samples are curved and need to be made manual-
Projection method
ly. The wheel is pressed onto the surface with a
A new accelerated polishing method using
high-pressure water was developed jointly by
normal load of 391 N. It usually takes about 6 hr
Laboratoire des Chausses of the Ministre des
to complete the test. The tire is free to rotate on its
Transport du Qubec (MTQ) and the French Lab-
axis and is driven by the friction between the grit
oratoire Ponts et Chausses (LRPC). This method
and the pavement samples. Coarse grit is used to
uses high-pressure water (10 MPa) and a fine
accelerate the wear and fine grit to accelerate pol-
abrasive pointed at an angle of 40 to the pave-
ishing. Water is used to wet the pavement sur-
ment surface. The sample is placed on a table that
face. Additional details on the test equipment and
is computer-controlled to move in increments of
procedure can be found in the British standard
0.25 mm in the XY direction (Fig. 24). The water
procedure BS 812 (British Standards Institution
and abrasive are collected in the chambers below
1989).
the test device. The fine abrasive is recycled for
future testing. The sample is 150 mm by 100 mm
Small-wheel circular track polishing machine
(Fig. 25) and can be manufactured mechanically
The small-wheel circular track polishing
using a rolling wheel compactor or a kneading
machine is similar to the BAWPD discussed
above (ASTM E 660 1995), but the track is in the
compactor. The test takes 3 hr per sample.
The sample is removed and its friction proper-
horizontal plane and can hold up to 12 circular,
ties are determined using the British skid resis-
15-cm-diameter test specimens. The test track is
tance tester. The frictional properties obtained
91 cm in diameter and has four smooth wheels
from the tester are identified as the polishing by
driven at a rate of 30 rpm around the test track.
projection coefficient (Cpp). Figure 26 shows
This device is currently being updated by North
a reasonable relationship between the Cpp and
Carolina State University. Instead of a circular
on-road BPN values.
track, the device will be a linear track.
Figure 24. Water projection device.
Figure 25. Specimen for projection method.
16
to contents
Previous Page
