【国外标准】 Standard Test Method for Maximum Media Density for Dead Load Analysis of Vegetative (Green) Roof Systems

5.1 This test method describes simple laboratory methods that provide reproducible measurements of critical media properties, and permit direct comparisons to be made between different media materials.5.2 The density of mixed media materials will vary depending on the degree to which they are subjected to compaction and the length of time that the material is allowed to hydrate and subsequently drain. Most green roof media materials have a large capacity to absorb and retain moisture. Furthermore, moisture will drain gradually from the media following a hydration cycle. The maximum media density measured in this procedure approaches the density at the theoretical saturation point.5.3 Existing methods for measuring the capillary-moisture relationship for soils (Test Method D2325) rely on sample preparation procedures (Test Methods D698) that are not consistent with the conditions associated with the placement of green roof media materials. This procedure is intended to provide a reproducible laboratory procedure for predicting the maximum media density, moisture content, air-filled porosity, and water permeability under conditions that more closely replicate field conditions on green roofs.5.4 The value of this test method to the green roof designer is that it provides an objective measure of maximum probable media density (under drained conditions) for estimating structural loads. It also provides a method for estimating the lower limit for the water permeability of the in-place media. This latter value is important when considering drainage conditions in green roofs. Finally, the maximum media water retention has been shown to be a useful indicator of the moisture retention properties of green roof media.1.1 This test method covers a procedure for determining the maximum media density for purposes of estimating the maximum dead load for green roof assemblies. The method also provides a measure of the moisture content, the air-filled porosity, and the water permeability measured at the maximum media density.1.2 This procedure is suitable for green roof media that contain no more than 30 % organic material as measured using the loss on ignition, as described in Test Methods E177, Test Method C. The test specimen should be a bulk oven-dried sample prepared according to Test Methods E177, Test Method A.1.3 The maximum media density and associated moisture content measured in this procedure applies to drained conditions near the saturation point.1.4 The test method is intended to emulate vertical percolation rates for water in green roofs.1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.6 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, health, and environmental practices and to determine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.