Initial Ride Quality of Hot-Mix Asphalt Pavements

Abstract

Ride quality assessed with an inertial profiler on flexible pavement was used to provide initial information on the following key issues: repeatability associated with international roughness index (IRI) values for a wide range of hot-mix asphalt (HMA) material variables, timing of acceptance testing for initial ride quality, IRI changes with type of roadway, influence of stops and starts in the paving operation on ride quality, identification of “bump,” and effect of grinding on IRI. IRI was calculated for 25-ft intervals instead of the standard 0.1 mi (528 ft) for all testing to highlight local anomalies such as bumps due to paving stoppages. Results indicate that the standard deviation of three replicate passes with an inertial profiler is 5 in./mi (includes 46 HMA mixes on the Auburn University National Center for Asphalt Technology test track). IRI measurements with time suggest that initial acceptance testing can be conducted within 7 days, which allows more flexibility in scheduling by the agency. Limited traffic also slightly reduces the IRI values, which is to the contractor's advantage. IRI values are suggested for two-lane county roads and medium- to high-traffic facilities. Separate IRI ranges are indicated for each of these categories on the basis of the type of HMA construction: new, repair and overlay, and mill and overlay. These ranges are set for best and good practices (continuous paving, no stoppages; consistent supply of trucks, very short stops). IRI values greater than 125 in./mi in any given 25-ft interval indicate a bump; bumps can be ground so that these areas have IRI values of less than 100 in./mi.