Three road surfaces of the RUBIT type, i.e. asphaltic concrete mixed with rubber granulate, so-called rubberized asphalt, have been tested for external noise emission. These have been compared with a conventional, smooth asphaltic concrete surface (HAB12T) and a conventional, rough chip seal surface (Y1 8-12). Similarly, three cement concrete surfaces have been tested in parallel project where the same reference surfaces were used. The RUBIT surfaces all contained 3 % rubber and had 12 mm maximum chip size. They were, however, in somewhat different conditions; one surface being quite new and one being two years old and densely trafficked. The tests have been performed with the so-called trailer method. A special trailer constructed to measure tire/road noise, from the Technical University of Gdansk, has been used. Sound levels as well as frequency spectra have been measured. Five different types of car tires have been used for the tests: one smooth reference tire, two "summer" type tires, one "winter" type tire and one studded "winter" tire. These cover more or less the whole range of car tires, regarding noise emission. The results show that the RUBIT surfaces emitted noise equivalent to that from the reference surfaces. The exceptions were that the "summer" tires gave 1-3 dB(A) higher noise levels on the oldest RUBIT surface than on the other surfaces (including the reference surfaces), and the non-studded "winter" tire gave the lowest noise on the rough reference surface. Consequently, traffic noise reduction can not be used as an argument for using RUBIT surfaces of the types tested here. If a RUBIT surface shall have a potential to reduce traffic noise to a considerable extent, it must probably have an unrealistic large proportion of rubber. Concerning cement concrete surfaces they proved to be more noisy than the conventional bituminous surfaces used as references here. The highest difference was noticed between a rough chip seal and the cement concrete surfaces for a tire with a winter tread pattern. In all cases the high-frequency noise (over 1 kHz) and low-frequency noise (below 250 Hz) was much higher on the cement concretes than on the bituminous surfaces. The differences between cement concrete surfaces of different age and wear were relatively small. (A)
Abstract