatures above 4C (40F), with cure achieved within 24 to 72 hours.
However, several specially formulated polyurethanes have been commercially available
that have the potential for low-temperature use. A commercial urethane resin system known
as EP system (manufactured by Ashland Chemical Co., Columbus, Ohio 43216) can be
cured at temperatures as low as 30C (20F) as a neat solution or mixed with sand, while
maintaining low viscosity and good workability for cast-in-place construction without add-
ing any heat or protection from freezing.
Phenolic resins
Phenolic resins are the reaction product of one or more of the phenols with one or more
of the aldehydes. The use of substituted phenols and the aldehydes other than formalde-
hyde is very limited. Resins based on resorcinol can be cured at room temperature. Among
the aldehydes, furfural is the only one in commercial use other than the various forms of
formaldehyde. The presence of furfural makes the cured resin softer. Also, furfuryl alcohol
can be mixed with the resin to reduce the viscosity of the mix and allow higher filler ratio.
Commercial phenolic resin-based concretes made with BP Chemical J50/010L with acid
catalyst Phencat 15 and Foduth Chemical IR 1271 with acid catalyst CS 30 can be cured at
room temperature with higher levels of the catalyst. For lower catalyst amount, application
of pressure and heat may be required.
Phenolic concretes are claimed to possess equivalent mechanical properties and supe-
rior fire and chemical resistance to all other types of resin concrete developed to date. They
are high-temperature performance materials, have good resistance to corrosion and micro-
biological attack, do not absorb water, and have high resistance to attack by a range of
common chemicals. Phenolics are affected by alkalis and by oxidizing acids. They are
resistant to weak acids, solvents, detergents, and hydrocarbons. Extended exposure to weath-
ering and UV can cause failure.
Phenolic concrete is tougher and stiffer than ordinary concrete and is usually as tough as
polyester concrete. The level of the acid catalyst that can be successfully used in phenolic
concrete has been shown to be determined by the mix and casting process, type of catalyst,
and temperature. No cold weather use has been found for phenolic concrete.
Acrylics
Acrylic and methacrylic acid and their esters are included in the acrylic group. However,
the most important plastic in the family of acrylic resins is polymethyl methacrylate (PMMA),
a colorless transparent plastic with a higher softening point, better impact strength, and
considerably better outdoor weathering properties than polystyrene.
PMMA has received the attention of most of the work in polymer concrete development
in the United States in the last several years, especially for the repair of concrete. Benzoyl
peroxide is the most commonly used initiator, and N,N-dimethylparatoluidine and dim-
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