ENGINEERING BULLETIN
ULTRAVIOLET LIGHT
DEGRADATION OF
GEOTEXTILES
EROSION CONTROL
BACKGROUND
Ultraviolet (UV) light degradation is a process in which the strength of a geotextile is damaged or reduced by exposure to
sunlight. The type of geotextile and the location of exposure affect the time it takes to degrade a geotextile. The basic mechanism for photo-initiated degradation is the same for all polymer materials. Ultraviolet light degradation occurs when energy
from sunlight breaks the bonds within the polymer structure. The energy from sunlight can be divided into three categories by
wavelength; ultraviolet, visible, and infrared. Wavelength distributions for sunlight are shown in Figure 1. Those wavelengths
above 400 nm form the visible and infrared light spectrums and do not cause degradation of the polymers used in geotextiles.
For polymers commonly used in geotextiles, degradation is typically caused by wavelengths in the UV range, less than 400 nm.
Photons with wavelengths longer than the critical wavelengths for any bond making up the molecular chains will have no effect
on the chemical structure, therefore causing no degradation. Wavelengths less than about 280 nm, while potentially very damaging to polymer materials, are filtered by the earth’s atmosphere and are not generally a factor as can be seen in Figure 1.
Figure 1 - Wave lengths in natural sunlight at Miami, Florida and in the xenon-arc device used in ASTM
D-4355. From Atlas Material Testing Technology
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VARIABLES IN UV STABILITY OF GEOTEXTILES
There are a number of variables affecting the UV stability of geotextiles related both to the fabric and the environment in which
it is exposed. The local environment has a significant impact on the rate of UV degradation, both with respect to the intensity of
sunlight and the temperature. Even the exposed slope orientation toward the sunlight makes a difference. Figure 2 shows the
results of tests on samples of Propex geotextiles exposed at three locations in the United States. In general, the United States
southwest is more severe than the southeast and the rate of degradation is much less in the north.
Manufacturers add a number of stabilizers to geotextile fibers and yarns to enhance their stability. The amount and nature of
these stabilizers impact the stability of fabrics. UV degradation penetrates into the yarn or fiber from the surface toward the
core. Thus, a larger diameter yarn or fiber will degrade more slowly than a smaller yarn or fiber of the same composition. Woven
geotextiles, with their much coarser yarns, will generally degrade more slowly than nonwoven geotextiles. This can be seen in
Figure 2. Since UV degradation starts at the surface of geotextiles, a thicker fabric will also degrade more slowly than thinner
fabrics. So Propex nonwoven Geotex® 801 (about 8 oz/sq. yd.) will degrade more slowly under the same exposure conditions
than Geotex 351 (about 4 oz/sq. yd.). This difference in degradation rate is less pronounced for nonwoven geotextiles above
about 8 ounces per square yard. Heavier weight nonwovens are at the high side of the nonwoven bands shown for nonwovens
in Figure 2.
Figure 2 - Results of tests on Propex geotextiles exposed outdoors for up to 18 months at three locations
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TESTING UV STABILITY
The standard method for evaluating the UV stability of a geotextile is given in ASTM D-4355. In this method, a xenon-arc
light source is used and specimens are exposed to the light under controlled conditions of temperature and humidity. This
light source closely mimics natural sunlight in the UV range as shown in Figure 1. There are also exposure methods that use
fluorescent light sources. These are not approved for use on geotextiles. The xenon-arc exposure test is considered an index
test and results cannot be used directly for an end use. There is a general correlation between the xenon-arc exposure and
outdoor exposure, but the results cannot be used directly. The test uses a combination of high light intensity and elevated
temperature to degrade the specimens more rapidly than would be experienced in a natural environment in the same amount
of time. The samples are typically exposed for 500 hours in the device. After exposure, a specific physical property (usually
two inch strip tensile strength, ASTM D-4632) is tested. This is then compared to the properties of the unexposed fabric to
determine percent of the original strength the exposed specimens retained for the specific time period under consideration.
The nationally recognized AASHTO M 288 specifications for geotextiles used in highway applications require minimum
strength retentions of 50% of their pre-exposure strength after 500 hours of exposure as specified in ASTM D-4355 for most
applications and 70% after 500 hours of exposure for silt fence. All Propex geotextiles are stabilized to provide at least 70%
strength retention after 500 hours exposure according to ASTM D-4355.
PROTECTING GEOTEXTILES FROM UV DEGRADATION
The simplest way to prevent ultraviolet light degradation in a geotextile is to prevent sunlight from reaching the fabric. Once
covered by soil, asphalt or other material, the potential for degradation is removed. Thus geotextiles should be covered as soon
as possible after removing the protective wrapper. Geotextile manufacturers add a variety of stabilizers or additives to the
resin used in producing geotextiles to make the polymers more stable against ultraviolet light degradation. These stabilizers
limit degradation for typical installation times but do not provide protection for extended periods. To minimize UV degradation,
project specifications should be written to limit exposure to a maximum of 14 days. Where longer exposure may be required,
samples of the exposed fabric should be taken periodically and tested to verify that a detrimental amount of strength loss has
not occurred. The protective wrapper on rolls of geotextile when shipped should remain in place until the material is installed.
REFERENCES
1. ASTM, 2014, “ASTM D-4355-14: Standard Test Method for Deterioration of Geotextiles by Exposure to Light, Moisture
and Heat in a Xenon Arc Type Apparatus,” American Society for Testing and Materials, West Conshohocken, PA.
2. Baker, T.L., “Long-Term Relationship of Outdoor Exposure to Xenon-Arc Test Apparatus Exposure,” Geosynthetics ‘97,
Long Beach, March, 1997, pp 177-190.
3. ASTM, 2008, “ASTM D-4362-08: Standard Test Method for Grab Breaking Load and Elongation of Geotextiles,”
American Society for Testing and Materials, West Conshohocken, PA.
4. AASHTO, “Standard Specification for Geotextile Specification for Highway Applications, AASHTO Designation: M 288-05,”
American Association of State Highway and Transportation Officials, Washington, D.C., 2005.
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FLEXIBILITY
The Flexibility of a RECP, measured in inch-pounds, indicates its ability to maintain intimate contact with the soil. A stiff RECP
will not easily follow the contours of the slope or channel, while a more flexible RECP will maintain direct contact with the soil
even when undulations occur. The consequences of a lack of Flexibility, i.e. a lack of intimate contact with the soil, are erosion
beneath the RECP and vegetation growing under the RECP (tenting) as opposed to growing in and through the RECP. A higher
Flexibility value indicates a stiffer RECP and a lower Flexibility value indicates a more flexible RECP. While Flexibility and Tensile
Strength are generally directly related, the RECP construction has a definite impact on this relationship. Generally, RECPs with
multiple components, such as stitching, fused joints, or attached geogrids in attempt to artificially increase the RECPs Tensile
Strength tend to be stiffer, more rigid materials.
UV RESISTANCE
UV Resistance is a crucial property for every RECP in every application, whether it is vegetated or unvegetated. UV Resistance
is reported as a percent of tensile strength retained of a RECP after a certain period of accelerated UV exposure when
compared to the original tensile strength of the RECP. The following relationships in Table 1 are generally seen when comparing
UV Resistance to functional longevity:
UV Resistance (ASTM D-4355)
80% at 1,000 Hours
90% at 3,000 Hours
90% at 6,000 Hours
Functional Longevity
10 Years
25 Years
50 Years
Table 1 - UV Resistance vs. Functional Longevity
TENSILE STRENGTH
The Tensile Strength of a RECP is the primary property that determines the initial and long term performance of the RECP when
non-hydraulic stresses are encountewred. Non-hydraulic, mechanical stresses encompass installation loading, mechanical
loading, maintenance loading, debris loading, and animal loading. When the Tensile Strength of the RECP is not adequate to
account for all of the non-hydraulic stresses incurred during the life of the project, non-hydraulic failure occurs, i.e. ripping or
tearing of the RECP, lessening if not eliminating the improved hydraulic performance provided by the RECP.
ENVIRONMENTAL CONSIDERATIONS
Every slope, channel, stream, levee, and shoreline restoration or stabilization must consider the environmental impacts
of proposed treatment. The preferred remediation techniques use biodegradable or natural materials to minimize the
environmental impacts. However, when project design factors, such as shear stress, velocity, loadings, etc… exceed that of
natural vegetation, the use of permanent, non-degradable RECPs must be considered. The use of biodegradable or natural
materials in these more severe applications can result in a material failure, causing a loss of vegetation, sediment pollution,
and in turn less infiltration of water into the soil.
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PIN SPACING
ARVS
Figure 3 - Typical Anchor / Pin Pattern
SUMMARY
As the use of RECPs continue to grow, the knowledge and use of consistent design considerations must grow as well. When
utilizing RECPs the design engineer must consider the hydraulic, non-hydraulic, and environmental factors in order to select
the appropriate solution for the problem at hand. For additional design support and installation consideration please contact
Propex’s Engineering Services at (423) 553-2450 or at:
InfrastructureSolutions@propexglobal.com
REFERENCES
1. Miller, S. J., J. C. Fischenich, and C. I. Thornton. 2012. Stability thresholds and performance standards for flexible lining
materials in channel and slope restoration applications. EBA Technical Notes Collection. ERDC TN-EMRRP-EBA-13.
Vicksburg, MS: U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi. http://cw-environment.
usace.army.mil/eba/
2. Erosion Control Technology Council (ECTC). 2008. Installation guide for rolled erosion control products (RECPs) including
mulch control nettings (MCNs), open weave textiles (OWTs), erosion control blankets (ECBs), and turf reinforcement
mats (TRMs). St. Paul, MN.
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