Long-Term Performance of Polymer Concrete for Bridge Decks (2012)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

3 SCOPE In 2007, TRB issued a problem statement, NCHRP Topic 39-11, Performance of Thin Polymer Overlays for Bridge Decks. The scope of the topic included the following statement: Thin polymer overlays, which consist of a polymer binder; e.g., epoxies, polyesters, or methacrylates, and aggregates are constructed with a thickness of no more than 25 mm (1.0 in.). They have the advantages of (1) adding very little dead load; (2) very fast cure times; (3) shallow depths that eliminate need for raising approach slabs; (4) transition from overlaid lane to non-overlaid lane during construction; (5) low permeability; (6) long- lasting wearing surface; and (7) frictional resistance. Many thin polymer overlays have been installed and it is critically important to summarize their performance in one document. Considerable performance history over the past 20 years is now available and the synthesis study collected information on a variety of topics: (1) previous research, specifications, and procedures on TPOs; (2) performance based on field applica- tions; (3) the primary factors that influence the performance, including traffic, chemical contamination, alkali–silica reac- tion, corrosion, concrete strength, air content, moisture, envi- ronment including temperature and climate, use of tire chains and studs, methods of removing existing concrete, aggre- gate, surface preparation, material compatibility including substrate, treatments, and patching; (4) current construction guidelines related to surface preparation, mixing and place- ment, consolidation, finishing, and curing; (5) repair proce- dures; (6) factors that influence the performance of overlays, including life-cycle cost, benefits and costs, bridge deck con- dition, service life extension, and performance; and (7) suc- cesses and failures of TPOs, including reasons for both. Information was gathered from state departments of transportation (DOTs) and Canadian provinces, a literature review, a survey of vendors, and selected interviews. MAJOR DEFINITIONS The focus of this report is TPOs. There are several impor- tant distinctions to be made. The overlays are noncementi- tious, that is, there is no hydraulic cement such as portland CHAPTER ONE INTRODUCTION BACKGROUND Polymer concrete (PC) overlays were first used in the 1950s as single layers of coal tar epoxy broomed onto the concrete substrate and seeded with fine aggregate. These overlays were not very impermeable, nor were they durable under traf- fic. In the 1960s, an oil-extended epoxy was used to improve the performance. By the mid-1970s, polyester-styrene res- ins and methyl methacrylate monomer systems were being placed using the broom-and-seed method (1). Premixed PC that was screeded in place began to be used. In many cases, the thicker, more brittle layers delaminated because of ther- mal incompatibility of the overlay and substrate. Through increased attention to monomer and resin formulations and a better understanding of the causes of delamination and other distresses, the performance of thin polymer overlays (TPOs) has increased significantly. Con- siderable efforts have gone into improving the resistance to chemical and mechanical attack and into understanding the requirements for surface preparation, mixing and placing the PC, and in curing (2). Initially, the reviews of TPOs were not favorable. For example, in 1984 Furr (3) stated concerning sand-filled epoxy TPOs, “these overlays generally have proved to be a poor solution to the surfacing and waterproofing problem.” He went on to say that of 12 states, only one had found one epoxy that had performed well. However, since that time, the improvement in performance has been substantial, although some problems still exist. It is now understood that flexible resins used in thin layers with wear-resistant aggregates are essential in producing TPOs that are thermally compatible with the concrete decks and are long wearing (3). It was learned in this survey of states and provinces that most problems occur because of errors in workmanship. The use of TPOs has increased significantly in recent years. Sprinkel (4) reports that before 1990, 139 TPOs had been placed. There was a threefold increase between 1990 and 1999, with 416 additional overlays having been placed. Considerable experience and data now permit more informed conclusions to be drawn relating to best practices for constructing TPOs.

4 Reference Information System (TRIS) was a major source of information. Professor Yoshihiko Ohama of Nihon Uni- versity in Japan has maintained a complete bibliography on concrete-polymer materials over the past several years, and his database, which was last updated in 2007, was used in this review (5). The proceedings of the International Con- gress in Polymers in Concrete were searched for information along with other conference proceedings that were potential sources of information. The American Concrete Institute (ACI) has published many papers on TPOs in journals and in special publica- tions. ACI Committee 548 Polymers in Concrete has also published several documents on TPOs including a Guide for Polymer Concrete Overlays (1) and a specification for epoxy TPO construction (2). AASHTO has published Guide Specifications for Poly- mer Concrete Bridge Deck Overlays, which has been widely adopted, at least in part, by many agencies (6). Survey of Transportation Agencies, Material Suppliers, and Contractors Survey forms were developed and sent to state DOTs and Canadian provinces. Selected vendors and selected contrac- tors that have had experience with TPOs were surveyed by telephone. The agency survey forms, contained in Appendix A, were e-mailed to agencies. Contractors and vendors were interviewed by telephone. Some follow-up telephone inter- views with agencies were conducted to obtain additional information. REPORT ORGANIZATION The report is organized in the following manner: • Chapter One—Introduction • Chapter Two—Literature Findings and Specifications • Chapter Three—Performance of Overlays from Surveys and Interviews • Chapter Four—Proven Practices • Chapter Five—Repair • Chapter Six—Conclusions • References • Bibliography • Glossary of Terms • Appendix A: Questionnaires • Appendix B: Stresses in Overlays • Appendix C: Warranty and Payment Bond The information obtained from the various sources was reviewed to obtain the background on the topics listed in the scope. The information was grouped into the subtopics used in the chapters. The factors that influence performance cement; the binder is a polymer. The overlays are thin, typi- cally less than 1 in. in thickness and often 0.5 in. or less. The substrate is normally a portland cement concrete bridge deck, although in a few instances steel decks or concrete pavements have been used. Definitions taken in part from ACI 548.5R-96 Guide for Polymer Concrete Overlays (1) are given in the Glossary at end of the report. A few of the more important definitions are presented in this section. Epoxy resin—A resin that contains epoxy groups princi- pally responsible for its polymerization. Monomer—A small molecule from which much larger polymer molecules can be made, usually in liquid form for concrete applications. Multiple-layer overlay—Two or more layers of polymer concrete bonded to concrete; normally each layer consists of an application of resin with aggregate broadcast into the surface. Polymer—The product of polymerization, more com- monly a rubber or resin consisting of large molecules formed by polymerization. Polymer concrete (PC)—A composite material in which the aggregate is bound in a matrix with a polymer binder. Premix overlay—The method of initially blending a poly- mer binder, with fine and coarse aggregate and fillers, if used, and then mixing until all particles are completely wetted. Once the composite has been mixed as required, it is trans- ported and placed. The term applies to polymer concrete. Resin—A natural or synthetic, solid or semisolid organic material of indefinite and often high molecular weight, with a tendency to flow under stress. It usually has a softening or melting range and usually fractures conchoidally. Slurry overlay—Overlay applied by placing an applica- tion of resin or monomer followed by broadcasting aggregate onto the surface. Thin polymer overlays (TPOs)—One or more layers of polymer concrete bonded to concrete, normally 1 in. or less in thickness. METHODOLOGY FOR OBTAINING INFORMATION Literature Review A literature review was conducted that included the most likely sources of information on TPOs. The Transportation

5 were derived from these sources. The best practices are a summary of the knowledge that has produced overlays that have performed well as reported by the states and provinces. Little information on costs and repairs was obtained from the literature and from surveys and interviews. For this rea- son, these issues are addressed in only a cursory manner.