Roughness Index Measured with Triple-Point and Line Lasers in Textured and Nontextured Strips

Practitioners have often wondered whether, during ride measurement with inertial devices, the motion of the laser through pavement texture introduces nonrepresentative values of international roughness index (IRI), particularly in certain textures. In response to this problem, a special texture study created a nontextured 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 nontextured 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 an nontextured 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.