Paper by RIFFEL from ISCR 8th 1998 Lisbon Portugal
With the development of draining concrete as a super whispering surface, the German Cement Industry has signalled a new era for the concrete structure. This special draining concrete is a so-called like-grained concrete with a cavity content of 20 - 25 vol.-%. The individual aggregate grains are cemented with a cement paste, modified with a plastic dispersion, with the result that the structure is stable an long-lasting. The considerable reduction in the noise created by the tyres on the road surface (rolling noise) can be explained by the fact that the air compressed between the vehicle tyres and the road surface can escape into the cavity of the open-pore surface beneath the tyres and thus does not make a hissing noise as the tyres roll over the surface. The high-frequency tyre noise range above 1000 Hz is thus considerably reduced. There is one further positive acoustic effect of the open-pore concrete structure, that is the high sound absorption capacity of the road surface. Here, the sound waves created by the vibration of the tyres as well as the engine noise are absorbed to a high degree - up to 100% within certain frequency ranges - that is, the sound energy is converted by the road surface into heat.