ASTM D8212-24e1 PDF

SIGNIFICANCE AND USE 4.1 The determination of the tensile force-elongation values of geogrids provides index property values. This standard practice shall be used for the determination of radial properties, judgment of conformity of product manufactured, and acceptance of commercial shipments of geogrids. 4.2 The standard strain at which this practice is applied is 2 %, as this has been established and accepted over the years as the lowest strain at which consistent measurement of the properties of geogrids can be achieved. However, if a customer or specifier requires calculation at a lower strain, this can be done provided the higher standard deviation this can give is accepted. 4.3 In cases of dispute arising from differences in reported results when using this standard practice for acceptance testing of commercial shipments, the purchaser and supplier should conduct comparative tests and calculations 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 which are as homogeneous as possible and which are from a lot of material of the type in question. The 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 Student's t-test for unpaired data and an acceptable probability level chosen by the two parties before the testing began. If a bias is found, either its cause must be found and corrected or the purchaser and supplier must agree to interpret future results in light of the known bias. 4.4 This standard practice is applicable to all geogrids with two or three sets of ribs in which variation of tensile properties between different sets of parallel ribs is 20 % or less. For multiple-layered geogrids, it should be applied to each layer individually and the results for all layers summed in each radial di... SCOPE 1.1 This practice presents a method for determining in-air index values (see Note 1) of the radial load and radial stiffness at low strain in each symmetric direction of a balanced geogrid (see Note 2) subjected to 360° radial strain. This determination is based on tensile test results from testing in accordance with Test Method D6637/D6637M and an analysis of the radial force balance in each symmetric direction across a circle of geogrid that is assumed to be strained uniformly in all radial directions to a low strain level. 1.2 Symmetric directions relative to the machine direction: 1.2.1 For geogrids with square or rectangular apertures: 0°, 45°, 90°, 135°. 1.2.2 For geogrids with triangular apertures: 0°, 30°, 60°, 90°, 120°, 150°. Note 1: These index properties are not to be used for design or performance purposes. Note 2: A balanced geogrid is one in which the manufacturer’s specification indicates that variation of tensile properties between different sets of parallel ribs is 20 % or less. 1.3 This practice will facilitate comparisons of the radial tensile properties of different balanced geogrids and judgment of conformity of product manufactured and acceptance of commercial shipments of geogrids by standardizing the data used and the method by which the calculations are performed. 1.4 This standard practice is restricted in application to geogrids with two sets of parallel ribs arranged at nominally 90° to each other or three sets of parallel ribs arranged at nominally 60° to each other with one set lying in the cross-machine direction. 1.5 Further, this practice is restricted to 20 % variation in the specified unit tensile properties of the different sets of ribs in a geogrid in order to enable the development of the mathematics that use these properties of each set of ribs in the geogrid. This generates index values for the unit tensile properties in the nominal directions as outlined in ...