erties of the pavement surface are usually deter-
mined in the laboratory using either the British
portable skid resistance tester or the North Caro-
lina State University variable-speed friction
tester. Both these test methods are standardized
by ASTM.
With respect to accelerated polishing, the tests
are mostly done on wheel tracking systems.
Examples of such tests are the small-wheel circu-
lar track wear and polishing machine, the Georgia
skid tester, and the British polishing wheel. Some
of these devices were fabricated by individual
state DOTs or by universities and are not avail-
able commercially. The French have developed a
polishing method using high-pressure water on a
pavement surface. The equipment is less complex
Figure 19. Measurement of diameter of sand patch.
than the circular wheel and appears to correlate
well with changes in the frictional properties due
Surface drainage test
to polishing. The following discussion will start
The amount of time for a surface to drain can
with the two friction testers currently standard-
also be used as an indicator of the surface texture.
ized by ASTM followed by descriptions of several
A drainage meter (Moore 1966), 13 mm in diame-
accelerated polishing devices.
ter and 13 mm in height containing a known vol-
ume of water under atmospheric pressure, is
Friction measurement devices
placed on the pavement surface. A rubber ring is
glued to the bottom of the cylinder and acts simi-
British portable skid resistance tester
larly to tire treads on the pavement surface. The
The British skid resistance tester (BSRT) (Fig.
amount of time taken for the water to flow out of the
20), also called the British pendulum skid tester,
tank is related to the macrotexture of the pave-
can be used both in the laboratory and in the
ment surface. High flow rates indicate high macro-
field. The tester consists of a pendulum that is
free to swing through 180. A rubber shoe slider is
texture depths.
attached to the bottom end of the pendulum. In
the position shown in Figure 20, the pendulum
Microstructure characterization
The change in the microstructure of a pavement
contains potential energy. When released, the
surface is difficult to quantify and can be inferred
potential energy is converted to kinetic energy
from the changes in its frictional properties. This is
that is dissipated by friction on the rubber shoe,
done using an accelerated polishing device and a
which slides over the surface. A graduated scale
friction measurement system. The frictional prop-
on the pendulum registers the maximum swing
Figure 20. British portable skid resistance tester.
13
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