ASTM D7748-12
(Test Method)Standard Test Method for Flexural Rigidity of Geogrids, Geotextiles and Related Products
Standard Test Method for Flexural Rigidity of Geogrids, Geotextiles and Related Products
SIGNIFICANCE AND USE
This test method is considered satisfactory for manufacturing quality control testing of a specific geosynthetic; however, caution is advised since information about between-laboratory precision is incomplete. Comparative tests as directed in 5.1.1 may be advisable.
In case of a dispute arising from differences in reported test results when using this test method for acceptance testing of commercial shipments, the purchaser and the supplier should conduct comparative tests to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a minimum, the two parties should take a group of test specimens that are as homogeneous as possible and that are from a lot of material of the type in question. Test specimens should then be randomly assigned in equal numbers to each laboratory for testing. The average results from the two laboratories should be compared using the appropriate statistical analysis and an acceptable probability level chosen by the two parties before testing is begun. If a bias is found, either its cause must be found and corrected or the purchaser and the supplier must agree to interpret future test results with consideration to the known bias.
This test method is not suitable for very limp geosynthetics or those that show a marked tendency to curl or twist at a cut edge.
The stiffness of a geosynthetic may change with storage.
No evidence has been found showing that bending length is dependent on specimen width. The tendency for specimens to curl or twist will affect the result, because of the rigidity provided at the edge. Consequently, the edge effect is less of an issue for a wider strip.
SCOPE
1.1 This test method covers the measurement of stiffness properties of geogrids, geotextiles and geogrid-geotextile composites all of which are referred to as geosynthetics within this standard. Bending length is measured and flexural rigidity is calculated through use of the cantilever test procedure.
1.1.1 This test method employs the principle of cantilever bending of the geosynthetic under its own mass.
1.2 This test method applies to geogrids, geotextiles and geogrid-geotextile composites.
1.3 This test method is for manufacturing quality control purposes only, to ensure uniformity and consistency of flexural rigidity for a specific product from roll to roll and lot to lot.
1.4 The values stated in SI units are to be regarded as the standard. The U.S. customary units may be approximate.
1.5 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.
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Designation:D7748–12
Standard Test Method for
Flexural Rigidity of Geogrids, Geotextiles and Related
Products
This standard is issued under the fixed designation D7748; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2 Definitions of Terms Specific to This Standard:
3.2.1 bending length, n—a measure of the interaction be-
1.1 This test method covers the measurement of stiffness
tween geosynthetic weight and geosynthetic stiffness as shown
properties of geogrids, geotextiles and geogrid-geotextile com-
by the way in which a geosynthetic bends under its own
posites all of which are referred to as geosynthetics within this
weight.
standard. Bending length is measured and flexural rigidity is
3.2.1.1 Discussion—Bending length reflects the stiffness of
calculated through use of the cantilever test procedure.
a geosynthetic when bent in one plane under the force of
1.1.1 This test method employs the principle of cantilever
gravity.
bending of the geosynthetic under its own mass.
1.2 This test method applies to geogrids, geotextiles and
4. Summary of Test Method
geogrid-geotextile composites.
4.1 A specimen is slid at a specified rate in a direction
1.3 This test method is for manufacturing quality control
parallel to its long dimension, until its leading edge projects
purposes only, to ensure uniformity and consistency of flexural
from the edge of a horizontal surface. The length of the
rigidity for a specific product from roll to roll and lot to lot.
overhang is measured when the tip of the specimen is de-
1.4 The values stated in SI units are to be regarded as the
pressed under its own mass to the point where the line joining
standard. The U.S. customary units may be approximate.
the top to the edge of the platform makes a 0.724 radians
1.5 This standard does not purport to address all of the
(41.5°) angle with the horizontal. From this measured length,
safety concerns, if any, associated with its use. It is the
the bending length and flexural rigidity are calculated.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5. Significance and Use
bility of regulatory limitations prior to use.
5.1 This test method is considered satisfactory for manufac-
turing quality control testing of a specific geosynthetic; how-
2. Referenced Documents
2 ever, caution is advised since information about between-
2.1 ASTM Standards:
laboratory precision is incomplete. Comparative tests as
D123 Terminology Relating to Textiles
directed in 5.1.1 may be advisable.
D1776 Practice for Conditioning and Testing Textiles
5.1.1 In case of a dispute arising from differences in
D4354 Practice for Sampling of Geosynthetics for Testing
reported test results when using this test method for acceptance
D4439 Terminology for Geosynthetics
testing of commercial shipments, the purchaser and the sup-
D4759 Practice for Determining the Specification Confor-
plier should conduct comparative tests to determine if there is
mance of Geosynthetics
a statistical bias between their laboratories. Competent statis-
D5261 Test Method for Measuring Mass per Unit Area of
tical assistance is recommended for the investigation of bias.
Geotextiles
As a minimum, the two parties should take a group of test
3. Terminology specimens that are as homogeneous as possible and that are
from a lot of material of the type in question. Test specimens
3.1 For common definitions of terms in this test method,
should then be randomly assigned in equal numbers to each
refer to Terminology D123 and Terminology D4439
laboratory for testing. The average results from the two
laboratories should be compared using the appropriate statis-
This test method is under the jurisdiction of ASTM Committee D35 on
tical analysis and an acceptable probability level chosen by the
Geosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechani-
cal Properties. two parties before testing is begun. If a bias is found, either its
Current edition approved Feb. 1, 2012. Published March 2012. DOI: 10.1520/
cause must be found and corrected or the purchaser and the
D7748–12
supplier must agree to interpret future test results with consid-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
eration to the known bias.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7748–12
5.2 This test method is not suitable for very limp geosyn- the absence of such an agreement, take the number of geosyn-
thetics or those that show a marked tendency to curl or twist at thetic rolls specified in D4354.
a cut edge.
7.2 —For acceptance testing, take a swatch extending the
5.3 Thestiffnessofageosyntheticmaychangewithstorage.
width of the geosynthetic and approximately2m(6ft) along
5.4 No evidence has been found showing that bending
the machine direction from each roll or piece in the lot sample.
length is dependent on specimen width. The tendency for
For rolls of geosynthetic, take a sample that will exclude
specimens to curl or twist will affect the result, because of the
geosynthetic from the outer wrap of the roll or the inner wrap
rigidity provided at the edge. Consequently, the edge effect is around the core of the roll of geosynthetic, or any end piece.
less of an issue for a wider strip.
7.3 Direction of Test—Consider the long dimension of the
specimen as the direction of test.
6. Apparatus
7.4 Number of Test Specimens—From each laboratory sam-
pling unit, take five specimens from the machine direction and
6.1 Flexural Rigidity Tester (Fig. 1).
6.1.1 Horizontal Platform, with a minimum area of 100 by five specimens from the cross-machine direction as applicable
900 mm (4 by 36 in.) and having a smooth low-friction, flat to a material specification or contract order.
aluminum surface. A leveling bubble shall be incorporated in 7.5 Cutting Test Specimens—Cut the specimens to be used
the platform.
for the measurement of machine direction with the longer
6.1.1.1 Indicator, inclined at an angle of 0.724 6 0.01 dimension parallel to the machine direction. Cut the specimens
radians (41.5 6 0.5°) below the plane of the platform surface.
to be used for the measurement of the cross-machine direction
6.1.1.2 Movable Slide, consisting of a metal plate not less with the longer dimension parallel to the cross-machine direc-
than 50 by 200 mm (2 by 8 in.) by approximately 3 mm (1/8
tion. Label to maintain specimen identity.
in.) thick and having a mass of 270 6 5 g (0.6 6 0.01 lb).
7.5.1 Take specimens, representing a broad distribution
6.1.1.3 Scale and Reference Point, to measure the length of
across the width and length, preferably along the diagonal of
the overhang
thelaboratorysample,andnonearertheedgethanone-tenthits
6.1.1.4 Specimen Feed Unit, motorized set to 120 mm/min
width. Ensure specimens are free of folds, creases, or wrinkles.
(4.75 in./min) 65 %, or manual equivalent.
Avoid getting oil, water, grease, etc. on the specimens when
handling.
7. Sampling and Test Specimens
7.5.2 For geogrids and geotextile-geogrid composites cut
specimen such that the specimen include two (2) geogrid
7.1 Lot Sample—As a lot sample for acceptance testing,
apertures in width or a minimum of 5 by 90 c
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