National Academies Press: OpenBook

Chip Seal Best Practices (2005)

Chapter: Chapter Two - Summary of Information Collected

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Page 9
Suggested Citation:"Chapter Two - Summary of Information Collected." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Page 9
Page 10
Suggested Citation:"Chapter Two - Summary of Information Collected." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Page 10
Page 11
Suggested Citation:"Chapter Two - Summary of Information Collected." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
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Page 11

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.

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

11 Aggregate selection is largely a cost function of availabil- ity and transportation distance. Local geography largely deter- mines the quality of the aggregate, and it is common for agen- cies to opt for a marginal quality (i.e., at the low end of the specifications) local aggregate owing to cost considerations. The quality of aggregate is important to the overall success of the chip seal program. As aggregate quality decreases, a num- ber of constructability problems, such as dust and degradation of the aggregate during handling, may arise from using poor- quality aggregates located within proximity to the project. The Australians have been known to be willing to pay for high- quality aggregate imported from great distances to ensure the quality of their chip seals (Austroads Provisional . . . 2001). Finally, different types of aggregate are more suited to certain binders as a result of electrostatic compatibility, and this fac- tor requires the chip seal designer to consider the electrostatic compatibility of local aggregate during binder selection. CHIP SEAL—ART OR SCIENCE? Traditional thought in the United States has portrayed chip seals as an art rather than a science (Wegman 1991). Beliefs that chip seal design is simply a “recipe” prevail to this day. The reasoning behind this is that the majority of North Amer- ican chip seal practice is based on local empirical experience rather than on sound engineering principles. The main reason FIGURE 5 Summary of survey responses.

to approach chip seal as an art is derived from the uncertain- ties and variability that exist with all chip seal projects. There- fore, the experience of the construction crew, familiarity with the local materials, and suitable equipment usage are consid- ered to be the critical factors for project success. Because the variability and uncertainties that affect the chip seals are inde- pendent of the design parameters, proponents of chip seal as an art argue that a formal design procedure is futile. One of the major difficulties involved in the design of material appli- cation rates is nonuniformity of the existing pavement sur- face. Such conditions necessitate binder rate adjustments in the field at the time of construction, a phenomenon that under- mines formal design. This realm of thought contends that if chip seal projects require field adjustments to application rates, formal design is simply a tool for estimating quantities. SOUND ENGINEERING PRINCIPLES Australia, New Zealand, South Africa, and the United King- dom have all developed their chips seal programs based on a greater set of engineering principles than those used by highway agencies in Canada and the United States. For exam- ple, all of the overseas agencies actually measure surface tex- ture using a sand circle test to characterize the existing pave- ment surface. In addition, all of the overseas agencies find it necessary to carry out surface hardness tests by using spe- cialty testing equipment such as a penetrometer or ball pene- tration device, to determine the nominal size of the aggregate to be used in their advanced design methodologies. The use of these sound engineering principles reduces the uncertainty and variability associated with chip sealing to the point where field adjustments of binder and aggregate application rates are minimized. Not only do these sound engineering principles seek to optimize material application rates, but they have fur- nished a platform on which to develop and enforce specifica- tions to an extent where performance-driven contracts trans- fer the risk of the project to the contractor (Sprayed Sealing Guide 2004). As such, they have moved the chip seal project from the maintenance world and into the construction con- tract arena. Figure 6 shows the survey responses addressing the issue of using in-house maintenance personnel. It can be observed that the majority of the U.S. respondents are per- forming most, if not all, of their chip seal program internally. The situation is reversed in Australia, Canada, and New Zealand, where most of the work is contracted out. CHIP SEAL TERMINOLOGY One of the difficulties in communicating technical matters between highway agencies is the result of the different tech- nical terms that are inherent to the chip seal process. This is further exacerbated because practitioners invariably believe that the terminology that they use is indeed technically cor- 12 rect. The Texas DOT (TxDOT) study found that definitions for common terms such as “flushing,” “bleeding,” “ravel- ing,” and “shelling” varied from district to district within that single state (Gransberg et al. 1998). As a result, an engineer in one district who defines the condition as one in which the chip seal is losing its aggregate as “raveling” may make a call for guidance to another engineer in a district where the con- dition is called “shelling” and the term “raveling” is applied only to hot-mix asphalt pavement distress. Because of the different local definitions, the first engineer may be given incorrect advice on how to rectify the problem. This synthesis study expanded its reach beyond the United States and found additional chip seal terminology in Canada, the United Kingdom, South Africa, Australia, and New Zealand. Thus, an effort was made to assemble a chip seal glossary, which is found following the References. For that glossary, chip seal terms were captured from both the litera- ture search and the survey responses. Definitions were devel- oped for each and an attempt was made to correlate those terms that have similar definitions in a manner that allows an easy reference for readers of this report. This report uses the terminology found in the Strategic Highway Research Program’s Distress Identification Man- ual for the Long-Term Pavement Performance Project (1993) to the greatest extent possible to maintain a consistent termi- nology. It is recommended that the reader frequently refer to the glossary to ensure that full understanding of the report’s contents and that the reader is not assigning his or her own local meanings to the terms contained in the report. The remaining chapters discuss both the literature review and survey responses in tandem. The objective is to report what was found in the literature and then allow the reader to use the survey results to either confirm or refute the state- ments in the literature. This method will then be used to dis- till the overall results of this synthesis into a list of best prac- tices for each subject, by chapter. 27 12 1 4 0 8 1 0 3 0 5 10 15 20 25 30 N o. o f R es po ns es US Canada AU, NZ, UK, SA >50% <50% None FIGURE 6 Use of in-house resources to complete chip seal program.

Next: Chapter Three - Chip Seal Design »
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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 342: Chip Seal Best Practices examines ways to assist in the development and implementation of pavement preservation programs by identifying the benefits of using chip seal as part of a preventive maintenance program and by highlighting advanced chip seal programs in use around the world. The report includes approximately 40 best practices in the areas of chip seal design methods, contract administration, equipment practices, construction practices, and performance measures. According to the report, the increased use of chip seals for maintenance can be a successful, cost-effective way of using preventive maintenance to preserve both low-volume and higher-volume pavements.

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