|
|
| Line 7: |
Line 7: |
| | use as decoration in concrete plaster | | use as decoration in concrete plaster |
| | | | |
| − | ===Best Practices in Glass Recycling ===
| + | |
| − | Developing Specifications for Recycled Glass Aggregate
| |
| − | *'''Material:''' Recycled Glass
| |
| − | *'''Issue:''' <br>
| |
| − | Glass is a relatively new construction aggregate material. The term “glass aggregate”
| |
| − | includes, for this Best Practice, 100% glass, glass-soil, and glass-aggregate mixtures. In general, glass
| |
| − | aggregate is durable, strong, easy to place, and easy to compact. The material can be used for
| |
| − | construction applications including general backfill, roadways, utility backfill, drainage medium, and in
| |
| − | miscellaneous uses such as landfill cover and underground storage tank backfill. For each application,
| |
| − | the material should be specified based on the cullet content, gradation, debris level, and compaction
| |
| − | level. Criteria for developing the specifications for any aggregate rely on a combination of technical
| |
| − | data and practical historical experience. Currently, the availability of such criteria for glass aggregate
| |
| − | is limited. This lack of information is a barrier to the increased use of the material. <br>
| |
| − | '''Best Practice:''' <br>
| |
| − | This best practice presents quality control measures applicable for all glass aggregate.
| |
| − | The intent is to define the general parameters that must be considered when developing specifications. A
| |
| − | more detailed development of specifications for glass aggregate in load-supporting (see the Behavior of
| |
| − | Glass Aggregate under Structural Loads) and non-loaded applications (see Glass in Non-Structural
| |
| − | Construction Applications) are presented in separate Best Practices.
| |
| − | Processing and Mixing: Specifications may require that the processed glass be blended with natural
| |
| − | aggregate to a specific percentage. Because blending adds extra costs and can be difficult in the field, the
| |
| − | specifying engineer should give serious consideration to the need for uniform blending. In many drainage or
| |
| − | non-structural applications, it may be permissible to switch between 100% glass and 100% natural aggregate
| |
| − | during the job without sacrificing quality. In structural applications, it may be more important to attain
| |
| − | uniform blending. The blending process should prevent segregation of particles and debris. <br>
| |
| − | '''Gradation.''' <br>
| |
| − | From an engineering standpoint, it has been shown that 1, 3⁄4, 1⁄2, or 1⁄4-inch minus cullet all
| |
| − | perform well in appropriate applications. Glass of 1⁄4-inch minus has a grain size close to that of a fine to
| |
| − | coarse sand, whereas glass of 1⁄4-inch plus is similar to a fine to coarse gravel. In general, cullet particles
| |
| − | over one inch in size become platy in shape and are susceptible to breaking and chipping. A cullet fill
| |
| − | containing greater than 10% of such coarse particles can experience gradation change during transportation
| |
| − | and compaction, and possibly volume reduction upon loading. On the other hand, glass particles smaller
| |
| − | than US No. 200 sieve will have a large surface area and can retain a relatively large quantity of moisture. A
| |
| − | cullet fill containing greater than 10% of such fine particles can become sensitive to moisture content during
| |
| − | compaction, and may be difficult to use during wet weather. The specifying engineer should begin with the
| |
| − | same gradation as is required for natural aggregates in the application, then consider whether the function of
| |
| − | the glass is to replace the natural aggregate with the same gradation or complement it with a gradation that
| |
| − | improves the density of the fill. <br>
| |
| − | '''Debris Level:''' <br>
| |
| − | Debris may be defined as any materials that may impact the performance of the engineered
| |
| − | fill if present in sufficient quantities. Organic materials may decay and result in volume reduction. Metals, ceramics, and plastic, if present in large enough quantities, can affect the engineering properties. A visual
| |
| − | classification method has been developed for field determination of debris level. See the Visual
| |
| − | Inspectionfor Glass Construction Aggregate Best Practice. The debris level obtained using this visual
| |
| − | procedure is much higher than the debris content measured by weight or volume. This is because paper
| |
| − | residue, which appears to represent 10% by two-dimensional classification, may actually be less than 2% by
| |
| − | volume or weight. Finally, a specification should always indicate that no hazardous materials are allowed. <br>
| |
| − | '''Compaction'''.<br>
| |
| − | In order to achieve the desired engineering properties in the field, glass aggregate should be
| |
| − | compacted to a specified minimum level in the field. The compaction levels are typically specified using
| |
| − | maximum dry densities determined in the laboratory. For 100% cullet, the compaction data is found using a
| |
| − | Standard Proctor test (ASTM D698). For glass-soil or glass-aggregate mixture, a Modified Proctor test
| |
| − | (ASTM D1557) is typically used. The desired level of compaction is generally 90 to 95% of maximum dry
| |
| − | density. The glass processor should keep data on the dry density of processed glass from that facility, and,
| |
| − | if possible, a lab confirmation should be performed for the specific job.
| |
| − | The level of compaction should be field-verified by in-situ testing. The frequency of testing is typically one
| |
| − | per 2,500 square feet of fill but not less than one per lift of fill. Nuclear densometers are the most
| |
| − | commonly used device for density testing. However, due to the porous and heterogeneous nature of the
| |
| − | material, modifications to the common test procedures should be specified when appropriate. Such
| |
| − | modifications are presented in the following Best Practices: <br>1) Compaction of Glass Aggregate,<br> 2) Density
| |
| − | Test of Glass Aggregate Using a Nuclear Densometer, and<br> 3) Moisture Content Test of Glass Aggregate
| |
| − | Using a Nuclear Densometer. <br>
| |
| − | '''Design Considerations.'''<br>
| |
| − | Considerations should be made regarding the exposure of the general public to
| |
| − | cullet fills. Depending on the application, landscaping soil and vegetation, asphalt pavement, or concrete
| |
| − | could be used to cover the cullet fills. Also, considerations should be made regarding cullet fills which are
| |
| − | placed in contact with synthetic liners, geotextile, PVC pipes or pipes with protective coatings.
| |
| − | Implementation: This Best Practice presents a starting point for specifying engineers to begin to
| |
| − | consider the kinds of construction applications in which they will use recycled glass aggregate. Given the
| |
| − | considerations above, engineers should judge their own potential uses based on the properties of glass
| |
| − | aggregate, the availability of properly processed glass, and local economics. <br>
| |
| − | '''Benefits:''' <br>The material behaviors of cullet fill and thus the criteria for developing specifications are
| |
| − | similar to those of natural sand and gravel. Dissemination of the best practice information presented here
| |
| − | will help engineers, contractors and permitting authorities to be familiar with cullet fill materials and
| |
| − | ultimately increase their potential use in construction. <br>
| |
| − | '''Application Sites:''' <br>Glass processing facilities, construction sites, and testing laboratories. <br>
| |
| − | ===Contact:=== For more information about this Best Practice, contact CWC, (206) 443-7746, e-mail
| |
| − | info@cwc.org.
| |
| | | | |
| | ===References:=== | | ===References:=== |
