From an engineering point of view, crumb rubber has a number of special thermo-mechanical and chemico-physical properties. Crumb rubber is made by shredding scrap tires and as such, it is a particulate material free of fiber and steel. It is made commercially available in 50-pound bags or 2000-pounds bulk bags. The size of the rubber particles is graded. The finest one can be as small as about 0.2mm (Mesh #80) and below, The gradation commonly used in rubberized asphalt pavement is between about 2.0 mm to 0.5 mm (Mesh #10 to Mesh #40). Crumb rubber is light in weight and is durable. It can last for a long period of time in a natural environment. From the safety consideration, crumb rubber is a non-toxic and inert material.
The idea to explore the possible application of crumb rubber in the noise reduction application merges from the fact that  bulk rubber panels have a much better sound absorption capability than concrete blocks/slabs do. Now, since crumb rubber is made in a state of loose granules, using crumb rubber to make panels provides the opportunity that the panels now may be fabricated in the way that they can contain a large percentage of air voids. Rubber panels containing high air porosity will certainly increase the sound absorption capability in comparison with bulk (zero porosity) rubber panels.
More importantly, crumb rubber is a recycled material, as more is consumed, the better it will be to help reduce so-called the scrap tire pollution. Also, considering that most new noise barriers recently developed or under development are made from plastic that is a high-energy-consumption product made by chemically processing fossil oils, and the resource for fossil oils on earth is limited. Therefore, the choice is obvious that developing crumb rubber for its application in noise-reduction can lead to a