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OCR for page 47
47 GLOSSARY OF TERMS Accelerator --See Initiator. Polymer --The product of polymerization, more commonly a rubber or resin consisting of large molecules formed by Catalyst --See Initiator. polymerization. Cross-linking agent --Bifunctional or polyfunctional Polymerization --The reaction in which two or more mole- monomer whose addition to a polymer system increases cules of the same substance combine to form a compound the rigidity, resistance to solvents, and softening point of containing the same elements, and in the same propor- the polymer. tions, but of high molecular weight, from which the origi- Curing agent --See Initiator and Hardener. nal substance can be regenerated, in some cases only with extreme difficulty. Epoxy resin --A resin that contains or did contain epoxy groups principally responsible for its polymerization. Polymer concrete (PC) --A composite material in which the aggregate is bound in a matrix with a polymer binder. Flash point --The lowest temperature at which the vapor of a combustible liquid can be made to ignite momentarily Porosity --The ratio, usually expressed as a percentage, of in air. the volume of voids in a material to the total volume of the material, including the voids. Glass transition temperature (Tg) --The temperature at which an amorphous material (such as glass or a high Premix placement --The method of initially blending a polymer) changes from a brittle, vitreous state to a plastic polymer binder, with fine and coarse aggregate and fill- state. ers, if used, and then mixing until all particles are com- pletely wetted. Once the composite has been mixed as Hardener --The chemical component added to epoxy resins required, it is transported and placed. Term applies to that causes the resin to harden or cure. polymer concrete. Inhibitor --Free-radical scavengers added to monomers to Prepackaged polymer concrete --Polymer concretes whose react with and deactivate the free radicals in growing individual components (that is, monomer or resin, fillers, polymer chains, and to act as antioxidants to prevent and aggregates) are premeasured and packaged by the polymerization by oxidation product reaction during manufacturer for a prescribed sequence of introduction monomer storage. into the mixing process. Initiator --Agent that initiates growth of polymer chains by Promoted-catalytic method --A polymerization method decomposing into free radicals that actually start the that uses promoters or accelerators to cause the decompo- chain's growth; often incorrectly called a catalyst. sition of organic peroxide initiators, and subsequent Microcracks --Small, numerous, noncritical cracks that can release of free radicals that allow polymerization to take develop in hardened concrete in the matrix and at matrix place at ambient temperature without the need for an aggregate interfaces both prior to the concrete receiving external source of energy. external loads or during loading. Promoter --See Initiator. Monomer --A small molecule from which much larger poly- Resin--A natural or synthetic, solid, or semisolid organic mer molecules can be made; usually in liquid form for material of indefinite and often high molecular weight, with concrete applications. a tendency to flow under stress. It usually has a softening or Monomer depletion --The loss of monomer because of melting range and usually fractures conchoidally. evaporation from the surface of hardened concrete prior Shelf life --Maximum interval during which a material may to the polymerization process associated with the produc- be stored and remain in a usable and safe condition. tion of polymer-impregnated concrete. Silane coupling agent--Silicon compounds having the gen- Multiple-layer overlay --Two or more layers of polymer eral formula (HO)3SiR were R is an organic group compat- concrete bonded to concrete; normally each layer con- ible with thermoplastic or thermosetting resins. They are sists of an application of resin with aggregate broadcast used to enhance the chemical bond of organic polymers to into the surface. inorganic materials such as sand, rock, glass, and metals. Plasticizer --Chemical additions to monomers to improve Slurry overlay --Overlay applied by placing an application the flexibility of inherently brittle polymers. of resin or monomer followed by broadcasting aggregate onto the surface.

OCR for page 47
48 Solvent --A liquid capable of dissolving another substance. Thin polymer overlays (TPOs) --One or more layers of polymer concrete bonded to concrete, normally 1 in. or Thermal-catalytic method --A polymerization method that less in thickness. uses chemical initiators that are dissolved in the mono- mer before introducing the mixture into the concrete. The Viscosity --Friction within a liquid owing to mutual adher- subsequent application of external heat then causes the ence of its particles. Low-viscosity liquid monomers flow polymerization to occur at a rapid rate. more easily into the pores of concrete at ambient tempera- tures and pressures than do high-viscosity monomers. Thermosetting --Term applied to synthetic resins that solid- ify or set on heating or curing and cannot be remelted.