Neeraj Buch

Effective layer temperature prediction model and temperature correction via falling weight deflectometer deflections

Surface deflections and backcalculated layer moduli of flexible pavements are significantly affected by the temperature of the asphalt concrete (AC) layer. The correction of these deflections and moduli to a reference temperature requires the determination of an effective temperature of the AC layer. In light of this, a new temperature prediction model for determination of the AC temperature on the basis of a database approach is presented, and temperature correction factors for AC modulus are developed. Temperature datum points (n = 317) and deflection profiles (n = 656) were collected from the six in-service test sites in Michigan. Temperature datum points (n = 197) from three of the test sites were used to develop the temperature prediction model, and data from the remaining sites were used for validation. The temperature prediction model developed has an R2 value greater than 90 percent and an F-statistic significantly greater than 1.0. For further validation of the temperature prediction model, temperature datum points (n = 18,444) from seven Seasonal Monitoring Program sites (Colorado, Connecticut, Georgia, Nebraska, Minnesota, South Dakota, and Texas) were obtained from DATAPAVE, version 2.0 (Long-Term Pavement Performance program database). The validation results suggested that the model could be adapted to all seasons and other climatic and geographic regions. The major improvements over existing models are that (a) the model does not require temperatures for the previous 5 days, (b) it takes into account temperature gradients due to diurnal heating and cooling cycles, and (c) it needs fewer parameters than other published models. The effect of temperature prediction error on the performance prediction was also investigated.

Development of Fatigue Cracking Prediction Model for Flexible Pavements

Fatigue cracking is one of the major failure modes in flexible pavements. Prediction of fatigue life is commonly encountered in the mechanistic-empirical (M-E) flexible pavement design as a transfer function that relates the pavement responses to pavement performance. Thus, development of accurate fatigue cracking prediction models is an ongoing pursuit of the pavement engineering community. This has resulted in a plethora of fatigue prediction models ranging from purely mechanistic to empirical. This paper presents the development of a mechanistic-empirical fatigue cracking prediction model using data from in-service flexible pavements in Michigan, USA. For further validation, three flexible pavement design cases were obtained from the Michigan Department of Transportation (MDOT) and were then compared to the proposed M-E design using the proposed fatigue cracking prediction model as a transfer function.

Experimental Investigation of Effects of Dowel Misalignment on Joint Opening Behavior in Rigid Pavements

Experimental investigations were conducted to determine the fundamental joint opening behavior of concrete pavements and to evaluate the effects of dowel misalignment on this behavior. The parameters included in the experimental investigations were the number of dowel bars (one, two, three, or five) at the joint, the dowel misalignment type (horizontal, vertical, or combined), misalignment magnitude (0, 1/36, 1/18, 1/12, 1/9 rad), and uniformity across the joint. The effects of these parameters were evaluated for the joint opening behavior and structural distresses observed in the specimens. Forty-seven instrumented laboratory-scale specimens of pavement slabs with doweled joints were tested. The experimental results include the load per dowel-joint opening behavior and observations of structural distress. These results indicate that (a) all pavement joints are initially locked, and opening displacements occur after the load per dowel exceeds 5 to 7 kN or the average bond shear stress exceeds 0.22 to 0.30...

Development of traffic inputs for Mechanistic-Empirical Pavement Design Guide in Michigan

Characterizing traffic and developing accurate and desirable traffic inputs for the new Mechanistic–Empirical Pavement Design Guide (MEPDG) are critical but challenging activities. The purpose of this study was to develop a process for characterizing traffic inputs in support of the new MEPDG for the state of Michigan. These traffic characteristics include monthly distribution factors, hourly distribution factors, truck traffic classifications, axle groups per vehicle, and axle load distributions for different axle configurations. Axle weight and vehicle classification data were obtained from 44 weigh-in-motion and classification stations located throughout the state of Michigan to develop Level 1 (site-specific) traffic inputs. Cluster analyses were conducted to group sites with similar characteristics for development of Level 2 (regional) inputs. Finally, data from all sites were averaged to establish the statewide Level 3 inputs. The effects of the developed hierarchical traffic inputs on the predicted performance of rigid pavements were investigated with the MEPDG models. An algorithm based on discriminant analysis was developed to acquire the appropriate Level 2 traffic characteristic inputs for pavement design. For pavement analysis and design, it is recognized that site-specific data should be used wherever available. For projects in which site-specific data are not available, it is necessary to know whether Level 2 or Level 3 data are acceptable at a minimum for design. The MEPDG was used to investigate the impact of traffic input levels on predicted pavement performance for rigid pavements. The results of the analysis showed that for pavement design in Michigan, statewide averages should be used instead of MEPDG Level 3 data.

COST-EFFECTIVE PREVENTIVE MAINTENANCE: CASE STUDIES

With most of the highway systems in place, emphasis has shifted from design and construction to preservation and expansion. Unfortunately, the engineering skills, knowledge, and experience required to preserve the systems are significantly different than those required to originally design and build the systems. The experience gained in the initial phase, although important, is not in itself sufficient to preserve the systems. Pavement preservation is defined as the sum of all activities undertaken to provide and maintain serviceable roadways. This includes corrective maintenance and preventive maintenance, as well as minor rehabilitation projects. A cost-effective pavement preservation program requires a systematic and comprehensive engineering management of, and a solution to, pavement network problems. Preventive maintenance (PM) is defined by AASHTO as the “planned strategy of cost-effective treatments to an existing roadway system and its appurtenances that preserves the system, retards future deterioration, and maintains or improves the functional condition of the system (without increasing the structural capacity).” Hence, PM actions must be taken on pavements in relatively good condition. The development and implementation of a cost-effective PM program faces several obstacles: political debate, budget constraints, lack of education, and the existing practice of “worst pavements are first.” Some state highway agencies have overcome these obstacles, and they are harvesting the success of their PM programs. The state of the practice of three agencies—those of Arizona, Montana, and Pennsylvania—is presented and discussed.

Experimental and Analytical Investigations of Mechanistic Effects of Dowel Misalignment in Jointed Concrete Pavements

This paper presents the results of experimental and analytical investigations on the effects of dowel misalignment on the joint opening behavior and distress in concrete pavement joints. It focuses on the development of three-dimensional (3-D) finite element models for computing the complex stress states and resulting damage in concrete pavement joints with misaligned dowels and, through experimental results, their validation. The concrete pavement is modeled by using a damage–plasticity material model, which uses concepts of damage–plasticity formulation in compression and cracking combined with damage elasticity in tension. The longitudinal bond between the steel dowel and the concrete is modeled in two parts. First, the longitudinal bond resulting from chemical adhesion, mechanical interlock, and static friction (in the aligned state) is modeled by means of spring elements. The nonlinear force–deformation relationship for the spring elements is derived from specific experimental results. Second, the longitudinal bond resulting from transverse interaction between steel dowels and the concrete pavement is modeled by surface-to-surface contact interaction elements and associated friction models. The 3-D finite element models are validated by the results of experimental investigations. These validated models provide significant insight into the 3-D stress states and principal stresses that develop in concrete pavement joints with misaligned dowels. They are used to evaluate analytically the effects of misalignment type, magnitude, uniformity, and distribution on the 3-D stress states and resulting damage in concrete pavements.

Analytical Investigation of the Effects of Dowel Misalignment on Concrete Pavement Joint Opening Behaviour

Experimental and analytical investigations were conducted to evaluate the effects of dowel misalignment on the joint opening behaviour and associated distresses in concrete pavement joints. The experimental investigations focused on pavement specimens with one or two misaligned dowel bars at the joints, and the results included the pull-out force-joint opening responses and the observations of damage (spalling, cracking, etc.). Numerical models of the pavement specimens were developed to gain additional insight into the behaviour, 3D stresses and strains, and localised damage associated with the misaligned dowel bars. These models accounted for (a) concrete inelasticity in compression and cracking in tension and (b) the longitudinal bond and the transverse interaction between the dowel and the concrete pavement. The models were verified using experimental results and used to identify the occurrence of various material damage limit states (debonding, concrete cracking, etc.) on the joint opening behaviour. The verified models were used to conduct parametric analyses to expand the experimental database and develop comprehensive knowledge of the effects of dowel misalignment on joint opening behaviour. The results were used to develop recommendations for dowel misalignment tolerances.

MECHANISTIC-EMPIRICAL RUT PREDICTION MODEL FOR IN-SERVICE PAVEMENTS

Rutting is a major mode of failure in flexible pavements. Development of accurate predictive rut performance models is an ongoing pursuit of the pavement engineering community. This has resulted in a plethora of rut prediction models ranging from purely mechanistic to empirical. Presented is the development of a mechanistic-empirical rut prediction model that uses data from 39 in-service flexible pavements from Michigan. The proposed model accounts for the rut contribution of the subgrade, subbase, base, and asphalt concrete layers. The model addresses inventory-type variables like pavement cross section, ambient temperature, and asphalt consistency properties. The applicability of the model was validated by using data from 24 Long-Term Pavement Performance–Global Positioning System (GPS) sites. For 19 of the 24 GPS sites, the predicted rut depth was within 5 mm of the measured rut depth.

FLEXIBLE PAVEMENT DESIGN IN MICHIGAN: TRANSITION FROM EMPIRICAL TO MECHANISTIC METHODS

Michigan is rapidly moving toward adopting and using a mechanistic-empirical design for flexible pavements. To facilitate the transition from empirical to mechanistic design methods, the Michigan Department of Transportation contracted the development of software called the Michigan Flexible Pavement Design System (MFPDS). This software provides a holistic framework for analyzing and designing flexible pavements. MFPDS includes modules for AASHTO design, linear and nonlinear mechanistic analysis, backcalculation, and mechanistic design (including overlay design). The software incorporates enhanced elastic layer and finite element models within an easy-to-use Windows user interface and can be used on a routine basis. New response models to predict fatigue life and rut depth also were developed as part of this effort and are included in MFPDS. New pavements and overlays may be designed to limit predicted distresses to user-specified threshold values. The features of the mechanistic analysis and design approaches used are presented.

Development of Dowel Looseness Prediction Model for Jointed Concrete Pavements

The results of an in-depth study of factors that affect dowel looseness in jointed concrete pavements are presented. The laboratory investigation revealed the influence of aggregate type (in relation to oxide content), aggregate texture and shape, bearing stress (dowel diameter and crack width), load magnitude, and number of load cycles on the magnitude of dowel looseness and the subsequent loss in load transfer efficiency across saw-cut joints. A discussion is included on the development of an empirical-mechanistic dowel looseness prediction model based on the experimental results. Results of the sensitivity analysis of the dowel looseness prediction model (using laboratory data) are also presented. An associated scope of this research was to develop a relationship between dowel looseness and loss of load transfer efficiency. The sequential use of the dowel looseness prediction model and its relationship to load transfer efficiency allows the design engineer to predict load transfer characteristics of a ...