Introduction to asphalt-rubber pavement noise reducing characteristics

Freeway noise in the United States of America (USA) has been greatly alleviated by employing 25 mm open graded Asphalt-Rubber Friction Course (ARFC). The use of asphaltrubber (AR) pavements in the USA has been successful in several states. AR binder used in the hot mix asphalt is a mixture of 80 percent hot asphalt (bitumen), and 20 percent ground scrap tyre crumb rubber by weight of asphalt. The resultant AR binder mixture is added hot to a hot open graded mineral aggregate to produce ARFC mixture as the final wearing course of the pavement structure. Typically, the ARFC mixes contain 9 to 10 percent AR binder and their use has been primarily focused on reducing thermal and reflective cracking, and highway noise. This paper discusses the benefits of ARFC as a pavement noise mitigation strategy. The paper reviews the experience in the USA with using AR pavements to reduce the pavement noise by 3-12 decibels (dB). In addition, sound intensity measurements taken close to the tyre/pavement interface have shown that ARFC surfaces are effective in reducing noise by 4 to 6 dB compared with traditional dense graded asphalt concrete, and by 6 to 12 dB compared to cement concrete surfaces. In addition, AR has been successfully utilized in the mitigation of daily thermal variances in Portland Cement Concrete pavements, improved skid resistance, reduced roughness, and reduction of emission rates of tyre wear per km driven.