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31 Repairs be made using compatible polymer patching Problems Encountered materials supplied or specified by the TPO manufac- turer, which eliminates paying for traffic control twice Material suppliers observed the following problems that may and having to build in an extra 28 to 56 days to let the lead to poor performance of TPOs: patches cure, dry, and outgas; Diamond grinding be specified for very rough decks to Poor deck condition; save on the cost of shot blasting and to minimize the Cracking and delamination of deck; resin consumption; Inadequate concrete cover on steel; A mandatory 4-hour curing period is too long in hot Bidding followed by requirement that they must pro- weather; 1 hour is often enough and can be verified vide technical support on site; and by the impact hammer and/or screwdriver test; peak Obtaining all three surface preparation requirements: exotherm or maturity might also work to confirm the clean, dry, and sound. curing, especially for thicker overlays; The specifications requiring the airless spray applica- Recommendations tion for high-molecular-weight methacrylate sealers and primers be eliminated because of the difficulty To improve the quality of TPOs, material suppliers recom- in keeping the spray guns calibrated; by the time the mend that-- problem is discovered, considerable improperly mixed resin has been applied; Technical representatives be trained; TPO applications always be restricted to warm and dry Manufacturer's representative be on site to oversee periods; and work; Warranties for 5 years be required. The deck be in good condition; Deck be clean and dry; Deck cleaning texture be specified as ICRI CSP 7, but MATERIAL SUPPLIER INTERVIEWS can accept 6; Multiple-layer TPOs be used for epoxy systems; Seven material supplier representatives were interviewed Minimum tensile elongation be 50% for epoxy systems; by telephone. The questionnaires are in Appendix A. Two Aggregate have a Mohs hardness of 7; suppliers had been involved with approximately 1,000 TPOs AASHTO Task Force 34 recommendations (6 ) be and another two with hundreds each. The others, however, followed; were involved in at least 10 bridges. Their companies pri- For polyester systems specifications, have contractor marily supply epoxy resin systems. One company, however, make an investment in volumetric mixers with readouts supplies the majority of the polyester premix systems used in and plural components, paving machine with automatic North America. Collectively, they have worked in 13 or more grade control, and shot-blasting equipment; and states and Canada. Specification must require experience.