Emmanuel G Fernando

Evaluation of Predicted Pavement Response with Measured Tire Contact Stresses

A uniform circular vertical contact stress is commonly assumed in representing wheel loads in pavement analysis procedures. However, experimental measurements have shown that actual loading conditions are nonuniform and depend on tire construction, tire load, and tire inflation pressure. Predicted pavement response from three-dimensional (3D) finite element (FE) and layered elastic programs were compared to establish guidelines for modeling wheel loads in current layered elastic pavement analysis programs to provide a better approximation of pavement response parameters for design and evaluation. Tire contact pressure was measured with the stress-in-motion pad. In addition, tire contact pressure measurements from a previous study conducted at the University of California at Berkeley were obtained. Available contact pressure measurements on four tires were used to predict pavement response with a 3D FE program, which permitted input of measured tire contact pressures at various tire loads and tire inflation pressures. Horizontal strain at the bottom of the asphalt layer, compressive strain at the top of the subgrade, and principal stresses at different depths were predicted. Similar predictions were generated with layered elastic theory with two different representations of contact pressure and contact area. From predicted strains, service life for a range of pavements, tire load, and tire inflation pressures were estimated with limiting strain criteria. In addition, Mohr-Coulomb (MC) yield function values were calculated from predicted principal stresses at different depths. The MC yield function values and pavement life estimates from 3D FE and layered elastic analyses were compared with established guidelines for modeling wheel loads using existing layered elastic procedures.

Application of Profile Data to Detect Localized Roughness

The application of profile data to detect areas of localized roughness is illustrated. The approach presented is based on the deviations of the profile from the moving average coupled with the use of a smoothness statistic, computed from the profile, to estimate the change in pavement smoothness with correction of surface irregularities. In this way, the significance of a surface defect is evaluated on the basis of its contribution to the overall roughness of a pavement section. The approach is illustrated by using profile data from an in-service pavement. By simulating the response of the profilograph to the measured profile, the peak deviations from the moving average were observed to track the bump locations from the simulation.

Analysis procedure for load-zoning pavements

Most load-zoned roads in Texas are still posted with a gross vehicle weight limit of about 260 kN, corresponding to the legal load limit at the time these roads were designed and built. Since the load from a vehicle is transmitted to the pavement through its axles, establishing load limits based on axle load and axle configuration is a more rational approach than the one currently used. In recognition of the need for a better methodology of load-zoning pavements, the Texas Department of Transportation funded a project to develop a procedure for evaluating load restrictions on the basis of axle load and axle configuration. Research efforts conducted at the Texas Transportation Institute led to the development of the Program for Load-Zoning Analysis (PLZA), which pavement engineers may use to evaluate the need for load restrictions and to determine, as appropriate, the single- and tandem-axle load limits based on a user-prescribed reliability level. To predict the induced pavement response under surface wheel loads, PLZA uses a layered elastic pavement model that permits users to characterize pavement materials as linear or nonlinear. The predicted horizontal strain at the bottom of the asphalt layer and the vertical strain at the top of the subgrade are used to evaluate pavement performance. To combine the effects of different axle loads and axle configurations, PLZA uses Miner’s hypothesis of cumulative damage to predict service life and the probability of pavement failure within a prescribed analysis period. The methodology for load-zoning is described, and its application using data collected on in-service pavements is demonstrated.

APPLICABILITY OF NEW FLEXIBLE PAVEMENT SMOOTHNESS SPECIFICATION FOR ASPHALT OVERLAYS

The Texas Department of Transportation plans to implement smoothness specifications based on profilograph testing for all asphalt concrete paving projects as part of its construction quality control/quality assurance program. Smoothness specifications have been developed for newly constructed asphalt and portland cement concrete pavements. In a move to develop a similar specification for asphalt concrete overlays, the Texas Transportation Institute was asked to evaluate the applicability of the existing flexible pavement smoothness specifications for the quality control and quality assurance of pavement rideability on overlay construction projects. This study was intended to provide the state with the information necessary to evaluate the improvement in ride quality that may be expected from placement of asphalt overlays, particularly for thin overlays [38 to 51 mm (1.5 to 2 in.)], which are generally constructed in Texas. To collect data to determine whether the existing specification can be implemented for overlay construction work, TTI monitored a number of overlay projects during the 1994 calendar year. Profilograph measurements were made during these projects before any surface preparation, after surface preparation, and after placement of the asphalt concrete overlay. All of the projects monitored involved thin overlays. The data collected indicate that the existing smoothness specifications can be implemented on overlay projects, provided that appropriate surface preparations (e.g., milling, level-ups) are conducted to correct existing surface distresses before placement of the overlay.

Methodology for Detection of Defect Locations in Pavement Profile

Pavement smoothness has become a standard measure of pavement quality. Transportation agencies strive to build and maintain smoother pavements. Road users generally perceive the quality of a pavement on the basis of how well it rides, which is severely affected by the presence of defects (bumps or dips) in the pavement profile. Defects are corrected according to the smoothness specifications prescribed by respective agencies. The effectiveness of any method used to identify defect locations depends on the decrease in roughness obtained on correction of the defects. Following this line of thought, this paper presents a method for the detection of defects based on a comparison of the original profile with a target or a desired profile. The proposed methodology is based on the international roughness index (IRI) gain function for the identification of defect locations to improve smoothness in pavements. This method uses the discrete Fourier transform to help identify defect locations on the basis of deviations of the original profile from the target or the smoothened profile. Areas with defects have a higher deviation from the smoothened profile than areas without defects. This method also estimates the contribution of each defect to roughness. Roughness statistics, such as the IRI and the present serviceability index, are used in the proposed approach to determine the severity of each defect. In addition, the use of a quarter-truck transfer function instead of the IRI gain function is demonstrated to illustrate consideration of dynamic load criteria for the detection of defects. The approach is illustrated through the use of profile data collected for in-service pavement sections.

EVALUATION OF ACCURACY OF SURFACE PROFILERS

The Texas Department of Transportation (TxDOT) is implementing smoothness specifications based on profilograph testing as part of its construction quality control/quality assurance (QC/QA) program. Automated California-type profilographs are now used in most tests, in which the equipment is pushed over a prescribed wheelpath. It appears that smoothness specifications will continue to be based on the profilograph, at least for the short term. However, in view of advances in profiling technology, it becomes prudent to investigate other methods of measuring surface profiles and to develop smoothness specifications based on profilers that offer greater accuracy and higher production rates. In pursuit of its goal of providing smooth pavements, TxDOT initiated a research project with the Texas Transportation Institute to develop a smoothness specification for asphalt concrete overlays based on the new generation of pavement profilers, which offer greater accuracy in profile measurement relative to the profilographs now used in construction projects. Among other things, this research project evaluated a number of profile-measuring devices to establish the availability of equipment for implementing a new profile-based smoothness specification in Texas. This evaluation showed that lightweight profilers provide a basis for developing and implementing smoothness specifications that are based on surface profile. Since surface smoothness is commonly monitored using inertial profilers in pavement condition surveys conducted for pavement management, having the initial profile allows highway agencies to tie the as-built smoothness to the rest of the performance history and thus maintain a consistent historical record of surface smoothness throughout the pavement life cycle.

Index for Evaluating Initial Overlay Smoothness with Measured Profiles

An index was developed for evaluating the acceptability of initial overlay smoothness based on surface profile measurements. The proposed index predicts the change in overlay service life due to differences between the target surface profile assumed in the design and the as-built profile. From theoretical considerations, the change in overlay life, based on reflection cracking, was found to be a function of the fracture characteristics of the overlay mix and the variability in vehicle dynamic loading due to unevenness in the surface profile. The index for evaluating initial overlay smoothness was applied using profile data from actual overlay projects. Using the final surface profile, the index is applicable to projects where the overlay thickness is more than 64 mm or where surface preparations, such as milling to grade or in-place recycling, are used to correct or remove existing surface distress. Implementation of the proposed index in a smoothness specification will require the use of surface profilers and the simulation of vehicle dynamic loads from measured profiles.

Part 3: Pavement Surface Properties-Vehicle Interaction: Methodology for Detection of Defect Locations in Pavement Profile

Pavement smoothness has become a standard measure of pavement quality. Transportation agencies strive to build and maintain smoother pavements. Road users generally perceive the quality of a pavement on the basis of how well it rides, which is severely affected by the presence of defects (bumps or dips) in the pavement profile. Defects are corrected according to the smoothness specifications prescribed by respective agencies. The effectiveness of any method used to identify defect locations depends on the decrease in roughness obtained on correction of the defects. Following this line of thought, this paper presents a method for the detection of defects based on a comparison of the original profile with a target or a desired profile. The proposed methodology is based on the international roughness index (IRI) gain function for the identification of defect locations to improve smoothness in pavements. This method uses the discrete Fourier transform to help identify defect locations on the basis of deviatio...

Evaluation of Relationship Between Profilograph and Profile-Based Roughness Indexes

The relationship between the profilograph profile index (PI) and the international roughness index (IRI) is evaluated. To accomplish this evaluation, profile data taken on 48 overlaid test sections were used in profilograph simulations to predict the profilograph response to the measured profiles. The PIs determined were then correlated with IRIs computed from the profile data to evaluate relationships between these roughness statistics. The results show that the PI based on the null blanking band is more strongly related to the IRI than the corresponding index determined using the 5-mm blanking band. In view of the general acceptance of the IRI as a statistic for establishing surface smoothness based on profiles, the results suggest that a profilograph specification based on the null blanking band is preferable to a similar specification based on the 5-mm blanking band, which may mask certain components of roughness that are otherwise picked up if no blanking band is used.

Quality Assurance for Automated and Semi-Automated Pavement Condition Surveys

Automated and semi-automated pavement distress surveys are being used increasingly to collect pavement condition data. This data, along with other information, is used to measure pavement performance and support pavement maintenance, preservation, and rehabilitation decisions. Generally, these automated and semi-automated systems consist of image capturing technology (i.e., hardware) and image processing and analysis algorithms (i.e., software). This paper provides a review of quality assurance practices for automated and semi-automated pavement condition surveys, including quality of images, accuracy and repeatability of measurements, data delivery requirements, equipment calibration, and control and verification sites. The information on these practices was obtained through a review of seven request for proposals (RFPs) issued by seven state departments of transportation (DOTs) between 2010 and 2015, and supplemented by a review of three manuals for these surveys.