ASTM G90-98

Standard Practice for Performing Accelerated Outdoor Weathering of Nonmetallic Materials Using Concentrated Natural Sunlight

SCOPE
1.1 Fresnel-reflecting concentrators employing the sun as source are utilized in the accelerated outdoor exposure testing of nonmetallic materials.
1.2 This practice covers a procedure for performing accelerated outdoor exposure testing of nonmetallic materials using a Fresnel-reflector accelerated outdoor weathering test machine. The apparatus (see Figs. 1a and 1b) and guidelines are described herein to minimize the variables encountered during outdoor accelerated exposure testing.
1.3 This practice does not specify the exposure conditions best suited for the materials to be tested but is limited to the method of obtaining, measuring, and controlling the procedures and certain conditions of the exposure. Sample preparation, test conditions, and evaluation of results are covered in existing methods or specifications for specific materials.
1.4 The Fresnel-reflector accelerated outdoor exposure test machines described may be suitable for the determination of the relative durability of materials exposed to sunlight, heat, and moisture, provided the mechanisms of chemical or physical change, or both, which control the rates of acceleration factors for the materials do not differ significantly.
1.5 This practice establishes uniform sample mounting and in-test maintenance procedures. Also included in the practice are standard provisions for maintenance of the machine and Fresnel-reflector mirrors to ensure cleanliness and durability.
1.6 This practice shall apply to specimens whose size meets the dimensions of the target board as described in 8.2.
1.7 For test machines currently in use, this practice may not apply to specimens exceeding 13 mm ( 1/2 in.) in thickness because cooling may be questionable.
1.8 Values stated in SI units are to be regarded as the standard. The inch-pound units in parentheses are provided for information only.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 09-Dec-1998
• ICS: 19.040 - Environmental testing
• Technical Committee: G03 - Weathering and Durability
• Drafting Committee: G03.02 - Natural and Environmental Exposure Tests

Relations

• Replaced By: ASTM G90-05 - Standard Practice for Performing Accelerated Outdoor Weathering of Nonmetallic Materials Using Concentrated Natural Sunlight
• Effective Date: 01-Oct-2005
• Referred By: ASTM G178-16(2023) - Standard Practice for Determining the Activation Spectrum of a Material (Wavelength Sensitivity to an Exposure Source) Using the Sharp Cut-On Filter or Spectrographic Technique
• Effective Date: 10-Dec-1998
• Referred By: ASTM D5105-05(2019) - Standard Practice for Performing Accelerated Outdoor Weathering of Pressure-Sensitive Tapes Using Concentrated Natural Sunlight
• Effective Date: 10-Dec-1998
• Referred By: ASTM G183-15(2023) - Standard Practice for Field Use of Pyranometers, Pyrheliometers and UV Radiometers
• Effective Date: 10-Dec-1998
• Referred By: ASTM D6577-15(2019) - Standard Guide for Testing Industrial Protective Coatings
• Effective Date: 10-Dec-1998
• Referred By: ASTM D4364-13(2022)e1 - Standard Practice for Performing Outdoor Accelerated Weathering Tests of Plastics Using Concentrated Sunlight
• Effective Date: 10-Dec-1998
• Referred By: ASTM G156-17 - Standard Practice for Selecting and Characterizing Weathering Reference Materials
• Effective Date: 10-Dec-1998
• Referred By: ASTM D4141/D4141M-22 - Standard Practice for Conducting Black Box and Solar Concentrating Exposures of Coatings
• Effective Date: 10-Dec-1998
• Referred By: ASTM E816-15(2023) - Standard Test Method for Calibration of Pyrheliometers by Comparison to Reference Pyrheliometers
• Effective Date: 10-Dec-1998
• Referred By: ASTM D5722-20 - Standard Practice for Performing Accelerated Outdoor Weathering of Factory-Coated Embossed Hardboard Using Concentrated Natural Sunlight and a Soak-Freeze-Thaw Procedure
• Effective Date: 10-Dec-1998
• Referred By: ASTM G141-09(2021) - Standard Guide for Addressing Variability in Exposure Testing of Nonmetallic Materials
• Effective Date: 10-Dec-1998
• Referred By: ASTM D6763-16(2022) - Standard Guide for Testing Exterior Wood Stains and Clear Water Repellents
• Effective Date: 10-Dec-1998
• Referred By: ASTM F1164-19 - Standard Test Method for Evaluation of Transparent Plastics Exposed to Accelerated Weathering Combined with Biaxial Stress
• Effective Date: 10-Dec-1998
• Referred By: ASTM G113-22 - Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic Materials
• Effective Date: 10-Dec-1998
• Referred By: ASTM G147-17 - Standard Practice for Conditioning and Handling of Nonmetallic Materials for Natural and Artificial Weathering Tests
• Effective Date: 10-Dec-1998

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G 90 – 98
Standard Practice for
Performing Accelerated Outdoor Weathering of Nonmetallic
Materials Using Concentrated Natural Sunlight
ThisstandardisissuedunderthefixeddesignationG 90;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 Fresnel-reflecting concentrators using the sun as source
are utilized in the accelerated outdoor exposure testing of
2. Referenced Documents
nonmetallic materials.
2.1 ASTM Standards:
1.2 This practice covers a procedure for performing accel-
D 859 Test Method for Silica in Water
erated outdoor exposure testing of nonmetallic materials using
D 1014 Practice for Conducting Exterior Exposure Tests of
a Fresnel-reflector accelerated outdoor weathering test ma-
Paints on Steel
chine. The apparatus (see Fig. 1 and Fig. 2) and guidelines are
D 1435 Practice for Outdoor Weathering of Plastics
described herein to minimize the variables encountered during
D 1898 Practice for Sampling of Plastics
outdoor accelerated exposure testing.
D 4141 Practice for ConductingAccelerated Outdoor Expo-
1.3 This practice does not specify the exposure conditions
sure Tests of Coatings
best suited for the materials to be tested but is limited to the
D 4517 Test Method for Low-Level Total Silica in High-
method of obtaining, measuring, and controlling the proce-
Purity Water by Flameless Atomic Absorption Spectros-
dures and certain conditions of the exposure. Sample prepara-
copy
tion, test conditions, and evaluation of results are covered in
E 772 Terminology Relating to Solar Energy Conversion
existing methods or specifications for specific materials.
E 824 Test Method for Transfer of Calibration from Refer-
1.4 The Fresnel-reflector accelerated outdoor exposure test
ence to Field Radiometers
machines described may be suitable for the determination of
E 891 Tables for Terrestrial Direct Normal Solar Spectral
the relative durability of materials exposed to sunlight, heat,
Irradiance for Air Mass 1.5
and moisture, provided the mechanisms of chemical or physi-
E 903 Test Method for SolarAbsorptance, Reflectance, and
cal change, or both, which control the rates of acceleration
Transmittance of Materials Using Integrated Spheres
factors for the materials do not differ significantly.
G 7 Practice for Atmospheric Environmental Exposure
1.5 This practice establishes uniform sample mounting and
Testing of Nonmetallic Materials
in-test maintenance procedures. Also included in the practice
G 24 Practice for Conducting Exposures to Daylight Fil-
are standard provisions for maintenance of the machine and
tered through Glass
Fresnel-reflector mirrors to ensure cleanliness and durability.
G 113 Terminology Relating to Natural and Artificial
1.6 This practice shall apply to specimens whose size meets
Weathering Tests of Nonmetallic Materials
the dimensions of the target board as described in 8.2.
2.2 Other Standards:
1.7 For test machines currently in use, this practice may not
SAE J576 Plastic Materials for Use in Optical Parts Such as
apply to specimens exceeding 13 mm ( ⁄ in.) in thickness
Lenses and Reflectors of Motor Vehicle Lighting Devices
because cooling may be questionable.
SAE J1961 Accelerated Exposure of Automotive Exterior
1.8 Values stated in SI units are to be regarded as the
Materials Using a Solar Fresnel-Reflector Apparatus
standard. The inch-pound units in parentheses are provided for
information only.
3. Terminology
1.9 This standard does not purport to address all of the
3.1 Definitions—Definitions of terms common to G 3 dura-
safety concerns, if any, associated with its use. It is the
bility standards can be found in Terminology G 113.
responsibility of the user of this standard to establish appro-
Annual Book of ASTM Standards, Vol 11.01.
1 3
This practice is under the jurisdiction ofASTM Committee G-3 on Weathering Annual Book of ASTM Standards, Vol 06.01.
and Durability and is the direct responsibility of Subcommittee G03.02 on Natural Annual Book of ASTM Standards, Vol 08.01.
and Environmental Exposure Tests. Annual Book of ASTM Standards, Vol 11.02.
Current edition approved Dec. 10, 1998. Published March 1999. Originally Annual Book of ASTM Standards, Vol 12.02.
published as G 90 – 85. Last previous edition G 90 – 94. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G90
FIG. 1 Schematic of Fresnel-Reflecting Concentrator Accelerated Weatering Machine Single Axis Tracking
4. Significance and Use a single material between separate, although supposedly iden-
tical, exposures carried out for the same duration or number of
4.1 Results obtained from this practice can be used to
exposure cycles. In addition, results from exterior exposures
compare the relative durability of materials subjected to the
can vary due to seasonal or annual differences in important
specific test cycle used. No accelerated exposure test can be
climatic factors. Because of the variability between materials
specified as a total simulation of natural or field exposures.
and in results obtained using this practice and the variability in
Results obtained from this practice can be considered as
results from exterior exposures, use of a single acceleration
representative of natural or field exposures only when the
factor relating x hours of this accelerated exposure to y months
degree of comparative performance has been established for
or years of exterior exposure is not recommended. If accelera-
the specific materials being tested.
tion factors are determined, they must be based on results from
4.2 The relative durability of materials in natural or field
a sufficient number of separate accelerated exposures so that
exposure can be very different depending on the location of the
data relating times to failure in each exposure can be analyzed
exposure because of differences in UV radiation, time of
using statistical methods. In addition, use of acceleration
wetness, temperature, pollutants, and other factors. Therefore,
factors assumes that the degradation mechanism is the same in
even if results from a specific accelerated test condition are
both conventional and accelerated exposures.
found to be useful for comparing the relative durability of
materials exposed in a particular exterior location, it cannot be 4.4 This practice is best used to compare the relative
assumed that they will be useful for determining relative performance of materials tested at the same time in the same
durability for a different location. fresnel reflector device. Because of possible variability be-
4.3 Variations in results may be expected when operating tween the same type of exposure devices, comparing the
conditions vary within the limits of this practice. For example, amount of degradation in materials exposed for the same
there can be large differences in the amount of degradation in duration or radiant energy at separate times, or in separate
G90
FIG. 2 Dual Axis Tracking
TABLE 1 Fresnel-Reflector Test Machine Typical Spray Cycles
devices running the same test condition, is not recommended.
This practice should not be used to establish a “pass/fail”
Daytime Nighttime
Cycle
Spray Dry-Time Spray Dry-Time
approval of materials after a specific period of exposure unless
Cycles/h Cycles/h
Duration Duration Duration Duration
performance comparisons are made relative to a reference
1 8 min 52 min 1 8 min 52 min 3 during
material exposed simultaneously, or the variability in the test is
the night
2 no water spray no water spray
defined so that statistically significant pass/fail judgements can
A
3 no water spray 3 min 12 min 4
be made.
4.5 It is strongly recommended that at least one control test
A
This is the cycle specified in Procedure C of Practice D 4141.
specimen be exposed with each test. The control test specimen
should meet the requirements of Terminology G 113, and be
chosen so that its degradation mechanism is the same as that of
difference between the machines is the addition of a water
the test specimen. It is preferable to use two control test
deliverysystemtothedeviceusedinCycles1and3.Useofthe
specimens, one with relatively good durability and one with
specific cycle should relate to end use of the material and
relatively poor durability.
should be agreed upon by all interested parties.
4.6 The use of at least two replicates of each control test
5.1.1 The Fresnel-reflector test machine is a follow-the-sun
specimen and each material being evaluated is recommended
apparatus having flat mirrors so positioned that the sun’s rays
to allow statistical evaluation of results.
strike them at near-normal incident angles while in operation.
5. Apparatus
The mirrors are arranged to simulate tangents to a parabolic
troughinordertoreflectsunlightuniformlyontothespecimens
5.1 Test Machines—Fresnel-reflector test machines used in
Cycles 1, 2, and 3 of Table 1 are nearly identical. The only in the target area (see Fig. 1, Fig. 2, and Fig. 3).
G90
FIG. 3 Schematic of Optical System for a Fresnel Reflecting Concentrator Accelerated Weathering Machine
5.1.2 The test machine is equipped with a blower to cool the elevation. The axis of the target area remains parallel to the
test specimens. The air is directed over the specimens by an ground. The machine rotates about horizontal and vertical axes
adjustable deflector along one side of the target area. For to keep the target area in focus.
unbacked mounting, air is also directed under the specimens. 5.5 Nozzles—The test machine used in Cycles 1 and 3 of
This limits the increase in surface temperatures of most Table 1 is provided with a nozzle assembly for spraying water
specimens to 10°C above the maximum surface temperature onto the specimens during exposure. Fan spray nozzles which
that would be reached when identically mounted specimens are provides a uniform fine mist over the specimen area are
exposed to direct sunlight at normal incidence at the same time recommended.
and location without concentration.
6. Reagents and Materials
5.2 Mirrors—The Fresnel-reflector system mirrors of ma-
chines currently in use have a typical specular, spectral 6.1 Water Quality:
reflectancecurvesuchasthatpresentedinFig.4.Othermirrors 6.1.1 The purity of water used for specimen spray is very
may be used providing they meet the requirements of 6.2. important.Without proper treatment to remove cations, anions,
5.3 Photoreceptor Cells—Two photoreceptor cells, such as organics, and particularly silica, exposed panels will develop
silicon solar cells, are installed near the top of the air tunnel on spots or stains that do not occur in exterior exposures.
the side facing the sun.A“T” shadow maker is mounted above 6.1.2 Water used for specimen spray shall leave no objec-
the cells to illuminate equally one-half of each cell when the tional deposits or stains on the exposed specimens. It is
test machine is in proper focus. As one cell receives more strongly recommended that the water contain a maximum of
radiation than the other, the balance is disturbed and a signal is 1-ppm solids and a maximum of 0.2-ppm silica. Silica levels
furnished through an amplifier to a reversible motor which should be determined using the procedures defined in Test
adjusts the machine to maintain focus. Methods D 859 or D 4517. Prepackaged analysis kits are
5.4 Tracking System—The test machine shall be equipped commercially available that are capable of detecting silica
with a system to keep the target area in focus throughout the levels of less than 200 parts per billion (ppb).Acombination of
day. Several options are possible. deionization and reverse osmosis treatment can effectively
5.4.1 Single-axis tracking with manual altitude adjustment produce water with the desired purity. If the spray water used
(Fig. 1a). The test machine’s axis is oriented in the north/south is above 1-ppm solids, the solids and silica levels must be
direction, with the north pole being altitude-adjustable to reported.
account for seasonable variations in solar altitude at zenith. 6.1.3 If specimens are found to have deposits or stains after
5.4.2 Dual axis tracking (Fig. 2). The test machine is exposure in the apparatus, the water purity must be checked to
equipped with two sets of photoreceptor cells, one to control determine if it meets the requirements above. On some
the azimuth rotation of the machine, the other to control the tilt occasions,exposedspecimenscanbecontaminatedbydeposits
G90
FIG. 4 Specular Reflectance of Mirror Material
from bacteria that can grow in the purified water used for 8. Test Specimens
specimen spray. If bacterial contamination is detected, the
8.1 Users of the accelerated outdoor exposure test method
entire system used for specimen water spray must be flushed
described should follow the statistical procedures for sampling
with chlorine and thoroughly rinsed before resuming expo-
presented in Practice D 1898.
sures.Although it does not always correlate with silica content,
8.2 The maximum length and width of specimens cannot be
it is recommended that resistivity of water used for specimen
larger than the length or width of the target area, or both.
spray be continuously monitored and that exposures be discon-
8.3 The air-cooling process and mechanism may limit
tinued whenever the resistivity falls below 1 MV.
specimen thickness to 13 mm ( ⁄in.) or less.
6.2 The mirrors used on Fresnel-reflector test machines
8.4 Fig. 5 shows typical mounting for specimens smaller
shall be flat and shall have specular ultraviolet reflectance of
than the maximum allowable size. The leading edge of
65 % or greater at 310-nm wavelength as measured by Test
specimens to be mounted closest to the airflow shall be aligned
MethodE 903orothermethodfoundtogiveequivalentresults.
with the leading edge of the target boards so as not to disrupt
Fig. 4 presents typical and minimum acceptable specular
the airflow. Specimens shall not be mounted in a manner that
reflectance curves.
disrupts the uniform airflow used for cooling.
7. Safety Precautions
9. Specimen Mounting
7.1 Suitable eye protection shall be required when working
9.1 Specimens are to be mounted facing the mirror array on
with Fresnel-reflector test machine
...