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40 CHAPTER 5 Data Analysis This chapter presents the analyses of the data obtained Spectral Analyses from the measurements on the test sections. These analyses Noise Spectrum Analysis--Identification of undesirable were used to provide a basis for developing a process and tonal frequencies (high, medium, and low tones). detailed sample/guide specifications for selecting texture Power Spectral Density (PSD) Analysis of Texture--Fast types. Fourier Transform (FFT) to separate the wavelengths The analyses recognized the limitations of the data (e.g., con- and amplitudes of the texture profiles into wavebands. crete and aggregate properties data) and focused on the texture Texture and Noise Spectrum Comparisons--Cross wavelengths because of their reported influence on pavement comparisons of texture and noise spectra to identify friction and noise. As indicated previously, wavelengths fall texture wavelengths with significant bearings on noise primarily in the 2-in. (50-mm) and less range and are largely frequencies. characterized as macro-texture and micro-texture. Comparative/Qualitative Analyses Friction is highly dependent on the ranges of texture. Comparison of Textures by Site/Location--Direct/head- Micro-texture contributes significantly to friction on dry to-head comparisons of performance (initial and/or as roads at all speeds and to wet roads at slower speeds. Macro- a function of time/traffic) of textures at individual test texture significantly influences friction on wet roads at higher sites/locations. speeds. Therefore, the durability of friction is governed by the Texture Durability Analysis--Evaluation of micro- polish and abrasion properties of exposed aggregate and by texture and macro-texture durability. the wear properties of the mix. Noise Comparison of Textures--Comparison of noise Noise is mostly a function of macro-texture and the lower characteristics by general texture categories and evalua- wavelength levels of mega-texture. Other factors, such as tion of effects of specific texture dimensions on noise. pavement porosity and stiffness, have been reported to affect Relationship of Near-Field Noise with Interior and Pass- noise, but to a much lesser degree. Because the pavements By Noise. tested in this study were all conventional, low-porosity pave- Statistical Analyses ments with similar stiffness levels, these factors were not con- Texture Depth Measurement Procedure--Correlation sidered in the analyses. Thus, the analysis of noise focused on analysis of texture depth measured using a high-speed the influence of macro- and lower mega-texture characteris- profiler and CT Meter. tics (e.g., texture depth, direction, orientation/bias, and spec- Test Site/Location Performance Analysis--Analysis of trum parameters) and to some extent on the noise influence variance (ANOVA) and Tukey groupings of texture of wear properties of the concrete on durability. performance (i.e., texture, friction, and noise) within Chapters 3 and 4 summarized the field testing results of individual test sites/locations. existing and newly constructed test sections, respectively. National-Level Analysis of Texture, Friction, and Noise-- These summaries represent the performance characteristics ANOVA and regression analysis of texture, friction, (quantifications of texture, friction, and noise levels) of dif- noise, and site/location (i.e., traffic, climate, and selected ferent surface textures at a specific point in time. For a better pavement variables) data from all texture test sections. understanding of the results and to apply them to the devel- Noise-Texture Relationship--Multiple regression analy- opment of a texture selection process, the following detailed sis of texture parameter data (i.e., direction, depth, orien- data analyses were conducted: tation, spectral parameters) and near-field SI noise data.