Profile measurement tests that could be adapted
using a specially designed camera. With the aid
for the laboratory include the texturemeter, linear
of a stereo comparator and a parallax bar, relative
traverse, light, and wear/roughness meter tests.
heights can be measured using stereo photos of
The texturemeter, developed by the Texas Trans-
successive points on the surface.
portation Institute, consists of a series of evenly
Other methods such as casting, molding, ink,
spaced vertical parallels in a frame. With the
and photographic emulsion prints have been
exception of two, the rods can move vertically
used to obtain the surface texture. Detailed study
and are independent of one another. A string is
of the magnified cast or print is then made in the
attached to the movable end and to the frame.
laboratory.
The texturemeter produces a straight line on a
smooth surface and a dial indicator has been cali-
Macrotexture characterization
brated to zero. If there are any irregularities, the
string produces a zig-zag line and results in a dial
Sand patch test
reading greater than zero. The reading is propor-
The sand patch test (ASTM E 965 1995) is used
tional to the coarseness of the macrotexture: the
to assess the average macrotexture depth of a
coarser the surface, the higher the reading.
pavement surface. Values over 0.80 mm are con-
Other methods that use microscopes and/or
sidered excellent. Below 0.60 mm, the macrotex-
light are the linear traverse, light, and the wear
ture is inadequate and can lead to extremely slip-
and roughness meter. The linear traverse method
pery conditions (Tremblay et al. 1995).
developed by the Kansas Highway Commission
The test involves placing a known volume of
uses a motorized lathe and a stereo microscope
material on the dry surface of the test specimen.
with the shaft of a potentiometer attached to the
Figure 17 shows the predetermined volume of
microscope focusing shaft. The specimen is
test material in the container and test specimen.
moved transversely under the microscope. The
The test material is made from solid round glass
operator keeps the surface under constant focus,
spheres graded between the no. 60 and no. 80
thus changing the potentiometer voltage. This
sieves. This material is then spread into a circular
results in a tracing of the surface texture.
patch with a disk (Fig. 18). The diameter of the
Surface texture can also be determined by light
patch is measured (Fig. 19). At least four meas-
sectioning. In this method, a beam of light is
urements are made, and the average diameter is
used to determine the average surface macrotex-
passed through a slit at an angle. Based on the
ture depth (MATXd). The macrotexture depth is
reflection of the light, the apparent profile height
calculated from the following equation:
can be determined mathematically.
The wear/roughness meter also uses light to
4V
measure the mean wear height and mean texture.
MATXd =
(6)
πD2
The data from this device provide a surface plot
of maximum depth and distribution of the peaks
where V is the test material volume and D is the
of the observed surface. Details on this device can
average diameter of area covered by the test
be found in Rosenthal et al. (1969).
material.
Texture can also be quantified with topographic
measurements of pavement surface using stereo
photography. Pairs of photographs are taken
Figure 17. Containers of test materials for sand patch
Figure 18. Circular patch of test material.
test.
12
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