Assessment of the performance of asphalt rubber layers on noise abatement

Layers with a very high content of rubber have shown to be very effective on noise abatement despite their reduced durability. On the contrary, layers with a rubberized asphalt binder have shown to be durable, but their performance regarding noise abatement is not consensual yet. This paper aims at assessing the effect of the use of layers with rubberized asphalt binder on noise abatement. For this purpose seven road sections with different surface types, among which five gap graded and three with rubberized asphalt have been selected. In these road sections the tyre-road noise generated by a heavy truck and two light vehicles at three levels of speed were measured by means of pass-by tests. Surface texture tests were also performed. The results focused on the noise level variation versus speed, the average noise level for each speed level versus type of surface and the average noise level variation with regards to a reference surface. Mixtures with rubberized asphalt did not show a significantly better performance. In fact, the same performance may be achieved with other type of gap graded thin mixtures. The results obtained might be better explained if other parameters than the rubberized asphalt binder are taken into account. Further research on the effect of porosity and texture on noise generation is being done. It is intended to perform absorption tests in all the surfaces analysed in order to study this issue in depth and fully understand the effect of the rubber on noise generation

Silent surfaces : an experience in Portugal

It is acknowledged that traffic noise affects human behaviour and health. Measures aiming at mitigating the impact of traffic noise are not always viable in urban areas. In Portugal, road designers have recently started to consider silent surfaces as alternative within their road pavement projects. In this paper the tire-surface noise of three surface layers integrated in a rehabilitation project carried out in an urban road that carries more than 40000 vehicles per day is assessed: i) one dense asphalt layer with limited maximum aggregate size, following the SILVIA recommendations for low noise surfaces; ii) two very-thin surfaces with different grading, which are an adaptation of the very-thin layers widely used in France to Portuguese conditions. The surface layers were constructed consecutively, involving segment lengths with more than 500 m. The surface texture was measured using a high speed profilometer. Skid resistance was also measured. The noise level was measured both by pass-by tests with selected traffic (trucks and light vehicles) at several speeds and by close proximity tests. The thin layers tested provided very good noise reduction values, especially at high speeds, and had a better performance than gap graded asphalt rubber surfaces frequently used in Portugal