TM 5-818-8/AFJMAN 32-1030
CHAPTER 2
GEOTEXTILES IN PAVEMENT APPLICATIONS
2-1.
Applications
2-3. Reflective Crack Treatment for Pave-
ments
This chapter discusses the use of geotextiles for
asphalt concrete (AC) overlays on roads and air-
in pavement rehabilitation projects. Conditions
fields and the separation and reinforcement of
that are compatible for the pavement applications
materials in new construction. The functions per-
of geotextiles are AC pavements that may have
formed by the geotextile and the design consider-
transverse and longitudinal cracks but are rela-
ations are different for these two applications. In
tively smooth and structurally sound, and PCC
an AC pavement system, the geotextile provides a
pavements that have minimum slab movement.
stress-relieving interlayer between the existing
The geographic location and climate of the project
pavement and the overlay that reduces and re-
s i t e have an important part in determining
tards reflective cracks under certain conditions
whether or not geotextiles can be successfully used
and acts as a moisture barrier to prevent surface
in pavement rehabilitation. Geotextiles have been
water from entering the pavement structure.
successful in reducing and retarding reflective
When a geotextile is used as a separator, it is
cracking in mild and dry climates when tempera-
placed between the soft subgrade and the granular
ture and moisture changes are less likely to
material. It acts as a filter to allow water but not
contribute to movement of the underlying pave-
fine material to pass through it, preventing any
ment; whereas, geotextiles in cold climates have
mixing of the soft soil and granular material
not been as successful. Figure 2-2 gives guidance
under the action of the construction equipment or
in using geotextiles to minimize reflective crack-
subsequent traffic.
ing on AC pavements. Geotextiles interlayers are
recommended for use in Areas I and II, but are not
2-2. Paved Surface Rehabilitation
recommended for use in Area III. Since geotextiles
a. General. Old and weathered pavements con-
do not seem to increase the performance of thin
tain transverse and longitudinal cracks that are
overlays, minimum overlay thicknesses for Areas I
and II are given in figure 2-2. Even when the
both temperature and load related. The method
climate and thickness requirements are met, there
most often used to rehabilitate these pavements is
has been no consistent increase in the time it
to overlay the pavement with AC. This tempo-
takes for reflective cracking to develop in the
rarily covers the cracks. After the overlay has
overlay indicating that other factors are influenc-
been placed, any lateral or vertical movement of
ing performance. Other factors affecting perfor-
the pavement at the cracks due to load or ther-
mance of geotextile interlayers are construction
mal effects causes the cracks from the existing
techniques involving pavement preparation, as-
pavement to propagate up through the new AC
phalt sealant application, geotextile installation,
overlay (called reflective cracking). This movement
and AC overlay as well as the condition of the
causes raveling and spalling along the reflective
underlying pavement.
cracks and provides a path for surface water to
b. Surface Preparation. Prior to using geotex-
reach the base and subgrade which decreases the
tiles to minimize reflective cracks, the existing
ride quality and accelerates pavement deteriora-
pavement should be evaluated to determine pave-
tion.
ment distress. The size of the cracks and joints in
b. Concept. Under an AC overlay, a geotextile
the existing pavement should be determined. All
may provide sufficient tensile strength to relieve
cracks and joints larger than inch in width
stresses exerted by movement of the existing
should be sealed. Differential slab movement
pavement. The geotextile acts as a stress-relieving
should be evaluated, since deflections greater than
interlayer as the cracks move horizontally or
0.002 inch cause early reflective cracks. Areas of
vertically. A typical pavement structure with a
the pavement that are structurally deficient
geotextile interlayer is shown in figure 2-1. Im-
should be repaired prior to geotextile installation.
pregnation of the geotextile with a bitumen pro-
Placement of a leveling course is recommended
vides a degree of moisture protection for the
when the existing pavement is excessively cracked
underlying layers whether or not reflective crack-
and uneven.
ing occurs.
c. Geotextile Selection.
2-1
Previous Page
