ABSTRACT
In 1999, four research sections were constructed in Oester Soegade in Copenhagen, Denmark, to investigate the performance of porous bituminous surfacings in practice. Three of the research sections were surfaced with a double layer porous asphalt surfacing, and a fourth reference section was surfaced with a conventional dense Asphalt Concrete surfacing. The objective of the study was to investigate the durability of double layer porous bituminous surfacings under Danish weather conditions and to measure the variations in the noise levels during the lifetime of the surfacings. This paper describes the investigations made of the permeabilities and the void distributions for the three porous asphalt test sections and their comparison with the noise level measurements made along all four test sections. Permeability measurements were carried out using the Beckers tube method and noise level measurements applied the “Statistical Pass-By Method” (ISO 11819-1: 1997). The test sections were constructed in August 1999 and permeability and noise level measurements were made in September of the same year. In addition, permeability was measured before and after every flushing operation on the porous bituminous surfacings. A strict programme of flushing of the surfacing was followed, with flushing carried out in November/December and April/May of every year. Noise level measurements were carried out on all sections in June/July 2000 and again in the same months in 2001. For one of the test sections, additional noise measurements were also made in November 2000. In connection with construction of the test sections in 1999, in addition to conventional bituminous mixture tests, a number of cores were taken for preparation of Plane and Thin sections. These investigations, together with the results from regular permeability measurements, gave an indication of the mechanism and rate of clogging of the voids in the surfacings. The Thin sections also provided useful information about the condition of the surfacings, for example, whether stripping of the binder was beginning to occur. The results from the permeability and noise level measurements show that some form of relationship exists between them. However, it was not possible to identify any definite effect from the flushing operations, as no significant difference could be detected between permeability measurements made before and after flushing. As anticipated, the Thin section investigations from the cores extracted after more than one year’s traffic, showed that clogging occurred in the top 10–25 mm of the surfacings.
