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Transverse joint faulting is a distress that develops in unbonded concrete overlays (UBOL). Historically, faulting models used for predicting the performance of a UBOL have not accounted for the effects of the interlayer between the overlay and the existing pavement on the development of faulting. This is a significant limitation since characteristics of the interlayer play a primary role in the rate at which faulting develops in UBOLs. To develop a more robust faulting prediction model for UBOLs, enhancements were made to the current process to address this limitation. This includes the use of a structural response model that can account for the effects of the interlayer properties on the response of the UBOL. Additional enhancements include the use of a deflection basin of the overlay (in lieu of corner deflections of an equivalent slab system for accumulating differential energy [DE]), the incorporation of an erosion model that can account for the erodibility of the interlayer material, the adjustment of the incremental faulting equations to accommodate small slab sizes that are common in UBOLs, and a national calibration using faulting data from in-service UBOLs. This enhanced faulting model has been implemented in the mechanistic-empirical design tool Pitt UBOL-ME.

Transverse joint faulting is a common distress that develops in unbonded concrete overlays (UBOLs). In the previous predictive faulting model for UBOLs, artificial neural networks (ANNs) were train...

Transverse joint faulting is a common distress in bonded concrete overlays of asphalt pavements (BCOAs), also known as whitetopping. However, to date, there is no predictive faulting model available for these structures. Therefore, the intended research is to develop a predictive faulting model for BCOAs. In addition, it is important to be able to account for conditions unique to BCOA when characterizing the response in a faulting prediction model. To address this, computational models were developed using a three-dimensional finite element program, ABAQUS, to accurately predict the response of these structures. These models account for different depths of joint activation, as well as full and partial bonding between the concrete overlay and existing asphalt pavement. The models were validated with falling weight deflectometer (FWD) data from existing field sections at the Minnesota Road Research Facility (MnROAD) as well as at the University of California Pavement Research Center (UCPRC). A fractional factorial analysis was executed using the computational models to generate a database to be used in the development of the predictive models. The predictive models, based on artificial neural networks (ANNs), are used to rapidly estimate the structural response at the joint in BCOA to environmental and traffic loads so that these responses can be incorporated into the design process. The structural response obtained using the ANNs is related to damage using the differential energy concept. Future work includes the implementation of the ANNs developed in this study into a faulting prediction model for designing BCOA.

Unbonded concrete overlay of concrete pavement (UBOL) is an effective rehabilitation method involving the construction of a new concrete pavement over a deteriorated concrete pavement, separated by an interlayer. While UBOL is used in practice to improve the structural capacity of existing concrete pavements, the performance of the interlayer is not currently accounted for in the pavement mechanistic–empirical design process. Therefore, the objective of this research is to improve prediction of UBOL performance by accounting for the effects of asphalt interlayer consolidation on the development of longitudinal cracks in the wheelpath. First, a laboratory investigation was performed using beams cut from in-service pavements in Michigan, Minnesota, and Pennsylvania to assess the susceptibility of permanent deformation of asphalt interlayers. This data was utilized in conjunction with a finite element analysis to develop/calibrate a permanent deformation prediction model for dense graded asphalt interlayers. The framework of the model follows that of the permanent deformation prediction model for asphalt surface pavements incorporated into the American Association of State Highway and Transportation Officials (AASHTO) Mechanistic–Empirical Pavement Design Guide. In addition, a field analysis was conducted, using the Long-Term Pavement Performance (LTPP) database, to assess longitudinal cracking in the wheelpath caused by permanent deformation in asphalt interlayers. The laboratory-calibrated permanent deformation model was then validated using the performance data for UBOLs in the LTPP database and deformation thresholds for asphalt interlayers were established. This research resulted in the development of a framework for the prediction of longitudinal crack development in UBOLs because of permanent deformation in the asphalt interlayer.

There are several methods for determining the stiffness of asphalt concrete in an existing pavement. The three primary methods are: dynamic modulus testing in the laboratory, predictive equations, and falling weight deflectometer (FWD) testing. Asphalt over asphalt (AC/AC) overlay design procedures allow the use of multiple methods to characterize fatigue damage in the existing asphalt concrete. Therefore, understanding the difference between these methods is critical for AC/AC overlay design. The differences between the methods for determining asphalt concrete stiffness and how these differences are related to FWD load magnitude and asphalt temperature are examined. Data from the Federal Highway Administration’s Long-Term Pavement Performance Program (LTPP) are used in this investigation. It is found that the stiffness determined through FWD testing and backcalculation is generally less than that estimated using the Witczak predictive equation and binder aging models. Furthermore, it is found that both FWD load magnitude and asphalt temperature have a significant effect on the difference between backcalculated and estimated stiffness of asphalt concrete. Backcalculated stiffness increases relative to estimated stiffness as FWD load and temperature increase. These effects must be considered when multiple methods of determining asphalt concrete stiffness are used interchangeably for overlay design.

Drying shrinkage and coefficient of thermal expansion (CTE) are key material properties that affect the long-term performance of a concrete pavement. The importance of these two properties will continue to increase as extreme heat events occur more frequently with climate change. Standard laboratory tests performed to quantify these properties do not replicate the in-situ slab conditions such as spatial and temporal variation in moisture levels. As a result, laboratory-determined material property values may not accurately reflect the response of the pavement to changes in temperature. In this research, strain data from a 16-year-old in-service jointed plain concrete pavement was studied with a focus on the variation in drying shrinkage and response to temperature change. Drying shrinkage over time was estimated at different locations within the slab. Additionally, the structural coefficient of thermal expansion (SCTE) was determined as the strain response of the slab to unit changes in temperature. The frequency and amount of monthly rainfall was compared with SCTE results to explain seasonal variation in SCTE values. The results indicate that slab restraint conditions affect both the development of drying shrinkage and the SCTE of the pavement. Additionally, this study shows that both drying shrinkage and SCTE are not constant through the pavement structure, and both parameters are affected by the moisture content of the concrete. The SCTE was up to 23% larger and 22% smaller than the CTE determined through laboratory testing. In addition, only 31% of the laboratory measured ultimate drying shrinkage was realized in the slab.

Transverse joint faulting is a common distress in unbonded concrete overlays (UBOLs). However, the current faulting model in Pavement mechanistic-empirical (ME) is not suitable for accurately predicting the response of UBOLs. Therefore, to develop a more accurate faulting prediction model for UBOLs, the first step was to develop a predictive model that would be able to predict the response (deflections) of these structures. To account for the conditions unique to UBOLs, a computational model was developed using the pavement-specific finite element program ISLAB, to predict the response of these structures. The model was validated using falling weight deflectometer (FWD) data from existing field sections at the Minnesota Road Research Facility (MnROAD) as well as sections in Michigan. A factorial design was performed using ISLAB to efficiently populate a database of fictitious UBOLs and their responses. The database was then used to develop predictive models, based on artificial neural networks (ANNs), to rapidly estimate the structural response of UBOLs to environmental and traffic loads. The structural response can be related to damage through the differential energy concept. Future work will include implementation of the ANNs developed in this study into a faulting prediction model for designing UBOLs.

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.

Transverse joint faulting is a common distress in bonded concrete overlays of asphalt pavements (BCOAs), also known as whitetopping. However, to date, there is no predictive faulting model available for these structures. To account for conditions unique to BCOA, a computational model was developed using a three-dimensional finite element program, ABAQUS, to predict the response of these structures. The model was validated with falling weight deflectometer (FWD) data from existing field sections at the Minnesota Road Research Facility (MnROAD) as well as at the University of California Pavement Research Center (UCPRC). A large database of analyses was then developed using a fractional factorial design. The database is used to develop predictive models, based on artificial neural networks (ANNs), to rapidly estimate the structural response at the joint in BCOA to environmental and traffic loads. The structural response will be related to damage using the differential energy concept. Future work includes the implementation of the developed ANNs in this study into a faulting prediction model for designing BCOA.

A statistical classifier was developed to interpret falling weight deflectometer data for the detection of voids under jointed concrete pavement slabs. The classifier was trained with the Seasonal Monitoring Program sections in the Long-Term Pavement Performance (LTPP) database and data from the Minnesota Road Research Facility. A two-level cross-validation process was used to assess the performance of existing void detection methods, according to a threshold of a single variable, and the least absolute shrinkage and selection operator (LASSO) classifier, which is based on several variables. Simple void detection methods based on the normalized 9,000-lb deflection were found to perform better than void detection methods based on variable deflection analysis. The LASSO classifier outperformed any of the existing void detection techniques. The LASSO classifier was validated through two field trials in Pennsylvania and an LTPP general pavement section in which significant faulting had developed.

Composite pavement structures are constructed mainly either as Portland cement concrete (PCC)-over-PCC or hot mix asphalt (HMA)-over-PCC. Several successful in-service projects have been reported in Europe. The design and construction of these sections in the United States, however, still require effort. The current study includes the analysis of the response of three different composite pavement sections to the environmental loads. These sections were constructed in May of 2010 at the Minnesota Road Research Facility. The sections are constructed in three individual cells, Cell 70, a HMA-over-PCC with recycled concrete aggregate (RCA), Cell 71, exposed aggregate concrete (EAC)-over-RCA and Cell 72, EAC-over-economical concrete. All cells were heavily instrumented with thermocouples, moisture sensors, and static and dynamic strain gauges. This study characterises the structural response of HMA-over-PCC pavements and also PCC-over-PCC to the environmental loads.

This study evaluates the modeling of different base types under new jointed plain concrete pavements (JPCP) in the AASHTO Pavement ME Design Guide. It was found that the Pavement ME overestimated the stress in JPCP for unbonded stabilized bases and granular bases and underestimated the stress for bonded stabilized bases when compared to other models. The error in stress estimation results from modeling an unbonded base with a bonded-but-weightless base in the structural model, which is critical when the environmental loading is predominant and/or the base is stiff. Because the separation between layers that are not bonded cannot be accommodated, the behavior of a granular base cannot be accurately reflected, especially not by an elastic continuum. Keywords: Pavement ME Design, Jointed plain concrete pavement, Transverse cracking model, Stabilized base, Granular base, Finite element

Bonded concrete overlays of asphalt pavements (BCOAs) are becoming a common rehabilitation technique used for distressed hot mix asphalt (HMA) roadways. The original design procedures were based primarily on data from instrumented pavements and finite element modelling. They were governed by the assumption that the failure mechanism was a function of the overlay thickness. However, field observations have indicated that the actual failure modes are dictated by slab size. The newly developed Bonded Concrete Overlay of Asphalt Mechanistic-Empirical design procedure (BCOA-ME) presented here is valid for overlays that are between 2.5 and 6.5 in (64–154 mm), and includes five primary enhancements to the Portland Cement Association and Colorado Department of Transportation procedures that have been traditionally used: 1.) the failure mode is dictated by the joint spacing; 2.) a new structural model for longitudinal cracking for 6-ft × 6-ft (1.8 m × 1.8 m) concrete overlays has been developed to better p...

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.

A bonded concrete overlay on asphalt (BCOA) is a rehabilitation method for moderately distressed asphalt pavements by relatively thin plain cement concrete or fiber-reinforced concrete slabs. The joint load transfer behavior for BCOAs plays a significant role in the long-term performance. Poor load transfer across the joints of the concrete slabs initiates debonding of the asphalt layer from the concrete slabs, which promotes the development of corner cracks or longitudinal cracks. However, because of the tediousness involved in characterizing the joint load transfer behavior of BCOAs, this important aspect is not accounted for in many available mechanistic–empirical BCOA design procedures. The influences of joint load transfer behavior on the performance of BCOA are discussed. The joint load transfer behavior for BCOAs with 1.52- × 1.83-m (5- × 6-ft) slabs and 1.22- × 1.22-m (4- × 4-ft) slabs is analyzed with the finite element method. The load transfer contributed by the asphalt layer, as well as the concrete slab, is characterized as a function of the BCOA design features. Finally, a method is proposed to determine the nondimensional joint stiffness (AGG*) for BCOAs as a function of the structural design features of the pavement section. The AGG* is significant in that it is the factor commonly used to characterize joint load transfer behavior when pavements are designed with a mechanistic-based design approach.

AASHTOWare Pavement ME Design, software developed from the AASHTO Mechanistic–Empirical Pavement Design Guide (MEPDG), uses performance data extracted primarily from the long-term pavement performance database to calibrate the performance prediction models for rigid pavements. In this study, factorial designs were generated as a subset of the national rigid pavement database for calibration of the MEPDG rigid pavement performance models. Three separate factorial designs were included for each rigid pavement performance model for (a) jointed plain concrete pavement (JPCP) transverse cracking, (b) JPCP faulting (doweled and undoweled), and (c) continuously reinforced concrete pavement punchouts. Experimental design variables for each model were selected to provide the broadest possible representation of key design, construction, and environmental features. The three performance models were then calibrated with the developed factorial matrices. The results were presented along with the calibration procedure. A validation of the calibrated models was then conducted with sites not included in the factorial matrices. An evaluation compared design slab thicknesses required to meet specified performance criteria determined with these and other previously established calibration coefficients. Finally, conclusions and recommendations based on the experiences gained conducting this study are provided.

Longitudinal cracking has been identified as the predominant distress in thin bonded whitetopping with a 1.83-m (6-ft) longitudinal joint spacing. However, the structural models in existing...

Bonded concrete overlays on asphalt pavement (BCOA) offer a rehabilitation method for moderately distressed asphalt pavements. A performance review of the BCOA projects constructed in diffe...

Curvature due to temperature curling and moisture warping has a large effect on the performance and assessment of jointed plain concrete pavements (JPCP). Accurate curvature prediction can ...

Pavement design has evolved from a purely empirical approach to a more mechanistic-based approach. One of the primary distresses considered when designing jointed plain concrete pavements is faulting. The development of faulting is largely a function of the load transfer efficiency at the joints. For undoweled joints, the load is primarily transferred through the aggregate interlock provided by the texture resulting from the meander in the transverse crack propagating off from the sawed joint. This paper shows how volumetric surface texture, a measurement of the surface texture at the crack face, can be used for this purpose. A method is presented for estimating the joint stiffness parameter, Jagg, required for the faulting prediction model incorporated into the AASHTOWare Pavement ME Design software based on the measured surface texture. This method allows the effects of aggregate size, type, and quantity to be captured and joint stiffness to be quantified when faulting is being predicted.

This study focused on identifying the zero-stress time (TZ) in jointed plain concrete pavements (JPCPs). TZ is the time when the concrete slab is sufficiently strong to deform (thermally expand or contract and thus curl) despite the existing external restraints, including the friction at the base-slab interface. It is critical to be able to identify TZ so that the temperature gradient present in the slab at TZ, known as the built-in temperature gradient, can be characterized. In this study, TZ was established through the instrumentation of 36 concrete slabs in four JPCP construction projects. Strain-temperature behavior in each slab was used to identify TZ. The slabs in each project were paved at different times of the day (morning, noon, early afternoon, and late afternoon) to investigate the effects of the ambient curing conditions on TZ. The degree of hydration at TZ (αTZ) was established for each slab. The field data were used in the development of a model for predicting αTZ as a function of the concrete water-to-cement ratio, unit weight, early-age elastic modulus, and slab thickness.

Bonded whitetopping is a thin concrete overlay on a distressed asphalt pavement. The existing design procedures for bonded whitetopping assume the failure mode is a function of the overlay thickness. It has been traditionally assumed that the failure mode for thin whitetopping [overlay thickness greater than 102 mm (4 in.) but less than 152 mm (6 in.)] is transverse cracking, and the failure mode for ultrathin white-topping [overlay thickness between 51 mm (2 in.) and 102 mm (4 in.)] is corner cracking. However, the performance of in-service whitetopping overlays indicates that the actual failure mode is dictated more by slab size than by overlay thickness. For both thin and ultrathin whitetopping with 1.8-m (6-ft) joint spacing, cracks initiate at the bottom of the overlay at the intersection of the transverse joint and the wheelpath and propagate longitudinally. At times, these cracks will continue to propagate in the longitudinal direction and intersect the adjacent transverse joint; at other times, they will turn on a diagonal and propagate toward the lane–shoulder joint. To verify this failure mechanism observed in the field further, a three-dimensional finite element model subjected to environmental and wheel loads was developed. The results support the proposed failure mode, showing that the critical tensile stress is indeed in the wheelpath and at the bottom of the portland cement concrete overlay. This type of failure results in a longitudinal crack.

Development of design procedures for bonded whitetopping overlays has been based on the assumption that failure mechanisms are a function of overlay thickness; namely, thin whitetopping results in longitudinal cracking and ultrathin whitetopping results in corner cracking. However, field data from whitetopping sections indicate that failure modes are dictated by slab size rather than overlay thickness. The revised procedure presented here for thin whitetopping and ultrathin whitetopping offers four primary enhancements to the Portland Cement Association and Colorado Department of Transportation procedures that traditionally have been used: (a) the failure mode is dictated by the joint spacing and not the overlay thickness, (b) the stress adjustments factors have been calibrated with an extensive data set, (c) the equivalent gradients to be used as the design input are defined according to the pavement structure and geographical location of the project and, (d) the effect of temperature change on hot-mix asphalt stiffness is considered. Comparisons of the predicted performance for the revised procedure with the actual performance for four separate projects showed that the predicted thicknesses are reasonable. It was also found that the predicted thickness obtained with the revised procedure was sensitive to the thickness of hot-mix asphalt, the level of traffic, and the modulus of rupture of the portland cement concrete, as expected.

A bonded concrete overlay of asphalt (BCOA), also known as whitetopping, is a thin concrete overlay placed upon a distressed asphalt pavement. The asphalt-resilient modulus is kept constant in current BCOA design procedures. This practice results in an underestimation of the damage as compared to when the hourly temperature variation of the asphalt is considered. The framework to establish an equivalent asphalt modulus involves generating a database of hourly middepth asphalt temperatures. This database should include hourly temperatures for different BCOA structures and a large range of geographical locations representing different climatic conditions. The hourly middepth asphalt temperatures are then used to generate hourly asphalt moduli using master curves. Through fatigue equivalency, the equivalent asphalt moduli are calculated for each month. In order to establish the relationship between the asphalt modulus and middepth temperature, the United States was divided into seven different zones ...

The reasonableness of the models in the Mechanistic-empirical Pavement Design Guide (MEPDG) used to predict the performance of the continuously reinforced concrete pavements (CRCPs) was evaluated in this study. The MEPDG punchout, crack width and spacing and load transfer efficiency (LTE) models were evaluated through a factorial sensitivity study. The input matrix was defined to reflect ‘real-world’ design situations. It was found that, contrary to the 1993 American Association of State Highways and Transportation Officials (AASHTO) Design Guide, crack width must be below 0.5 mm to maintain adequate performance. Additionally, based on the performance predictions from the MEPDG, a crack spacing of less than 1.8 m ensures a crack width of less than 0.5 mm, which is another contradiction with the approach in the 1993 Guide.

This research evaluates the reasonableness of the Mechanistic-Empirical Pavement Design Guide (MEPDG) version 1.0 to predict the joint faulting and transverse cracking of jointed plain concrete pavements (JPCPs). This is accomplished by carrying out a full factorial sensitivity analysis, considering material properties, pavement design features, climates and traffic. This study considers the interaction and correlation between these inputs and was designed to reflect the real conditions that occur in practice. Based on over 3000 runs, the sensitive parameters in the joint faulting model and the transverse cracking model were identified. In general, the analysis indicates JPCP models perform well. However, some counterintuitive results were also found.

The effective linear temperature gradient is a significant input needed to characterize the effects of environmental loadings when available pavement design procedures are used for bonded concrete overlays on asphalt (BCOA), also known as thin or ultrathin whitetopping. Establishing such an input is challenging and therefore has not been well guided in current BCOA design procedures across the country. Guidance is provided on suitable values for the effective equivalent linear temperature gradient (EELTG) that can be used in the design of ultrathin BCOAs. The EELTG is expressed as a function of the climatic conditions, geographical location, and design features of the BCOA: longitude, latitude, elevation, annual mean percentage of sunshine, overlay panel size, 28-day modulus of rupture for the portland cement concrete, and thickness of the hot-mix asphalt layer. Typical values for the annual mean percentage of sunshine are recommended to facilitate implementation of the proposed guideline in the current design procedures.

Slab curvature, which represents the response of concrete pavement slabs to environmental loads, influences the location and magnitude of critical slab stresses and affects long-term pavement performance. The purpose of this study was to measure the changes in temperature and moisture profiles in a newly constructed concrete pavement and to determine both the overall deformed shapes of the slabs as well as the relative contributions of built-in and transient environmental effects over time. Data were collected from an instrumented jointed plain concrete pavement (JPCP) over a 2-year period. Slab curvatures were computed or predicted using measurements of temperature and moisture conditions in the slab, static strain measurements, and pavement surface profile measurements. It was found that the additional restraint provided by the dowel and tie bars does not appear to significantly reduce slab curvature resulting from daily temperature fluctuations or from reversible drying shrinkage. It does have a substa...

This research evaluates the ability of the Mechanistic–Empirical Pavement Design Guide (MEPDG) to accurately predict the performance of jointed plain concrete pavements (JPCPs). This is accomplished by comparing predicted performances with observed performances for the in-service mainline test cells at Mn/ROAD. These comparisons indicate that MEPDG performance predictions for JPCP are most accurate when the default (constant) built-in equivalent temperature difference of − 5.5°C is used instead of a site-dependent value. It appears that significant portions of the error of estimation can be explained by the sensitivity of the performance models to variability in hardened concrete properties (modulus of rupture, modulus of elasticity and coefficient of thermal expansion) and pavement structural features (slab thickness, joint spacing, subbase type and bond condition). Predictions of slab cracking were found to be highly sensitive to these parameters. In addition, the MEPDG cracking model seemed not to fit ...

This paper evaluates the implementation of the built-in temperature difference input parameter in the Mechanistic–Empirical Pavement Design Guide (MEPDG) for the design of jointed plain concrete pavements (JPCPs). The pavement distress, in terms of transverse cracking, is expected to be minimised when the transient temperature difference is equal in magnitude to the built-in temperature difference but of the opposite sign. However, this study shows that a built-in temperature difference of − 6.5°C minimises the cracking prediction for JPCPs. This optimum value of − 6.5°C coincides with the default value in the MEPDG of − 5.5°C, which was established through the nationwide calibration. The cause of this phenomenon is further investigated by taking into account the traffic loading time, slab thickness, joint spacing and reversible shrinkage, but none of these factors are able to explain this anomaly. The results from this study indicate that the built-in gradient should not be an input but is merely a calib...

Hundreds of bonded portland cement concrete (PCC) overlays of hot-mix asphalt (HMA) pavements are being constructed in the United States and around the world. Increasing interest in this rehabilitation method has led to a need to define further the most common forms of distresses, quantify the extent of influence of design parameters on performance, and develop rational design guidelines. This study evaluates the performance of in-service pavements to establish criteria for when reflection cracks might develop. Reflection cracking is dictated by the thickness of the PCC overlay and HMA layer, panel size, climatic conditions, and accumulated vehicle loads. When the relative stiffness of the PCC overlay and HMA layer (defined during the coldest month of the year) falls below the critical value one, reflection cracking develops. The rate of development is a function of the load-related stress in the overlay. The performance analysis of the in-service pavements also verify the benefits of joint sealing and the use of small diameter dowel bars for high volume roadway applications.

The primary objective of this research effort is to determine if temperature gradients affect the ability to use falling weight deflectometer (FWD) testing to monitor pavement joint performance and detect voids under the corners of the slab. A field investigation was performed at the Minnesota Road Research System test facility to meet this objective. It was found that gradients can have an effect on the results of FWD testing for rigid pavements. Although the load transfer efficiencies measured for doweled slabs were not found to be affected by slab temperature or temperature gradients (even when poor joint performance was exhibited), load transfer efficiencies measured for the undoweled slabs were greatly influenced by the presence of a gradient. There even appears to be a higher correlation between the gradient present at the time of testing and the average temperature of the slab for the pavement designs and environmental conditions included in this study. Gradients present at the time of testing also affect the ability to detect voids beneath the slab. Large positive gradients produced negative void parameters (indicating that a void was not present), whereas large negative gradients produced large positive void parameters (indicating that a void was present). This study found that loss of support under the slab could be identified even when the joints were locked if gradients were not present. On the basis of these findings, it is important to determine the complete temperature profile throughout the depth of the slab at the time of testing so that this information can be considered when the deflection data are interpreted.

Construction curling and warping produces a built-in gradient, which takes place as the result of changes in temperature and moisture that occur prior to the hardening of Portland cement concrete (PCC) pavements. The slab remains flat in the presence of this gradient because the plastic concrete has not developed sufficient stiffness to generate stress or strain. The new Guide for the Design of New and Rehabilitated Pavement Structures has shown the importance of quantifying the built-in gradient. In this study, the magnitude of the built-in gradient was quantified along with the early-age response of the slab to environmental loads. It was found that the equivalent linear temperature gradient at the time of set was

The focus of this study is to provide a detailed analysis of the strain that develops as a result of environmental loads. The study characterizes slab response immediately after construction (first 72 h after paving) and also addresses seasonal effects over the first 10 months following construction. A heavily instrumented test section was constructed on SR-22 in Murrysville, Pennsylvania, to help characterize slab response to environmental loads better. Static strain and climatic data collected through the first 10 months after construction (August 2004 through June 2005) were analyzed to interpret pavement response to environmental loads as a function of location with respect to joint proximity, depth within the slab, and level of restraint applied to the slab. Many things were also learned about the strain that develops in the slab over the first 10 months after construction. The average strain in the fall was around –450 μstrain, whereas the average strain in the winter was –600 μstrain. The ambient temperatures increased during the spring and summer; this resulted in a decrease in the average strain to –250 μstrain. Thermal strain was found to be twice as high as the drying shrinkage the first winter after construction. A substantial amount of drying shrinkage occurred within the first 50 days after construction. Variations in drying shrinkage occur not only through the depth of the slab but also across the surface of the slab.

The Minnesota Department of Transportation constructed an ultrathin whitetopping (UTW) project at three consecutive intersections on US-169 at Elk River, Minnesota, to gain more experience with both the design and the performance of UTW. Distinct cracking patterns developed within each test section. The UTW test sections with a 1.2- ×1.2-m (4- ×4-ft) joint pattern included corner breaks and transverse cracks. Corner breaks were the primary distress in the test section with a 1.8- ×1.8-m (6- ×6-ft) joint pattern, although very little cracking was exhibited. The Minnesota Road Research Facility UTW test sections on I-94 allow comparisons of the same UTW design on hot-mix asphalt (HMA) pavements with different structural capacities to be made. The strain and deflection measurements emphasize the importance of the support provided by the HMA layer. A reduction in this support occurs when the temperature of the HMA is increased or when the HMA begins to ravel. During evaluations of whether UTW is a viable rehabilitation alternative, cores should be pulled from the pavement to determine if the asphalt is stripping and if the asphalt layer has adequate thickness. UTW can be successfully placed on as little as 76 mm (3 in.) of asphalt, if the quality of the asphalt is good. The cores should also reveal whether the asphalt layer is of uniform thickness and whether stripping and raveling have occurred. If the asphalt layer is of uniform thickness and stripping and raveling have not occurred, UTW is a good option for use in the rehabilitation of asphalt pavements.

Thin and ultrathin whitetopping overlays are becoming a more common method of pavement rehabilitation. It is important to gain information on the types of distresses that occur in the overlays and effective repair techniques. In 1997 the Minnesota Department of Transportation constructed several thin and ultrathin whitetopping test cells at the Minnesota Road Research (Mn/ROAD) facility. Typical distresses included corner breaks, transverse cracks, and reflective cracks. The finite element program ISLAB2000 was used to investigate stress patterns and their relation to the distresses. Different techniques for repairing ultrathin whitetopping were investigated. Various techniques were also used to deter reflective cracking, including various bond-breaking materials and full-depth sawing at strategic locations along the longitudinal joint to prevent cracks from propagating into adjacent panels at misaligned transverse joints. Four of the six sections had present serviceability indexes (PSIs) greater than 3.5 before the repairs, showing that a good level of performance has been maintained after 4.7 million equivalent single-axle loads. The two sections that exhibited the largest drop in PSI were the overlays with 1.2- × 1.2-m (4- × 4-ft) panels. The repairs made in sections containing these panels have brought the PSI back up to an acceptable level (PSI > 3). The thin and ultrathin whitetopping test sections at Mn/ROAD have shown that whitetopping is a viable rehabilitation alternative for asphalt pavements. The importance of choosing an optimum panel size was exhibited. It has also been shown that when necessary, it is easy to repair ultrathin whitetopping sections. Various techniques for repairing each type of distress have been summarized.

The volumetric surface texture (VST) test was developed at the University of Minnesota to provide an estimate of the load transfer potential available through aggregate interlock across a concrete fracture plane. It can also provide an estimate of the abrasion that has taken place since fracture. A study was undertaken to validate the VST concept and test procedures. The factors investigated in this study include the effects of aggregate characteristics on measured surface texture and the effects of measured surface texture on crack and undoweled joint performance, as indicated by deflection-based load transfer efficiency. Deflection, load, and crack width data were collected for both field and laboratory slabs, and VST testing was performed with companion specimens for these slabs. This study has shown that the VST test provides a means of accurately measuring surface texture so that the selection of concrete aggregates can be performed with consideration of potential aggregate interlock at cracks and undoweled joints. Performance prediction equations were developed to provide an early indication of how cracks and undoweled joints will perform before a particular aggregate size, type, gradation, or blend is used in an actual pavement.

State highway agencies in Connecticut, Kansas, Minnesota, Wisconsin, and Wyoming have successfully designed and constructed rigid pavements containing recycled concrete aggregate (RCA). Success has been attributed in part to the minimization of old mortar content in the RCA during recycling processes, thereby controlling the total mortar content of the new portland cement concrete (PCC) mixture, or to the achievement of higher-than-expected compressive strengths through adjustments in mix proportions, or both. There was no clear correlation between mortar content and cracking distresses in field investigations, although one project did exhibit significantly more slab cracking in the recycled pavement than in the corresponding control pavement. The increased cracking may have been due to the large differences in total mortar content between the recycled and control sections. In general, the recycled PCC pavements considered in this study have performed comparably with their conventional PCC pavement counterparts, including the recycled pavements that incorporated RCA derived from concrete affected by D-cracking and alkali-silica reactivity (ASR). There is, however, evidence of small amounts of localized recurrent ASR in the recycled Wyoming pavement. Whether this reactivity will eventually develop into widespread distress remains to be seen.