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Abstract

The friction of pavement is mainly determined by the microtexture of the surface layer. However, the finer degree of microtexture makes it impossible to observe with naked eye. The object of this study was to develop a High Definition Scan Texture Machine (HDSTM) with 2D Laser CCD to support previous research on the correlation between texture and friction. In addition, this study proposed seven different parameters and sought to find an index for an ideal correlation that could represent the entire pavement texture. By assessing the test results, the Segment of Average Profile Depth (SAPD) was selected as the texture parameter for the threshold standard of pavement friction out of various 2D texture parameters. The SAPD had high correlation with British Pendulum Number (BPN) in wet and dry surface conditions and the texture data had sufficient samples to support the high correlation with BPN. Based on the results of in this study, 2D texture, SAPD, is recommended as an important index for engineers to evaluate the surface friction in the Highway Maintenance Office. Due to the influence of extreme weather, the accumulated water on road surfaces may not be fully channeled out via the vertical and horizontal slope of the road design. Thin water films may form, reducing the friction between the vehicle tires and the pavement surface and creating a skid situation for vehicles. This study, through a literature review and research of the characteristics of pavement surface texture, sought to identify the key influence of friction and structuralize the relationship between surface texture and friction. The High Definition Scan Test Machine (HDSTM) was utilized for its accuracy to improve artificial operation error of measuring texture from the Sand Patch Method. This study tried to discover the correlation between texture and friction. Chen et al. (2010) claimed that high definition laser CCD could be used to measure texture for friction prediction. Xie et al. (2008) estimated the Friction Number (FN) by using the texture laser test. Their research applied the laser system with standards of 12 bit digital resolution and a 150 kHz frequency of 5 mils max test resolution. It was installed and testing was conducted on a vehicle with speeds over 60 miles/hr, and laser detecting pavement surface accuracy was achieved up to 0.03 mm (Xie et al., 2008). Lin (2008) had a preliminary study of correlation between one dimension pavement texture and friction and developed a pavement High Definition Circular Texture Machine (HDCTM), had a higher definition than the conventional CTM, to accurately classify the depth of the shallow and deep textures. The statistical analysis of simple regression was adopted to discover the relationship between the sum of the texture and the BPN. The correlation coefficient () and the coefficient of determination (R2 ) were 0.7 and 0.6, respectively. The sum of texture in his study had high correlation with BPN. Under the condition of wet dense-graded asphalt concrete (DGAC), the correlation coefficient and the coefficient of determination between the surface texture and the BPN were 0.5 and 0.3, respectively, which reflected a norm of middle correlation. Hanson et al. (2004) claimed that the results was no significant difference between CTM and Sand Patch Method. Oliver (2009) claimed that the pavement surface texture was the main source of the friction. The finer textures would be able to provide a brake-ability of vehicle below 60-70 km/hr, whereas rough textures would be able to provide a brake-ability of vehicle above 90-100 km/hr. Tighe et al. (2009) claimed that to ensure the safety of a moving vehicle, the contact between the tires and the pavement required substantial friction. From the pavement surface engineering, two parameters were defined: microtexture and macrotexture. Microtexture mainly provides for a more direct contact between the tires and the pavement, whereas the macrotexture provides for the function of pavement drainage. The skid resistance of pavement surfaces is mainly determined by the microtexture of the surface. Another study found that available friction fluctuates at 0.35 BPN per 1°C change in prevailing ambient or pavement surface temperature with an overall eight BPN seasonal fluctuation (Alauddin et al., 2010). Several researchers claimed that larger mean texture depth leads to better skid resistance. It is important to maintain the function of drainage of the texture on manhole covers (Chou and Lee, 2013). The main motivation for this study was to extend the previous research with improved laser CCD and test methods. By capturing the surface texture using two Laser CCD, in comparison with the previous single-point laser, a much clearer distribution of the condition of textures within the scanned area was accomplished. For the same reason, in order to obtain more stable data collection, development of newer test instruments was required to support the analysis of texture characteristics. This study subsequently applied the standards of ASTM E 2157 to develop a High Definition Scan Texture Machine (HDSTM) with 2D Laser CCD to support the study on the correlation between texture and friction.

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