ABSTRACT
Polymers are produced by combining a large number of small molecular units by the chemical process known as polymerisation to form long-chain molecules. Polymers are usually made in one of two polymerisation processes. In condensation-polymerisation the linking of molecules creates by-products, usually water, nitrogen or hydrogen gas. In addition-polymerisation no by-products are created. The principal thermosetting polymers that are used in construction are polyesters, vinylesters and epoxies. Thermosetting polymers are formed in a two-stage chemical reaction when a polymer is reacted with a curing agent. Thermoplastic polymers may readily be processed into sheets or rods or complex shapes in one operation, which is often automated. Polymer grids are used in civil engineering as the reinforcement for soil in reinforced earth. Continuous sheets of thermoplastic polymers, generally polypropylene or polyethylene, are extruded to very fine tolerances and with a controlled structure.
