ASTM D 7568 : 2012

1.1 This specification covers a type of plastic lumber product, defined as polyethylene-based structural-grade plastic lumber (SGPL), for use as main framing members, including joists, stringers, beams, columns; and secondary framing members, including planking, posts and bracing; in outdoor structures such as decks, boardwalks, docks, and platforms.

1.2 This specification is applicable to solid, rectangular SGPL products where polyethylene resin (non cross-linked) is the continuous phase and is at least 50 % of the product (by weight).

1.3 This specification is not applicable to plastic lumber products containing cellulosic materials as additives, fillers or fiber reinforcements.

1.4 SGPL products covered by this specification shall not be used as tensile members.

1.5 SGPL products are produced using several different manufacturing processes. These processes utilize a number of polyethylene resin material systems that include varying proportions of fillers, fiber reinforcements, and other chemical additives.

1.6 Due to thermodynamic effects that result in outer-surface densification during manufacture, SGPL products are typically non-homogeneous in the cross-section. This standard does not address materials that have been modified from their original cross-section.

1.6.1 The cross-section non-homogeneity is addressed in the material property assessments in this document only for applications in which the product cross-section is not modified by cutting, notching, or drilling. For products modified in this manner, additional engineering considerations are required and they are beyond the scope of this document.

1.7 For purposes of this standard, an SGPL product is a specific combination of polyethylene resin, together with fillers, reinforcements, and additives. Each formulation is to be identified as a distinct and different product, to be tested and evaluated separately.

1.8 Diverse and multiple combinations of both virgin and recycled polyethylene material systems are permitted in the manufacture of SGPL products.

1.9 Fiber reinforcements used in SGPL include manufactured materials such as fiberglass (chopped or continuous), carbon, aramid and other polymeric materials.

1.10 A wide variety of chemical additives are typically added to SGPL formulations. Examples include colorants, chemical foaming agents, ultraviolet stabilizers, fire retardants, lubricants, anti-static products, heat stabilizers, and coupling agents.

1.11 Diverse types and combinations of filler systems are permitted in the manufacturing of SGPL products. Fillers that cause the product to fail the requirements of 6.13 are not permitted in the manufacturing of SGPL products.

1.12 In order for a product to be classified as SGPL, it must meet the minimum stress and modulus criteria consistent with the specific product as marked, and additionally the properties specified in Section 6 of this specification.

1.13 This specification pertains to SGPL where any reinforcement is uniformly distributed within the product. When reinforcement is not uniformly distributed, the engineering issues become substantially more complex. For this reason, such products are not covered in this document.

1.14 Products that fail at strains of less than 0.02 (2 %) when tested in flexure in accordance with 6.6 are not compatible with the underlying assumptions of Annex A1 and are beyond the scope of this standard (see Note 1).

Note 1—Calculation of time-dependent properties in Annex A1 is based on the assumption that the product does not fail in a brittle manner. The 2 % strain limit was selected based on the judgment of the task group members that created Annex A1.

1.15 This specification addresses issues relevant to a buyer’s requirements for SGPL products and has therefore been developed in the format of a procurement specification.

1.16 Criteria for design are included as part of this specification for SGPL products.

1.17 Use of SGPL members in application will typically require the design of structural connections. Connection design between SGPL members falls outside the scope of this standard.

1.18 The values are stated in inch-pound units, as these are currently the most common units used by the US construction industry. Equivalent SI units are indicated in parentheses.

1.19 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.

Note 2—There is no known ISO equivalent to this Standard.