Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
92 Conclusions Major conclusions of the study consist of the following: ⢠PCC surface textures with the overall lowest noise levels include the longitudinal diamond-ground and longitudi- nal grooved textures, followed by longitudinal-tine and longitudinal-drag textures. High levels of friction can be achieved with ground, grooved, and tined textures, partic- ularly if good-quality aggregate is used in the concrete mix- ture. Friction for longitudinal-drag textures can become inadequate if a deep texture (MTD > 0.8 mm [0.03 in.]) is not achieved at time of construction and/or polish-susceptible aggregate is used. ⢠Although uniformly spaced transverse-tine textures can produce moderate levels of overall noise, they are highly prone to creating objectionable tones. Closer spacing (0.5 in. [12.7 mm] or less) and shallower grooves can help reduce pavementâtire whine and overall noise. Variably spaced transverse-tine and skewed transverse-tine textures can result in moderately low levels of overall noise and can significantly reduce or eliminate objectionable tonal spikes. High levels of friction can be achieved with all three of these textures, particularly if good-quality aggregate is used. ⢠Although the EAC and shotblast textures evaluated in this study showed relatively high overall noise and low-to- moderate friction, the number of sections included in the evaluation (1 of each) was insufficient for a proper deter- mination of noise and friction characteristics. Additional research is needed to verify indications from other coun- tries that low levels of noise and adequate levels of friction can be successfully achieved with these textures. ⢠Asphalt surfacings tested in this study (thin HMA overlay and proprietary ultra-thin bonded wearing course) exhib- ited low to moderately low overall noise and moderately high levels of friction. Depending on the surfacing type and the hardness of the aggregate in the existing concrete sur- face, re-texturing via longitudinal diamond grinding or grooving can be more cost-effective than application of an asphalt surfacing. ⢠Based on extensive friction/micro-texture testing and avail- able concrete mixture information, the use of higher qual- ity aggregates in the concrete mixture helps maintain the micro-texture qualities needed for friction. ⢠Loss of concrete pavement macro-texture over time/traffic is greatest for diamond-ground textures (0.015 to 0.02 in. [0.4 to 0.5 mm]) and lowest for longitudinally grooved and dragged textures (0.002 to 0.003 in. [0.05 to 0.08 mm]). The geometric shape (i.e., narrow fins) of the diamond- ground texture results in more substantial loss than textures with no grooves (drag textures) or those that have well- defined, widely spaced, and structurally sound grooves (longitudinal-groove textures). ⢠Considerable differences exist between texture depth mea- surements obtained using the CT Meter and the high-speed profiler. Although the difference in sampling rates of the two devices is probably a factor, the texture type and direc- tion are more profound factors, with longitudinal textures creating greater measurement difficulties for the high-speed profiler. ⢠PSD analysis of pavement surface texture indicated that near-field SI noise is generally related to the PSD texture parameters L4/L63, A1/A2, and PW. ⢠Detailed efforts to model SI as a function of various texture parameters (not just PSD texture parameters) were some- what successful; the best predictive model (R2 = 0.77) yielded SI as a function of A1/A2, RMS, and texture direction. Cor- relation analyses further indicated that reducing higher wavelength texture and increasing lower wavelength texture (i.e., decreasing the L4/L63 or A1/A2 ratios, and reducing PW) results in reduced noise. ⢠ANOVA and regression analysis of texture (excluding PSD texture parameters), friction, and noise measurement data collected on all test sections, combined with other perti- C H A P T E R 7 Conclusions and Recommendations for Future Research
93 nent available test section data (e.g., age/traffic data, cli- mate data, and pavement data), indicated that near-field SI noise is influenced to a large extent by texture depth and by texture type and direction. Also, SI is increased as the num- ber of traffic applications is increased and the number/ frequency of joints is increased. Recommendations for Future Research The following are recommendations for future research: ⢠Perform additional field testing on the existing test sections and the newly constructed test sections included in this study to allow for an evaluation of the long-term friction, noise, and durability characteristics of different texture forms. ⢠Conduct a study of the effects of aggregate used in the concrete surface layer on texture durability. ⢠Continue to evaluate and model textureânoise relationships for various surface textures, with special consideration of PSD texture parameters. ⢠Conduct investigations to enhance the methods for field- measuring friction and noise characteristics of pavement surfaces. ⢠Conduct investigations of EAC and other textures to develop a better understanding of the friction, noise, and durability characteristics of these and others.