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SUMMARY Pavement patching is one of the most extensive and expensive pavement maintenance activi- ties undertaken by highway agencies at all levels. Because of the costs and resources involved in this massive undertaking, there are significant benefits to be attained by managing patching programs in the most cost-effective manner. This synthesis summarizes current practices for patching both concrete and asphalt pave- ments. The intent is to document the state of the practice for patching relatively small-scale surface defects in concrete and asphalt pavements. Larger scale patching, wedge and level (or level-up patching), and pre-overlay patching are not addressed. Both reactive and planned patching are addressed. The synthesis covers management or administrative issues, materials, methods, equipment, specifications and tests, traffic control, and other aspects of patching operations. The Strategic Highway Research Program (SHRP) had three contracts dealing, in part, with pavement patching. These efforts led to evaluations of various materials for patching asphalt and concrete pavements, standardized terms for different patch installation proce- dures, and a prototype automated patching vehicle. This synthesis compares current practices with those recommended through these SHRP projects to see what changes have been made since the close of the SHRP program. The information contained herein was collected through extensive literature reviews of U.S. and international sources, summarized in chapter two; and electronic surveys and follow- up phone and e-mail interviews, summarized in chapter three. A total of 49 survey responses were received from U.S. state highway agencies, a 96.1% response rate. Responses were also obtained from 20 local agencies across the United States. In addition, a similar survey was distributed in the United Kingdom and Ireland, where 36 responses were received from national, county, and city agencies, as well as three maintenance contractors. Five responses were received from Canadian agencies (three provincial and two cities). The U.S. local and international responses are presented in chapter four. Four case examples are offered in chap- ter five to demonstrate common practices and innovations. The conclusions from the syn- thesis, gaps identified in the existing knowledge, and areas for future research, as identified through the surveys, are summarized in chapter six. Almost all U.S. states place great importance on pavement patching. Only a few states (five of 49), predominantly in areas of the country where freezing temperatures are uncommon, indicated that they did not consider patching to be a major component of their maintenance programs. There are similarities and differences in patching practices across the states. The distresses addressed by patching and the triggers that call for patching are similar, both for the states and local agencies in the United States and internationally. Engineering judgment is extensively relied upon to determine when and where to patch, the type of patch to install, and when patching is not an appropriate repair to make. Many agencies have guidelines to promote consistency across district or regional lines and to improve pavement service levels overall. PAVEMENT PATCHING PRACTICES
2 The materials used for patching vary widely, but fall into several general categories. Asphalt materials are most commonly used for temporary patching of both concrete and asphalt pave- ments. Permanent patches on concrete pavements are commonly made with cementitious materials of varying types, depending on the type of patch, type of roadway, and how long the patch can be allowed to cure or set. Epoxies and other polymeric materials are sometimes but less commonly used, largely because of the costs and complexity in handling and placement. On asphalt pavements, hot mix asphalt remains the preferred material for semi-permanent patching; however, the use of spray injection patching is increasing and the performance is reportedly approaching semi-permanent status in some states. This success, however, has not been found in all states. Transportation agency employees do most of the patching in states and local agencies, espe- cially for reactive patching. Some states are making increasing use of maintenance contracts; however, these are still not common. Maintenance contracts are much more common overseas. Traffic control measures vary considerably depending on factors such as the duration of the patching process, type of roadway, and traffic volumes. No major differences were noted between the types and locations of agencies and the traffic control measures implemented. SHRP research led to the development of manuals for patching potholes and partial depth repair of spalls on concrete pavements. For the most part, the recommendations in those man- uals have been widely implemented. The patching materials evaluated in the SHRP studies are mostly still on the market, although there have been some formulation and name changes. SHRP-recommended tests for patching materials have been implemented to some extent; however, some recommended tests for workability and cohesion are not commonly used. The automated patching vehicle developed under SHRP never progressed beyond the proto type stage and reportedly did not perform as designed. Although the device itself was not implemented as designed, the concept of using spray injection patching has been widely imple- mented and is basically the same as that part of the SHRP prototype. The use of spray injection patching, which performed well in the SHRP research, has increased dramatically and is quite common in many states. On concrete pavements, partial depth patching, which performed well in the SHRP research, has also been widely implemented. The use of proprietary patching materials or higher quality generic patching materials has also increased. The 110 agencies and organizations responding to the survey reported various needs for additional research, especially with regard to new or innovative materials, new procedures, cost-effectiveness, and comparison of different patching materials. There were a number of similarities in the needs expressed through the survey by the responding state, local, and international agencies.
