Chip Seal Best Practices (2005)

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110 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 form sent to those survey respon- dents indicating that they had a chip seal best practice they wanted to share. The forms were then reviewed, and tele- phone interviews were arranged to clarify any details that were not self-evident. In this manner, two case studies were selected as representative of best practices that spoke to issues identified by the survey responses. 1. New Zealand Contractor, Fulton Hogan—Variable Transverse Application Design 2. San Diego County, California—Geotextile-Reinforced Chip Seals The first case discusses one agency’s method for dealing with the variation in road surface in the transverse direction. This is the issue that North American agencies try to over- come by using variable nozzles and adjusting binder rates in the field. The second case details the success in using geo- textiles to combat reflective cracking through the seal and to eliminate the need to crack seal before chip sealing, which eliminates one source of flushing. CASE STUDY—VARIABLE TRANSVERSE APPLICATION DESIGN Agency: Fulton Hogan Limited, Christchurch, New Zealand Name of Project or Practice: Variable Transverse Appli- cation Design What Is the Best Practice? Currently, Fulton Hogan is testing its design methods to calculate binder application rates for wheelpaths, between wheelpaths, shoulders, and centerline. Discussion The trials have shown that application rates calculated by using the traditional method can be adjusted downward by up to 30% in the wheelpaths and still produce a quality chip seal. The application rate can be adjusted upward by more than 30% on the shoulders and centerline. The traditionally cal- culated application rate appears to be appropriate for the area between the wheelpaths. The results from the trials have given Fulton Hogan’s chip seal designers the confidence to reduce their traditionally cal- culated application rates by 10% to 20% in the wheelpaths and higher where excess binder is evident in the wheelpaths for all reseals for which Fulton Hogan has the responsibility for the performance of the seal (Note: performance is mea- sured by texture depth after 12 months). This practice is gen- erally happening in the six regions where Fulton Hogan pos- sesses Multispray variable transverse capable distributors. Project Specific Data The Tai Tapu trial in 2000 had the following results: • First trial—included three short trial lengths within a 700-m reseal; • Site—a straight section of two-lane state highway; • Average annual daily traffic—2000; • Design adjusted for 5% heavy trucks; • Target application rate—1.90 L/m2 of binder; • Lowest application rate in wheelpath—1.47 L/m2; • Highest application rate on shoulder—2.46 L/m2; • Highest application rate between wheelpaths and cen- terline application rate—2.1 L/m2; • Chip used—Grade 3 single-sized 16-mm to 13-mm chip, with an average least dimension of 8.61 mm; and • Average sand circle before sealing—177 mm. Performance of Practice The traditional design method calculates an average applica- tion rate for the whole road surface, which is not applicable to any particular area. The result of using this application rate is that the shoulders and centerline suffer chip loss and the wheelpaths receive an excess of binder that in the long term results in flushing. The use of variable transverse distribution to lower the application rates in the wheelpaths prevents the loss of texture in the wheelpaths, extending the life of the seal and the pavement surfacing. Conservative estimates based on results so far estimate a 25% to 30% increase in life cycle. Plans for This Best Practice Fulton Hogan will continue to construct trial sections for full monitoring. The monitoring includes texture and skid monitoring of the trials and the traditional treatment adja- cent to the trial sections. Fulton Hogan plans to continue reducing the application rates in the wheelpaths as a matter of course where the organization’s contractual relationships make them responsible for the long-term performance of the seal. APPENDIX D Innovative Chip Seal Case Studies

111 CASE STUDY—GEOTEXTILE-REINFORCED CHIP SEALS Agency: San Diego County, California Name of Project or Practice: Geotextile-Reinforced Chip Seals What Is the Best Practice? The county of San Diego’s Department of Public Works has found chip sealing over pavement-reinforcing fabric (fabric) as a cost-effective method of preventive maintenance for roads in the desert area of the county. This method is done to elimi- nate the need to crack seal the thermal cracked bituminous sur- face, prevent premature aging of the roadway, and extend the life of the roadway. This practice has eliminated the need for crack sealing. Figure D1 shows the existing road’s surface before installation of the geotextile and the chip seal. The construction operation consists of three separate operations—placing fabric, chip seal, and fog seal—on high- speed and low-speed roads. The method of how and when the products are placed is determined by the traveling speed of the motoring public, not the volume of traffic. Project Specific Data The Borrego Springs Trial in 1987 had the following results: • Maintenance contracts—1996, 1999, 2000, and 2001; • Type—Conventional chip seal over pavement reinforc- ing fabric; • Traffic data—1,300 or less annual daily traffic (Note: traffic speeds are typically 55 mph); • Number of lanes—2; • Binder used—PMCRS2h; and • Aggregate used—Medium and medium-fine. Construction Method 1 (High-Speed Roads) Method 1 is used for roads that have high-speed traffic and require pilot car-assisted traffic control to reduce the speed of the traveling public to 25 mph (40 km/h) during construc- tion operations. • Phase 1—Apply paving asphalt, fabric, and sand cover, followed by rolling to seat the fabric into the paving asphalt. Remove excess sand. Apply polymer-modified asphalt emulsion and crushed aggregate (chips) and fol- low with rolling to seat the chips into the emulsion. Remove excess chips. • Phase 2—Apply fog seal. Phase 2 is performed 7 to 14 days after Phase 1. Construction Method 2 (Low-Speed Roads) Method 2 is used for roads that have low-speed traffic. Posted speed limits are already 25 mph (40 km/h); therefore, pilot car-assisted traffic control is not required. • Phase 1—Apply paving asphalt, fabric, and sand cover, followed by rolling to seat the fabric into the paving asphalt. • Phase 2—Remove excess sand. Apply polymer-modified asphalt emulsion and crushed aggregate (chips) and fol- low with rolling to seat the chips into the emulsion. Phase 2 is performed 5 to 10 days after Phase 1. • Phase 3—Remove excess chips. Apply fog seal. Phase 3 is performed 7 to 14 days after Phase 2. The preferred method of placement is Method 2. This allows the paving fabric binder to harden overnight and to allow traffic to provide additional seating of the fabric for sev- eral days before the chip seal is placed. Both methods are placed successfully in Borrego Springs; each method has ben- efits depending on the roadway’s environment (traffic speed). Performance of Practice This practice has eliminated the need for crack sealing in the desert area of the county. The test section set in 1987 is still in place and performing to date. A life-cycle cost analysis was performed on the trial section. Considering the width of the surface cracks on roadway surfaces in Borrego Springs, San Diego County found chip sealing over fabric to be more cost-effective than chip sealing with ground rubber/paving asphalt binder, or chip sealing without fabric. Plans for This Best Practice San Diego County plans to routinely use this practice in the desert community where thermal surface cracks on the asphalt concrete pavement are present. Fabric placement is not recommended for roads with steep grades, winding curves, or at intersections with controlled stops. The county anticipates not placing fabric on intersection radii, tight curves, steep grades, or the last 100 ft approaching a con- trolled stop intersection. The county will continue to place chip seals at these locations.FIGURE D1 Geotextile installation on cracked road surface.