University of California Pavement Research Center

In late 2015, Caltrans requested that 26 recently constructed concrete projects be tested for smoothness in terms of the International Roughness Index (IRI). The stated purpose was to observe measured IRI on projects accepted after a standard special provision (SSP) change that Caltrans made in 2013 and that was incorporated into the 2015 Construction Contract Standards. The projects provided 52 test sections for evaluation, consisting of three types of paving work: (1) diamond grind on existing pavement, (2) new continuously reinforced concrete pavement, and (3) new jointed plain concrete pavement. The project plans had completion dates from May 2010 to December 2014, and contract acceptance dates from April 2014 to October 2015. Caltrans did not identify which projects had the new SSP or specification change in its contract documents. The IRI data were collected from October 2016 to December of 2016. The IRI data collected included the effects of paving, any corrective grinding required to meet contract acceptance, and the increased roughness caused by traffic over post-construction periods of one to more than two and a half years. At the time of testing in 2016, the UCPRC test vehicle was equipped with a point laser in the left wheel path and a wide spot laser in the right wheel path. The data presented in this technical memorandum are primarily from the wide spot laser because the current standards require the wide spot laser. In general, the IRI measured by a point laser can be unduly increased due to the surface texture of the pavement, which is part of the reason for moving toward a wide spot laser. The construction specification considers both wheel paths and not just the right wheel path tested in this project. The IRI data using the wide spot laser in the right wheel path alone showed that 22% of the 0.1 mi. long sections met the construction standard of 60 in./mi. when measured one to two and a half years after construction. Based on the results from the right wheel path and the wide spot laser, 67% of the right wheel path sections are in good condition with IRI values between 60 and 94 in./mi., 28% are in acceptable condition with IRI values between 95 and 170 in./mi., and 5% are in poor condition with IRI values of 170 in./mi. or greater. Although Caltrans did not identify which projects included the new specification, a trend was observed that projects completed later had lower IRI values than those completed several years earlier.