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64 TABLE 51 MINNESOTA DOT CASE STUDY FACTS Item Data Binder CSS-1 using PG 49-34 asphalt binder Aggregate Type II Mineral filler Type I portland cement Job Mix Formula--Typical Aggregate 100% Portland cement 1.75% + 0.25% Water As required Binder 12.5% and 16.5% + 0.4% Test Specification--Typical Residual asphalt 8% to 8.5% Softening point 128oF Penetration 163 Excess asphalt loaded wheel Not available Wet stripping Not available Compatibility Pass Location Minnesota Road Test Facility Albertville, MN AADT--Test road 80 truck passes per day Distress Level Before Microsurfacing IRI (m/km) 1.24 to 3.25 (52.6 to 57.6 in./mile) Rut depth (mm) 8 to 46 (0.33 to 1.81 in.) Friction number Not applicable Length of Test Period 2 years Snowplowing? Yes AADT = average annual daily traffic. A 11% to 40% decrease for lanes constructed with rut- SUMMARY AND EFFECTIVE PRACTICES fill and wear course mixtures, A 7% decrease for 102-kip load-configuration lanes, This chapter presented six case studies that each demon- and strated a particular aspect of microsurfacing practice. The A 32% decrease for 80-kip load-configuration lanes. case studies covered projects in both northern and southern · Early results from this research show that the soft asphalt climates, in the United States and Canada, on rural and urban concrete microsurface design has a moderate effect in highways, and on both asphalt and concrete pavements. In decreasing transverse reflected cracks. summary, the case studies highlighted the robust ability of · Data . . . also suggest that the soft asphalt concrete microsurfacing to effectively address many common pave- microsurfacing is effective at reducing rutting (Johnson ment distresses while enhancing skid resistance, ride quality, et al. 2007). aesthetics, and extending the service lives of the pavements upon which they are placed. This chapter produced 16 Lessons Learned lessons learned and 4 effective practices. The effective prac- tices are as follows: This case study project documents the results of using a softer asphalt binder in the microsurfacing JMF. Two lessons learned 1. Microsurfacing can be effectively employed on roads can be derived from this case study project. where routine winter snow removal is a factor if the underlying pavement is structurally sound. · Microsurfacing furnishes a promising means to reduce 2. Microsurfacing is the proper alternative to enhance skid the amount of transverse reflective cracking; and resistance in areas where the frictional characteristics of · The amount of binder can be successfully varied in the the road's surface are to be restored to safe operating field to enhance microsurfacing ability to fill ruts. limits. 3. When using microsurfacing to improve ride quality on Effective Practices jointed plain concrete pavements the spreader box can be modified to furnish better support across the joints This case study yielded the following effective practice. and the flexible rubber strike-off would be replaced with a rigid strike-off. The microsurfacing binder amount can be reduced by 1% 4. The microsurfacing binder amount can be reduced by to 2% in rut filling and scratch courses upon which a wear- 1% to 2% in rut filling and scratch courses upon which ing course will be applied. a wearing course will be applied.