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

OCR for page 109
111 CASE STUDY--GEOTEXTILE-REINFORCED of the traveling public to 25 mph (40 km/h) during construc- CHIP SEALS tion operations. Agency: San Diego County, California Phase 1--Apply paving asphalt, fabric, and sand cover, Name of Project or Practice: Geotextile-Reinforced followed by rolling to seat the fabric into the paving Chip Seals asphalt. Remove excess sand. Apply polymer-modified asphalt emulsion and crushed aggregate (chips) and fol- What Is the Best Practice? low with rolling to seat the chips into the emulsion. Remove excess chips. The county of San Diego's Department of Public Works has Phase 2--Apply fog seal. Phase 2 is performed 7 to found chip sealing over pavement-reinforcing fabric (fabric) 14 days after Phase 1. 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- Construction Method 2 (Low-Speed Roads) face, prevent premature aging of the roadway, and extend the life of the roadway. This practice has eliminated the need for Method 2 is used for roads that have low-speed traffic. crack sealing. Figure D1 shows the existing road's surface Posted speed limits are already 25 mph (40 km/h); therefore, before installation of the geotextile and the chip seal. pilot car-assisted traffic control is not required. The construction operation consists of three separate Phase 1--Apply paving asphalt, fabric, and sand cover, operations--placing fabric, chip seal, and fog seal--on high- followed by rolling to seat the fabric into the paving speed and low-speed roads. The method of how and when the asphalt. products are placed is determined by the traveling speed of Phase 2--Remove excess sand. Apply polymer-modified the motoring public, not the volume of traffic. asphalt emulsion and crushed aggregate (chips) and fol- low with rolling to seat the chips into the emulsion. Project Specific Data Phase 2 is performed 5 to 10 days after Phase 1. Phase 3--Remove excess chips. Apply fog seal. Phase The Borrego Springs Trial in 1987 had the following results: 3 is performed 7 to 14 days after Phase 2. Maintenance contracts--1996, 1999, 2000, and 2001; The preferred method of placement is Method 2. This Type--Conventional chip seal over pavement reinforc- allows the paving fabric binder to harden overnight and to ing fabric; allow traffic to provide additional seating of the fabric for sev- Traffic data--1,300 or less annual daily traffic (Note: eral days before the chip seal is placed. Both methods are traffic speeds are typically 55 mph); placed successfully in Borrego Springs; each method has ben- Number of lanes--2; efits depending on the roadway's environment (traffic speed). Binder used--PMCRS2h; and Aggregate used--Medium and medium-fine. Performance of Practice Construction Method 1 (High-Speed Roads) This practice has eliminated the need for crack sealing in the Method 1 is used for roads that have high-speed traffic and desert area of the county. The test section set in 1987 is still require pilot car-assisted traffic control to reduce the speed 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 FIGURE D1 Geotextile installation on cracked road surface. chip seals at these locations.