A variety of polymeric binders to produce mortar and concrete are commercially avail-
able. These include various thermosetting resins, tar-modified resins, resin-modified as-
phalts, and vinyl monomers. Different kinds of binders are popular in different countries;
these are dictated mostly by availability and cost. For example, in Japan, the binders for
polymer mortar are chiefly epoxy resins, unsaturated polyester resin, such as polyester-
styrene systems, vinyl ester resin, and methyl methacrylate monomer whereas, for the poly-
mer concrete products, the common binder is unsaturated polyester resins. On the other
hand, the most common polymeric binder types in the United States and western Europe
are methyl methacrylate monomer, unsaturated polyester, and epoxy resins, among which
the unsaturated polyester resin has the lowest cost. Furan resin, mainly the furfural-acetone
resin, is widely used in the former Soviet Union and east European countries. In addition to
these conventional manufactured synthetic resins, application of recycled monomers and
polymers to the synthetic binders has also been made recently.
Polymeric binders cannot set or harden by themselves, and for this reason various initia-
tors, promoters, and hardeners are selected and added to the polymeric binders at the time
of mixing the mortar and concrete. As mentioned earlier, polymeric binder systems are
quite different from the ordinary hydraulic cement systems; like their regular cement coun-
terpart, there are various guidelines published by the American Concrete Institute for the
use of polymer concretes.
Unsaturated polyester and vinyl ester resins
Unsaturated polyesters are condensation polymers formed by the reaction of polyols
and polycarboxylic acids with olefinic unsaturation being contributed by one of the reac-
tants, usually the acid. The polyols and polycarboxylic acids used are usually difunctional
alcohols (glycols) and difunctional acids such as phthalic and maleic. Water is produced as
the by-product of esterification reaction and is removed from the reaction to drive the poly-
esterification reaction to completion. All of the materials used must be at least difunctional
to make the polyesterification reaction possible.
Unsaturated polyesters copolymerize with monomers having olefinic unsaturation much
more rapidly than they homopolymerize, so most unsaturated polyesters are used as mix-
tures with reactive, usually liquid, monomers. Of such monomers, styrene is by far the most
used monomer. Styrene used in polyester resins is low in cost, provides low-viscosity
resins at reasonable monomer levels, and copolymerizes readily with unsaturated polyester
alkyd at various temperatures. Laboratory tests indicate that for optimum workability, the
styrene content is 45 to 50% of the resin content, although styrene content as low as 35 wt%
has been used. The copolymerization chemistry of unsaturated polyester alkyds and unsat-
urated monomers is usually initiated by free radicals generated by the decomposition of
peroxides, azo compounds, or free radicals generated by the use of medium- to high-energy
radiation, such as ultraviolet light or electron beams. Commercially, visible-light-cure poly-
esters are also available and the curing occurs independently of ambient conditions. Micro-
wave curing of polyester resins has also been demonstrated.
Commercial polyester resins have been demonstrated to be useful at curing tempera-
tures as low as 10C (14F) without many handling difficulties. Polyesterstyrene con-
crete products have several advantages for the rehabilitation of portland cement concrete.
They are highly abrasion-resistant and impermeable to water and road salts, and are effec-
tive in thin layers ranging from 3/8 to 1 inch thick, thereby reducing dead load and clear-
ance problems. They are well suited to night work in heavy traffic areas where bridge or
road closures must be kept as brief as possible. The resins to produce the concrete are
relatively inexpensive and are readily available. The vinyl esters also are available as grouts
or toppings for concrete repair, although their curing properties sometimes limit their use to
applications above 10C (50F). There is one concern with the polyester concrete: research
has shown that the compressive strength of polyester concrete decreases as temperature
increases, and thus the durability may be a problem under cycling temperatures.
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