ME Design Research Articles

Sensitivity of Rigid Pavement Performance Predictions to Individual Climate Variables using Pavement ME Design

AbstractFive individual climate variables are required as climatic inputs in a pavement design using Pavement ME Design (PMED, a pavement design tool). While it is believed that all five climatic v...

Sensitivity Index comparison of pavement mechanistic-empirical design input variables to reflective cracking model for different climatic zones

One of the main types of distress observed in Asphalt Concrete (AC) overlays is reflective cracking, and a reflective cracking model has been recently incorporated into the latest released version of AASHTOWare Pavement ME Design (PMED) software. This study documents the complete results of the sensitivity with respect to the design inputs and material properties of reflective cracking distress predicted by the PMED software. Six representative locations distributed across different climate zones of the United States were considered for studying the effects of climate extremities on changes in predicted reflective cracking distress. One-at-a-time (OAT) sensitivity analyses was performed to determine the Normalized Sensitivity Index (NSI), with two scenarios considered for OAT analyses: (i) sensitivity of short-term reflective cracking prediction (i.e., the year when predicted distress reached 4000 ft/mile) and (ii) sensitivity of long-term reflective cracking prediction (20-year design life). The summary of NSI ranking for varying traffic levels are presented.

Fatigue performance assessment of recycled tire rubber modified asphalt mixtures using viscoelastic continuum damage analysis and AASHTOWare pavement ME design

Improving fatigue cracking resistance of asphalt mixtures is an important issue that concerns roadway agencies, public and industry. There are various, well-established methods for improving the material characteristics, such as polymer modification methods. Recycling/reusing scrap tire rubber in asphalt pavements has also been an interest of engineers. As such, many different methods of scrap tire rubber (herein called crumb rubber) modification alternatives are being developed. This study focused on a comparative evaluation of the fatigue cracking resistance of various base and recycled tire rubber modified asphalt mixtures, including the relatively new and innovative devulcanized rubber (DVR), crumb rubber terminally blend (CRTB), crumb rubber wet process (CRWET), original/base PG58-28 and softer PG58-34 binders, by using Push-Pull Viscoelastic Continuum Damage (PP-VECD) analysis and AASHTOWare Pavement Mechanistic Empirical Design (Pavement ME) software. The results of the study revealed that rubberized asphalt mixtures provided better fatigue lives than the base and softer binders did. Especially, DVR mixtures outperformed at high strain levels, implying they can be used for heavy traffic roads to enhance the fatigue life of asphalt pavements. Both PP-VECD and Pavement ME produced results that showed similar trends.

Development of Rutting Model for Indian Highways Based on Rut Depth Simulations from AASHTOWare Pavement ME Design Software

AbstractA majority of the approaches currently available for predicting rutting suggest limiting the vertical compressive strains on top of the subgrade in a pavement structure. Such approaches do ...

Limiting Strain Distribution Criteria for Perpetual Pavement Design Using AASHTOWare Pavement ME Design

Perpetual asphalt pavement designs have been based on controlling horizontal strains at the bottom of the asphalt layer and vertical strains on top of the subgrade to prevent bottom-up fatigue cracking and subgrade rutting, respectively. Traditionally, single strain thresholds had been used as limits where damage accumulation begins and propagates. The concept of strain distributions was introduced at the National Center for Asphalt Technology (NCAT), and it was found to better represent the wide response spectrum in asphalt pavements caused by the different loading and environmental conditions. This concept was developed based on information and data collected from the NCAT Pavement Test Track, and from this a limiting strain distribution was created to assist with perpetual pavement design. Several studies analyzed the criteria using pavement responses calculated from PerRoad predicted strains in Test Track sections and existing perpetual pavements. A limitation of the AASHTOWare Pavement ME Design software is its inability to output the pavement responses necessary for perpetual pavement design. The objective of this study was to analyze pavement response data predicted from an integration of the AASHTOWare Pavement ME Design software outputs and a JULEA based program developed at NCAT to create a limiting strain distribution for perpetual pavement design using the AASHTOWare Pavement ME Design software. Strains were calculated for Test Track sections using these tools and based on the results a limiting strain distribution was developed. This limiting strain distribution was then further evaluated using eight sections that won Perpetual Pavement Awards. Results showed that the horizontal strain distributions obtained from Test Track sections could differentiate the sections with cracking and the sections that did not crack. In the further evaluation, the horizontal strain distributions from the perpetual pavements did not exceed the limiting strain distribution developed from the Test Track sections, except for a section which surpassed it by a small margin at the 80th and higher percentiles. Vertical strains were also determined for these pavements and the current 200 microstrains at 50th percentile design criteria was met by all the sections.

Evaluation of four different climate sources on pavement mechanistic-empirical design and impact of surface shortwave radiation

ABSTRACT This paper compares the predicted distresses (via in the AASHTOWare Pavement ME Design software (PMED)) of asphalt concrete (AC) and jointed plain concrete pavement (JPCP) using four different climate data sources. These sources also include the Modern Era Retrospective Analysis for Research and Application (MERRA) Versions 1.0 and 2.0 (MERRA-1 and MERRA-2). Pavement performance predictions generated using these data showed disagreement among some of the climate data sources, especially for MERRA-2. Comprehensive diurnal and other time-series analyses of the raw climate data found significant disagreements in the percent sunshine estimates. Percent sunshine is used in the PMED environmental effects model to semi-empirically estimate the downwelling shortwave radiation reaching the pavement surface. Both MERRA data (MERRA -1 and MERRA-2) independently provide direct predictions of downwelling surface shortwave radiation (SSR). The direct model predictions of SSR were used to back calculate ‘synthetic’ per cent sunshine for input into the PMED. The use of the synthetic per cent sunshine derived from the predicted SSR eliminated nearly all discrepancies in the predicted pavement performance using MERRA-1 versus MERRA-2 data. Based on these results, the authors recommend that SSR rather than per cent sunshine be used as a direct input to the PMED.

Avaliação da resistência e da deformação resiliente de quatro solos de subleitos rodoviários no estado do Rio Grande do Sul

O presente artigo apresenta o estudo do comportamento de quatro solos com origens geológicas diferentes, quanto à sua resistência e deformação resiliente, comumente empregados em subleitos rodoviários no estado do Rio Grande do Sul. A metodologia aplicada consistiu em ensaios de caracterização física e mecânica, obtenção da curva característica dos solos, além de simulações numéricas assistidas por dois programas computacionais: AEMC e AASHTOWare Pavement ME Design. Os resultados indicaram que os limites descritos em norma para utilização dos solos como material de subleito foram satisfeitos. Verificou-se que uma variação de ± 2% no teor de umidade provocou considerável alteração na resistência desses materiais, evidenciando a influência da sucção na resistência ao cisalhamento dos solos. As análises mecanicistas permitiram constatar a limitação do método de dimensionamento do DNIT, principalmente no que tange à ruptura por fadiga, além de destacar a importância do módulo de resiliência no comportamento da estrutura como um todo.

Preliminary Local Calibration of Performance Prediction Models in AASHTOWare Pavement ME Design for Flexible Pavement Rehabilitation in Oregon

AbstractThe Oregon Department of Transportation (ODOT) is in the process of implementing the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG) for new pavement sections. However, the vast ...

Implementation of AASHTOWare Pavement ME Design Software for Asphalt Pavements in Kansas

Many highway agencies are transitioning from the 1993 AASHTO pavement design guide to the AASHTOWare Pavement ME Design (PMED). Pavement performance models embedded in the PMED software need to be calibrated for new and reconstructed hot-mix asphalt (HMA) pavements. Twenty-seven newly constructed HMA pavements were used to calibrate the prediction models—twenty-one for calibration and six for validation. Local calibration for permanent deformation, top-down fatigue cracking, and the International Roughness Index (IRI) models was done using the traditional split-sample method. Comparison with the results from the 1993 AASHTO design guide for ten new HMA pavement sections with varying traffic levels was done. The results show that the thicknesses obtained from locally calibrated PMED are within 1 inch of the AASHTO 1993 design guide prediction for low to medium-low traffic. For sections with high traffic level, the 1993 AASHTO design guide yielded higher thickness than PMED. The PMED implementation strategies adopted in Kansas and relevant concerns are discussed. Finally, an automated calibration technique has been proposed to help highway agencies to perform periodic in-house calibration of the performance models.

Traffic inputs for pavement ME design using Oklahoma data

Mechanistic-empirical pavement design guide (MEPDG) or Pavement ME Design requires traffic inputs in three levels based on the availability of data and the importance of the project. The availability of site-specific (Level 1) traffic data is generally limited due to expensive cost and the accuracy of Level 3 average is unsatisfactory, and therefore the intermedium level (Level 2) traffic data need to be developed. Using multiple years of weigh-in-motion (WIM) and vehicle classification data from Oklahoma, this paper starts with a comprehensive check of the traffic data quality, and generates site-specific traffic inputs that are required in Pavement ME Design. Cluster analysis is then applied to develop homogeneous groups for each traffic input. Subsequently, decision tree model and multinomial regression model are developed for the selection of appropriate traffic clusters under given site design conditions. In addition, a case study is included to evaluate the variations of pavement performance at various levels of traffic inputs.

Development of a modulus of subgrade reaction model to improve slab-base interface bond sensitivity

ABSTRACT In the Pavement ME Design, the modulus of subgrade reaction (k-value) is characterised by the dense liquid or Winkler model, which does not consider the interface bond within the supporting media. In this study, a modified k-value model was developed to take into account the shear interaction between concrete slab and base course. Formulation of the modified k-value model contained four steps: (a) correction of cross anisotropic base modulus; (b) development of a submodel for slab-base equivalent thickness; (c) development of a formula for slab-base interface shear bonding; and (d) determination of k-value using the calculated shear bonding and the deflection patterns of falling weight deflectometer (FWD). A large number of rigid pavement structural and strength properties and the corresponding FWD deflection patterns data were collected from the Long-Term Pavement Performance database and used to calculate the modified k-value. These were compared against the k-values using the existing ‘backcalculated best-fit approach’. The results showed that the modified k-values changed significantly due to the consideration of cross anisotropy and slab-base interface bonding. Finally, an artificial neural network (ANN) approach was employed to predict the modified k-values for the given pavement structures, layer moduli and interface bonding ratios.

New calibration approach to improve Pavement ME Design thermal cracking prediction: mixture-specific coefficients – the Michigan case study

Local calibration of the TCMODEL implemented in the Pavement ME Design software has been challenging for many States. This is primarily due to the nature of its mathematical formulation, which is extremely sensitive to the fracture parameter n and the Performance Grade (PG) of the asphalt binder. By simply changing the low PG by one grade, the TCMODEL can predict from zero cracking to the maximum amount of cracking possible. However, this level of sensitivity is not observed in the field. Since the model itself cannot be modified in the Pavement ME Design software, its sensitivity may be adjusted by using mixture-specific local calibration coefficient (k). This approach seems to overcome the problem of the high sensitivity of the TCMODEL and provides very good predictions. However, estimation of mixture-specific k at the design stage of a road can be difficult. To overcome this difficulty, a practical equation was developed using the Multi-Gene Genetic Programming technique so that mixture-specific k-values can be estimated from the asphalt mixture volumetrics as well as other inputs used in the Pavement ME Design software (e.g. |E*| and Indirect Tensile Strength at −10°C). While the equation itself may only be applicable to Michigan mixtures, the general form of the equation is a good starting point for others to develop similar equations in different regions.

Faulting development in concrete pavements and overlays

ABSTRACT The faulting model currently adopted in the Pavement ME design procedure accounts for the pavement response, climatic conditions, traffic, and erodibility of the base. The same faulting model is applied to all jointed concrete pavements regardless of the pavement structure (conventional concrete pavement, unbonded concrete overlay, bonded concrete overlay, etc.). This implies the pumping mechanism is the same for all pavement structures. It also assumes that the rate of the development of faulting and the maximum faulting that will occur is the same regardless of the pavement structure. The focus of this study is to investigate the mechanisms contributing to the development of voids beneath the slabs and faulting for a range of pavement structures. The results are used to determine the suitability of applying one faulting model to all pavement structures. The focus is directed toward undoweled structures since dowelled joints significantly reduce the potential for the development of faulting. It was found that the development of faulting is delayed, develops at a slower rate, and the magnitude of the faulting tends to be higher in overlays as compared to that in jointed plain concrete pavements. In conclusion, a single faulting model is not suitable for application for all pavement structures.

The effect of axle load spectra from AASHTO method on flexible pavement performance

Currently, methods used for pavement design are empirical and based on experiments conducted in the 1960s. Due to the number of variables that can influence an empirical analysis, the National Cooperative Highway Research Program (NCHRP) proposed a mechanistic-empirical method. Based on this method, the MEPDG (Mechanistic-Empirical Pavement Design Guide) software was developed and later, its improved version, the AASHTO Ware Pavement ME Design. In both software versions, default values were developed from traffic data of the United States. However, characteristics of the Brazilian traffic are different from characteristics in the United States. Therefore, this study aimed to verify the effect on national pavement performance due to the use of the default axle load spectra that are available on both software versions. Thus, computer simulations were performed using Brazilian axle load spectra, based on data collected at the Imigrantes Highway in Sao Paulo, and using the default load spectra of the software. The results show that the Brazilian axle load spectra studied damages more the national pavement than the default spectra of the software. Therefore, it is not recommended the use of default spectra for designing Brazilian highways similar to the one studied, because this would lead to under-designed structures.

Effect of joint spacing and pavement thickness on concrete overlay performance

Concrete overlays provide cost-effective maintenance and rehabilitation strategies for pavement systems. A database has been developed in Iowa that records the historical performance of overlays based on records of International Roughness Index (IRI) and Pavement Condition Index (PCI) over a 20-year period. Based on these data concrete overlay service life has been modeled for various joint spacings. The data demonstrate that durability and service life can be improved. A review of PCI data indicates that improving construction quality to eliminate premature failure has the potential to add at least 10 years to the service life of PCC overlays. Even though concrete overlay technology is not a new concept, most of its design procedures still follow empirical methods, therefore this study applied AASHTOWare Pavement ME Design (Version 2.3.1) software to identify the effects of design para ms on concrete overlay service life. The theoretical insights provided by Pavement ME Design were compared with historical performance data and used to provide recommendations with respect to optimized joint spacing in overlay pavement structures. Comparison of the historical performance-related data with Pavement ME Design software results indicates that the Pavement ME Design software is conservative in predicting concrete overlay service life.

Development of Structural Design Guidelines for Porous Asphalt Pavement

Porous asphalt pavements allow designers to introduce more sustainability into projects and lessen their environmental impact. Current design procedures are based primarily on hydrologic considerations; comparatively little attention has been paid to their structural design aspects. As their use grows, a design procedure and representative material structural properties are needed to ensure that porous pavements do not deteriorate excessively under traffic loads. The objective of this project was to develop a simple, easy to apply design procedure for the structural design of porous asphalt pavements. Two methodologies were considered for such a structural design procedure: ( a) the 1993 AASHTO Pavement Design Guide empirical approach, and ( b) the mechanistic–empirical approach employed by the AASHTOWare Pavement ME Design software. A multifactor evaluation indicated the empirical 1993 AASHTO design procedure to be the most appropriate platform at this time. It is noted, however, that both design procedures lack validation of porous asphalt pavements against field performance. AASHTO design parameters and associated material characteristics are recommended, based on an extensive literature review. For “thin” open-graded base structures (12 in. or less), the AASHTO procedure is performed as published in the 1993 Guide. For “thick” base structures (>12 in.), the base/subgrade combination is considered a composite system which supports the porous asphalt layer; an equivalent deflection-based approach is described to estimate the composite resilient modulus of the foundation system, prior to applying the 1993 AASHTO design procedure.

Mechanistic-Empirical design of perpetual pavement

Perpetual pavements use multiple, durable asphalt layers to produce a safe, smooth, long-lasting road. The pavement design begins with a strong, yet flexible bottom layer that resists tensile strain caused by traffic, and thus stops cracks from forming at the bottom of the pavement. Four perpetual pavement sections were designed and constructed in 2005 and currently are scheduled for rehabilitation for top-down surface cracking. These cracks have been confirmed by full-depth cores. This study revisited the design of these perpetual pavement sections using now available PerRoad and AASHTOWare Pavement ME Design software to investigate whether the design assumptions were correct. Fatigue lives of these sections were also evaluated based on bottom-up cracking. Layer moduli were backcalculated from the falling weight deflectometer (FWD) deflection data using the EVERCALC software. Tensile strains at the bottom of the asphalt layer were then computed. Results showed that predicted strain values derived from the mechanistic response models were lower than the tensile strains computed using moduli from the FWD deflection data. The required asphalt thickness from PerRoad was relatively higher than the asphalt thickness obtained from the AASHTOWare Pavement ME Design software over a 50-year design period. The study identified the most successful perpetual pavement design as the one with a rich bituminous mix in the base layer.

Approaches for local calibration of mechanistic-empirical pavement design guide joint faulting model: a case study of Ontario

ABSTRACT The Mechanistic-Empirical Pavement Design Guide (MEPDG) has been employed by agencies as an innovative method for pavement design since the National Cooperative Highway Research Program (NCHRP) Project 1-37A was implemented in 2004. Over the years, the MEPDG has evolved into the AASHTOWare Pavement ME Design software (AASHTOWare®). Local calibration of the performance models in the AASHTOWare® is a crucial and challenging task to improve the effectiveness of its application. The accuracy of the calibration depends on efficient methods and validation processes. This paper aims at developing local calibration methods for joint faulting prediction model of Jointed Plain Concrete Pavement (JPCP). This study not only focuses on improving the prediction accuracy of the joint faulting model but also demonstrating the various optimisation procedures in detail. A total of 27 representative JPCP sections were used in the processes of calibration. Three optimisation approaches were used: (1) One-At-a-Time (OAT) through the trial-and-error procedure, (2) generalised reduced gradient (GRG) using MS Excel® Solver, and (3) Levenberg-Marquardt Algorithm (LMA) fitting the functions. The prediction accuracy of local models was improved as compared with the global ones. Average Bias (AB) reduced from 0.3083 to 0.0578, and Standard Error of the Estimate (SEE) reduced from 0.3345 to 0.1912. Among the three local calibration approaches, approach 2 and approach 3 had more significant improvement on results than approach 1. Finally, the integral procedures were provided for local calibration in Ontario.

Structural performance and sustainability assessment of cold central-plant and in-place recycled asphalt pavements: A case study

This paper aimed at assessing the structural performance and sustainability of cold recycled asphalt pavements. Four cold recycling technologies were investigated, including the cold central-plant recycling with emulsified and foamed asphalt binders (i.e., CCPR-E and CCPR-F), and the cold in-place recycling with emulsified and foamed asphalt binders (i.e., CIR-E and CIR-F). Firstly, the laboratory tests were conducted to comprehensively evaluate the dynamic modulus, rutting, and cracking performance of cold recycled asphalt mixtures. Subsequently, these laboratory results were used to determine the inputs of cold recycled asphalt mixtures for the Pavement ME Design program, which was employed to predict the pavement performance. Meanwhile, the National Center for Asphalt Technology also constructed four cold recycled pavement sections in the field. The monitored and predicted pavement performance showed similar trends in the first two years, but the Pavement ME Design program over predicted the rut depth of these sections. The pavement performance results confirmed that the bottom-up fatigue cracking was a negligible distress mode for cold recycled asphalt pavements. In the following, the life cycle cost analysis and life cycle assessment were conducted to evaluate the four different cold recycling projects. The life cycle cost analysis results demonstrated that all of the four cold recycling projects yielded less net present values than the HMA project. The life cycle assessment data indicated that the cold recycling technologies reduced the energy consumption by 56–64%, and decreased the greenhouse gas emissions by 39–46%. Finally, this study found that the overlay and asphalt treated base thicknesses and climatic conditions had significant impact on the performance of cold recycled asphalt pavements.

Quantifying the impact of coefficient of thermal expansion of overlay concrete on unbonded concrete overlay performance

With the advancement in pavement design and performance analysis procedures, the coefficient of thermal expansion (CTE) of concrete has emerged as a significant design input with a direct impact on concrete pavement performance parameters including transverse cracking, joint faulting, and pavement roughness. CTE is the measure of change in concrete volume with temperature change and the resulting curling of concrete pavement slab is directly proportional to CTE. Un-Bonded Concrete Overlay (UBCO) is a cost-effective and sustainable rehabilitation technique on Jointed Plain Concrete Pavements (JPCP) to improve the performance of deteriorated concrete pavements. This study examines the effects of variability of CTE on the performance of unbonded JPCP overlays for two different climatic regions. Simulations were conducted using AASHTO pavement ME design software with varying CTE values in the range of 6.8–10.8 micro-strain/°C and keeping all other design variables as constant. The performance predictions were evaluated for different values of CTE and the results indicated that with an increase in CTE value, the performance of UBCO is adversely affected by the increase in pavement distresses. Amongst all the performance parameters, transverse cracking is the most significantly affected parameter with the change in CTE. The impact of geometric properties of overlay pavement including transverse joint spacing and slab thickness on the pavement performance was also analyzed which indicated that these have a direct impact on the performance parameters. The overlay performance can be improved by increased overlay slab thickness or reduced joint spacing and with these modifications, the adverse effects of higher CTE can be compensated. Field performance data of UBCO extracted from the LTPP database showed that the pavement ME design software can accurately predict the performance of UBCO pavement systems.