By mixing rubber with aggregate used for fill and/or embankement in civil construction, the reliance on rock mined from the earth can be reduced.
The compressible nature of rubber makes it the perfect additive as it can be easily handled and compacted as most all aggregate must be in a civil construction application. There are numerous studies and academic papers supporting this idea.
Because this would be used in either a non-structural or sub-surface application, appearance does not matter. Since the idea is to use it as an additive the only solution would be the correct percentage of mixture, and this would be the highest percentage of rubber without sacrificing long-tested and accepted performance standards of aggregate.