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40 CHAPTER SIX CONCLUSIONS Thin polymer overlays (TPOs) have become a widely Involvement of resin supplier or manufacturer to assist used construction method in North America for protect- contractor in proper handling, mixing, and application ing bridge surfaces, restoring skid resistance, and a bridge of resins; and preservation treatment for extending the lives of decks. Thermal compatibility that requires low-modulus res- The use of TPOs tripled from 1990 to 1999 and more than ins and compatibility of resins and repair materials. quadrupled from 1999 to 2008. More than half of the states and several of the Canadian provinces have used TPOs. TPOs have an important role in bridge maintenance and AASHTO, the American Concrete Institute, and a number protection. They are particularly appropriate in high-traffic of states have developed specifications for the construction areas in which lane closures must be minimized and for of TPOs. structures that cannot accommodate significant increases in dead load. When constructed properly, TPOs can provide a Three types of overlays are widely used: multiple layer service life of 20 to 25 years. that consists of two or more layers of resin and aggregate; slurry that consists of a single layer of primer, resin, and aggregate followed by a seal coat; and premixed that uses RESEARCH NEEDS resin and aggregate mixed in continuous batching machines or concrete mixers and placed on decks using screeds. The Research is needed to improve the performance and to most common resins and monomers are epoxies, polyester- extend the life of TPOs. Suggested areas of research include styrenes, methacrylates, and epoxy-urethanes. Most agen- cies use contractors to install TPOs, but some use their Development of resins, including those from recycled own forces. plastics, that will perform under extreme conditions, such as very low or very high temperatures, heavy traf- TPOs give the best performance when applied to decks fic volumes, or heavy loads; that are in good condition. TPOs must be constructed in Development of polymer concretes that will self-heal accordance with established principles to provide good per- in the event of cracks and delamination; formance. The most important factors for the success of Development and validation of tests that will more TPOs are-- accurately predict long-term performance of polymer concrete systems when used in a wide range of tem- Sound, dry substrate that requires quality repair peratures, heavy loads, and heavy traffic volumes; procedures; Improved analytical techniques to select material prop- Adequate preparation to provide a clean, textured dry erties and thicknesses of TPOs to perform satisfacto- surface; rily in the intended conditions; and Environment including dry and warm weather; Development of nondestructive test procedures that Experienced applicator and good workmanship to will accurately determine whether the condition of ensure proper application of materials; bridge decks is suitable for TPO application.