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10 CHAPTER TWO SUMMARY OF INFORMATION COLLECTED SCOPE OF RESEARCH between the average daily traffic (ADT) levels at which U.S. and Canadian agencies use chip seals. Both of these As mentioned earlier, a comprehensive review of the litera- statements support the finding in the literature review that ture on chip seals provided a solid theoretical as well as anec- the experience of the transit personnel appears to be a major dotal foundation for the review of chip seal practices and factor for achieving chip seal success. Other success factors experiences. More than 120 published articles, representing are discussed as they are encountered in the subsequent 80 years of research on chip seals and PM, were reviewed for chapters. this synthesis. Technical information relating to emerging practices, problems solved, and lessons learned have been The survey responses were also divided according to identified and investigated. The findings can be divided into AASHTO climatic region. Surprisingly, trends were not the following seven basic categories: observed. This finding will be discussed in detail later in this chapter. Another surprising result was the almost total 1. Design methods, reliance on asphalt emulsion binders. Only three responding 2. Contract administration, U.S. state DOTs indicated that they regularly used hot asphalt 3. Material selection, cement binders in their maintenance chip seal programs. 4. Equipment practices, 5. Construction practices, REGIONAL CONTEXT 6. Performance measures, and 7. Case studies in excellence and innovation. The importance of evaluating the findings of this synthesis within a regional context is critical. Chip seal practices gen- CHIP SEAL SURVEY erally vary by region as a result of three factors: local cli- matic conditions, binder availability, and local aggregate A survey intended for those public highway and road agen- quality. Information from the literature review and survey cies that were expected to use chip seals in their mainte- has been grouped into logical sets based on regional charac- nance program was prepared and administered. In addition teristics. It is anticipated that agencies located in roughly the to the survey sent to the chief maintenance engineer in each same climatic regions and using similar sources of aggregate state department of transportation (DOT), surveys were will have similar chip seal programs. sent to points of contact at the federal, municipal, and county levels as well as to international highway authorities The role that climate and weather play in chip seal opera- in Australia, Canada, New Zealand, South Africa, and the tions cannot be overstated. It is accepted that ambient tem- United Kingdom. A copy of the survey is contained in peratures at the time of construction closely affect the Appendix A, and the full results of the responses are con- quality of the chip seal (Benson and Gallaway 1953; Connor tained in Appendix B. Ninety-two individual responses rep- 1984). Emulsions are generally believed to be less sensitive, resenting 42 states, 12 U.S. cities and counties, 10 Canadian in comparison with hot applied asphalt cements, to failure provinces, 1 Canadian territory, 2 Canadian cities, 4 Aus- during cool weather construction when ambient temperatures tralian provinces, 2 New Zealand provinces, 2 public agen- are low and aggregates are damp (A Basic Emulsion Manual cies from the United Kingdom, and 1 from South Africa 1997). Also, because emulsions require much lower applica- were received. tion temperatures (130°F to 185°F) than do hot applied asphalt cements (300°F to 350°F), they are more suitable for Analysis of the survey responses showed that the United chip seal work later in the season when average nighttime States and Canada have very similar practices, and they are temperatures start to decline. On the other hand, high ambi- quite different from those employed overseas. Figure 5 ent air and surface temperatures can be a problem with emul- summarizes the salient elements of the survey with regard sions, reducing the viscosity of binder to such a point that to North America. One can observe that the distribution aggregate retention is adversely affected (A Basic Emulsion of states and provinces that reported good results with Manual 1997). The bottom line on the climatic context is their chip seal program is fairly evenly distributed across underscored by the requirement to install all chip seals in the the continent. Additionally, one can observe the similarity warmest, driest weather possible in the region.