National Academies Press: OpenBook

Chip Seal Best Practices (2005)

Chapter: Chapter Nine - Best Practice Case Studies

« Previous: Chapter Eight - Chip Seal Performance Measures
Page 60
Suggested Citation:"Chapter Nine - Best Practice Case Studies." 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 61
Suggested Citation:"Chapter Nine - Best Practice Case Studies." 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 61
Page 62
Suggested Citation:"Chapter Nine - Best Practice Case Studies." National Academies of Sciences, Engineering, and Medicine. 2005. Chip Seal Best Practices. Washington, DC: The National Academies Press. doi: 10.17226/13814.
×
Page 62
Page 63
Suggested Citation:"Chapter Nine - Best Practice Case Studies." 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 63

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61 INTRODUCTION On the basis of the survey responses, case studies were iden- tified to detail findings that have the potential to disseminate chip seal best practice in a timely manner. Each of the case studies was drawn from a best practice case study form, which was sent to those survey respondents indicating the performance of their chip seals as “excellent.” This chapter first looks at those factors that the agencies with excellent results have in common with regard to their chip seal proce- dures and processes. Then it presents the salient elements of individual responses for representative programs in a stan- dard format, permitting the reader to compare and contrast the various programs. COMMON CHARACTERISTICS OF EXCELLENT CHIP SEAL PROGRAMS The following respondents reported that they achieve excel- lent results from their chip seal programs. Their responses were separated from those of respondents in general for addi- tional analysis. • Arkansas State Highway and Transportation Department; • Colorado DOT—Alamosa, Grand Junction, Montrose, Sterling, and Trinidad; • Idaho Transportation Department; • Nevada DOT; • Oklahoma DOT; • Texas DOT—Austin District; • WSDOT; • Austin, Texas; and • Lubbock, Texas. The most striking factor among just those respondents that rated their chip seal program results as excellent is that all responded that they use chip seals as a PM tool by fol- lowing a specific PM cycle. Those agencies reported that they typically use a 5-year PM cycle and expect to get a 6-year service life from their seals. These two numbers are significant in that the planned PM cycle is shorter than the expected life of the chip seal. This confirms that these agen- cies are truly committed to using chips seal as a pavement preservation technique. Their level of confidence is further confirmed, because they have an average of 7,000 lane miles of sealed pavement surfaces (DOT district level for all but the two cities), and that they do chip sealing on a range of 150 to 20,000 lane miles per year at an average cost of about $2.6 million annually. Most use both in-house and contract crews to apply their chip seals and achieve satisfactory results with both types of crews, although 10 of 13 agencies believe that in-house seals produce a better final result. The major distress observed with the in-house chip seals is bleeding, especially at intersections, and the major distress observed with contract chip seals is early loss of aggregate. This finding makes sense, because chip seal contractors will have a strong incentive to maximize production rates that may lead to less attention being given to achieving adequate embedment. Design and Material Selection All but one of the best practice case study agencies formally design their chip seals (including empirical design usage based on past experience), and they use a procedure that has been in use for an average of 21 years. Eight respondents entrust the design to their own maintenance engineers, using qualitative design input factors to develop the design. All use modified binders, with polymers and crumb rubber being the most common modifiers. These agencies also select roads that have a distress level rated at moderate or less and whose structural cross section is rated as fair or better. They use some type of pavement condition rating as the trigger point to consider the selection of chip seals for extending the life of the pavement. This finding is highly significant, in that as a group, the agencies demonstrate their understanding of both the advantages and limitations of chip seal technology. In other words, they are “putting the right seal on the right road at the right time” (Galehouse 2003). Contracting and Construction The group’s chip seal season typically runs from May to September, and they use unit-price contracts. They gener- ally are not concerned about restricting chip seals to roads with low-volume traffic, with 11 of the 13 agencies chip sealing roads having ADT of more than 5,000 vehicles, including 3 agencies that use chip seals on roads with ADTs greater than 20,000 vehicles. The agencies appear to be interested in keeping up to date with the state of the art in chip seal construction equipment, as evidenced by the knowledge that most require computerized controls on CHAPTER NINE BEST PRACTICE CASE STUDIES

the distributor, and half require computerized controls on the chip spreader as well. All require the use of pneu- matic rollers and specify some control on rolling by spec- ifying roller passes, maximum roller speed, or roller weight. Most perform crack sealing to prepare the surface for chip sealing. The agencies’ specifications require the ambient air tem- perature to be in the range of 60°F to 70°F before chip seal- ing can begin. The majority impose reduced speed limits of an average of 35 mph on newly sealed roads. They enforce those limits by using flaggers and/or pilot cars for a time after sealing from as little as 30 min to as much as 3 days before opening, with an average of approximately 4 to 6 h. All of these agencies perform their own inspection and require dis- tributor calibration before sealing. Nine of these agencies also require spreader calibration in their contracts or in their internal procedures, or both. Performance Bleeding is the most prevalent reported long-term distress that appears in their chip sealed roads, and these respondents noted the use of rigorous QC testing. The major cause of failure shortly after construction is weather related (rain or an unex- pected temperature drop), followed by dusty or dirty aggregate. The major public-user complaint is damage caused by loose aggregate. Eleven of 13 described the pavement ride of their roads as either good or excellent after chip sealing. Finally, they also undertake follow-up to maintain their chip seals with rou- tine crack sealing and sometimes fog sealing to maintain the integrity of the asphalt membrane for the life of the chip seal. SPECIFIC DATA FROM PROGRAMS WITH EXCELLENT RESULTS Tables 14 and 15 have been developed to furnish the reader with specific details on agencies that reported excellent results from their chip seal programs. Three states, Colorado, Idaho, and Texas, provided multiple responses to the survey. These responses were not consolidated, for each was unique to a given district. Both tables reflect practices grouped according to the traffic volume limitations imposed by the local chip seal usage policy. The impression that one gets from looking at these tables is that all the agencies that reported excellent chip seal per- formance appear to not only have introduced a high degree of prescriptive specification into their programs, but they also are using the benefits that can be accrued by the advances in material science, such as the use of modified binders, robust 62 QC testing programs, and state-of-the-art construction equip- ment in their chip seal programs. One also notices that there is very little difference between those agencies that restrict chip seal usage to lower-volume roads and those that rou- tinely use the system on high-volume roads. The one major difference is that those that apply PM chip seals on high- volume roads ensure that the underlying pavement’s condition is generally good. Thus, they are not trying to use their chip seal program for short-term repair. CASE STUDY CONCLUSIONS AND BEST PRACTICES Two major conclusions were reached in view of the afore- mentioned case studies in chip seal excellence. First, those agencies that use chips seals as a PM measure appear to be able to replicate success. They treat the technology as a science and use formal design procedures that have been adjusted by the experience gained over a large number of years. Because they use chip seals for PM, they do not apply it to roads with severe distress or poor structural conditions, and once they do apply chip seals, they invest in maintaining the asphalt membrane by routine crack sealing and/or fog sealing. Second, these agen- cies transfer a high degree of specificity from their design process to their construction contracts or in-house mainte- nance procedures. Again, such a procedure allows them to replicate past success. The following best practices can be gleaned from this chapter’s analysis: 1. Viewing chip sealing as a PM tool to be applied on a regular cycle reinforces the pavement preservation ben- efits of the technology. 2. Chip seals can be successfully used on high-volume roads if the agency’s policy is to install it on roads where pavement distresses are minimal and the struc- tural integrity of the underlying pavement is in good condition. 3. Both hot asphalt cement and emulsified asphalt binders can be used successfully on high-volume roads. The selection of binders modified by polymers or crumb rubber seems to reinforce success. 4. In-house maintenance personnel are best used to install chips seals in areas where the greatest care must be taken to achieve a successful product. 5. Requiring chip seal contractors to use state-of-the-art equipment and to control the rolling operation enhances chip seal success. 6. An aggressive QA and QC testing program combined with close inspection leads to chip seal success.

63 Item Colorado DOT Alamosa Idaho DOT Boise WSDOT Olympia Average ADT Limitation ADT < 5,000 ADT < 5,000 ADT < 2,000 Chip Seal Season May to September June 15 to Sept. 1 May to August Major Binders Used HRFS, HRFS-2P CRS-2P CRS-2, CRS-2P Modifiers Used Polymers, anti- stripping agents Polymers, crumb rubber Polymers Aggregate Used Natural gravels Trap rock, natural gravels Granite, natural gravels, basalt Aggregate Sizes Used 3/8 in. 3/8 in. 1/2 in. and 3/8 in. Design Method Individual Kearby Empirical Design Done By In-house maintenance engineer No response In-house design engineer Design Method Usage 13 years 10 years 30 years Distress Level of Underlying Surface Moderate Moderate Moderate Structural Condition of Underlying Surface Good Fair Fair Computerized Control Required on Distributor/Chip Spreader Yes/Yes Yes/No Yes/Yes Specified Controls on Rolling Number of passes and maximum speed Roller weight and maximum speed Roller weight Traffic Control Measures Reduced speed, interim pavement markings, flaggers, pilot cars Reduced speed, interim pavement markings, flaggers, pilot cars Reduced speed, interim pavement markings, flaggers, pilot cars Time to Open to Reduced Speed Traffic 10 min 4 h As soon as possible Aggregate QC Tests % fracture Flakiness Anti-strip Presence of clay Gradation X X X X X X X X X X Methods to Maintain Seal after construction Crack seal Chip seal patch Sanding Fog seal None reported X X X X X X TABLE 14 CASE STUDIES FOR CHIP SEAL USE ON LOW-VOLUME ROADS

64 Item Colorado DOT Grand Junction Texas DOT Austin City of Lubbock, Texas Average ADT Limitation ADT > 20,000 ADT > 20,000 ADT > 20,000 Chip Seal Season May to September May to October May to October Major Binders Used HRFS-2P AC15, AC15-5TR CRS-2P Modifiers Used Polymers Polymers, latex, anti- stripping agents crumb rubber Polymers Aggregate Used Natural gravels, lightweight Precoated trap rock, precoated limestone, precoated lightweight Natural gravels Aggregate Sizes Used 1/2 in. and 3/8 in. 1/2 in. and 3/8 in. 1/2 in. and 3/8 in. Design Method Individual Modified Kearby Empirical Design Done By In-house maintenance engineer In-house design engineer In-house design engineer Design Method Usage Not reported 22 years 5 years Distress Level of Underlying Surface None to moderate Moderate Moderate Structural Condition of Underlying Surface Excellent Good Not reported Computerized Control Required on Distributor/Chip Spreader Yes/No Yes/No Yes/Yes Specified Controls on Rolling Rolling pattern Roller weight and maximum speed Rolling pattern Traffic Control Measures Reduced speed, interim pavement markings, flaggers, pilot cars Reduced speed, interim pavement markings, flaggers, pilot cars Reduced speed, interim pavement markings, flaggers Time to Open to Reduced Speed Traffic 3 h Varies 30 min Aggregate QC Tests % fracture Flakiness Decant Anti-strip Presence of clay Gradation Not reported X X X X X X X X X X Methods to Maintain Seal after construction Crack seal Chip seal patch Lime slurry Fog seal X X X X X X TABLE 15 CASE STUDIES FOR CHIP SEAL USE ON HIGH-VOLUME ROADS

Next: Chapter Ten - Conclusions and Suggestions for Future Research »
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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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