(5) Grab Elongation. Elongation may be due to the reorientation of the
fibers in a fabric when stressed or due to the stretching of the fibers.
Increased elongation reduces the amount of stress in the fabric and thereby
the effectiveness of the fabric as a reinforcement.
(6) Asphalt Retention. The characteristic of paving fabric that measures
the ability to retain and hold asphalt while in place. The normal units on
this measure is weight/unit area.
(7) Equivalent Opening Size. The openings in a fabric noted in standard
sieve sizes which are commonly used to refer to soil particle sizes.
(8) Modulus of Elasticity. The rate of increase of stress with respect to
strain below the proportional limits. The modulus of elasticity is thus equal
to the slope of the initial straight line portion of a stress-strain diagram.
(9) Coefficient of Water Permeability. A measure of the flow of water
through a permeable media. This coefficient has units of velocity, e.g.
cm/sec.
Test procedures for evaluating the above properties are summarized in
Table 19.
3. CRITERIA FOR USE OF FABRICS
a. General. To achieve reinforcement from the use of fabrics in asphalt
pavement, their range of application must not be overextended. Fabrics have
been used successfully in many applications but, likewise, have failed to
improve pavement performance in many of the same situations. Experience has
shown, although no long-term performance data is yet available, that some of
the fabrics do enhance the life of thin asphaltic resurfacings. When used
with asphalt overlays of 3 inches (75mm) or less, reduced reflection cracking
can be achieved. The fabric not only retards or reduces reflection cracking
but prevents surface infiltration of water. Fabrics have shown good
performance when used on pavements with fatigue cracking (alligator skin
pattern), longitudinal construction joint cracks in asphalt pavement, and the
longitudinal joint between portland cement concrete pavement widened with
flexible pavement. In general, fabrics have not proven to serve as well on
cracks that are greater than 1/4 inch (6.25mm) wide. In these cases, the
fabrics have not prevented a significant amount of reflection cracking but
are believed to protect the pavement from surface water intrusion.
b. Overlay Thickness. Overlay thickness design should be accomplished
using approved methods. Fabrics should not be used with overlays thicker than
3 inches (75mm). Performance to date has not verified any economic advantage
in thicker overlays. Likewise, fabrics
Change 1, September 1985
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