Tyre - Road Noise, Surface Characteristics and Material Properties

Noise levels due to road traffic have reached intolerable high levels in and around many urban areas all around the world. Because of health reasons and reasons of well- being these noise levels have to be reduced. The noise produced from the interaction between the rolling tyre and road surface is one of the most important contributions in the overall traffic noise. Therefore solutions for noise level reduction have to be found in that interface. A noise reducing pavement is considered as an effective way to reduce the tyre - road noise from the source where it generates. Towards further understanding and improvement of the noise reduction ability of pavements, research was carried out in this PhD thesis to determine the relationship between the road material properties, surface characteristics and the noise levels, and to develop models which can be used for guiding the design of noise reducing pavements. As one of existing road surfaces, the thin layer surfacing eliminates the tyre - road noise by combining a small surface texture and a high porosity. In recent years, it became popular for using it on urban and provincial road sections in the Netherlands and some other European countries. Replacing porous asphalt with thin layer surfacings on highways is also considered an option in the Netherlands. As there are limited investigations on the relation between tyre - road noise and the influencing parameters for this type of surface, the research in this thesis focuses on thin layer surfacings. The study starts with a review of existing researches on tyre - road noise. It provides basic knowledge about tyre - road noise and the influencing parameters related to the road surface. The related measurement methods and models developed were summarized. Comments were made on these existing studies and the shortcomings were pointed out. A research plan was then proposed based on the comments of the current researches and aiming for improving the existing knowledge of tyre - road noise on thin layer surfacings. Measurements were carried out for investigating the influence of mixture compositions on surface characteristics. Both laboratory and in-situ measurements were involved. In the laboratory tests, thin layer surfacing samples with different mixture compositions were designed and produced; core samples were also used which were drilled from trial road sections in the Netherlands. The surface characteristics studied included: surface texture, sound absorption, mechanical impedance and stiffness. Methods for testing the surface characteristics and mixture compositions were discussed. Experimental work was also undertaken for developing new methods in testing the surface characteristics. A contribution of this thesis to tyre - road noise related measurement is the application of a new type of technology for measuring the sound absorption of a road surface. It is based on testing the sound pressure and sound particle velocity close to the sample surface. According to the analysis of the test results, this measurement method proved to provide reliable results of sound absorption for road surface samples. Furthermore, suggestions were given for the application of the method in road engineering measurements. Surface characteristics and mixture compositions of thin layer surfacings were then measured. The influence of the material properties on surface characteristics, including texture, sound absorption, mechanical impedance and stiffness, were observed based by comparing test results obtained on materials with different mixture compositions. Moreover, in the study, the degree of connectivity of air voids in the road surface sample was determined. A relationship between the mechanical impedance and stiffness of road surface material was also developed. Comments were given for noise reduction by taking into account the mechanical impedance of road surfaces. The investigation of the effect of surface characteristics on tyre - road noise was performed by means of statistical analyses. Data used in the analysis were from thin layer surfacing sections in the Netherlands. The two important surface characteristics, surface texture and sound absorption were taken in to account. Correlation analysis and linear regression analysis were adopted for observing the relationship between the surface characteristics and noise levels. The individual effect of a certain surface characteristic can be reflected by the regression equations. Furthermore, the influence of driving speed of the vehicle, the tyre types and small changes of surface characteristics were also discussed. In the end, a model which predicts the tyre - road noise levels for thin layer surfacings was developed. The model was built by means of regression analysis by using the data from the laboratory measurements and an existing database. With the model, noise levels can be predicted using a small number of input parameters of material properties or surface characteristics. The model was validated by using data from in service thin layer road surfaces. The model can be used for predicting noise levels and helps to improve the design of noise reducing surfaces.Structural EngineeringCivil Engineering and Geoscience