The low in-place density of tire derived aggregate (TDA) makes them attractive for use as lightweight fill for embankments constructed on weak ground and backfill for retaining walls. TDA, also know as tire shreds or chips, are scrap tires that have been cut into 50 to 300 mm (2 to 12 in.) pieces. There are many examples of projects that have successfully used TDA as lightweight fill. However, as illustrated by three projects built in 1995 that experienced internal heating reactions, care is needed to properly design and construct TDA fills. The underlying cause of these problems was a combination of oxidation of exposed steel belts and freshly cut surfaces on rubber pieces. The lessons learned from these projects resulted in design guidelines to limit internal heating of TDA fills. Nine projects have now been built in accordance with the guidelines. Internal measurements show that TDA temperatures are similar to background soil levels, indicating the effectiveness of the guidelines. Moreover, effective construction specifications have been developed that often result in lower construction costs than competing lightweight fill materials.
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