Transportation Research Record: Journal of the Transportation Research Board

The success of a rehabilitation project that involves replacement of the asphalt concrete (AC) overlay on a concrete pavement often depends on the assessment of the existing conditions and the repair of critically weak locations. In a case study, a rolling dynamic deflectometer (RDD) was used to collect continuous deflection profiles at different stages in such a project. The project, conducted by the Texas Department of Transportation, was located in the Atlanta District. The condition of the pavement was monitored with an RDD in each stage. The stages ranged from before milling of the original AC overlay to 22 months after the placement of a new overlay. The deflection profiles measured after milling were used to identify locations with a high potential for reflection cracking. After the new overlay was placed, profiling was repeated at three different times to (a) monitor changes at locations of previously high deflections, (b) evaluate the effectiveness of full-depth repairs, and (c) group different AC test sections of the new overlay according to the condition of the underlying concrete pavement. It was found that the continuous deflection profiles obtained at the start of a rehabilitation project can be used to identify high-deflection locations that, if not repaired, will likely deteriorate rapidly after the new overlay is placed. The continuous deflection profile measured on the concrete pavement after milling was particularly helpful in identifying high-deflection locations that were irregularly spaced. Continuous deflection profiles, measured at various times after placement of the new overlay, effectively tracked the zones of deterioration.

Cold in-place recycling (CIR) is a pavement rehabilitation method that processes an existing hot-mix pavement, sizes it, mixes in additional asphalt cement, and lays it back down without off-site hauling and processing. The added asphalt cement is typically emulsified asphalt. A recent development in CIR technology is the use of expanded (foamed) asphalt rather than emulsified asphalt to bind the mix. This combination of CIR and expanded asphalt technologies is termed cold in-place recycled expanded asphalt mix (CIREAM). The Ministry of Transportation Ontario (MTO) constructed a CIREAM trial section on Highway 7 in July 2003. The 5-km CIREAM trial section was constructed adjacent to an 8-km section on which conventional CIR was performed. CIREAM placement resulted in a smooth, hard, uniform surface that provided an excellent platform for paving operations. The CIREAM placement progressed in a continuous and efficient manner, with 5 km placed over a 3-day period. Indirect tensile strength testing was carried out on both materials during construction. Falling weight deflectometer (FWD) testing and evaluation of pavement roughness and rutting by the use of MTO's automatic road analyzer (ARAN) were carried out. Resilient modulus testing of core samples of the CIR material and CIREAM was also carried out. The results of the FWD, ARAN, and resilient modulus tests indicated that the CIR and CIREAM pavements were performing similarly. A field review 1 year after construction showed no discernible distortion, rutting, or cracking. On the basis of short-term results, CIREAM appears to be an acceptable in-place recycling and rehabilitation strategy that provides an economical alternative to conventional CIR, reduces curing time, and extends the construction season.

The application of reliability analysis during pavement design is essential to an understanding of the effects of variability on the quality of pavements so that those pavements can provide safe and comfortable service to the public. As well as being durable in service, these pavements must have minimum life-cycle costs (LCCs). Strategic analysis of pavement evaluation and repair (SAPER) software (Version 2.0) is an analysis tool developed on behalf of FHWA to assist with the evaluation and selection of appropriate strategies for the maintenance, rehabilitation, and reconstruction (MRR) of concrete pavements at the project level, where design reliability is incorporated through a decision-making process (DMP). This paper describes the current practice for including reliability concepts in the SAPER software. It addresses the reliability approach used in a DMP and for prediction of pavement life extension for various distress models and the associated LCCs that incorporate reliability analysis for candidate MRR strategies. It shows that the reliability approach used in a DMP provides a simple, practical, and precise way to take into account the various factors that control pavement performance. The results for typical examples of pavement strategy selection approaches with various reliability parameters indicate that these parameters play an important role and must be considered through MRR strategy selection.

The condition of pavements in northwestern Pennsylvania was extremely poor in the early 1980s. Several methods of pavement rehabilitation of asphalt-surfaced highways were used to improve pavement performance and the management of pavement investment. This paper analyzes the performance of a number of these sections after 21 years. The results from the analysis show that, relative to conventional milling and leveling with placement of an overlay, the appropriate application of stress-absorbing membrane interlayers (SAMIs) and of cold in-place recycling has been effective for both performance and relative cost-effectiveness. The analysis also shows that for a subsequent generation of rehabilitation, the benefit of these treatments continues to be evident. As a result of this study, it is recommended that highway owners seriously evaluate rehabilitation treatments other than conventional milling and leveling with placement of an overlay. The performance of SAMI and cold-recycled sections in this instance has more than justified the additional expense of the construction.

Many agencies place hot-mix asphalt overlays on deteriorating jointed or cracked portland cement concrete pavements to improve the ride, protect the pavement structure, and reduce noise. Reflection cracking of the joints and preexisting cracks through the overlay is a persistent problem. In climates such as that in Wisconsin, the initial reflective cracks often appear within a year or two. The Wisconsin Department of Transportation and the City of Milwaukee tried a fine-aggregate, asphalt-rich, polymer-modified asphalt mix interlayer to absorb joint movements, delay reflective cracking, and protect the existing pavement. Four Wisconsin projects are discussed. In the first project, constructed in 1996, the interlayer showed no effect on delaying reflection cracking within the first 3 years. Later projects, however, included specifications for performance-related design tests for flexural beam fatigue and Hveem stability and were overlaid with improved mixtures to complement the flexible interlayer. The later projects showed an average 42% improvement in the time to the appearance of surface cracks compared with the control sections. Furthermore, cores taken from the projects showed that even when the overlay cracked, some of the interlayer samples did not, even under severe conditions, thus further protecting the underlying pavement structure. Other major factors contributing to the cracking delay included the type of concrete pavement, concrete patches, and climate.

Rehabilitation of urban highways is a critical issue confronting the California Department of Transportation because the state has a significant inventory of overaged, heavily trafficked urban highways showing extensive signs of distress. This paper presents the innovative pavement rehabilitation technologies and techniques that the agency applied in the first asphalt concrete (AC) project for its Long-Life Pavement Rehabilitation Strategies (LLPRS) program. A 4.4-km stretch of deteriorated concrete pavement on I-710 in Long Beach was rehabilitated successfully with 230 mm of AC overlay or 325 mm of full-depth AC replacement during eight 55-h weekend closures. The pilot project proved that the accelerated (fast-track) rehabilitation with 55-h weekend closures is a viable option that can drastically shorten the overall construction time and lessen the negative effects of construction in an urban area. The project also proved that AC pavement designed to provide a design life of 30-plus years can be constructed in a series of weekend closures even on the most heavily loaded truck route in the state. The construction-monitoring study indicated that contractor productivities were noticeably improved (through the learning effect) as weekend closures were repeated. In addition, the pay factor clause in the contract effectively encouraged the contractor's awareness of quality. The traffic measurements study showed that traffic operated at free-flow speeds throughout the surrounding highways and arterial roads during the construction weekends. It is expected that the construction and traffic management techniques adopted in this project will be used in LLPRS projects on California urban highways with high-traffic volumes.

In 1988 the Strategic Highway Research Program purchased four falling weight deflectometers (FWDs). During the acceptance testing it became evident that an improved procedure for calibration was needed to determine whether the specifications for the precision and the accuracy of the sensors were achieved. The authors were responsible for developing the procedure. This paper reports on the steps taken during the development of the calibration protocol. The reasons underlying the equipment and the procedures chosen are discussed. The sources of error in FWD measurements are identified, and ways that have been used to reduce those errors are reported. The goal was to reduce the systematic (bias) error to less than 0.3% through calibration. This level of error ensures that the random measurement error is larger than the systematic error for all pavement deflections less than 600 μm [24 mils (1 mil = 0.001 in.)]. Experience has shown that most highway pavements deflect less than 600 μm. The effects of FWD measurement errors on backcalculated pavement moduli are briefly reviewed. Verification of the protocol by several means showed that the calibration goal was achieved. Subsequent experience with the calibration protocol has shown that it has been effective and that it ensures high quality in the FWD data.

The transverse profilograph has been recognized as one of the most accurate devices for the measurement of rut depth. However, interpretation of surface transverse profile measurements poses a major challenge in determining the contributions of the different layers to rutting. A literature review has shown that the actual rutting mechanism can be estimated from a surface transverse profile for determination of the relative contribution of the layers to rutting. Unfortunately, much of the research yielded no verification or data. In addition, some techniques presented cannot be used if the rut depth is not well pronounced. Other techniques may be costly and time-consuming. The present research developed an approach that integrates (a) falling weight deflectometer and core data along with 3.6-m transverse profile measurements to assess the contributions of different pavement layers to rutting and (b) identifies the presence (or absence) of instability within the asphalt surface layer. This approach can be used regardless of the magnitude of the rut depth. On the basis of the analysis conducted, absolute rut depth should not be used to interpret the performance of the asphalt mixture. In addition, continued instability may not result in an increase in rut depth because the rutted basin broadens as traffic wander compacts or moves the dilated portion of the mixture. The approach developed appears to provide a reasonable way to distinguish between different sources of rutting. The conclusions drawn from analysis of the approach agreed well with observations from the trench cuts taken from four sections.

The determination of the moduli of subsurface stabilized layers in pavements with unknown and variable layers and thin asphalt layers is a challenging problem. Reliable estimation of moduli cannot be obtained from backcalculation of falling weight deflectometer data. In addition, for many stabilized layers, full-depth intact cores cannot be obtained from the field, and hence, laboratory determination of the moduli is not possible. Analysis of the seismic property of a pavement is a well-known method for estimation of the surface modulus of the pavement. This paper proposes a simple methodology on how seismic data acquired on the pavement surface can be effectively used to estimate the modulus of the surface layer as well as those of the subsequent subsurface layers of a flexible pavement. A research study was conducted on three hot-mix asphalt pavements with a foamed asphalt (FA) stabilized base in Maine. These three pavements were tested with both portable seismic and falling weight deflectometer equipment. Cores were taken from the same locations and tested in the laboratory for their resilient moduli. The modulus values obtained from different tests were compared, the effect of temperature on the modulus of the FA was evaluated, and the deflections computed from layered elastic analysis by use of the predicted modulus of the FA layer were compared with the observed deflections. It is concluded that the portable seismic equipment can be used to determine accurate moduli of subsurface stabilized layers. The practical advantages of using such equipment warrant further study for refinement of the method.

The falling weight deflectometer (FWD) is commonly used to perform project-and network-level structural evaluations. Some highway agencies perform network-level FWD testing as a part of their pavement management systems to assess in situ structural capacity, remaining service life, and current rehabilitation needs. Through prediction models, future condition and needs are also estimated. In contrast, project-level FWD testing is typically performed as part of the rehabilitation design process. Calibrated FWD equipment provides repeatable data for a pavement section (i.e., data obtained with the same unit, at the same location, and under similar conditions). However, different FWD devices manufactured by the same or different manufacturers do not necessarily provide similar deflection basins when they test the same section, even if they are calibrated. This paper summarizes the results of a study performed for the New Jersey Department of Transportation to assess the differences among the FWD devices available in New Jersey and to correlate the results obtained with the different devices. Two rounds of testing were performed on flexible and rigid pavement sections located in the FAA William J. Hughes Technical Center in Atlantic City. The first testing cycle was performed in November 2002, and the second was performed in May 2004. The analysis results indicate that significant differences in repeatability and reproducibility may exist between different FWD devices.

The reliability concept provides a means of incorporating some degree of certainty into the pavement design process to ensure that the outcomes of the process will provide acceptable levels of service until the end of the intended design life. Pavement structural performance and rehabilitation design are highly dependent on the in situ layer properties. Pavement layer thickness is an essential input in backcalculation analysis performed with measured surface deflections to evaluate the in situ structural capacity of a pavement. Inaccurate thickness information may lead to significant errors in the backcalculated layer moduli and, hence, in the rehabilitation design. Because pavement layer thickness has some degree of variability (normal variability), it is important to consider this variability in the backcalculation analysis and rehabilitation design. A procedure was developed to implement the reliability concept in backcalculation analysis to account for the normal variability in layer thickness within structurally homogeneous sections. This procedure was developed on the basis of in situ layer information obtained from a ground-penetrating radar study performed for the New Jersey Department of Transportation. This paper provides an overview of the procedure, along with the results of the pilot implementation of the procedure. This reliability procedure complements the reliability factor of the 1993 AASHTO pavement design guide, as the latter reliability factor does not account for the in situ layer thickness.

A condition assessment procedure for pavement layers that uses multiload-level falling weight deflectometer (FWD) deflections is presented. A dynamic finite element program that incorporates a stress-dependent soil model was used to generate the synthetic deflection database. On the basis of the data in this database, the relationships between surface deflections and critical pavement responses, such as the stresses and strains in each layer, have been established. The FWD deflection data, distress survey results, temperature, and laboratory testing results used to develop this procedure were collected from the Long-Term Pavement Performance project database. Research efforts also focused on the effect of the FWD load level on the condition assessment procedure. The results indicate that the proposed procedure can estimate the asphalt concrete (AC), base, and subgrade layer conditions. The AC layer modulus and the tensile strain at the bottom of the AC layer were found to be better indicators of the condition of the AC layer than the deflection basin parameter. It was also found that the structurally adjusted base damage index and base curvature index were good indicators for prediction of the stiffness characteristics of the aggregate base and subgrade, respectively. An FWD test with a load of 71.2 kN or less does not improve the accuracy of this procedure. The results from the study of the nonlinear behavior of a pavement structure indicate that the deflection ratio obtained from multiload-level deflections can predict the type and quality of the base and subgrade materials.

The seed moduli chosen for backcalculation analysis of multilayer flexible pavements can have significant impacts on the performance of backcalculation software and, sometimes, the final solutions of the backcalculated moduli. Practically all backcalculation programs provide internally generated seed moduli for backcalculation analysis. However, as the internally generated seed moduli do not always produce satisfactory results, the use of user-input seed moduli is generally encouraged. With the aim of providing useful guidance in the choice of seed moduli, a seed modulus generation algorithm, 2L-BACK, for multilayer flexible pavements based on a closed-form modulus backcalculation solution for two-layer flexible pavement structures was developed. The proposed algorithm does not require any subjective judgment by the user. An evaluation analysis of the effectiveness of the proposed procedure is presented by the use of two types of backcalculation software, MICHBACK and EVERCALC, and is based on measured and computed data for flexible pavement segments from the Long-Term Pavement Performance project. A comparison was made of the backcalculation program performance and the computed moduli of solutions obtained from internally generated seed moduli and those obtained from seed moduli generated by the proposed algorithm. It was found that the proposed seed modulus generation algorithm led to enhanced program performance of MICHBACK with respect to convergence characteristics and the accuracies of the backcalculated solutions. In comparison, the corresponding improvements for the case of EVERCALC were less. The proposed seed modulus generation algorithm does not suffer from the location and pavement type transferability constraints of most regression-based seed modulus generation methods. The results of the study suggest that the algorithm can be effectively incorporated into backcalculation software for multilayer flexible pavements.

A simple phenomenological damage model based on the number of load applications, the critical response, and the material modulus was used with three sets of experimental data: (a) the decrease in the modulus of an asphalt concrete (AC) under laboratory, direct tension fatigue testing; (b) the decrease in the modulus of a pozzolan–lime-stabilized sand under accelerated loading in a full-scale pavement testing facility; and (c) the increase in the permanent strain at three levels of two subgrade materials, also under full-scale accelerated loading. The model is shown to be capable of describing the damage reasonably well for all three cases, though with some limitations. For the direct tension tests with AC, the rate of damage was underpredicted for two of six samples under controlled stress testing, whereas the prediction for all 10 controlled strain tests was good. For freeze–thaw conditions, the model for permanent strain in the subgrade also tended to underpredict the damage rate. The simple damage model may be useful for incremental–recursive pavement design or for pavement management systems.

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.

The international roughness index (IRI) and the half-car roughness index (HRI) are the two commonly used roughness indices for pavement management, decision making, prioritization, budgeting, and planning. This work presents a new statistic, termed the full-car roughness index (FRI), for calculation of roughness from longitudinal pavement profiles. FRI is calculated from a single, equivalent profile that is a composite of four corner profiles based on both civil and mechanical engineering principles. More specifically, the full-car (four-wheel) model combines the rear and front suspension systems through an interdependent relation of motion with the longitudinal axle. To validate this model, the FRI values for different pavement sections are determined for sampling roughness measurements from several states and provinces. Then, the behavior of FRI is compared with that of IRI and HRI. The methodology of assessment uses a Monte Carlo simulation for calibration and validation of the index. Correlations derived from this sensitivity analysis on the basis of regression analysis arrive at a conversion chart to propose conversion values from these indices to FRIs. Overall, this paper suggests that the mechanical response of the proposed full-car model is more representative of the characteristics of a real vehicle than the response of a quarter- or half-car model. The results also indicate that FRI is less sensitive to the governing factors that account for the quarter-car simulation and thus provides an index that is unique, insightful, and more effective in the characterization of ride quality.

Because of the evident advantages associated with the smooth tire for the measurement of pavement friction, many highway agencies have become interested in the smooth tire. Pavement friction is the result of tire–pavement interaction. Because of the differences between ribbed and smooth tires, experiences with the ribbed tire may not apply to the smooth tire. Therefore, it is of great importance to evaluate those issues associated with the use of the smooth tire in network pavement inventory friction testing, such as variations in the friction testing system, seasonal friction variations, spatial friction variations, and temporal friction variations. The Indiana Department of Transportation (InDOT) has been using the smooth tire in the network pavement inventory friction test program since 1996. Large amounts of friction data have been obtained in the InDOT friction test track and network pavements. This paper presents the variations in the friction measurements obtained with the smooth tire because of testing system errors and seasonal and temperature effects. The paper also presents the spatial and temporal variations in the friction measurements. It was thought that the results provided in this paper would be useful for highway agencies for determination of test cycle, test spacing, and friction corrections for their network pavement inventory friction testing programs.

Hydroplaning on wet pavement occurs when a vehicle reaches a critical speed and causes a loss of contact between its tires and the pavement surface. This paper presents the development of a three-dimensional finite volume model that simulates the hydroplaning phenomenon. The theoretical considerations of the flow simulation model are described. The simulation results are in good agreement with the experimental results in the literature and with those obtained by the well-known hydroplaning equation of the National Aeronautics and Space Administration (NASA). The tire pressure–hydroplaning speed relationship predicted by the model is found to match well the one obtained with the NASA hydroplaning equation. Analyses of the results of the present study indicate that pavement microtexture in the 0.2- to 0.5-mm range can delay hydroplaning (i.e., raise the speed at which hydroplaning occurs). The paper also shows that the NASA hydroplaning equation provides a conservative estimate of the hydroplaning speed. The analyses in the present study indicate that when the microtexture of the pavement is considered, the hydroplaning speed predicted by the proposed model deviates from the speed predicted by the smooth surface relationship represented by the NASA hydroplaning equation. The discrepancies in hydroplaning speed are about 1% for a 0.1-mm microtexture depth and 22% for a 0.5-mm microtexture depth. The validity of the proposed model was verified by a check of the computed friction coefficient against the experimental results reported in the literature for pavement surfaces with known microtexture depths.