Streaking
Streaking results when alternate longitudinal strips of a
surface treatment or seal coat contain different quantities of binder,
due to lack of uniformity of application of the binder inch by inch
across the surface. The dark streaks which exist in this condition
occur when there is not enough asphalt binder to hold the cover
aggregate in place, and part of the cover stone has been torn out
by traffic. These dark streaks are points of weakness at which the
complete seal coat or surface treatment will wear away first under
traffic. Streaking can reduce skid resistance, cause vehicle steering
problems, and lead to a serious reduction in the normal life expectancy.
In addition to shortening the service life, streaking can
be so pronounced that it interferes with the steering of a car on
the road and can cause the vehicle to weave, thereby affecting the
safety of traffic.
Some of the more common causes of streaking are mechanical
faults, improper or poor adjustment, and careless operation of bituminous
distributors. Another frequent cause is applying the bituminous
binder at too low a temperature, so that it is not fluid enough
to fan out properly from the nozzles on the spray bars.
Other common causes of streaking requiring mechanical correction
are:
- operating with a portion of the spray nozzles partially or completely clogged (faulty strainers or absence of strainers is sometimes at least partly responsible for this)
- using spray nozzles of different sizes, different makes, and different rates of discharge in the same spray bar
- operating when some of the nozzles have not been set vertically and at the proper angle in the spray bar
- using damaged or badly worn spray nozzles
- employing spray bars in which the center-to-center spacing of the nozzles is not uniform.