The study of the relationship between IRI and 3m-straightedge acceptance specification

Abstract

Due to the expectation of high pavement riding quality by road users, road agencies must enhance their ability to evaluate and manage pavement roughness. As technology has developed, manual and random sampling methods for pavement roughness evaluation have gradually been replaced by fully automated computer systems. Subsequently, the international roughness index (IRI) that is time-stable, transportable, relevant, and valid, was developed and has been generally accepted worldwide. However, some Asian countries still use a 3m-straightedge to evaluate pavement roughness under a fixed sampling interval and determine construction acceptance levels by calculating the standard deviation. To examine the correlation between IRI and standard deviation of the 3 m straightedge, this paper first utilizes power spectral density (PSD) and pavement profile simulation to analyze the measured longitudinal profiles in the long-term pavement performance (LTPP) database. The results demonstrate that the IRI values are positively correlated to PSD values in short wavelengths (0.5 to 3 m), while standard deviation and PSD values are negatively correlated. The index stability of the standard deviation as well as the IRI for the same pavement section is investigated in detail. This paper utilizes the pavement profile reversing simulation to analyze 195 longitudinal profiles of freeway and urban roads in Taiwan. The results show that the larger the PSD values in short wavelengths, the greater the variation of the standard deviation due to different measuring points. It concludes that the standard deviation of the 3 m straightedge is not appropriate for use as the acceptance index for any pavement sections with relatively rough surface, say IRI> 2 m/km. From the findings of this study, a revised acceptance specification of standard deviation, 1.4 mm, for 3 m straightedge is proposed for the Taiwan Freeway authority before IRI is fully adopted in Taiwan.