Polymers have been used in concrete as construction materials since the 1950s. The use of polymer concrete materials for highway and bridge deck applications has been increasing in the United States since the 1970s. As the traffic volume grows, the benefits of the quick repairs possible with polymer concrete materials will likely lead to continued growth of the polymer concrete industry.

What is Low Modulus Epoxy Concrete Overlay?
Low Modulus Epoxy Concrete Overlay is a polymer concrete formed by polymerizing a monomer and aggregate mixture. It has properties that make it highly desirable as a bridge deck overlay, among other things. Although these specifications focus on the use of polymer concrete for bridge deck overlays, it has many other uses, including building panels and tiles, cultured marble, pipe and liners, flooring, pilings, railroad ties and crossings, machine bases, adhesives, anchors, and grouts. Polymer concrete materials are also ideal for patching bridge decks.

How is Low Modulus Epoxy Concrete Overlay Applied?
Multiple-layer overlays, also called broom-and-seed overlays, involve distributing a polymer binder or resin on the existing, prepared bridge deck followed by broadcasting gap-graded aggregate. The polymer binder can be distributed by broom, squeegee, or spray bar. The aggregate can be broadcast over the top by hand, shovel, or automated spreading device. Two or three layers of resin and aggregate are typically used, resulting in an overlay approximately 6 to 9 mm (0.25 to 0.3 75 in) thick.

What Properties Does It Have?
Polymers are long molecules composed of repeating or random chains of smaller molecules called monomers. Certain chemicals, or catalysts, cause a reaction known as polymerization, which combines monomer and polymer molecules into polymer chains and causes the polymer chains to link together into even longer chains and three-dimensional networks. This chemical process is used to transform a liquid resin into a solid mass. The polymer network binds aggregate particles together in a polymer concrete.

Depending on the formulation of polymer used, polymer concrete can exhibit different properties. Some of the features that are generally true of polymer concrete include the following:

• rapid curing at ambient temperatures
• good bond strength to concrete bridge decks and other surfaces
• high flexural, tensile, and compressive strength
• very low or negligible permeability
• good long-term freeze-thaw durability
• low dead load, when compared to conventional or polymer-modified concrete overlays
• high friction resistance, depending on the aggregate used
• resistance to deicing salts, acids, petroleum products, etc.

It is also generally true that polymer concrete is relatively expensive in terms of initial material unit costs. These high costs can, however, be mitigated by the small volume of material required relative to hydraulic cement concrete and by the reduction in other construction costs, such as raising end dams, joints, and scuppers. Life cycle costs may be lower than for other rehabilitation techniques. Also, consideration of traffic control and user costs attributable to construction delays can make polymer concrete overlays attractive because placement can be accomplished in hours with short lane closure times.