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62 the distributor, and half require computerized controls QC testing programs, and state-of-the-art construction equip- on the chip spreader as well. All require the use of pneu- ment in their chip seal programs. One also notices that there matic rollers and specify some control on rolling by spec- is very little difference between those agencies that restrict ifying roller passes, maximum roller speed, or roller chip seal usage to lower-volume roads and those that rou- weight. Most perform crack sealing to prepare the surface tinely use the system on high-volume roads. The one major for chip sealing. difference is that those that apply PM chip seals on high- volume roads ensure that the underlying pavement's condition The agencies' specifications require the ambient air tem- is generally good. Thus, they are not trying to use their chip perature to be in the range of 60°F to 70°F before chip seal- seal program for short-term repair. ing can begin. The majority impose reduced speed limits of an average of 35 mph on newly sealed roads. They enforce CASE STUDY CONCLUSIONS those limits by using flaggers and/or pilot cars for a time after AND BEST PRACTICES 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 Two major conclusions were reached in view of the afore- these agencies perform their own inspection and require dis- mentioned case studies in chip seal excellence. First, those tributor calibration before sealing. Nine of these agencies agencies that use chips seals as a PM measure appear to be able also require spreader calibration in their contracts or in their to replicate success. They treat the technology as a science and internal procedures, or both. use formal design procedures that have been adjusted by the experience gained over a large number of years. Because they Performance use chip seals for PM, they do not apply it to roads with severe distress or poor structural conditions, and once they do apply Bleeding is the most prevalent reported long-term distress that chip seals, they invest in maintaining the asphalt membrane by appears in their chip sealed roads, and these respondents noted routine crack sealing and/or fog sealing. Second, these agen- the use of rigorous QC testing. The major cause of failure cies transfer a high degree of specificity from their design shortly after construction is weather related (rain or an unex- process to their construction contracts or in-house mainte- pected temperature drop), followed by dusty or dirty aggregate. nance procedures. Again, such a procedure allows them to The major public-user complaint is damage caused by loose replicate past success. aggregate. Eleven of 13 described the pavement ride of their roads as either good or excellent after chip sealing. Finally, they The following best practices can be gleaned from this also undertake follow-up to maintain their chip seals with rou- chapter's analysis: tine crack sealing and sometimes fog sealing to maintain the integrity of the asphalt membrane for the life of the chip seal. 1. Viewing chip sealing as a PM tool to be applied on a regular cycle reinforces the pavement preservation ben- efits of the technology. SPECIFIC DATA FROM PROGRAMS WITH 2. Chip seals can be successfully used on high-volume EXCELLENT RESULTS roads if the agency's policy is to install it on roads Tables 14 and 15 have been developed to furnish the reader where pavement distresses are minimal and the struc- with specific details on agencies that reported excellent tural integrity of the underlying pavement is in good results from their chip seal programs. Three states, Colorado, condition. Idaho, and Texas, provided multiple responses to the survey. 3. Both hot asphalt cement and emulsified asphalt binders These responses were not consolidated, for each was unique can be used successfully on high-volume roads. The to a given district. Both tables reflect practices grouped selection of binders modified by polymers or crumb according to the traffic volume limitations imposed by the rubber seems to reinforce success. local chip seal usage policy. 4. In-house maintenance personnel are best used to install chips seals in areas where the greatest care must be The impression that one gets from looking at these tables taken to achieve a successful product. is that all the agencies that reported excellent chip seal per- 5. Requiring chip seal contractors to use state-of-the-art formance appear to not only have introduced a high degree equipment and to control the rolling operation enhances of prescriptive specification into their programs, but they also chip seal success. are using the benefits that can be accrued by the advances in 6. An aggressive QA and QC testing program combined material science, such as the use of modified binders, robust with close inspection leads to chip seal success.
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63 TABLE 14 CASE STUDIES FOR CHIP SEAL USE ON LOW-VOLUME ROADS Colorado DOT Idaho DOT WSDOT Item Alamosa Boise Olympia Average ADT ADT < 5,000 ADT < 5,000 ADT < 2,000 Limitation 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- Polymers, crumb Polymers stripping agents rubber Aggregate Used Natural gravels Trap rock, natural Granite, natural gravels 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 No response In-house design engineer engineer Design Method 13 years 10 years 30 years Usage Distress Level of Moderate Moderate Moderate Underlying Surface Structural Condition Good Fair Fair of Underlying Surface Computerized Yes/Yes Yes/No Yes/Yes Control Required on Distributor/Chip Spreader Specified Controls on Number of passes Roller weight and Roller weight Rolling and maximum speed maximum speed Traffic Control Reduced speed, Reduced speed, Reduced speed, Measures interim pavement interim pavement interim pavement markings, flaggers, markings, flaggers, markings, flaggers, pilot cars pilot cars pilot cars Time to Open to 10 min 4h As soon as possible Reduced Speed Traffic Aggregate QC Tests % fracture X X Flakiness X Anti-strip X X Presence of clay X X Gradation X X X Methods to Maintain None reported Seal after construction X X Crack seal X Chip seal patch X Sanding X X Fog seal
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64 TABLE 15 CASE STUDIES FOR CHIP SEAL USE ON HIGH-VOLUME ROADS Colorado DOT Texas DOT City of Lubbock, Item Grand Junction Austin Texas Average ADT ADT > 20,000 ADT > 20,000 ADT > 20,000 Limitation 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- Polymers stripping agents crumb rubber Aggregate Used Natural gravels, Precoated trap rock, Natural gravels lightweight precoated limestone, precoated lightweight 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 In-house design In-house design engineer engineer engineer Design Method Usage Not reported 22 years 5 years Distress Level of None to moderate Moderate Moderate Underlying Surface Structural Condition of Excellent Good Not reported Underlying Surface Computerized Yes/No Yes/No Yes/Yes Control Required on Distributor/Chip Spreader Specified Controls on Rolling pattern Roller weight and Rolling pattern Rolling maximum speed Traffic Control Reduced speed, Reduced speed, Reduced speed, Measures interim pavement interim pavement interim pavement markings, flaggers, markings, flaggers, markings, flaggers pilot cars pilot cars Time to Open to 3h Varies 30 min Reduced Speed Traffic Aggregate QC Tests Not reported % fracture X X Flakiness X X Decant X X Anti-strip X X Presence of clay X X Gradation Methods to Maintain Seal after construction X X X Crack seal X X Chip seal patch X Lime slurry Fog seal