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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.
