National Academies Press: OpenBook

Chip Seal Best Practices (2005)

Chapter: Chapter One - Introduction

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Suggested Citation:"Chapter One - Introduction." 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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Suggested Citation:"Chapter One - Introduction." 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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Suggested Citation:"Chapter One - Introduction." 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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7DEFINITION AND HISTORY A chip seal (also called a “seal coat”) is essentially a single layer of asphalt binder that is covered by embedded aggre- gate (one stone thick), with its primary purpose being to seal the fine cracks in the underlying pavement’s surface and pre- vent water intrusion into the base and subgrade. The aggre- gate’s purpose is to protect the asphalt layer from damage and to develop a macrotexture that results in a skid-resistant surface for vehicles. Chip seals and similar surface treatment use originated in the 1920s (Hinkle 1928). These early uses were predominantly as wearing courses in the construction of low-volume gravel roads. In the past 75 years, chip seals have evolved into maintenance treatments that can be suc- cessful on both low-volume and high-volume pavements. The popularity of chip seals is a direct result of their low ini- tial costs in comparison with those of thin asphalt overlays and other factors influencing treatment selection where the structural capacity of the existing pavement is sufficient to sustain its existing loads. Historically, most transportation agencies in North Amer- ica would allow their pavements to deteriorate to fair or poor condition (Beatty et al. 2002). As a result of the national pavement preservation initiative, funding agencies are becom- ing familiar with the cost-effectiveness of using preventive maintenance (PM) to preserve the infrastructure, and they are finding that chip seal research is worth the investment. Fig- ure 1 illustrates the concept of PM, whereby each dollar spent on maintenance before the age of rapid deterioration saves $6 to $10 in future rehabilitation costs (Hicks et al. 1999) and could conceivably save even more when user delay and traf- fic control costs are added to the bottom line. The focus of this synthesis was on summarizing the research and practices that point toward consistently suc- cessful chip seal projects. For this synthesis, a “best practice” is defined as any superior planning, design, or construction method that was found in the literature review and confirmed by survey responses. The project’s objective was to assist in the development and implementation of pavement preserva- tion programs by identifying the benefits of using a techno- logically advanced chip seal as part of a PM program. A great deal of research on chip seals has been performed in Aus- tralia, Canada, New Zealand, South Africa, the United King- dom, and the United States. Innovative and advanced chip seal programs have been identified with respect to critical factors that can be incorporated by other agencies. A comprehensive review of the literature on this subject has been completed to provide a solid theoretical as well as anecdotal foundation for the review of chip seal construction practices. The literature review furnished a global perspec- tive for identifying successful chip seal programs. Particular attention was paid to the sophisticated chip seals of Australia, New Zealand, South Africa, and the United Kingdom, as these nations consistently confirm chip sealing benefits and successful results on both low-volume and high-volume roads with routine service lives that are nearly double those assumed in North America, as shown in Figure 2. Addi- tionally, the subjects of end-product and performance spec- ifications, emerging construction methods and trends, and advanced design methodology have been covered to ensure that the latest developments in this field are considered as possible candidates for use in future research. A comprehensive survey was developed and North Amer- ican and international participation alike was encouraging. The survey emphasized identifying any critical and emerg- ing best practices. The survey was developed to focus on the specifics of design, contracting procedures, construc- tion methods, and performance measures. Figure 3 illus- trates the amount of chip sealed surfaces that are under authority of the agencies that responded to the survey. Note that international responses were tailored to reflect actual lane miles sealed. Survey analysis has been directed toward identifying practices that are likely to contribute to both successful and unsuccessful projects. After identification of such practices, a structured case study format was developed to clarify trends in the features of the best practices. The case study process illustrated lessons learned from highly successful practices. Considerable constructability improvements may be possible through emulating practices that have been iden- tified as critical to project success. CHIP SEALS AS A TOOL FOR PREVENTIVE MAINTENANCE Definition Pavement preservation is the long-term goal for most high- way agencies. Such action must be taken to not only protect the capital investment made when a roadway is constructed but also to maximize its ultimate useful life. Pavement preservation has its own unique definition that must be CHAPTER ONE INTRODUCTION

8The AASHTO definition of PM is a “planned strategy of cost-effective treatments that preserves and maintains or improves a roadway system and its appurtenances and retards deterioration, but without substantially increasing structural capacity” (Pavement Preservation . . . 1999). Thus, one can see that planned PM actions are actually a part of a much broader pavement preservation program. Benefits Chip seals are most frequently used as PM treatments on flexible pavements. The ideal benefits of applying a chip seal are obtained if the chip seal is applied early in a pavement’s life (i.e., before it exhibits a great degree of distress) and within the context of a PM program (Wade et al. 2001). A strict PM program whereby the roads are sealed at the end of every PM cycle may require several chip seals to be applied to the pavement’s surface for that pavement to reach its ser- understood for one to put it in context with PM. The pave- ment preservation definition developed by the FHWA Pave- ment Preservation Expert Task Group states that Pavement preservation is a program employing a network level, long-term strategy that enhances function pavement performance by using an integrated, cost-effective set of practices that extend pavement life, improve safety, and meet motorist expectations (Pavement Preservation . . . 1999). Furthermore, it is important that the reader understands that Pavement preservation is not a maintenance program, but an agency program. Almost every part of an agency should be involved. Success depends on support and input from staff in planning, finance, design, construction, materials, and main- tenance. Two other essentials for an effective program are long-term commitment from agency leadership and a dedi- cated annual budget (Galehouse et al. 2003). FIGURE 1 Preventive maintenance concept (Source: Galehouse et al. 2003). (PCI = pavement condition index.) 5.76 5.33 9.60 United States Canada AU, NZ, UK, SA Years FIGURE 2 Survey respondents’ chip seal service life (Source: Galehouse et al. 2003). (AU = Australia, NZ = New Zealand, UK = United Kingdom, SA = South Africa). 136,416 39,482 35,950 106,575 139,713 Australia Canada NZ UK US FIGURE 3 Lane miles of chip seal service life.

9vice life. The main concept behind implementing a PM cycle is to maintain the desired quality of the pavement without the development of major distresses. In contrast with routine maintenance, which is a reactive approach to repair pavement distresses, PM is a proactive approach to preserve and extend a pavement’s life (Seal Coat and Surface Treatment Manual 2003). In PM programs that use chip seals, practitioners believe that chip seals provide economically justifiable life extension benefits if applied at the correct time (Wade et al. 2001). Figure 4 shows the distribution of respondent agencies that strive to use chip seals as a PM practice. Chip seals are expected to provide at least 5 years of ser- vice; therefore, three or four chip seals may be necessary for a pavement to reach its design life. When applied on an exist- ing flexible pavement, a chip seal will provide a surface wearing course, seal the underlying pavement against water intrusion, enhance or restore skid resistance, and enrich the pavement surface to prevent the distresses caused by oxida- tion. Chip seals are generally effective in sealing fine cracks on the roadway surface, unless the cracks are indications of structural distresses. Chip seals are not expected to provide additional struc- tural capacity to the pavement, although it appears to be a common practice to apply chip seals to pavements that have structural distresses. Justification for chip sealing as a stop- gap procedure is straightforward; it is believed that the chip seal will reduce the rate of further deterioration until funds are made available for a conventional overlay. However, as a PM treatment, chip sealing on pavements that are not in good condition is not recommended practice and will likely be more expensive in the long run. Therefore, chip seal appli- cations should not be applied on badly cracked or weathered pavement surfaces where reconstruction, rehabilitation, or a conventional overlay is needed. Process The chip seal process begins in the planning stage when the pavement surface is analyzed to determine if a chip seal is an appropriate PM treatment. Surface characterization may con- sist of assessing the hardness, texture, and other measures of the structural condition of the pavement surface. If a chip seal is determined to be an appropriate treatment for the pave- ment, various surface preparation techniques are then per- formed on the surface. Crack repair, selected patching, lev- eling, presealing, and/or texturizing can be used to prepare the surface before chip sealing. These treatments should nor- mally be performed 6 to 12 months before the chip seal to allow sufficient time for curing. The surface needs to be free of foreign materials before material application. The applica- tion of the chip seal involves essentially four pieces of equip- ment: the binder distributor, aggregate spreader, rollers, and brooms. The binder distributor provides application of the binder to the pavement surface. A chip spreader immediately applies a uniform, predetermined rate of aggregate onto the binder. These two operations are at the heart of constructing a sur- face that is one stone thick and has enough binder to retain the aggregate, but not an excess amount of binder that causes the surface to bleed. Depending on the binder, aggregate, and actual type of chip seal being constructed, various rollers will be used to orient the aggregate to achieve appropriate embed- ment. Pneumatic rollers are typically found on all chip seal projects. The rollers are followed by the brooms that remove excess aggregate from the finished surface. This report will cover the aforementioned process in detail. The results of the literature review have been corre- lated with the survey responses to identify best practices. These best practices will be discussed in detail. Specific best practice case studies will also be presented and their essence discussed. 0 5 10 15 20 United States Canada AU, NZ, YES NO UK, SA FIGURE 4 Preventive maintenance practice by survey respondents.

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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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