Since using a polymer rather than Portland cement creates a considerably more costly material, polymer concretes are used only in applications where its higher cost is offset, for instance by it’s properties, lower labor cost or lower energy expenditures in processing and handling. Construction engineers and architects, therefore, need to be aware of its capabilities and limitations when considering polymer concrete for specific applications.
Polymer concrete is made up of dry, non-absorbent aggregate filler, and a polymer binder. Types of fillers include chalk, sand, crushed stone, gravel, limestone, granite, quartz, clay, expanded glass, and metallic fillers. Mixed with the filler in order to create the polymer concrete are a monomer or a prepolymer, a cross-linking hardening agent, and a catalyst. Other ingredients added to the mix include binding agents and fire retardants.
In some applications, fibre reinforcements are also added, such as metal or glass fibres or fibre mats. The polymer binder amount used is relatively small, depending on the size of the filler. Polymer content normally ranges from 5 to 15 percent of total weight, but can be up to 30 percent if required.
Pros and Cons of Polymer Concrete
Polymer concrete (PC) has higher tensile, flexural, and compressive strengths compared to Portland cement concrete, allowing the use of up to 50 percent less material, giving it a weight advantage. It cures quickly at ambient temperatures, with good adhesion to most surfaces.
Its very low water absorption makes it have good long-term durability in respect to freeze and thaw cycles. It can be used in standard wood and steel formwork and may be vibrated to fill voids in forms. In addition it allows the use of regular form-release agents. Finally, polymer concrete has good resistance to chemicals and other corrosive agents.
On the other hand, the visco-elastic properties of the polymer binder used in PC creates high creep values, which restricts it’s use in structural applications. Deformation response is greatly dependant on the exact formulation used as well as the mixing time and temperature at which it is mixed. Elastic moduli can range from 20 to about 50 GPa. Resulting strains from shrinkage vary with the polymer used, so must be taken into account.
Polymer binders used in PC are organic substances, with much lower heat resistance than inorganic materials like stone and cement. The heat resistance of polymer concrete depends on the type of polymer binder used, but in general, extended exposure to high temperatures will cause resin degradation and ultimately, loss of strength.
Safe working temperature limits is about 140 degrees F for continuous exposure, and about 212 to 250 F for short periods, such as during steam cleaning. Polymeric components in PC are flammable, but PC materials do not easily burn since they have a high percent of mineral filler and often contain fire-retardant additives.