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30 ing windshield damage and increasing aggregate embedment.
Besides restricting the speed of traffic through the work zone,
No. of Respondents
a pilot vehicle can stagger traffic movement on the new chip
20 seal to prevent vehicles from traveling in the same wheelpaths
and helping to embed stone retention outside of them (Asphalt
Seal Coats 2003).
10
It is good practice to delay the opening to normal traffic
0 speeds until the midday road surface temperature drops, such
One Pass Two Passes Three Passes as in the evening (McLeod 1969). The construction operation
should avoid opening the chip seal to uncontrolled traffic in
FIGURE 52 Typical brooming requirements. hot conditions when the ability of the binder to hold the
aggregate is reduced (McLeod 1969). Opening a freshly con-
structed chip seal to traffic during midday is not recom-
placement of the chip seal. Australian agencies follow the mended, because the binder is less viscous and there is an
sweeping operations with a roller to ensure that any disturbed increased chance of the loss of aggregate. Asphalt cements
aggregate is rolled back into place (Sprayed Sealing Guide are advantageous during hot weather because the roadway
2004). If embedment is visibly low after sweeping, a fog seal, can be quickly reopened to traffic.
which is a second application of binder sprayed on top of the
aggregate to enhance adhesion, should be applied to the chip
seal. The MDOT recommends that if the embedment is more CONSTRUCTION PRACTICES
than 80%, no fog seal be applied even if one is required by FOR HIGH-VOLUME TRAFFIC
contract (Maintenance Chip Seal Manual 2000).
Survey results indicated that chip seals may be highly effec-
tive on high-volume traffic roads. California, Colorado, and
TRAFFIC CONTROL Montana regularly construct chip seals on roads with greater
than 20,000 ADT and reported that the performance of their
Traffic control designed in accordance with the Manual on chip seals was either good or excellent. The belief that chip
Uniform Traffic Control Devices is not only vital to the safety seals are not suitable for high-volume traffic roads is rooted
of the traveling public and construction workers, it is also an in perceptions that chip seal projects on those roadways are
indispensable tool for achieving levels of orientation and predestined to failure because of the liability and claims
embedment beyond conventional rolling. Vehicle damage associated with damage to vehicles from loose aggregate
can also be prevented through adequate traffic control. Ample (Shuler 1990).
traffic control should be in full force for every chip seal proj-
ect. Generally, loose gravel signs complement signage that Several factors should be considered to prevent vehicle
indicates the reduced speed limits. damage for high-volume traffic applications. Common causes
of vehicle damage from chip seals include the application of
Traffic control is generally accomplished using signage, excess aggregate, inadequate low-speed traffic control, and
pilot vehicles, and flaggers during construction operations. poor sweeping (Shuler 1990). Shuler's recommendations for
The consensus among survey respondents was that the maxi- construction practices when constructing high-volume chip
mum speed limit should be 25 mph (40 km/h). A pilot vehi- seals are shown in Table 10. Sweeping is essential to high-
cle is recommended to not only provide safe passage to the volume traffic chip seal applications. Vehicle damage can be
traveling public at reduced speeds, but also to assist in reduc- avoided if the excess chips placed to minimize chip pickup on
TABLE 10
BEST PRACTICES FOR CONSTRUCTING HIGH-VOLUME CHIP SEALS
Practice Reason
Reduce excess aggregate Sweeping proficiency increased
Reduce aggregate size Larger aggregate causes more damage
Use of double chip seals Smaller aggregate in contact with tires
Use of lightweight aggregate Lower specific gravity causes less damage
Use of choke stone Locks in larger aggregate
Fog coat Improved embedment
Precoat aggregate Improved adhesion
Use of polymer modifiers Improved adhesion
Allow traffic on chip seal Vehicles provide additional embedment
Control traffic speed on chip seal Reduced whip-off
