Better Roads

October 2013

Better Roads Digital Magazine

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RoadScience The IRI summarizes the pavement roughness in terms of the theoretical response of a vehicle, they say, while the RN estimates user perception of ride comfort and provides a prediction of a mean panel rating from pavement profile. "It is an index without any units and can range from 0.0 to 5.0, where 5.0 represents a perfect ride and 0.0 corresponds to a virtually impassable road," they say. "Currently, the Florida Department of Transportation (FDOT) collects the pavement profiles using high-speed inertial profilers (HSIP) as standardized in ASTM E 950 and analyzes pavement roughness using RN, with the near future objective of implementing IRI for project smoothness acceptance on the state highway system." The state was able to confirm repeatability – thus reliability – of the HSIP in terms of IRI and RN for determining the ride quality, or smoothness, of the newly constructed, overlaid or rehabilitated flexible pavements. Even California – where the profilograph was developed – is switching to IRI rating of pavement smoothness. This year, Caltrans opened the Golden State's first certification and calibration site for inertial profiler devices and technicians, part of the department's move to update its pavement smoothness specifications to accommodate new measurement technology. In February 2013, Caltrans published a new hot-mix asphalt (HMA) spec that requires all pavement projects use the inertial profiler for measuring pavement smoothness in lieu of the California profilograph. A similar spec for concrete pavements was published earlier. "This new specification and certification site represents a quantum leap forward in the department's commitment to pavement smoothness," says Peter Vacura, head of asphalt pavements for the Caltrans Pavement Program. "These new devices will help transportation agencies and contractors build smoother- and safer-riding pavements for motorists, a safer working environment for highway workers and help improve gas mileage and cut down on GHG emissions." ProVAL eases pavement profiling Road agencies have an easier time putting all of this data together because of ProVAL, an engineering software application that allows users to view and analyze pavement profiles in many different ways. Developed by the Transtec Group under the aegis of the FHWA and the Long Term Pavement Performance (LTPP) program, ProVAL 3.4 – for Profile Viewing and Analysis – permits users to import profiles from various file formats and save them in a pavement profile standard file type. Entire projects' analyses can be saved, which preserves user information and analysis inputs. After analyses have been performed, the user can print a report of the original profiles and the results of any analyses performed. The profile data may be manipulated in many aspects, including cropping and filtering. Ride statistics such as the IRI and half-car roughness Index (HRI), mean roughness index (MRI) and ride number (RN) may be entered. The report types include full, fixed interval, and continuous; wavelength or frequency contents of profiles may be entered; and profilograph traces can be simulated. You can download the latest ProVAL from, where supporting information is available. Attaining smoothness: Every job is different With the movement toward more precise measurements of smoothness, the burden is on the contractor to meet smoothness specifications. Fortunately, equipment and techniques exist to make attaining specs and smoothness incentives easier. Careful milling provides the foundation for smooth asphalt overlay. So-called "fine milling" now is getting much more attention as thin surfacings and overlays become more popular, but it applies to conventional asphalt lifts as well. While thin surfacings provide durable driving surfaces, their thinness makes them vulnerable to variations in the pavement substrate on which they are placed. The evenness and smoothness of these thin surface treatments will depend mostly on the smoothness of the prepared surface, but that can be ensured by cold milling of the existing, worn surface with a fine-tooth drum. "With a conventional drum and relative to ground speed, the 'peaks-and-valleys' patterns will be relatively high and deep," says Jeff Wiley, senior vice president, Wirtgen America. "If you are not placing a lift that's thicker than 1- to 1-1/4-inches, the rough surface can reflect through to the paved surface. But with 5/16-inch bit spacing (or less) – the definition of a fine-toothed drum – an owner or contractor can minimize the potential reflection of the peaks and valleys through the thin lift surface." Cutter drums are continually undergoing analysis and improvement to enhance their performance in their abrasive environments. For example, in spring 2009, Roadtec introduced improvements to its line of cold planer cutter drums, 8 October 2013 Better Roads RoadScience_BR1013.indd 8 9/30/13 3:40 PM

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