National Academies Press: OpenBook

Chip Seal Best Practices (2005)

Chapter: Chapter Five - Material Selection

« Previous: Chapter Four - Contract Administration
Page 25
Suggested Citation:"Chapter Five - Material Selection." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 25
Page 26
Suggested Citation:"Chapter Five - Material Selection." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 26
Page 27
Suggested Citation:"Chapter Five - Material Selection." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 27
Page 28
Suggested Citation:"Chapter Five - Material Selection." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 28
Page 29
Suggested Citation:"Chapter Five - Material Selection." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 29
Page 30
Suggested Citation:"Chapter Five - Material Selection." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 30
Page 31
Suggested Citation:"Chapter Five - Material Selection." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 31

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.

INTRODUCTION Chip seal material selection is generally dependent on climatic conditions, binder and aggregate quality, product availability, and an organization’s experience with particular practices. Bituminous binders and cover aggregate make up the finished product. The bituminous binder’s functions are to seal the existing surface from water intrusion, provide an interfacial bond between the aggregate, and provide the adhesive that bonds the aggregate to the existing flexible pavement surface. The aggregates in a chip seal provide a number of functions. Cover aggregate should provide a good skid-resistant surface while being resistant to polishing, durable against abrasion effects, and resistant to the disintegration caused by weath- ering (Seal Coat . . . 1993). Material selection is becoming more complicated as technology enhancements are contin- ually developing adhesion agents, polymer modifiers, and geotextiles marketed for chip seal use. AGGREGATE SELECTION Aggregate selection is critical to determining which type of chip seal to use, which type of binder to design for, and which type of construction procedures to specify. The quality of aggregate is important to the overall success of the chip seal program, and quality involves a number of constructability issues about using aggregates that are clean, durable, and abrasion resistant. The cover aggregate is expected to transfer the load to the underlying surface. It should provide adequate skid resistance and should be durable against climatic effects and traffic wear. In North America, aggregate selection is a function of geography where availability and transportation distance essentially define the aggregate selection process. Local availability often constrains the quality of the aggre- gate, causing agencies to select lower-quality local aggregates based on cost and availability. This situation conflicts with philosophies in New Zealand and Australia, where aggregate is transported up to 500 mi to ensure the performance and longevity of their treatments (Beatty et al. 2002). They justify the added expense of using higher-quality aggregate with the benefits accrued in extended service life. The cost implica- tions of using the higher-grade aggregate in conjunction with the appropriate binder type should be carefully assessed using life-cycle cost analysis. Another consideration is the ionic compatibility of the aggregate with the selected binder to ensure that good adhesion is developed between the aggregate and the binder. This is especially critical when using emul- 26 sions, because they routinely come in either anionic or cationic forms. Size and Gradation The aggregate gradation plays a key role in the design, con- struction, and performance of chip seals. Aggregate size, typically referred to as nominal top size, is the smallest sieve through which all of the aggregate passes. The aver- age of the smallest dimension of the aggregate is referred to as the ALD (Hanson 1934/35). The nominal size of aggre- gate is selected based on traffic, surface condition, and type of chip seal. Larger aggregate particle sizes are generally more durable and less sensitive to variations in binder appli- cation rate (Gransberg et al. 1998). Additionally, as the binder material is meant to seal the surface, a larger-sized aggregate will result in a thicker binder layer, enhancing the quality of the chip seal. However, if not properly embedded and swept, larger aggregate can cause more damage to vehi- cles immediately after application. Its coarser texture also results in a chip seal with higher noise emissions. The sur- vey results shown in Figure 24 indicate that the most com- mon size for a single-course chip seal is usually a 3⁄8-in. (10-mm) chip. In addition, survey respondents commonly indicated that double-course seals usually have a 1⁄2-in. (12.5-mm) initial aggregate application, followed by a sec- ond aggregate application of approximately one-half that nominal size. The specified gradation should be such that the texture of the chip seal is consistent. Tight gradation bands, which ensure a uniformly graded aggregate, with minimal fines and dust, are necessary for a high-quality project. The literature review and survey responses show a consensus that single-sized aggregate with less than 2% passing the No. 200 sieve is considered ideal (Wegman 1991). The amount of fines in the gradation affects the binder’s ability to adhere to the aggregate. Because the amount of fines increases every time the material is handled, Minnesota requires a tighter specification of less than 1% passing the No. 200 sieve to allow for degradation during material movement and installation (Janisch and Galliard 1998). The ideal grading for an aggregate used in chip seals is one in which all the particles of stone are very close to one size, which helps ensure that the chip seal is only one-stone thick. Single-sized aggregate produces a constant embed- ment depth, which is a critical factor for the success of a chip seal. A uniformly graded aggregate provides a more consis- CHAPTER FIVE MATERIAL SELECTION

27 tent embedment that results in improved aggregate reten- tion, surface friction, and drainage capabilities of the seal (McHattie 2001). Table 5 lists typical chip seal gradations taken from various state DOT manuals in the United States. The reader’s attention is directed to the Minnesota gradation for choke stone. This was the only U.S. reference that fur- nished the specifications for this type of aggregate that would be used with the racked-in seals described in chapter three. Aggregate Shape The shape of cover aggregate is crucial to the successful per- formance of a chip seal. Aggregate shape is typically char- acterized by angularity. As the orientation of the embedded chip is important, cubical aggregate shapes are preferred because traffic does not have a significant effect on the final orientation of aggregate (Janisch and Galliard 1998). Cubi- cal materials tend to lock together and provide better long- term retention and stability. The quantity of flat particles in the aggregate can be determined by the Flakiness Index test (Seal Coat . . . 2003). A low Flakiness Index indicates that all the particles are near to having a cubical shape. Under traffic, elongated and flat particles will lie on their flattest side and become covered within the binder. As a result, flat- ter aggregate is more susceptible to bleeding in the wheel- paths. Because the orientation of cubical aggregate is not as susceptible to displacement by traffic, the opportunity for bleeding is reduced. The angularity of the aggregate, a characteristic that can be measured by testing for percent fracture, determines a chip seal’s propensity to damage by stopping or turning traf- fic (Wade et al. 2001). Australian practice requires that 75% of the aggregate have at least two fractured faces (Sprayed Sealing Guide 2004). Rounded aggregates, as indicated by low percent fracture, are susceptible to displacement by traf- fic because they provide the least interfacial area between the aggregate and binder. The roundness of the aggregate will determine how resistant the chip seal will be to turning and stopping movements. Aggregate Cleanliness Dust on the aggregate surface is one of the major causes of aggregate retention problems. Dust is defined as the per- centage of fine material that passes the No. 200 sieve. To improve the quality of the material, the percentage of fines passing the No. 200 sieve should be specified as a maximum of 1% at the time of manufacture (Janisch and Gaillard 1998). Dusty and dirty aggregate ultimately lead to problems with aggregate retention. Asphalt binders have difficulty bonding to dirty or dusty aggregate, causing the aggregate to be dis- lodged on opening to traffic (McLeod 1969). It is recommended that the aggregate be sprayed with water several days before the start of the project (Maintenance Chip Seal Manual 2000). Washing chip seal aggregate with clean, potable water before application may assist in removing fine particles that will prevent adhesion with the binder. In addi- tion, damp chips will assist the binder in wetting the rock, thus increasing embedment (Maintenance Chip Seal Manual 2000). In addition to washing with water, petroleum materials are sometimes used to clean the aggregate before application. Petroleum-based materials such as diesel fuel are commonly used to wash aggregate in Australia and New Zealand (Sprayed 0 5 10 15 20 25 30 35 40 45 5/8 in. (16.0 mm) 1/2 in. (12.5 mm) 3/8 in. (10 mm) N o. o f S ur ve y Re sp on de nt s FIGURE 24 Single application chip seal size. State and Gradations Sieve Size Alaska E Chip Arizona Low Traffic Arizona High Traffic Minnesota Aggregate Minnesota Choke Stone Montana Grade 4A South Dakota Type 1A South Dakota Type 1B 1/2 in. 100 100 100 100 100 — 100 100 3/8 in. 90–100 100 70–90 90–100 100 100 40–70 100 1/4 in. — 70–90 0–10 40–70 100 — — — No. 4 10–30 1–10 — 0–15 85–100 0–30 0–15 10–90 No. 8 0–8 0–5 0–5 0–5 10–40 0–15 0–5 0–30 No. 40 — — — — 0–5 — — 0–4 No. 200 0–1 0–1 0–1 0–1 0–1 0–2 0–1 — TABLE 5 TYPICAL GRADATIONS FOR CHIP SEAL AGGREGATE (% passing)

Sealing Guide 2004). Such practice is not likely to be found in North America owing to environmental restrictions. Aggregate Toughness and Soundness Resistance to abrasion, degradation, and polishing will ensure that the selected aggregate remains functional for the expected life span of the chip seal. It is desirable to use aggregates with resistance to polishing, as indicated through tests such as the British Wheel test (AASHTO T279, ASTM D3319). The results of this test indicate the polished stone value of the aggregate, and the Australians recommend a polished stone value in the range of 44 to 48 (Sprayed Sealing Guide 2004). Resistance to degradation and abrasion is also an important characteristic of suitable aggregate. The survey results indi- cated that testing for those characteristics is quite common and usually measured by the Los Angeles abrasion test (AASHTO T96, ASTM C131). Resistance to weathering and freeze-thaw degradation is generally measured by either magnesium sulfate loss or sodium sulfate loss (AASHTO T104, ASTM C88). Aggregate Type The literature review and survey responses revealed that aggregate selection is usually based on the availability and cost of aggregates within proximity to the project. Igneous, metamorphic, sedimentary, and manufactured aggregates have all been successfully used for chip sealing (Sprayed Sealing Guide 2004). Table 6 illustrates the varieties of aggregate used for chip seal projects, both domestically and abroad. Limestone, granite, and natural gravels are most widely used in North America. A comprehensive report studied the suitability of light- weight aggregate as cover stone for chip seals (Gallaway and Harper 1966b). That report indicated that lightweight aggre- gate proved to be a highly successful cover aggregate for chip seals. A more recent study showed that lightweight synthetic aggregate furnished a superior ability to retain its skid resis- tance (Gransberg and Zaman 2002). Such a phenomenon was highlighted by Australian and United Kingdom responses that stressed the use of calcined bauxite, a synthetic aggregate, in high-stress areas where chip polishing is an issue. Lightweight 28 aggregates carry the additional benefit of a significant reduc- tion in windshield breakage claims, because their specific gravity is approximately 25% of that of natural stone aggre- gate (Gallaway and Harper 1966b). However, lightweight aggregates are generally more expensive than natural aggre- gate and may have high water absorption. Figure 25 illustrates the proportion of respondents using synthetic aggregate. Cana- dian responses were excluded because none of the provinces responded that they regularly use synthetic aggregates. Precoated Aggregates Precoated aggregate can be used to increase the performance of the chip seal as well as to expedite the construction process (Harris 1955). The use of precoated aggregate improves aggre- gate binding properties, reduces dust in the aggregate, and results in better contrast between the pavement and its mark- ings. Precoating generally involves applying either a film of paving grade asphalt or a specially formulated precoating bitumen to the aggregate. Precoated aggregates considerably shorten the required curing time by minimizing the problems associated with aggregate dust and moisture. Reduced dust enhances the bonding between the aggregate and binder and reduces vehicle damage resulting from loose chips. Precoating the aggregate chips with asphalt before place- ment has been found to decrease the initial amount of chip loss (Kandhal and Motter 1991). In that same study, chips that were 90% precoated were found to have up to an 80% lower initial loss than uncoated aggregates. The amount of pre- coating asphalt is typically 0.8 to 2.4 gal/yd3 (4 to 12 L/m3) (Sprayed Sealing Guide 2004). The application rate depends on the size and absorptive properties of the aggregate, amount of moisture and dust present, and type of precoating material. Precoated aggregate is typically used with asphalt cement binders. When emulsion binders are used, the aggregate is usually not precoated because the precoating inhibits the breaking of the emulsion (Seal Coat . . . 2003). The rough surface of the aggregate provides the interface necessary for the emulsion to cure. The survey indicated that most U.S. and Canadian agencies do not precoat chip seal aggregates. The states in which pre- coating aggregate was used with asphalt cement binders were Type North America (%) Australia, New Zealand, United Kingdom, South Africa (%) Limestone 37 13 Quartzite 13 38 Granite 35 38 Trap Rock 13 25 Sandstone 10 25 Natural Gravels 58 25 Greywacke, Basalt 4 88 TABLE 6 NATURAL AGGREGATE USED FOR CHIP SEALS 29% 43% United States AU, NZ, UK, SA FIGURE 25 Proportion of agencies using synthetic aggregate.

29 Arizona, California, Colorado, Idaho, Louisiana, Rhode Island, Texas, and Wisconsin. All respondents from Australia, New Zealand, and South Africa indicated the use of precoated aggre- gate with asphalt cement binders. Alaska, Pennsylvania, Texas, and Wisconsin indicated that they also use precoated aggregate with emulsion binders. BINDER SELECTION The Asphalt Institute’s Asphalt Surface Treatments— Construction Techniques (1988) outlines the following require- ments for chip seal binders: • The binder should not bleed when applied at the appro- priate rate. • At the time of application, the binder needs to be fluid enough to uniformly cover the surface, yet viscous enough to not puddle or run off the pavement. • The binder should develop adhesion quickly and hold the aggregate tightly to the roadway surface. There are two main binder types used for chip seal opera- tions: asphalt cements and emulsified asphalts. Climate and weather play an extremely important role in chip seal binder selection. The selection of the binder should be influenced by surface temperature, aggregate, and climate of region during construction operations (McLeod 1969). One of the most important environmental factors to account for when using any bituminous binder is the ambient air temperature. It is accepted that ambient temperatures at the time of construc- tion closely affect the quality of chip seal (Gransberg et al. 1998). In hot weather, bleeding can be prevented with binder selection directed toward the use of “harder” hot applied asphalts and emulsions. During construction with low ambi- ent air temperatures, high humidity, or damp aggregate and pavement surfaces, emulsions are generally believed to be more successful than hot asphalts (Sprayed Sealing Guide 2004). As a result of differences in nomenclature between North America and overseas, international responses to questions about binder were not effective. Figure 26 is a graphical rep- resentation of binder selection practices in Canada and the United States. One specific practice that is apparent is that high float emulsions are more widely used in Canada than in the United States. Asphalt Cement Binders Some agencies use hot-applied asphalt cement as the binder for chip seals. Soft asphalt cement grades are recommended for use in chip seal applications (Asphalt Surface Treatments— Specifications undated). Adhesion agents may be added to these asphalt cements to enhance chip retention. Asphalt cements are advantageous because the roadway can be opened for traffic early after chip seal application and broom- ing. However, the disadvantages include high application temperatures, sensitivity to moisture in rock particles, and a requirement for more rolling energy. High working tempera- tures can also create safety concerns that may limit the appli- cation season to hot summer months. Harder asphalt cements hold cover stone more tightly, but initial retention is more dif- ficult to obtain (Benson and Gallaway 1966). Table 7 shows the typical hot asphalt binders being used in the United States, as found in the survey responses. Emulsion Binders Emulsified asphalts have three primary constituents: asphalt cement, emulsifying agent, and water (A Basic Emulsion Manual 1997). The asphalt cement is suspended in the water with the help of an emulsifier. At the time of the application of the binder, the water evaporates, leaving behind the resid- ual asphalt that bonds with the aggregate. One of the major concerns with using emulsions is the spreading time of the aggregate after the emulsion is applied. The phenomenon that occurs when the water evaporates is called “breaking,” evidenced when the binder’s color changes from brown to black. The aggregate chips must be applied and rolled before the emulsion has broken (Jackson 1990). This emulsion- specific issue indicates that if there is too long a wait, the ability for the rollers to properly seat the aggregate is greatly reduced. Emulsions can be either anionic or cationic depending on the chemistry created by the emulsifying agent. Generally, 9% 69% 100% 50% 70% 100% 19% Hot Asphalt Cement Emulsions Polymer Modifiers High Float Emulsions % of Agencies United States Canada FIGURE 26 Distribution of North American chip seal binder selection. Binder Type State DOT AC-10 Georgia AC15-P Texas AC15-5TR Arizona, Texas AC-20 Georgia TABLE 7 HOT ASPHALT CEMENT BINDER USE IN THE UNITED STATES

cationic emulsions outperform anionic emulsions on a chip seal project because they are less sensitive to weather, inher- ently have antistripping qualities, and are electrostatically compatible with more types of aggregate (McHattie 2001). Cationic emulsions have a positive charge, and because oppo- site charges attract, they are drawn toward most aggregate particles. Thus, a direct and very rapid bonding between the emulsion and an aggregate or pavement is possible. In add- ition, emulsions are not as sensitive as asphalt cements to the moisture in aggregate and in the atmosphere. Also, because excessive presence of water reduces the viscosity of the binder, emulsions require much lower material application temper- atures than asphalt cements. Asphalt emulsions are graded based on setting speed and the relative viscosity of the emul- sion. Table 8 lists emulsion use as found from the survey responses. High Float Emulsions High float emulsions are those emulsions that pass the float test (AASHTO T50, ASTM D139). High float emulsions allow for a thicker residual asphalt film on the aggregate, and this prevents runoff of the asphalt from the surface of the road (Seal Coat . . . 2003). The wetting agents used in this type of binder penetrate the dust coating and provide a good bond with the aggregate particles. Agencies that use high float emulsions commonly state that they used them in situations where local aggregate is excessively dirty or dusty and the cost to wash them to meet a specification of less than 1% passing the No. 200 sieve would be too expen- sive. This type of binder can be used with aggregates hav- 30 ing as much as 5% passing the No. 200 sieve (Janisch and Gaillard 1998). Modified Binders The survey results show that modified binders are used by most agencies, with the only limit to their use being the additional cost. The most common type of modification is through the use of polymers. Research has shown that polymer modification reduces temperature susceptibility, provides increased adhe- sion to the existing surface, increases aggregate retention and flexibility, and allows the roadway to be opened to traffic earlier (Zaniewski and Mamlouk 1996). Polymers are con- sidered to be beneficial in minimizing bleeding, aiding chip retention, and enhancing the durability of the chip seal, and they are recommended for high traffic volume roads and late season work (Shuler 1990; Wegman 1991). Integrating crumb rubber into chip seal binders has proven successful at mitigating reflective cracking, improving aggre- gate retention, and reducing noise emissions. When blended with bitumen, the binder behaves as an elastomer (Sprayed Sealing Guide 2004). In Australia, crumb rubber is added at a rate of 16% to 20% by volume (Beatty et al. 2002). Proprietary additives, known as adhesion agents, are used to improve the degree of wetting of the aggregate by the binder, thus enhancing the adhesion between the binder and aggregate. Adhesion agents are generally proprietary products. Therefore, their application rates are usually specified by their manufacturers. Also known as antistripping agents, these addi- Binder Type U.S. Locations Non-U.S. Locations CRS-1 Nevada None CRS-1H Kansas, Nevada None CRS-2 Connecticut, Iowa, Maryland, Michigan, Montana, Nevada, New York, North Carolina, Oklahoma, Utah, Virginia, Washington, Wisconsin Ontario CRS-2H Arizona, California, Texas None CRS-2P Arizona, Arkansas, Alaska, Idaho, Iowa, Louisiana, Michigan, Minnesota, Mississippi, Montana, Nebraska, North Carolina, New York, North Dakota, Oklahoma, Texas, Washington, Wisconsin, Wyoming New Zealand, Nova Scotia HFRS Alaska, Colorado, New York, Wisconsin British Columbia, Manitoba, Ontario, Saskatchewan, Quebec, Yukon HFRS-2P Colorado, New York, North Dakota, Oregon, Texas, Wisconsin, Wyoming Saskatchewan, Quebec Note: Includes city and county responses in state/province designation. TABLE 8 ASPHALT EMULSION BINDER USE IN THE UNITED STATES

31 tives may be added to either the binder or precoating asphalt (Sprayed Sealing Guide 2004). In addition, hydrated lime can also be used to enhance adhesion and improve a binder’s resistance to oxidation (Dickinson 1984). Figure 27 shows the polymer modified binders to be the most popular among respondents, with 57 agencies reporting that they regularly use them. AGGREGATE–BINDER COMPATIBILITY Adhesion between the aggregate and binder is governed by a number of variables, but most important is the type of aggre- gate. The adhesion between aggregate and binder is a func- tion of mechanical, chemical, and electrostatic properties (Yazgan and Senadheera 2003). Possible mechanical- and chemical-related factors include aggregate dust, moisture content, and binder temperature. Different types of aggregate are better suited to certain binders as a result of electrostatic charges (Sprayed Sealing Guide 2004). Basically, the binder and aggregate must have opposite charges. If this is not the case, the binder will not form a strong bond with the aggregate and it will ravel. Therefore, local aggregate is critical to deter- mining which type of chip seal to use, which type of binder to design for, and which type of construction procedures to spec- ify. In addition, porosity and the presence of water on the surface of the aggregate affect binder–aggregate compatibil- ity. Aggregate, which is quite porous, will actually lead to excessive absorption of the binder. Loss of aggregate shortly after construction is indicative of poor adhesion between the binder and aggregate. Before construction, it is essential to con- duct laboratory testing to determine the adhesion capability between the aggregate and the binder. An antistrip test, such as ASTM D1664 (AASHTO T182), will assist in determin- ing the compatibility between the aggregate and binder. This test may also highlight the need for an antistrip additive (Asphalt Seal Coats 2003). GEOTEXTILE- AND FIBER-REINFORCED SEALS The use of geotextiles and sprayed fibers is common prac- tice in Australia and New Zealand. A small number of geotextile-reinforced seals have been constructed in the United States with mixed success. Montana and Nevada responded that their trials were unsuccessful; however, Oklahoma and two counties in California reported that theirs were a success. International respondents unanimously believe that geotextile-reinforced seals are effective for treating badly cracked, oxidized, or structurally distressed pavements. The construction process basically involves placing a tack coat on the distressed pavement, spreading the geotextile on the tack coat, spraying the geotextile with binder, and then applying the aggregate. Figure 28 shows the mixed success rate of geotextile chip seals in the United States, yet overwhelming success in countries overseas. None of the Canadian provinces responded that they had performed trials with geotextile-reinforced seals. A fiber-reinforced seal usually involves blowing glass fibers onto an application of a polymer-modified binder, with the aggregate being spread quickly after this application. Fiber- reinforced chip seals require special purpose–built equipment to spray and apply the treatment. In general, these seals are not as effective as geotextile seals, but they are less costly (Sprayed Sealing Guide 2004). MATERIAL SELECTION CONCLUSIONS AND BEST PRACTICES The conclusions in this area are quite evident. First, the selec- tion of chip seal materials is project dependent, and the engi- neer in charge of design must fully understand not only the pavement and traffic conditions in which the chip seal will operate but also the climatic conditions under which the chip seal will be applied. It appears that the widespread use of emul- sion binder chip seals results from the notion that emulsions are less sensitive to environmental conditions during construction. Additionally, as emulsions are installed at a lower binder tem- perature, they are probably less hazardous to the construction crew. Binder performance can be improved through the use of modifiers such as polymers and crumb rubber. 57 28 19 32 0 20 40 60 80 100 No. of Agencies Polymers Latex Rubber crumb Antistripping agents 3 2 7 0 2 4 6 8 North America AU, NZ, UK, SA Yes No FIGURE 27 Use of binder modifiers. FIGURE 28 Success rate of geotextile-reinforced chip seals.

Next, the selection of the binder is dependent on the type of aggregate that is economically available for the chip seal project in the United States and Canada. That Australia and New Zealand are willing to bear additional aggregate costs to ensure the quality of their chip seals is something that should be seriously considered in North America. The aggregate should be checked to ensure that electrosta- tic compatibility is met with the type of binder specified. Also, precoating of the aggregate appears to be required for use with hot asphalt cement binders to ensure good adhesion after appli- cation. Finally, it appears that the use of geotextile-reinforced chip seal is promising and should be considered for those roads that have more than normal surface distress and for which an overlay is not warranted. Therefore, several best practices can be extracted from the foregoing discussion: 32 1. Conduct electrostatic testing of chip seal aggregate source before chip design to ensure that the binder selected for the project is compatible with the potential sources of aggregate. 2. Specify a uniformly graded, high-quality aggregate. 3. Consider using lightweight synthetic aggregate in areas where post-construction vehicle damage is a major concern. 4. Use life-cycle cost analysis to determine the benefit of importing either synthetic aggregate or high-quality natural aggregates to areas where availability of high- quality aggregate is limited. 5. Use polymer-modified binders to enhance chip seal performance.

Next: Chapter Six - Equipment Practices »
Chip Seal Best Practices Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

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.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!