Monitoring and optimizing the surface roughness of high friction exposed aggregate cement concrete in exposure process

Exposed aggregate cement concrete (EACCP) is a novel cement concrete, which has completely different roughness with the traditional cement concrete pavement since its roughness is formed by the exposure of the aggregate on the surface. A well-constructed EACCP can bring benefits to the road safety by improving its skid resistance. However, it is challengeable for user to control the exposing degree during the practical exposure process. This study aims to investigate the effect of exposure process on EACCP's roughness and skid resistance. To this end, two groups of EACCP specimens with the most commonly used 4.75-9.5 mm single-sized and 4.75-16 mm continuously graded gradation are prepared, respectively. Specifically, the specimens are purpose-scrubbed to creat seven levels of scrubbing degree. In addition, the three-dimensional data on the specimen surface was obtained by a laser scanner, and the surface roughness of EACCP was jointly characterized via (1) height parameters: the arithmetical mean height Sa and root-mean-squared (RMS) height Sq; (2) feature parameters: the peak density Spd, the arithmetic mean peak curvature Spc, (3) the Power spectrum density (PSD), (4) a purpose-designed parameter aggregate exposed height, and (5) the mean texture depth (MTD) measured by the sand patch method. Furthermore, the skid resistance is investigated by the joint use of the British Portable Pendulum and Dynamic Friction tester. For obtaining a reliable evaluation result, the measurements are carried out with different testing speeds and water film depths. The data analysis indicates that the roughness parameters changed with exposing process significantly, in which a close relationship between a MID and other parameters is evidently found. It is recommended to adopt MTD as the representative parameter for controlling and monitoring the scrubbing degree of EACCP to obtain a desirable roughness and better skid resistance. The results indicate that a EACCP could have a desirable skid resistance when its MTD is 0.72-0.80 mm. Results of this study contribute to the current knowledge by revealing the relationship between roughness parameters and skid resistance of EACCP, and providing a practical reference for exposing process, which may be of interest to road constructors. (C) 2019 Elsevier Ltd. All rights reserved.