Achieving a better match between ordered and actual performance of urban low-noise asphalts -exploring better solutions for noise abatement
Abstract and Figures
Thanks to the paradigm shift in noise abatement, over 1000 low-noise road surfaces have been constructed in urban areas in Switzerland in the last ten years. Until now, such road surfaces were often ordered according to a Swiss standard for semi-dense asphalts (SDA). The difficulty with low noise road surfaces in urban areas from a noise control point of view is that the acoustic performance often varies by more than 3-4 dB when newly constructed-a variability in product that is hardly acceptable to noise abatement professionals. This study investigates how a better match can be achieved between the ordered and the actual effect, by narrowing down the mixture design in the Swiss standard for SDA. For this purpose, several variants for a revised standard were analysed regarding the statistical risk of acoustic non-conformity. The analysis is based on a large dataset from a connected InterNoise22 paper where statistical analyses of acoustic measurement data and data from the laboratory tests of over 200 low-noise surfaces in Switzerland are presented. This paper makes recommendations for revised mixtures in an improved Swiss standard for SDA, carefully balancing the advantages of the different variants with the practical limitations they bring.
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... [2,3]. However, the decent performance gradually diminishes over time due to traffic load (mechanical damage and changes in macrotexture), as well as dirt accumulation (clogging of the open pores) [4,5,6,7]. The decrease in noise reduction over time is referred to as acoustic aging, which follows a different time scale compared to the mechanical aging of the surface ...
This study investigates the effectiveness of grinding techniques on special low-noise pavements as well as conventional asphalt surfaces in order to restore or enhance their noise-reducing properties. This study analyzes 17 different test tracks where grinding techniques were applied, featuring various surface types and stages of aging. The research employs Close-Proximity-Measurements (CPX) and additional methods to evaluate surface characteristics. Initial results reveal significant acoustic improvements from grinding, especially on surfaces with 4-and 8-mm maximum aggregate size. However, the durability of these measures varies, with 4 mm surfaces returning to baseline after 2-4 years, while 8 mm surfaces benefit for approximately 4 years. The study demonstrates that grinding methods can enhance acoustics through surface texture improvement and partially reactivating previously clogged pore spaces. The effectiveness depends on the initial acoustic state and grinding depth, emphasizing the importance of setting clear objectives for optimal results. In summary, this study underscores the effectiveness of grinding in enhancing the acoustic quality of low-noise road surfaces. Moreover, its integration into road surface maintenance strategies is a new tool for extending the functional and acoustic lifespan of low-noise road surfaces.
In many countries, porous asphalts (PA) have become an established measure to reduce road traffic noise on high-speed roads. For urban roads, 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 200 road surfaces is carried out to identify semi-dense asphalt (SDA) mixtures (with a void content between 8-18%) that lead to reliable noise reduction. Multivariate statistical analysis on over 1327 drill core examinations, 775 mixture examinations and 737 acoustic close-proximity (CPX) measurements allowed us to identify the important parameters explaining acoustic performance. With this set of relevant parameters a
Random Forest model was developed to determine the optimal target values and parameter ranges as a basis for standardisation. The resulting high performance low-noise SDA mixture is designed to have a noise reduction similar to PA road surface on motorways.
The development of effective and durable low-noise pavements remains a challenge since the required properties – a smooth surface texture and connected voids in the pavement – are often in conflict with some of the pavement's primary functions. To increase a low-noise pavement's technical and acoustical durability, many countries have developed semi-dense asphalt solutions with lower void content in comparison to traditional porous asphalt pavements. In the scope of the national noise-abatement program, over 400 semi-dense asphalts have been constructed in Switzerland as a noise mitigation measure. Practical experiences with semi-dense asphalts, however, show that their acoustic long-term performance can vary substantially. This study presents the results of a national research project in which the technical properties of acoustically good and bad performing low-noise pavements constructed since 2005 were analyzed. Multivariate statistical analysis was carried out using various parameters based on drill core analyses and bituminous mixture examinations of over 120 semi-dense asphalt pavements, to investigate the relationship between construction, mixture design and material-related parameters and the acoustic data from CPX (close-proximity) measurements. Based on these analyses, this paper presents the most critical factors for the successful design of semi-dense asphalt mixtures and offers guidelines aimed at guaranteeing the pavement's acoustic performance and durability. The study also illustrates why the traditional approaches used for designing porous asphalt mixtures do not necessarily work with semi-dense asphalt mixtures.
Low-noise road surfaces have become a popular and widely used measure in Switzerland to combat road traffic noise at its source. In total, 371 low-noise road surfaces have been constructed in urban areas over the last decade on road sections where traffic noise exceeded the legal limits. As with all conventional road surfaces, low-noise road surfaces become louder and lose some of their initial noise reduction properties over time. Research has shown that the loss of acoustic performance over time can vary substantially on different road sections. The explanations for this, however, remain unclear. Therefore, an extensive dataset of 778 CPX (close proximity) measurements was analysed and correlated with 14 environmental and traffic related variables obtained from spatial analysis to assess their influence on acoustic ageing behaviour of low noise road surfaces. Multivariate statistical analysis revealed that (1) frost has the strongest negative impact on acoustic durability of a low-noise road surface, increasing the risk of strong acoustic ageing (risk of a road surface to lose faster its initial noise reduction properties) importantly. (2) Traffic load also affects acoustic durability adversely, leading to a moderate increase of the risk for strong acoustic ageing. (3) Interestingly, the results suggest that ingress of dirt from agricultural activity does not have a negative impact on acoustic durability of the assessed low-noise road surfaces.
Acoustical measurements on 371 low-noise road surfaces, constructed over the last decade in urban areas in Switzerland, have shown that large initial noise reductions can be achieved. However, these surfaces change their noise-reducing characteristics over their lifetime as a function of age and wear. Information on the long-term acoustical performance of such road surfaces is currently not available. Such information is, however, of high importance for reliable cost-benefit analysis which serves as a crucial input for planning and decision making. This article aims to fill this gap by providing predictions for the acoustic long-term performance of these low-noise road surfaces. This study revealed that the ageing processes of road surfaces can in general be described by a logarithmic model depending on the surface age. It showed that the acoustic long-term performance of the 8 mm low void RS class is similar to the one of SMA 11 RS, even though considerable initial noise reductions were obtained. The acoustic long-term performances of 4 mm RS and 8 mm RS, however, are promising.
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