Line Laser and Triple Laser Quantification of the Difference in International Roughness Index Between Textured and Non-Textured Strips

Status:  Complete
Report Date:  07/31/2017


Practitioners have often wondered whether, during ride measurement with inertial devices, the motion of the laser through pavement texture introduces non representative values of international roughness index (IRI), particularly in certain textures. In response to this problem, a special texture study created a non-textured strip by a recession of the middle 4 ft of a texturing broom dragged longitudinally behind the paver. The study measured IRI and other surface properties in adjacent textured and non-textured strips by using a lightweight profiler outfitted with a line laser and a triple laser arranged in tandem. IRI measurements were performed after sufficient concrete strength gain and repeated as soon as the joints were sawn. The same measurements were repeated after the joints were deployed. Results showed a significant difference between the IRI of a textured strip and that of a non-textured strip. Further analysis indicated that, although texture appears to affect IRI, this effect was amplified by the type of laser used, as the triple laser appeared to indicate higher IRIs in comparison with the RoLine laser. Although the RoLine is not a reference profiler for IRI values unaffected by texture, the prevalence of the RoLine and the triple laser in construction acceptance testing is sufficient reason to be concerned about the difference inherent in the obtained results. Chi-square and t-test statistical analysis showed that laser type induced comparable and even higher IRI anomalies than did the experimental drag texture. In addition, the texture-induced IRI anomaly can be minimized by measuring smoothness for acceptance at least 2 weeks after paving. There was no significant difference in pavement noise in terms of on board sound intensity (OBSI) between textured and non-textured strips. The friction numbers derived from the Dynamic Friction Tester indicated a correlation between the nontextured and textured strip friction numbers in each of the 6 sections. This indicated that the finishing process before texturing continued to influence the microtexture even after the broom drag. This finding is limited to the texture types investigated. Therefore, extrapolation of these results to other textures should be done with caution due to anomalous laser induced IRI on certain textures.

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