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Accurate critical stress prediction is a key element for a mechanistic–empirical design of pavement structures. For unbonded concrete overlays (UBOL), the critical stress prediction procedure used by the current Mechanistic–Empirical Pavement Design Guide (MEPDG) has several shortcomings. The current MEPDG UBOL model only predicts top or bottom-critical longitudinal stresses, so transverse fatigue cracking is considered whereas longitudinal cracking, which has been observed in several in-service overlays, is ignored. The MEPDG critical stress prediction models assume that the UBOL and the existing pavement have the same deflection profiles, ignoring the separation between the overlay and the existing pavement. Various interlayer properties influencing critical overlay stress are also overlooked. In addition, the model only considers conventional lane width UBOLs and is unable to analyze short slab overlays. The latter has been gaining popularity as an attractive geometry for UBOLs. This paper documents the development of an improved procedure for computing UBOL critical stresses for conventional and short width slabs geometry. The procedure is able to predict critical transverse and longitudinal stresses at various locations taking into account interlayer stiffness and the presence of voids in the interlayer. Rapid solutions using neural networks were developed to enable computationally efficient UBOL critical stress prediction.

Unbonded concrete overlays (UBOL) are a preferred rehabilitation solution for distressed concrete pavements because the remaining pavement can be used as a strong support layer while an interlayer between the UBOL and the existing pavement mitigates potential distress reflections. Nevertheless, UBOL, as other types of jointed concrete pavements, experiences fatigue cracking as a major distress because of critical stress inflicted by traffic and environmental loading. Therefore, for proper UBOL performance, a cracking model that considers the specific UBOL characteristics is necessary. The AASHTO Mechanistic–Empirical Pavement Design (AASHTO M-E) cracking model, although the most advanced model for UBOL design currently available, still presents significant limitations. The model considers only transverse cracking, ignoring longitudinal cracking which has been reported by Departments of Transportation. Additionally, UBOL unique design features such as the effect of temperature variation throughout the existing concrete slab thickness and different interlayer properties are overlooked, resulting in crack predictions with unreliable trends. To address these issues, this paper proposes a modified UBOL cracking model. The proposed model was developed with a new approach for stress analysis and damage calculation considering different positions in the UBOL as well as modifications of the temperature data processing, and built-in curl analysis. The model was calibrated and validated using Long-Term Pavement Performance UBOL sections, and two sensitivity analysis are presented with a modified reliability analysis.

The Pavement ME transverse joint faulting model incorporates mechanistic theories that predict development of joint faulting in jointed plain concrete pavements (JPCP). The model is calibrated using the Long-Term Pavement Performance database. However, the Mechanistic-Empirical Pavement Design Guide (MEPDG) encourages transportation agencies, such as state departments of transportation, to perform local calibrations of the faulting model included in Pavement ME. Model calibration is a complicated and effort-intensive process that requires high-quality pavement design and performance data. Pavement management data—which is collected regularly and in large amounts—may present higher variability than is desired for faulting performance model calibration. The MEPDG performance prediction models predict pavement distresses with 50% reliability. JPCP are usually designed for high levels of faulting reliability to reduce likelihood of excessive faulting. For design, improving the faulting reliability model is as important as improving the faulting prediction model. This paper proposes a calibration of the Pavement ME reliability model using pavement management system (PMS) data. It illustrates the proposed approach using PMS data from Pennsylvania Department of Transportation. Results show an increase in accuracy for faulting predictions using the new reliability model with various design characteristics. Moreover, the new reliability model allows design of JPCP considering higher levels of traffic because of the less conservative predictions.

Conventional approaches to the local calibration of mechanistic-empirical (ME) pavement performance prediction models require the use of field data with low variability. However, these strict data requirements often lead to datasets with a limited number of observations. Local calibrations using such datasets permit the elimination of biases in predictions with 50% reliability, but might not provide an accurate evaluation of predictions of higher design reliability, which can exceed 90%. In this paper, we propose a novel approach to faulting model evaluation for concrete pavements that specifically focuses on high levels of reliability. To address the issue of limited dataset size, our approach leverages pavement management system (PMS) data, which are collected regularly and in large quantities at a local level. We also account for the presence of censored data from out-of-service or modified pavement sections. This permits the local calibration of performance prediction models, with a particular emphasis on the accurate prediction of pavement distress with high reliability levels, which is critical for the design of high-volume roads. To validate our methodology, we applied it to evaluate, modify, and calibrate the Pavement ME faulting model using Pennsylvania PMS data. The proposed methodology can be applied for the local calibration of other Pavement ME models.

Transverse crack pattern significantly affects performance of continuously reinforced concrete pavement (CRCP). However, field and modeled crack spacing are based on visual surveys of fully developed transverse cracks visible on the slab surface. Because of the difficulties in detecting incipient cracks in concrete slabs, the effect that such cracks may have on CRCP performance is not currently considered. To address this issue, this paper presents a non-destructive evaluation methodology based on an ultrasonic linear-array system for detection of incipient cracks in CRCP slabs. Two ultrasonic signal-processing techniques were used. First, the Hilbert Transform Indicator was used to identify the presence of damage in the concrete slab indicating potential crack locations. Then ultrasonic image reconstructions of these locations were used to further evaluate crack presence. The methodology was applied to four sections of an experimental short CRCP composed of 50-m long slabs – short in comparison to traditional CRCP. The locations of 58 potential incipient cracks were identified updating the short CRCP crack spacing; 10 of these incipient cracks were confirmed as surface-visible cracks in later visual surveys. Additionally, the methodology shows potential to detect undesired crack patterns such as cluster and Y-cracking before the cracks emerge on the slab surface.

Bonded concrete overlays of asphalt pavements (BCOA) consist of a concrete overlay placed on an existing asphalt or composite pavement. This technique is intended as a cost-effective rehabilitation solution for marginally distressed in-service asphalt or composite pavements. BCOA with panel sizes between 4.5 ft and 8.5 ft have become popular as they reduce curling stresses while keeping the longitudinal joints out of the wheelpath. The BCOA-ME (mechanistic empirical) design procedure and Pavement ME short jointed plain concrete pavement (SJPCP) module can both be used to design BCOA with mid-size panels. However, these design procedures differ in the assumptions used to develop the mechanistic computational model, fatigue models used to predict failure, treatment of environmental conditions, estimate of asphalt stiffness, consideration of structural fibers, the application of traffic loading, and the calibration process. This results in the procedures producing different overlay thicknesses and predicted distresses. The strengths and limitations of each procedure are evaluated and comparisons are made between the design thicknesses obtained from them.

An improved mechanistic empirical design procedure for unbonded concrete overlays of existing concrete pavements (UBOLs) should account for the effect of the interlayer on the structural response of the pavement. One approach is to use the Totsky model to characterize the interlayer. The Totsky model treats the interlayer as a bed of springs between two plates and is currently incorporated into the rigid pavement finite element software ISLAB. A difficulty encountered in implementing this model is that there are currently no guidelines as to what the interlayer k-value should be for different types of interlayers. The interlayer can be constructed of new or aged asphalt (open or dense graded) or a nonwoven geotextile fabric. To establish the k-values that accurately characterize each of these materials, an ISLAB model of a laboratory test was created so the k-values could be established by matching the measured and calculated difference between the deflections in the overlay and existing pavement. To supplement the use of the laboratory data in establishing the Totsky interlayer k-value, an analysis was carried out using falling weight deflectometer (FWD) data from UBOLs at the Minnesota Road Research Facility (MnROAD). Analyses were then performed to determine if the difference between k-values for different interlayer materials are statistically significant, and if the results from the laboratory analysis match those obtained from the MnROAD field data. The Totsky k-value recommended for use when modeling the response of an UBOL with an asphalt interlayer is 3500 psi/in and 425 psi/in for a fabric interlayer.

The compaction of asphalt concrete significantly affects long-term pavement performance. Although coring provides a relatively accurate way of assessing in-place density at specific locations, the coverage of the assessment is limited, especially at longitudinal joint locations. This can be particularly problematic because it is difficult to identify problematic locations that are likely to fail prematurely using current compaction assessment methods. Ground penetrating radar (GPR) provides an attractive nondestructive testing alternative for evaluation of compaction quality, especially with recent significant improvements in the GPR technology for this specific application. However, assessment of the air void content of the asphalt mix from the GPR-measured dielectric constant of the surface requires conversion of dielectric variation to air void content variation, which is the subject of this paper. An alternative to the commonly used model is proposed, leading to more justifiable predictions for low values of dielectric constants. The proposed model was used to interpret data from a 7-mi long asphalt overlay construction project. The results of the interpretation as compared with the results obtained with the conventional model show an improvement on the stability of the prediction at low air void contents, especially when core calibration data are limited and uncertainty is considered. These results are promising in the direction of reducing field cores necessary to have a stable model providing continuous compaction assessment of new asphalt pavement construction.

Development of a quiet diamond grinding configuration commenced in an initial laboratory effort at Purdue University, followed by research iterations from 2007 to 2010 at the pavement test track research facility (MnROAD) of the Minnesota Department of Transportation (DOT). This paper catalogues the stages in the development and deployment of the Next Generation Concrete Surface (NGCS) from the configuration development at MnROAD, coupled with the simultaneous development of a tire–pavement noise predictive model deployed on Interstate 94 near Saint Cloud, Interstate 35 in Duluth, and Interstate 394 in Minneapolis, Minnesota. NGCS in these projects caused noise reduction of 3 to 6 dB, representing 50% to 75% sound intensity reduction. Diamond grinding was performed on the preexisting textures: burlap drag on Interstate Highway 94 near Saint Cloud, transverse tining on Interstate Highway 35 in Duluth, and Ultra-Thin Bonded Wearing Course (UTBWC) on Interstate 394, Minnesota DOT exceeded the goal of not increasing the pregrind tire–pavement noise level by these rehabilitations. The predictive tire–pavement interaction noise model was validated in these deployments, including on Interstate 394, where the full acoustic benefit of NGCS had been attenuated by the anomalous effect of undulations reminiscent of the previous concrete–UTBWC interface, which had inadvertently conferred a background configuration to the new diamond-ground surface.

Development of a quiet diamond grinding configuration commenced in an initial laboratory effort at Purdue University, followed by research iterations from 2007 to 2010 at the pavement test track research facility (MnROAD) of the Minnesota Department of Transportation (DOT). This paper catalogues the stages in the development and deployment of the Next Generation Concrete Surface (NGCS) from the configuration development at MnROAD, coupled with the simultaneous development of a tire–pavement noise predictive model deployed on Interstate 94 near Saint Cloud, Interstate 35 in Duluth, and Interstate 394 in Minneapolis, Minnesota. NGCS in these projects caused noise reduction of 3 to 6 dB, representing 50% to 75% sound intensity reduction. Diamond grinding was performed on the preexisting textures: burlap drag on Interstate Highway 94 near Saint Cloud, transverse tining on Interstate Highway 35 in Duluth, and Ultra-Thin Bonded Wearing Course (UTBWC) on Interstate 394, Minnesota DOT exceeded the goal of not increasing the pregrind tire–pavement noise level by these rehabilitations. The predictive tire–pavement interaction noise model was validated in these deployments, including on Interstate 394, where the full acoustic benefit of NGCS had been attenuated by the anomalous effect of undulations reminiscent of the previous concrete–UTBWC interface, which had inadvertently conferred a background configuration to the new diamond-ground surface.

Reflective cracking can be a concern in unbonded concrete overlays of existing distressed concrete pavements. In these structures, an interlayer, commonly hot-mix asphalt (HMA) or a nonwoven geotextile fabric, is placed to isolate the overlay concrete from the existing concrete pavement. The interlayer minimizes interaction between the overlay and the existing concrete pavement, which helps prevent distress in the existing pavement from propagating into the overlay. In this study, a laboratory investigation was used to examine the influence of HMA and geotextile fabric interlayer systems on the potential for development of reflective cracking. A laboratory test was conducted by using stacked beam specimens separated by an interlayer to evaluate the potential for a discrete crack in the lower beam reflecting up through the interlayer and into the overlay beam. The study revealed that reflective cracking was more likely when there was loss of support beneath the existing pavement. Reflective cracking did not occur with any of the interlayer systems when the beam was fully supported. The nonwoven geotextile interlayers that were tested were more effective than the HMA interlayers at preventing reflective cracking. Even though the fabric interlayer had a higher load ratio than the HMA interlayers, a relatively large load was required to generate reflective cracking regardless of the interlayer type (HMA or fabric) and, therefore, both may be suitable interlayer alternatives for the prevention of reflective cracking.

The current methods for determining criteria for opening a roadway to traffic are often overly conservative, causing unnecessary construction delays and user costs. This problem can be explained, in part, by the purely empirical nature of the current methods. These criteria require wait periods after concrete placement or certain levels of compressive or flexural strength, or both, after concrete placement, and specific site conditions are not accounted for. Further, the effect of early traffic-related loads on long-term pavement behavior has not been quantified. In this study, the effect of early opening on pavement damage was reexamined through a laboratory study and analytical modeling. The result was a mechanistic-based procedure for evaluating the effect of early opening to traffic on the accumulation long-term damage; this procedure also accounts for critical factors such as climate, traffic level, and pavement design characteristics. The basis of this method is a modification of the fatigue damage analysis in the Mechanistic–Empirical Pavement Design Guide;this modification enables an analysis of traffic loading on the first 28 days of pavement life. The procedure also enables an update to predictions on the basis of as-built nondestructive testing measurements of the pavement. The output of the analysis is a quantitative damage prediction that allows the road owner to do a cost–benefit analysis of the timing for opening the road on the basis of the specific site and traffic characteristics. The results presented here show how innovated opening criteria based on load restrictions can allow for early opening while mitigating any adverse effect on the long-term pavement performance.

The current methods for determining criteria for opening a roadway to traffic are often overly conservative, causing unnecessary construction delays and user costs. This problem can be explained, in part, by the purely empirical nature of the current methods. These criteria require wait periods after concrete placement or certain levels of compressive or flexural strength, or both, after concrete placement, and specific site conditions are not accounted for. Further, the effect of early traffic-related loads on long-term pavement behavior has not been quantified. In this study, the effect of early opening on pavement damage was reexamined through a laboratory study and analytical modeling. The result was a mechanistic-based procedure for evaluating the effect of early opening to traffic on the accumulation long-term damage; this procedure also accounts for critical factors such as climate, traffic level, and pavement design characteristics. The basis of this method is a modification of the fatigue damage analysis in the Mechanistic–Empirical Pavement Design Guide;this modification enables an analysis of traffic loading on the first 28 days of pavement life. The procedure also enables an update to predictions on the basis of as-built nondestructive testing measurements of the pavement. The output of the analysis is a quantitative damage prediction that allows the road owner to do a cost–benefit analysis of the timing for opening the road on the basis of the specific site and traffic characteristics. The results presented here show how innovated opening criteria based on load restrictions can allow for early opening while mitigating any adverse effect on the long-term pavement performance.

Reflective cracking can be a concern in unbonded concrete overlays of existing distressed concrete pavements. In these structures, an interlayer, commonly hot-mix asphalt (HMA) or a nonwoven geotextile fabric, is placed to isolate the overlay concrete from the existing concrete pavement. The interlayer minimizes interaction between the overlay and the existing concrete pavement, which helps prevent distress in the existing pavement from propagating into the overlay. In this study, a laboratory investigation was used to examine the influence of HMA and geotextile fabric interlayer systems on the potential for development of reflective cracking. A laboratory test was conducted by using stacked beam specimens separated by an interlayer to evaluate the potential for a discrete crack in the lower beam reflecting up through the interlayer and into the overlay beam. The study revealed that reflective cracking was more likely when there was loss of support beneath the existing pavement. Reflective cracking did not occur with any of the interlayer systems when the beam was fully supported. The nonwoven geotextile interlayers that were tested were more effective than the HMA interlayers at preventing reflective cracking. Even though the fabric interlayer had a higher load ratio than the HMA interlayers, a relatively large load was required to generate reflective cracking regardless of the interlayer type (HMA or fabric) and, therefore, both may be suitable interlayer alternatives for the prevention of reflective cracking.

This paper describes research efforts sponsored by the Minnesota Department of Transportation (DOT) to update its rigid design procedure to take advantage of locally calibrated mechanistic–empirical models for performance and consequently design. The new procedure, MnPCC-ME, is based on the AASHTO Mechanistic–Empirical Pavement Design Guide(MEPDG) Version 1.1, but restricts the user to predetermined design input parameters. MnPCC-ME matches the MEPDG predicted performance at a fraction of the computation cost. The user is able to modify key design inputs for state and local pavement projects; the parameters include district climate files and traffic load spectra files (based on historical Minnesota DOT weigh-in-motion data). In addition, MnPCC-ME provides alternative reliability analysis, which is based on a Monte Carlo simulation of pavement performance predictions based on typical variability in slab thickness and flexural strength for Minnesota pavements. The MnPCC-ME program requires virtually no run time and outputs a project report with the recommended design thickness for given performance criteria and reliability level for the specified reliability analysis. Although this tool was developed for Minnesota local conditions, the approach developed in the study can be adopted by other transportation agencies for their region and conditions.

This paper investigates the ability of a generalized Westergaard model consisting of a viscoelastic plate on a viscoelastic Winkler foundation to describe deflections of both rigid and flexible pavements under dynamic loading. The pavement response to falling weight deflectometer (FWD) loading was simulated, and a semianalytical solution involving the use of a Hankel transform in space and a finite difference method in time was developed. The obtained solution was used to interpret FWD data collected at the Minnesota Road Research Facility. It was shown that a good match between the simulated and measured response data could be obtained for both rigid and flexible pavements if inertia and viscoelastic effects were accounted for. The proposed model is thus an attractive tool for analysis of pavement–vehicle interaction.

This paper investigates the ability of a generalized Westergaard model consisting of a viscoelastic plate on a viscoelastic Winkler foundation to describe deflections of both rigid and flexible pavements under dynamic loading. The pavement response to falling weight deflectometer (FWD) loading was simulated, and a semianalytical solution involving the use of a Hankel transform in space and a finite difference method in time was developed. The obtained solution was used to interpret FWD data collected at the Minnesota Road Research Facility. It was shown that a good match between the simulated and measured response data could be obtained for both rigid and flexible pavements if inertia and viscoelastic effects were accounted for. The proposed model is thus an attractive tool for analysis of pavement–vehicle interaction.

This paper describes research efforts sponsored by the Minnesota Department of Transportation (DOT) to update its rigid design procedure to take advantage of locally calibrated mechanistic–empirical models for performance and consequently design. The new procedure, MnPCC-ME, is based on the AASHTO Mechanistic–Empirical Pavement Design Guide(MEPDG) Version 1.1, but restricts the user to predetermined design input parameters. MnPCC-ME matches the MEPDG predicted performance at a fraction of the computation cost. The user is able to modify key design inputs for state and local pavement projects; the parameters include district climate files and traffic load spectra files (based on historical Minnesota DOT weigh-in-motion data). In addition, MnPCC-ME provides alternative reliability analysis, which is based on a Monte Carlo simulation of pavement performance predictions based on typical variability in slab thickness and flexural strength for Minnesota pavements. The MnPCC-ME program requires virtually no run time and outputs a project report with the recommended design thickness for given performance criteria and reliability level for the specified reliability analysis. Although this tool was developed for Minnesota local conditions, the approach developed in the study can be adopted by other transportation agencies for their region and conditions.

The physical properties of the aggregate base of a pavement system have a significant influence on the bulk mechanical properties of that system. Simulations based on the discrete element method provide a powerful method to investigate the mechanics of granular materials, but they are limited, particularly when it comes to representing moisture and finer particles. Established discrete element method simulations were adapted with additional terms to account for moisture and finer particles to model established tests of the aggregate base of a pavement system. The presence of moisture in unsaturated granular material was modeled by using published experimental work with consideration of the form of the standard liquid bridge model, and the finer particle content was modeled through an effective friction coefficient. This combined model was used to simulate the lightweight deflectometer test, an established in situ test for a measure of the modulus of an aggregate base, and the results were compared with estimated target values of aggregate bases for Minnesota roads. When either the model moisture content or model fines content was increased systematically, there was a decrease in the elastic modulus computed from the simulations, similar to trends seen in existing experimental data.

Deflection testing and analysis are routinely used to evaluate the spring load capacity of pavements and to design structural overlays. The current falling-weight deflectometer (FWD) deflection analysis process used by the Minnesota Department of Transportation was found to be unreliable. Traditionally, the process used to interpret FWD deflection measurements converted the measured maximum FWD deflection to an equivalent Benkelman beam deflection and compared it with the allowable deflection for a pavement with given asphalt surface thickness and anticipated traffic. Because the maximum FWD deflection is greatly affected by the subgrade stiffness, the computer program TONN may underestimate the allowable axle load for subgrades depending on the subgrade material. As a result, the researchers determined that the allowable axle load rating procedure should be revised. Those revisions and the development of a new rating procedure for low-volume roads are detailed.

The physical properties of the aggregate base of a pavement system have a significant influence on the bulk mechanical properties of that system. Simulations based on the discrete element method provide a powerful method to investigate the mechanics of granular materials, but they are limited, particularly when it comes to representing moisture and finer particles. Established discrete element method simulations were adapted with additional terms to account for moisture and finer particles to model established tests of the aggregate base of a pavement system. The presence of moisture in unsaturated granular material was modeled by using published experimental work with consideration of the form of the standard liquid bridge model, and the finer particle content was modeled through an effective friction coefficient. This combined model was used to simulate the lightweight deflectometer test, an established in situ test for a measure of the modulus of an aggregate base, and the results were compared with estimated target values of aggregate bases for Minnesota roads. When either the model moisture content or model fines content was increased systematically, there was a decrease in the elastic modulus computed from the simulations, similar to trends seen in existing experimental data.

Deflection testing and analysis are routinely used to evaluate the spring load capacity of pavements and to design structural overlays. The current falling-weight deflectometer (FWD) deflection analysis process used by the Minnesota Department of Transportation was found to be unreliable. Traditionally, the process used to interpret FWD deflection measurements converted the measured maximum FWD deflection to an equivalent Benkelman beam deflection and compared it with the allowable deflection for a pavement with given asphalt surface thickness and anticipated traffic. Because the maximum FWD deflection is greatly affected by the subgrade stiffness, the computer program TONN may underestimate the allowable axle load for subgrades depending on the subgrade material. As a result, the researchers determined that the allowable axle load rating procedure should be revised. Those revisions and the development of a new rating procedure for low-volume roads are detailed.

Concrete pavement thickness data were collected from sections of two concrete pavements with a nondestructive testing (NDT) device and by measuring concrete core thickness. The NDT device allowed thickness measurements every 15 ft compared with 1,000 ft for each core. Comparison of the core and NDT data showed that core thickness data do not capture the extreme peaks and valleys of pavement thickness variation. Further analysis of the core and NDT thickness data with the Minnesota Department of Transportation's concrete pavement thickness specifications highlighted that contractor pay deductions based on thickness deficiencies were not realized. Autocorrelation analysis of the data showed that concrete pavement thickness variation is not random but is correlated to thicknesses of lag between 30 and 270 ft. This correlation lag is a starting point for answering the question, how often must a thickness measurement be taken to accurately characterize the thickness variation of a concrete pavement?

In recent decades, state, local, and federal use of asphalt concrete overlays to rehabilitate portland cement concrete pavements has increased significantly. This growth has increased the attention given to mechanistic-empirical modeling of reflective cracking. This paper describes recent research that assessed and modified the state of the art in mechanistic-empirical modeling of reflective cracking. The research reviewed the original Mechanistic-Empirical Pavement Design Guide model and the CalME reflective cracking model. The paper also details research in which the CalME model was modified to facilitate its integration into the design guide for pavement projects of composite asphalt concrete over portland cement concrete.

This paper describes the development of an approach for the prediction of rutting of newly constructed composite pavements and asphalt overlays of existing concrete pavements [asphalt concrete over portland cement concrete (AC-PCC)]. The rutting model of the Mechanistic-Empirical Pavement Design Guide (MEPDG) and the CalME procedure being developed by the California Department of Transportation and the University of California Pavement Research Center are investigated, and a procedure for incorporating the CalME rutting model into the MEPDG framework is introduced. The goal is to provide pavement engineers with a procedure for rutting in AC-PCC design and analysis that does not require uncommon inputs and does not force the user outside the MEPDG framework. The paper describes the procedure's validation with experimental data from the Pavement Research Center and from the Minnesota Road Research Facility. A brief sensitivity analysis of the procedure for rutting in AC-PCC is presented.

Results of a blind test evaluation of various nondestructive testing techniques, including well-established methods such as chain dragging, rod sounding, and ground-penetrating radar, compared with an emerging ultrasonic array technology for determining the extent of concrete joint deterioration, are presented. Nondestructive testing at two concrete pavement joints at the Minnesota Road Research Facility was performed, and the results were independently evaluated and submitted to the Minnesota Department of Transportation. Significant discrepancies in subsurface deterioration assessments were observed between these techniques. Forensic evaluation (trenching and coring) was used to resolve the discrepancies in test results. It was concluded that the ultrasound array analysis was the only method that could accurately determine the horizontal extent of the deterioration otherwise undetected by the other available nondestructive evaluation methods. Additionally, ultrasonic tomography analysis was able to determine the depth of the deterioration. These results make this emerging technology an attractive alternative to traditional nondestructive testing methods for assessment of concrete pavement joints.

Results of a blind test evaluation of various nondestructive testing techniques, including well-established methods such as chain dragging, rod sounding, and ground-penetrating radar, compared with an emerging ultrasonic array technology for determining the extent of concrete joint deterioration, are presented. Nondestructive testing at two concrete pavement joints at the Minnesota Road Research Facility was performed, and the results were independently evaluated and submitted to the Minnesota Department of Transportation. Significant discrepancies in subsurface deterioration assessments were observed between these techniques. Forensic evaluation (trenching and coring) was used to resolve the discrepancies in test results. It was concluded that the ultrasound array analysis was the only method that could accurately determine the horizontal extent of the deterioration otherwise undetected by the other available nondestructive evaluation methods. Additionally, ultrasonic tomography analysis was able to determine the depth of the deterioration. These results make this emerging technology an attractive alternative to traditional nondestructive testing methods for assessment of concrete pavement joints.

In recent decades, state, local, and federal use of asphalt concrete overlays to rehabilitate portland cement concrete pavements has increased significantly. This growth has increased the attention given to mechanistic– empirical modeling of reflective cracking. This paper describes recent research that assessed and modified the state of the art in mechanistic– empirical modeling of reflective cracking. The research reviewed the original Mechanistic–Empirical Pavement Design Guide model and the CalME reflective cracking model. The paper also details research in which the CalME model was modified to facilitate its integration into the design guide for pavement projects of composite asphalt concrete over portland cement concrete.

This paper describes the development of an approach for the prediction of rutting of newly constructed composite pavements and asphalt overlays of existing concrete pavements [asphalt concrete over portland cement concrete (AC–PCC)]. The rutting model of the Mechanistic–Empirical Pavement Design Guide (MEPDG) and the CalME procedure being developed by the California Department of Transportation and the University of California Pavement Research Center are investigated, and a procedure for incorporating the CalME rutting model into the MEPDG framework is introduced. The goal is to provide pavement engineers with a procedure for rutting in AC–PCC design and analysis that does not require uncommon inputs and does not force the user outside the MEPDG framework. The paper describes the procedure's validation with experimental data from the Pavement Research Center and from the Minnesota Road Research Facility. A brief sensitivity analysis of the procedure for rutting in AC–PCC is presented.

Concrete pavement thickness data were collected from sections of two concrete pavements with a nondestructive testing (NDT) device and by measuring concrete core thickness. The NDT device allowed thickness measurements every 15 ft compared with 1,000 ft for each core. Comparison of the core and NDT data showed that core thickness data do not capture the extreme peaks and valleys of pavement thickness variation. Further analysis of the core and NDT thickness data with the Minnesota Department of Transportation's concrete pavement thickness specifications highlighted that contractor pay deductions based on thickness deficiencies were not realized. Autocorrelation analysis of the data showed that concrete pavement thickness variation is not random but is correlated to thicknesses of lag between 30 and 270 ft. This correlation lag is a starting point for answering the question, how often must a thickness measurement be taken to accurately characterize the thickness variation of a concrete pavement?

Modifications made to the Mechanistic-Empirical Pavement Design Guide (MEPDG) to accommodate the design of a newly constructed composite pavement system featuring a thin portland cement concrete (PCC) layer placed over another PCC layer (PCC-PCC pavement) are described. In previous versions of the MEPDG, a newly constructed PCC-PCC pavement project was considered a bonded PCC overlay of an existing PCC pavement. As a result of this simplification, the MEPDG was not consistent in its predictions for a newly constructed PCC-PCC pavement and its structurally equivalent single-layer analogue. To remedy this inconsistency, researchers suggested modifications to the Enhanced Integrated Climatic Model (EICM) used by the MEPDG in terms of (a) number of locations through the slab used by EICM to determine the thermal gradient and (b) EICM calculation of the subgrade spring stiffness (or k-value). Before-and-after MEPDG sensitivity analyses are included to justify the modifications developed and implemented into the MEPDG with the assistance of the MEPDG development team. This research was conducted under SHRP 2 R21, Composite Pavement Systems.

An important issue in extending the life of jointed plain concrete pavement is the proper construction and maintenance of transverse joints. The capabilities of an ultrasonic tomography device in providing information essential to joint rehabilitation decisions as well as the quality control of rehabilitation construction are presented. Testing was conducted at various partial-depth repair locations of a recently repaired in-service highway to determine the presence and extent of debonding between the partial-depth repair and the existing concrete. Testing also was conducted at the Minnesota Road Research Facility to evaluate the subsurface condition along various transverse joints. Real-time diagnosis with the intensity-based signals of the synthetic aperture focusing technique was successful in pinpointing the location of debonded concrete interfaces within partial-depth repairs. Ultrasonic tomography testing also showed the capability of identifying that a joint is in need of repair and subsequently diagnosing the extent of subsurface deterioration throughout the joint.

The SHRP 2 R21 project on composite pavement investigated the durability of various mixtures of portland cement concrete (PCC) used in the construction of a two-layer composite PCC pavement. Project consultants in Europe, where composite PCC over PCC pavement was more common than in the United States, advised the R21 research team to consider using the CIF (capillary suction, internal damage, and freeze-thaw) standard of the International Union of Laboratories and Experts in Construction Materials, Systems, and Structures (RILEM), Paris, rather than the familiar ASTM standards. As a result, the R21 project adopted the RILEM CIF standard to evaluate the freeze-thaw durability and salt scaling resistance of concretes. The research also explored a modified RILEM CIF test (using pure water instead of a sodium chloride solution in scaling tests) alongside the standard RILEM CIF tests. The paper describes this experience to expose other institutions and agencies in the United States to the RILEM standards for the freeze-thaw durability and salt scaling resistance testing of concretes.

An asphalt concrete overlay of a jointed plain concrete pavement is intended to extend the service life of the existing pavement structure. Also known as composite pavements, these structures exhibit features of both rigid and flexible pavements. Whereas the behavior of rigid pavements is mainly elastic, the behavior of an asphalt layer is dependent on load duration. At the same time, temperature curling causes nonlinear interaction with the foundation. The available structural models for composite pavements ignore the behavior of the asphalt layer that is load duration dependent when the composite pavement is subjected to a combination of temperature curling and traffic loads. Research was conducted to address the improvement of structural modeling of composite pavements that were subjected to slow-developing temperature curling and instantaneous traffic loads. A simplified procedure was developed that maintained compatibility with the Mechanistic-Empirical Pavement Design Guide. The procedure used a different asphalt modulus for curling than it did for axle loading and determined the total stresses in the pavement as a combination of the stresses from solutions of three elastic boundary value problems. The simplified procedure was compared with the existing design guide structural model for fatigue cracking in a jointed plain concrete pavement overlain with asphalt concrete. A framework for implementing the proposed procedure into the design guide was developed.

Delamination that occurs because of layer debonding or stripping between layers of hot-mix asphalt can cause distresses such as longitudinal cracking in the wheelpath and tearing in the surface. Because these distresses cannot be detected by visual inspection of the pavement, highway agencies are interested in finding nondestructive methods for detecting delamination to maintain roadway networks. A study evaluated an ultrasonic tomography device for detecting the type and severity of delamination with various focusing techniques. A comparison of blind ultrasonic tomography testing results versus construction of bonded and debonded conditions showed that ultrasonic tomography could detect delamination between new and old asphalt layers, as well as delamination of lifts within new asphalt pavement. B- and D-scan methods with the focusing technique of synthetic aperture were able to identify delamination between new and old asphalt interfaces, and a new focusing method developed at the University of Minnesota was used to identify delamination within asphalt lifts.

The SHRP 2 R21 project on composite pavement investigated the durability of various mixtures of portland cement concrete (PCC) used in the construction of a two-layer composite PCC pavement. Project consultants in Europe, where composite PCC over PCC pavement was more common than in the United States, advised the R21 research team to consider using the CIF (capillary suction, internal damage, and freeze–thaw) standard of the International Union of Laboratories and Experts in Construction Materials, Systems, and Structures (RILEM), Paris, rather than the familiar ASTM standards. As a result, the R21 project adopted the RILEM CIF standard to evaluate the freeze–thaw durability and salt scaling resistance of concretes. The research also explored a modified RILEM CIF test (using pure water instead of a sodium chloride solution in scaling tests) alongside the standard RILEM CIF tests. The paper describes this experience to expose other institutions and agencies in the United States to the RILEM standards for the freeze–thaw durability and salt scaling resistance testing of concretes.

Delamination that occurs because of layer debonding or stripping between layers of hot-mix asphalt can cause distresses such as longitudinal cracking in the wheelpath and tearing in the surface. Because these distresses cannot be detected by visual inspection of the pavement, highway agencies are interested in finding nondestructive methods for detecting delamination to maintain roadway networks. A study evaluated an ultrasonic tomography device for detecting the type and severity of delamination with various focusing techniques. A comparison of blind ultrasonic tomography testing results versus construction of bonded and debonded conditions showed that ultrasonic tomography could detect delamination between new and old asphalt layers, as well as delamination of lifts within new asphalt pavement. B- and D-scan methods with the focusing technique of synthetic aperture were able to identify delamination between new and old asphalt interfaces, and a new focusing method developed at the University of Minnesota was used to identify delamination within asphalt lifts.

An asphalt concrete overlay of a jointed plain concrete pavement is intended to extend the service life of the existing pavement structure. Also known as composite pavements, these structures exhibit features of both rigid and flexible pavements. Whereas the behavior of rigid pavements is mainly elastic, the behavior of an asphalt layer is dependent on load duration. At the same time, temperature curling causes nonlinear interaction with the foundation. The available structural models for composite pavements ignore the behavior of the asphalt layer that is load duration dependent when the composite pavement is subjected to a combination of temperature curling and traffic loads. Research was conducted to address the improvement of structural modeling of composite pavements that were subjected to slow-developing temperature curling and instantaneous traffic loads. A simplified procedure was developed that maintained compatibility with the Mechanistic–Empirical Pavement Design Guide. The procedure used a different asphalt modulus for curling than it did for axle loading and determined the total stresses in the pavement as a combination of the stresses from solutions of three elastic boundary value problems. The simplified procedure was compared with the existing design guide structural model for fatigue cracking in a jointed plain concrete pavement overlain with asphalt concrete. A framework for implementing the proposed procedure into the design guide was developed.

Modifications made to the Mechanistic–Empirical Pavement Design Guide (MEPDG) to accommodate the design of a newly constructed composite pavement system featuring a thin portland cement concrete (PCC) layer placed over another PCC layer (PCC–PCC pavement) are described. In previous versions of the MEPDG, a newly constructed PCC–PCC pavement project was considered a bonded PCC overlay of an existing PCC pavement. As a result of this simplification, the MEPDG was not consistent in its predictions for a newly constructed PCC–PCC pavement and its structurally equivalent single-layer analogue. To remedy this inconsistency, researchers suggested modifications to the Enhanced Integrated Climatic Model (EICM) used by the MEPDG in terms of (a) number of locations through the slab used by EICM to determine the thermal gradient and (b) EICM calculation of the subgrade spring stiffness (or k-value). Before-and-after MEPDG sensitivity analyses are included to justify the modifications developed and implemented into the MEPDG with the assistance of the MEPDG development team. This research was conducted under SHRP 2 R21, Composite Pavement Systems.

An important issue in extending the life of jointed plain concrete pavement is the proper construction and maintenance of transverse joints. The capabilities of an ultrasonic tomography device in providing information essential to joint rehabilitation decisions as well as the quality control of rehabilitation construction are presented. Testing was conducted at various partial-depth repair locations of a recently repaired in-service highway to determine the presence and extent of debonding between the partial-depth repair and the existing concrete. Testing also was conducted at the Minnesota Road Research Facility to evaluate the subsurface condition along various transverse joints. Real-time diagnosis with the intensity-based signals of the synthetic aperture focusing technique was successful in pinpointing the location of debonded concrete interfaces within partial-depth repairs. Ultrasonic tomography testing also showed the capability of identifying that a joint is in need of repair and subsequently diagnosing the extent of subsurface deterioration throughout the joint.

Ultrasonic tomography is an emerging technology that shows promise for quality assurance/quality control (QA/QC) during construction or for rehabilitation decisions about concrete pavements. However, the benefits of this emerging technology have not yet been fully captured for widespread use in highway infrastructure management. Verification of a state-of-the-art ultrasonic tomography device, MIRA, is presented through multiple field trials involving typical pavement constructability and rehabilitation issues. Field trials indicate that although the device is a useful portable pavement diagnostic alternative capable of consistent thickness measurement, reinforcement location, and distress evaluation, significant efforts and user expertise are required for measurement and data interpretation of large-scale application. Software was developed for a more productive, objective signal interpretation method with automated analysis of reinforcement location in continuously reinforced concrete pavement. This type of automation for multiple applications shows promise for the use of ultrasonic tomography to improve large-scale pavement QA/QC and rehabilitation projects in the future. Nevertheless, the research in the paper shows ultrasonic tomography to be an accurate, reliable, and convenient alternative or supplement to traditional techniques that can be used for a wide variety of small-scale pavement diagnostics applications.

Pervious concrete pavement must perform as both a stormwater management tool and a pavement. While much research has focused on porosity and permeability of pervious concrete, few guidelines exist for structural analysis and design of such pavement. In this paper, an existing pervious concrete pavement was analyzed for stiffness and fatigue by means of Westergaard's theory of a medium-thick plate on a Winkler foundation. The stiffness evaluation compared the responses of pervious and conventional concrete pavements to falling weight deflectometer stresses and to models created in ISLAB2005. Although pervious concrete had a lower modulus of elasticity than conventional concrete pavement, Westergaard's model adequately described the behavior of pervious pavements. Additionally, a fatigue analysis of pervious concrete was completed through use of the StreetPave fatigue model.

This paper describes research to evaluate modeling of the thermal behavior of concrete and composite pavements by the Enhanced Integrated Climatic Model (EICM), the climate-modeling package used in the Mechanistic-Empirical Pavement Design Guide (MEPDG). First, the study uses temperature data collected at the Minnesota Road Research Project (MnROAD) facility from portland cement concrete (PCC) and asphalt concrete (AC)-PCC pavements to investigate benefits of AC overlays on the thermal characteristics of PCC slabs. Furthermore, the study validates EICM predictions of thermal gradients through the slabs and investigates the effect of MEPDG-user inputs for thermal conductivity of PCC. Overall, the paper examines measured data from MnROAD for AC-PCC pavements and their single-layer PCC counter-parts and attempts to explain how similar pavement systems and their thermal characteristics are taken into account in the MEPDG. The paper concludes that evaluation of the material thermal inputs should be part of a process of local calibration and adaptation of the MEPDG.

Ultrasonic tomography is an emerging technology that shows promise for quality assurance/quality control (QA/QC) during construction or for rehabilitation decisions about concrete pavements. However, the benefits of this emerging technology have not yet been fully captured for widespread use in highway infrastructure management. Verification of a state-of-the-art ultrasonic tomography device, MIRA, is presented through multiple field trials involving typical pavement constructability and rehabilitation issues. Field trials indicate that although the device is a useful portable pavement diagnostic alternative capable of consistent thickness measurement, reinforcement location, and distress evaluation, significant efforts and user expertise are required for measurement and data interpretation of large-scale application. Software was developed for a more productive, objective signal interpretation method with auto-mated analysis of reinforcement location in continuously reinforced concrete pavement. This type of automation for multiple applications shows promise for the use of ultrasonic tomography to improve large-scale pavement QA/QC and rehabilitation projects in the future. Nevertheless, the research in the paper shows ultrasonic tomography to be an accurate, reliable, and convenient alternative or supplement to traditional techniques that can be used for a wide variety of small-scale pavement diagnostics applications.

This paper describes research to evaluate modeling of the thermal behavior of concrete and composite pavements by the Enhanced Integrated Climatic Model (EICM), the climate-modeling package used in the Mechanistic–Empirical Pavement Design Guide (MEPDG). First, the study uses temperature data collected at the Minnesota Road Research Project (MnROAD) facility from portland cement concrete (PCC) and asphalt concrete (AC)–PCC pavements to investigate benefits of AC overlays on the thermal characteristics of PCC slabs. Furthermore, the study validates EICM predictions of thermal gradients through the slabs and investigates the effect of MEPDG-user inputs for thermal conductivity of PCC. Overall, the paper examines measured data from MnROAD for AC-PCC pavements and their single-layer PCC counterparts and attempts to explain how similar pavement systems and their thermal characteristics are taken into account in the MEPDG. The paper concludes that evaluation of the material thermal inputs should be part of a process of local calibration and adaptation of the MEPDG.

Pervious concrete pavement must perform as both a stormwater management tool and a pavement. While much research has focused on porosity and permeability of pervious concrete, few guidelines exist for structural analysis and design of such pavement. In this paper, an existing pervious concrete pavement was analyzed for stiffness and fatigue by means of Westergaard's theory of a medium-thick plate on a Winkler foundation. The stiffness evaluation compared the responses of pervious and conventional concrete pavements to falling weight deflectometer stresses and to models created in ISLAB2005. Although pervious concrete had a lower modulus of elasticity than conventional concrete pavement, Wester-gaard's model adequately described the behavior of pervious pavements. Additionally, a fatigue analysis of pervious concrete was completed through use of the StreetPave fatigue model.

Climatic and environmental conditions have significant effects on pavement performance but have been inadequately considered in previous design methods. The Mechanistic-Empirical Pavement Design Guide (MEPDG) accounts for these effects through the use of the enhanced integrated climatic model. The present study examined the effects of climate on pavement performance predictions and the effects of climatic file generation by using MEPDG. The paper details the effort required to compare performance predictions for composite pavement consisting of asphalt cement over portland cement concrete (PCC) for 610 locations across the United States, with the use of MEPDG, Version 1.0. Analysis of the results was performed at the national, regional, and local levels. Although in general the results agree with the anticipated trends of environmental effects on pavement performance, the prediction of performance according to the predicted transverse cracking in the PCC layer was found to contain inconsistencies. These inconsistencies are attributed to the quality of the climatic data. The paper concludes that the MEPDG climatic database should be cleansed of incomplete or questionable climatic data files to ensure reliable performance prediction.

Cementitious stabilization of aggregates and soils is an effective technique to increase the stiffness of base and subbase layers. Furthermore, cementitious bases can improve the fatigue behavior of asphalt surface layers and subgrade rutting over the short and long term. However, it can lead to additional distresses such as shrinkage and fatigue in the stabilized layers. Extensive research has tested these materials experimentally and characterized them; however, very little of this research attempts to correlate the mechanical properties of the stabilized layers with their performance. The Mechanistic-Empirical Pavement Design Guide (MEPDG) provides a promising theoretical framework for the modeling of pavements containing cementitiously stabilized materials (CSMs). However, significant improvements are needed to bring the modeling of semirigid pavements in MEPDG to the same level as that of flexible and rigid pavements. Furthermore, the MEPDG does not model CSMs in a manner similar to those for hot-mix asphalt or portland cement concrete materials. As a result, performance gains from stabilized layers are difficult to assess using the MEPDG. The current characterization of CSMs was evaluated and issues with CSM modeling and characterization in the MEPDG were discussed. Addressing these issues will help designers quantify the benefits of stabilization for pavement service life.

The AASHTO interim Mechanistic-Empirical Pavement Design Guide (MEPDG) was recently introduced in the United States. Many state agencies have conducted validation and local calibration of the MEPDG performance prediction models. In this study, time history rutting performance data for pavement sections at the Minnesota Department of Transportation full-scale pavement research facility [Minnesota Road Research Project (MnROAD)] have been used for an evaluation and local calibration of the MEPDG rutting model. A detailed comparison of the predicted total rutting, asphalt layer rutting, and measured rutting is presented. The reason that a conventional MEPDG model calibration was not feasible is discussed. Also, a modification of the rutting model is recommended. It was found that the locally calibrated model greatly improved the MEPDG rutting prediction for various pavement designs in MnROAD conditions.

The AASHTO interim Mechanistic–Empirical Pavement Design Guide (MEPDG) was recently introduced in the United States. Many state agencies have conducted validation and local calibration of the MEPDG performance prediction models. In this study, time history rutting performance data for pavement sections at the Minnesota Department of Transportation full-scale pavement research facility [Minnesota Road Research Project (MnROAD)] have been used for an evaluation and local calibration of the MEPDG rutting model. A detailed comparison of the predicted total rutting, asphalt layer rutting, and measured rutting is presented. The reason that a conventional MEPDG model calibration was not feasible is discussed. Also, a modification of the rutting model is recommended. It was found that the locally calibrated model greatly improved the MEPDG rutting prediction for various pavement designs in MnROAD conditions.