Recommendations for the successful design of urban low-noise asphalts - findings from the statistics of over 200 mixtures

In many countries, low-noise road surfaces have become an established measure to reduce road traffic noise. The focus often is on the high-speed network, where porous asphalts (PA) have been used successfully for decades. For urban areas, however, the design of effective low-noise asphalt mixtures remains a challenge, as a pore structure is needed that does not clog at lower speeds. Frequently found solutions are fine textured asphalts in the medium void content range with small pores. The challenge in this particular range is to define mixtures that guarantee a certain acoustic performance. This is exactly where the study comes in: a combined statistical analysis of data from acoustic measurements and laboratory testing of over 200 road surfaces is performed to identify mixtures in the medium void content range (between 8-18% void content) that lead to reliable noise reduction. Multivariate statistical analysis on over 500 drill core examinations allowed us to identify meaningful subcategories of urban low-noise asphalt mixtures, each of which implying a certain effect mechanism and effectiveness in noise reduction. Based on this data, we give recommendations for successful grading curve ranges and other mixture design parameters for urban low-noise asphalts grouped into different performance categories.