Abstract
About 600,000 pieces of perlite blocks were used by Nippon Doro Kodan (Japan Highway Public Corporation) for the purpose of noise reduction in Meishin Expressway tunnels. The Properties of perlite blocks and the acoustic test results of these tunnels lined with them are as follows: 1. The total length of tunnels is about 7.5km and the work was completed in July, 1963. 2. Bulk specific gravity of perlite block is 0.9 approximately and its size is 19×39×10cm. 3. Sound adsorption coefficient of perlite block is about 0.5. 4. The "perlite block-lining area/total wall area" in tunnels is 0.16 therfore it is supposed that the mean value of sound absorption coefficient of wall is about 0.19. 5. Reverberation time in tunnels lined with perlite blocks is 4 sec. or less, on the other hand that without perlite blocks is 10sec. or more. 6. Noise reduction in tunnels lined with perlite blocks is 18-20db at 100m from noise sourse, that without perlite blocks is 2-3db in any case. From these test results, the authors are convinced that perlite block is effective sound absorber for tunnel.
