Acoustic field evaluation of asphalt mixtures with crumb rubber

The aim of this study is to characterize the acoustical behavior of bituminous mixtures fabricated with recycled rubber crumb. Acoustic field measurements of the tire/pavement interaction in close proximity to the contact patch were carried out with a trailer with a protective chamber (TiresonicMk4-LA²IC). The survey was conducted on a test track with several experimental sections paved with a gap-graded mixture. Different methods of incorporating crumb rubber in the mixture were used: (i) into binder and (ii) with the aggregate materials. Close proximity sound levels are assigned to the gap-graded mixtures containing rubber and compared to that of a reference mixture without rubber. It is shown that asphalt mixtures fabricated with the addition of crumb rubber to the aggregate material (dry process) managed to reduce the noise from the tire/pavement interaction up to 2 dB(A).     

Monitoring road surfaces by close proximity noise of the tire/road interaction

Applied acoustics is becoming an important field for civil infrastructure and environmental assessment, and road maintenance or rehabilitation strategies. In this research LA(2)IC has developed a GPS-based measurement techniques and apparatus on a test vehicle, for monitoring the acoustical properties of different road pavement surfaces with a reference tire. A field test on PA-12 Spanish porous pavement found in Ciudad Real is developed. The test procedure, a modification based upon the close-proximity method (CPX), relies on the use of three standard microphones situated very close to the tire/road contact patch. This procedure allows the simultaneous measurement of the sound emission synchronized to a GPS receiver, which permits tracking of the position of the sound emission. Geo-referenced sound spectra for every 10 m during individual passes of the test vehicle are analyzed to determine the tire/road noise emissions from tire/PA-12 pavement interaction. Noise levels of around 102 dB(A), with a variability of approximately 0.6 dB(A), are found at a reference vehicle speed of 85 kmh. The frequency spectrum analysis over the test section shows noticeable differences for frequencies above 1 kHz, where the tire/road noise generation mechanisms are dominated by air pumping.     

骨架密实型低噪声路面降噪机理的实验研究

配制了传统的沥青混凝土(AC)、碎石沥青玛蹄脂(SMA)、不同橡胶粉掺量的骨架密实型低噪声路面等3类共5个配比的沥青路面,采用驻波法测量了各类沥青路面的吸声系数。并且分析了橡胶粉掺量对密实型低噪声路面动态模量的影响,得出了结论,即在这些路面中,橡胶粉含量为3%的密实型路面的减振降噪效果最好。     

Assessment of asphalt concrete acoustic performance in urban streets

Geo-referenced close proximity rolling noise and sound absorption measurements are used for acoustical characterization of asphalt concrete surfaces in an urban environment. A close proximity noise map of streets with low speed limits is presented for a reference speed of 50 km/h. Different pavements and pavement conditions, common in urban streets, are analyzed: dense and semidense asphalt concrete, with Spanish denomination D-8 and S-12, respectively, and on the other hand, dense pavement at the end of its service life (D-8(*)). From the acoustics point of view, the most favorable surface, by more than 4 dB(A) compared with the S-12 mix, is the smoothest surface, i.e., the D-8 mix, even though it presents a minor absorption coefficient in normal incidence. Noise levels from dense surfaces (D-8) increase significantly over time, principally due to the appearance of surface defects such as cracks and ruts. Longitudinal variability of the close proximity tire/pavement noise emission and surface homogeneity are also analyzed.     

Evaluation of sound absorption capacity of asphalt mixtures

Noise generation is an environmental problem that affects human beings, animals and even plants. Several serious diseases have their development associated to the exposure of human beings to high levels of noise pressure, such as arterial hypertension, gastrointestinal changes, alterations in blood glucose and high heart rate, among others. Vehicle traffic is part of a group of noise-generating factors. Various mechanisms govern the generation and propagation of vehicle noises, which are produced mainly by motor vibration at speeds below 50 km/h and by the tire-pavement contact at speeds above 50 km/h. The noise generated by tire-pavement contact is the result of two components: aerodynamic noise (mainly related to the coating porosity), and mechanical noise (related to the coating texture). The noise generation according to these two components may be mitigated by using special asphalt mixtures. This work evaluates the sound absorption of four different types of asphalt mixtures (common dense-graded asphalt mixture, dense-graded rubberized asphalt mixture, rubberized porous coat with void volumes varying from 22% to 27%, and rubberized open-graded friction course) and the effect of granulometry and void volume of each mixture on the sound absorption coefficient. Mixture slabs were molded in a slab compactor developed by LCPC (Laboratoire Central des Ponts et Chaussées) and specimens were extracted from each one for assessing the sound absorption capacity in the laboratory. The acoustic behavior was evaluated according to standard ISO 10534-2, using impedance tubes. Results showed that sound absorption is strongly influenced by void percentage, interconnected void percentage and layer thickness.     

Study to analyze the effects of vehicles and pavement surface types on noise

The effects of vehicles and pavement surface types on noise have been investigated at the Korea Highway Corporation’s Test Road along the southbound side of the Jungbu Inland Expressway, South Korea. The study was conducted in 2005 and 2006 through field measurements at nine surface sections of asphalt concrete and Portland cement concrete pavements using eleven vehicles. For the road noise analysis, the sound power levels (PWLs) of combined noise (e.g., tire/pavement interaction noise and power-train noise together) and tire/pavement interaction noise using various vehicles were calculated based on the novel close proximity (NCPX) and pass-by methods. Then, the characteristics of the PWLs were evaluated according to surface type, vehicle type, and vehicle speed. The results show that the PWLs of vehicles are diversely affected by vehicle speed and the condition of the road surface.     

A novel sound absorber with recycled fibers coming from end of life tires (ELTs)

The use of material waste, coming from the fibers of fluff (a textile residue from grounded end of life tires, ELTs), in the manufacture of sound absorber products, can help to combat two different kind of problems, the disposal of this kind of waste and the noise control. This paper presents the results of a new absorber material obtained through thermal compression, using a residue that is currently used for its high calorific value. Through this process, a product with a higher added value and a lower cost has been obtained. Through testing of samples made with fluff, results for absorption coefficients and acoustic impedance have been obtained. In addition, composite samples have been tested. One of these samples is a composite made with a layer of ground tire rubber (GTR), obtained by sintering and adding another layer of fluff.     

The effects of pavement surface characteristics on tire/pavement noise

Pavement surface characteristics are major attributes to tire/pavement interactions and are considered as cost-effective options to mitigate traffic noise. The objective of this paper is to evaluate the effects of single and multiple pavement surface characteristics on tire/pavement noise levels. During the period from August 2009 to August 2011, noise levels and pavement surface characteristics are measured quarterly on impervious and open-graded asphalt pavements at 2009 NCAT test track. The linear regression analysis method and dominance analysis method are used to evaluate the effects of single and multiple pavement surface characteristics on noise levels, respectively. The results show that surface texture increases noise levels at lower frequencies (below 1600 Hz) especially on impervious asphalt pavements. Porosity decreases noise levels at every frequency (except at 2500 Hz) on open-graded asphalt pavements. These findings will help to design future low-noise asphalt pavements.     

Noise control by sonic crystal barriers made of recycled materials

A systematic study of noise barriers based on sonic crystals made of cylinders that use recycled materials like absorbing component is reported here. The barriers consist of only three rows of perforated metal shells filled with rubber crumb. Measurements of reflectance and transmittance by these barriers are reported. Their attenuation properties result from a combination of sound absorption by the rubber crumb and reflection by the periodic distribution of scatterers. It is concluded that the porous cylinders can be used as building blocks whose physical parameters can be optimized in order to design efficient barriers adapted to different noisy environments.     

Definition of road roughness parameters for tire vibration noise control

Road roughness plays an important role in the generation of tire vibration noise. However, it is unclear which kinds of road roughness parameters should be controlled to reduce the noise. In this paper, we define the essential road roughness parameters that govern tire tread vibration and provide information on tire/road noise abatement. The detailed effects of road roughness parameters on tire tread vibration are estimated using a tire/road contact model. The results reveal that pavement asperity height itself is not an essential parameter, but asperity height unevenness, asperity radius, and asperity spacing are important for the abatement of tire vibration noise.     

Developing a Durable Quiet Road Surface

Road traffic noise can have a significant impact on the quality of life for residents close to major road networks. One of the most effective measures for reducing the noise from road traffic, particularly on high-speed roads, is to ensure the use of a low noise road surface. Research on pavement construction and the measurement of its acoustic properties has shown that significant noise reductions can be achieved through the use of certain road surface types. However certain low noise road surfaces do not exhibit the desired durability associated with more traditional pavements, leading to costly and disruptive maintenance regimes.
This article looks at the mechanisms involved in tyre/road noise generation and how these interact with various road surface properties including a brief overview of some common surface types. It then goes on to explain how these concepts informed the development of an asphalt surfacing material with enhanced durability and good acoustic performance without compromising safety. Progress in testing the resulting Premium Asphalt Surfacing System (PASS) is outlined, including the completion of a successful network trial.     

Effect and importance of static-load on airflow resistivity determination and its consequences on dynamic stiffness

Airflow resistivity is a physical parameter which characterizes porous and fibrous sound absorbent materials. It is well-known that such property allows the evaluation of the acoustic behaviour of sound absorbent materials in various fields of application, including automotive noise mitigation, architectural acoustics and building acoustics. In structure-borne sound insulation, airflow resistivity is essential for the evaluation of the dynamic stiffness of porous and fibrous resilient insulating materials used as underlay in floating floors.However, an inconsistency between the dynamic stiffness and the airflow resistivity test conditions can be recognized. In order to evaluate dynamic stiffness of a resilient material, a static load of about 2 kPa is applied, while in airflow resistivity determination this condition is not explicitly required. As a result, the density of analyzed material, in dynamic stiffness and airflow measurements, is different. Since these two quantities are correlated, it is necessary to measure materials under the same conditions of applied static load.In this work the effects of static load (or density after compression) in airflow resistivity determination of various porous and fibrous resilient materials are investigated, and the consequent influence on dynamic stiffness is discussed. A simply empirical relation between density and airflow resistivity is also put forth.The main focus of this paper is to propose an harmonization among requirements of the Standards in order to prevent significant errors in dynamic stiffness determination and incorrect evaluations of the acoustic behaviour.     

Statistical classification of road pavements using near field vehicle rolling noise measurements

Low noise surfaces have been increasingly considered as a viable and cost-effective alternative to acoustical barriers. However, road planners and administrators frequently lack information on the correlation between the type of road surface and the resulting noise emission profile. To address this problem, a method to identify and classify different types of road pavements was developed, whereby near field road noise is analyzed using statistical learning methods. The vehicle rolling sound signal near the tires and close to the road surface was acquired by two microphones in a special arrangement which implements the Close-Proximity method. A set of features, characterizing the properties of the road pavement, was extracted from the corresponding sound profiles. A feature selection method was used to automatically select those that are most relevant in predicting the type of pavement, while reducing the computational cost. A set of different types of road pavement segments were tested and the performance of the classifier was evaluated. Results of pavement classification performed during a road journey are presented on a map, together with geographical data. This procedure leads to a considerable improvement in the quality of road pavement noise data, thereby increasing the accuracy of road traffic noise prediction models.     

Effect of High Aspect Ratio Fillers on the Performance of Styrene-Butadiene Rubber

Among the many material performance properties of vulcanized elastomers for tire tread application, rolling resistance and wet traction are particularly important since both greatly impact fuel efficiency and traction of a vehicle. Rolling resistance and wet traction are generally negatively correlated, i.e., with the increase in rolling resistance of a tire, its wet traction decreases. Silica nanofillers are often used for achieving the desired balance of wet traction and rolling resistance. However, the high cost of silica limits its wide spread application. In this research we studied the effects of using fillers with different aspect ratios (calculated by dividing the long dimension of a filler by its short dimension) on the performance of vulcanized styrene butadiene rubber (SBR), a common rubber for tire tread application. Three high aspect ratio fillers were used: aragonite calcium carbonate, wollastonite and carbon nanofiber. For comparison purpose, spherical silica filler was also included. We found that the high aspect ratio fillers were efficient in improving the wet traction and rolling resistance as well as enhancing the mechanical energy dissipation of SBR. Among the three high aspect ratio fillers studied, wollastonite provided the best wet traction and rolling resistance balance due to its high aspect ratio and compatibility with the base rubber. The effects of fillers induced crosslinking on the dynamic performance were also discussed.     

A novel approach to the acoustic characterisation of porous road surfaces

Porous road surfaces offer an effective means of reducing the generation and propagation of noise from road traffic. However, the porosity of these surfaces can deteriorate over time, leading to a reduction in their noise reducing properties. Efficient methods are therefore required for monitoring this performance. Existing techniques for performing in-situ measurements of acoustic absorption are unsuitable for use within the traffic stream. Static measurements using time domain Maximum Length Sequence (MLS) based techniques have been demonstrated to offer advantages over traditional techniques, presenting the opportunity for measurements under dynamic conditions. This paper describes the design of a system for carrying out dynamic MLS-based measurements. Results are presented which demonstrate that stable dynamic measurements can be carried out at speeds of up to 30 km/h.     

腐蚀声发射信号降噪方法

为了从复杂背景噪声中有效地检测出腐蚀声发射信号,采用短时分形维数和离散分数余弦变换相结合的降噪方法,利用声发射检测系统,对6% FeCl₃·6H₂O溶液中Q235钢板的全面腐蚀和局部腐蚀声发射信号进行了降噪处理。实验结果表明,腐蚀声发射信号分别加入白噪声、有色噪声和粉红噪声,在输入信噪比为0~15dB的条件下,此方法降噪效果与标准离散余弦、离散分数余弦变换方法相比,输出信噪比最高可提升8 dB。所述降噪方法对检测腐蚀声发射信号以及对金属剩余寿命的评价具有一定意义。      

Pavement temperature influence on close proximity tire/road noise

The aim of this work is to analyze the influence of the surface temperature on the acoustical behaviour of a semidense asphalt pavement located in an urban area. The sound levels emitted by the interaction between a reference tire and the asphalt pavement at different surface temperatures were measured with the trailer Tiresonic Mk4 LA²IC-UCLM rolling at a speed of 50 km/h. The analysis of the results shows that increasing pavement temperature leads to a reduction in the close proximity sound levels assessed at a rate of 0.06 dB(A)/°C. Moreover, spectral analysis confirms that both the mechanisms associated with vibration and impacts and those related to the friction and adhesion between tire and pavement in the contact patch could be affected by the variation of the surface temperature.     

瓦状阻尼橡胶块对高铁车轮减振降噪的影响分析

依据声学测试标准,为了评价某型高铁车轮在安装不同形式橡胶块装置后的减振降噪效果,在半消声室内基于B&K振动噪声测试分析系统,对裸轮和橡胶块车轮开展振动声辐射室内测试实验,并基于有限元方法对车轮模态进行了仿真分析。测试结果可知:相比裸轮,WA、WB车轮模态阻尼比显著增加,车轮的减振效果明显,其中WA车轮的减振效果略优于WB车轮。径向激励下,WA车轮声功率级降低了8 dB(A),WB车轮声功率级降低了5.5 d B(A);轴向激励下,WA车轮声功率级降低了8.2 dB(A),WB车轮声功率级降低了6.2 dB(A)。分析可知橡胶块装置能有效抑制车轮的滚动噪声和曲线啸叫,对车轮的减振降噪有积极作用。     

Surface impedance design with ground corrugation for mitigation of large-calibre gun blast noise

The surface impedance design approach is proposed for mitigating large-calibre gun blast noise. Surrounding the blast noise, we employ a group of concentric trenches with critical depths to dampen the propagation of the acoustic wave. These trenches behave like quarter-wavelength resonators and produce acoustic soft surfaces at their openings. The sound pressure is then mitigated over these soft surfaces by destructive interference and the wave attenuates rapidly along the ground surface. To evaluate the overall acoustic performance of such a design, we develop an efficient numerical solver by treating the geometry as a body of revolution (BOR). The symmetry of the structure in the revolution direction allows the 3D boundary integral equation (BIE) for acoustic wave scattering to be reduced to a 2D integral equation by the use of Fourier series expansions. Numerical experiments show that this model can effectively suppress the acoustic wave propagation horizontally and the reduction can reach about 15 dB for large-calibre gun noise with very low-frequency components.     

薄膜型声学超材料对低频振动的隔声特性分析

高效共振混合机工作频率为60 Hz,且系统处于共振,产生较大低频噪声。针对振动机械产生的有害噪声,分析了高效共振混合机低频高加速度共振混合过程的特点,得到了60 Hz低频声波穿透力强的特点,相比传统的以吸声材料构建的50～100 mm厚度、隔声效果小于10 dB的隔声罩,分析了薄膜型声学超材料在低频减振降噪中的隔声特性。通过多物理场仿真分析,60 Hz时隔声量为31.4 dB,确定了硅橡胶弹性薄膜的预应力和质量块的面密度;采用3D打印机快速成型技术,构建了隔声实验装置,分析了独立隔声单元、面密度、薄膜尺寸等隔声特性规律。基于人耳在实际环境中感受到的噪声强度,提出了噪声衰减量和插入损失的分析方法,在距离声源380 mm和1000 mm的位置,60 Hz时隔声量分别为27 dB和38 dB。研究成果丰富了低频隔声特性理论,为薄膜型声学超材料的工程设计和优化提供了技术支撑。