Evaluation of sound absorption capacity of asphalt mixtures

Noise generation is an environmental problem that affects human beings, animals and even plants. Several serious diseases have their development associated to the exposure of human beings to high levels of noise pressure, such as arterial hypertension, gastrointestinal changes, alterations in blood glucose and high heart rate, among others. Vehicle traffic is part of a group of noise-generating factors. Various mechanisms govern the generation and propagation of vehicle noises, which are produced mainly by motor vibration at speeds below 50 km/h and by the tire-pavement contact at speeds above 50 km/h. The noise generated by tire-pavement contact is the result of two components: aerodynamic noise (mainly related to the coating porosity), and mechanical noise (related to the coating texture). The noise generation according to these two components may be mitigated by using special asphalt mixtures. This work evaluates the sound absorption of four different types of asphalt mixtures (common dense-graded asphalt mixture, dense-graded rubberized asphalt mixture, rubberized porous coat with void volumes varying from 22% to 27%, and rubberized open-graded friction course) and the effect of granulometry and void volume of each mixture on the sound absorption coefficient. Mixture slabs were molded in a slab compactor developed by LCPC (Laboratoire Central des Ponts et Chaussées) and specimens were extracted from each one for assessing the sound absorption capacity in the laboratory. The acoustic behavior was evaluated according to standard ISO 10534-2, using impedance tubes. Results showed that sound absorption is strongly influenced by void percentage, interconnected void percentage and layer thickness.