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92 CHAPTER 7 Conclusions and Recommendations for Future Research Conclusions face, re-texturing via longitudinal diamond grinding or grooving can be more cost-effective than application of an Major conclusions of the study consist of the following: asphalt surfacing. Based on extensive friction/micro-texture testing and avail- PCC surface textures with the overall lowest noise levels able concrete mixture information, the use of higher qual- include the longitudinal diamond-ground and longitudi- ity aggregates in the concrete mixture helps maintain the nal grooved textures, followed by longitudinal-tine and micro-texture qualities needed for friction. longitudinal-drag textures. High levels of friction can be Loss of concrete pavement macro-texture over time/traffic achieved with ground, grooved, and tined textures, partic- is greatest for diamond-ground textures (0.015 to 0.02 in. ularly if good-quality aggregate is used in the concrete mix- [0.4 to 0.5 mm]) and lowest for longitudinally grooved and ture. Friction for longitudinal-drag textures can become dragged textures (0.002 to 0.003 in. [0.05 to 0.08 mm]). inadequate if a deep texture (MTD > 0.8 mm [0.03 in.]) is not The geometric shape (i.e., narrow fins) of the diamond- achieved at time of construction and/or polish-susceptible ground texture results in more substantial loss than textures aggregate is used. with no grooves (drag textures) or those that have well- Although uniformly spaced transverse-tine textures can defined, widely spaced, and structurally sound grooves produce moderate levels of overall noise, they are highly (longitudinal-groove textures). prone to creating objectionable tones. Closer spacing (0.5 in. Considerable differences exist between texture depth mea- [12.7 mm] or less) and shallower grooves can help reduce surements obtained using the CT Meter and the high-speed pavementtire whine and overall noise. Variably spaced profiler. Although the difference in sampling rates of the transverse-tine and skewed transverse-tine textures can two devices is probably a factor, the texture type and direc- result in moderately low levels of overall noise and can tion are more profound factors, with longitudinal textures significantly reduce or eliminate objectionable tonal spikes. creating greater measurement difficulties for the high-speed High levels of friction can be achieved with all three of these profiler. textures, particularly if good-quality aggregate is used. PSD analysis of pavement surface texture indicated that Although the EAC and shotblast textures evaluated in this near-field SI noise is generally related to the PSD texture study showed relatively high overall noise and low-to- parameters L4/L63, A1/A2, and PW. moderate friction, the number of sections included in the Detailed efforts to model SI as a function of various texture evaluation (1 of each) was insufficient for a proper deter- parameters (not just PSD texture parameters) were some- mination of noise and friction characteristics. Additional what successful; the best predictive model (R2 = 0.77) yielded research is needed to verify indications from other coun- SI as a function of A1/A2, RMS, and texture direction. Cor- tries that low levels of noise and adequate levels of friction relation analyses further indicated that reducing higher can be successfully achieved with these textures. wavelength texture and increasing lower wavelength texture Asphalt surfacings tested in this study (thin HMA overlay (i.e., decreasing the L4/L63 or A1/A2 ratios, and reducing PW) and proprietary ultra-thin bonded wearing course) exhib- results in reduced noise. ited low to moderately low overall noise and moderately ANOVA and regression analysis of texture (excluding PSD high levels of friction. Depending on the surfacing type and texture parameters), friction, and noise measurement data the hardness of the aggregate in the existing concrete sur- collected on all test sections, combined with other perti-