Shelley M Stoffels

Network-Level Pavement Roughness Prediction Model for Rehabilitation Recommendations

Pavement performance models are key components of any pavement management system (PMS). These models are used in a network-level PMS to predict future performance of a pavement section and identify the maintenance and rehabilitation needs. They are also used to estimate the network conditions after the application of various maintenance and rehabilitation alternatives and to determine the relative cost effectiveness of each maintenance and rehabilitation alternative. Change in pavement surface roughness over time is one of the most important performance indicators in this regard. A model for changes in the international roughness index (IRI) over time was developed through artificial neural networks (ANNs) pattern recognition, using information from the Specific Pavement Study (SPS)-5 asphalt concrete rehabilitation experiment extracted from FHWAs Long-Term Pavement Performance database. This model can be used to predict and compare pavement roughness variation trends after various rehabilitation alternatives. An example illustrates the implementation of the roughness model along with life-cycle cost analysis in making future pavement rehabilitation recommendations. Model testing results indicate prediction of IRI with minimal errors, and predicted future roughness trends match perfectly with the past performance. These findings indicate that the ANN model performs successfully in predicting IRI trends following each kind of treatment in the SPS-5 experiment. The ANN model was developed for the SPS-5 flexible pavement rehabilitation sections in a wet–freeze climate and may be applied for similar conditions. The example also shows that the detailed model development and implementation framework provided in this study can assist in network-level PMS decision making.

Optimization of Asphalt Pavement Modeling based on the Global-Local 3D FEM Approach

ABSTRACT This paper presents the use of three dimensional (3D) finite element modeling (FEM) techniques to determine asphalt pavement response to loading. In mechanistic-empirical pavement design, the properties of materials used in pavement layers must be specified before the pavement response to imposed loads can be determined. A numerical method is used to obtain the relaxation modulus of linear viscoelastic materials, such as asphalt concrete, from the dynamic modulus measured on specimens procured from the field. Linear elastic behavior is assumed for granular materials. In addition, regarding finite element modeling, key factors such as model geometry, material properties, load and boundary conditions, element type, and mesh refinement are discussed in detail. The adopted Global-Local (GL) FEM approach is capable of simulating pavement responses to multiple axle loads with different load configurations, speed, and temperatures.

PENNSYLVANIA SPS-6 PERFORMANCE AT 10 YEARS: EVALUATION OF CONCRETE PAVEMENT REHABILITATION STRATEGIES

With a long history of constructing jointed concrete pavements, Pennsylvania pursued the construction of Special Pavement Studies (SPS-6) sections for the rehabilitation of jointed concrete pavements experiment. After 10 years of service under very high loads on rural Interstate highways, a number of sections required renewal. The performances of the eight standard Strategic Highway Research Program sections, a control section, and three state supplemental sections were examined. The experiment included a broad range of treatments, including minimum and maximum concrete pavement restoration, the use of thin and thick overlays, and the use of crack or break and seat as well as rubblization as pretreatments for pavement overlays. Ten years after construction, many of the pavements that received the treatments are in need of major rehabilitation. This provides an opportune time to evaluate both the structural and functional performances of these test sections to date. Additionally, an evaluation of cost-effectiveness showed the importance of performing thorough evaluations of projects for rehabilitation and the potential benefit of rubblization of badly damaged jointed concrete pavements, a method used on the state supplemental sections, as a preoverlay strategy.

Reinforcement Tensile Behavior Under Cyclic Moving Wheel Loads

Numerous studies have revealed the benefits of using geogrids in a flexible pavement, especially for reducing permanent deformation. One of the questions that remain about the effectiveness of a geogrid in reinforcing of pavement is the extent to which the geogrid is engaged and mobilized throughout its service. This paper presents results of a laboratory study on various geogrid products embedded in flexible-pavement sections. The laboratory-scale pavement sections were subjected to cyclic moving wheel loads by using reduced-scale accelerated pavement testing (APT). During the APT, strains that developed in the geogrids were measured at intervals of loading applications by strain gauges installed in pairs on the upper and lower surfaces of the geogrid ribs. Permanent deformation of the subgrade was also measured at the same intervals of loading applications. The measurements of geogrid strains throughout the construction process indicated that the construction resulted in a considerable prestressing effect on the geogrids. Measurements from the individual strain gauges in pairs showed that the gauges installed on the upper surfaces of the ribs were in compression while those on the lower surfaces were in tension; the situation suggested a significant effect on the flexural deflection of the ribs on the tensile strain measurements from the strain gauges. Furthermore, it was observed that geogrid ribs in the longitudinal direction of traffic loading were not mobilized, while considerable strains were developed in geogrid ribs in the direction transverse to traffic loading. A clear correlation was found between the reinforcing forces developed in the geogrids and the performance of the reinforced subgrade in relation to resisting permanent deformation.

ROAD USER COST MODELS FOR NETWORK-LEVEL PAVEMENT MANAGEMENT

Life-cycle cost analysis (LCCA) of pavements is a process for evaluating total economic worth of a usable project segment by analyzing initial costs and discounted future costs, such as those for maintenance, reconstruction, rehabilitation, and resurfacing. One of the most important ingredients in the LCCA process, at either a network level or a project level, is the determination of road user cost (RUC) during maintenance and rehabilitation operations. RUC models are also important in contracting strategies, which take into account time for a project to be completed for award and payment. Methods used to date to determine RUC are exclusively analytical in nature. Microscopic estimates of traffic are used to determine RUC. CORSIM, a microscopic traffic simulation program developed by FHWA, was used for this research. Models for additional travel time, added fuel consumption, and RUC for standard two-to-one lane closure scenarios are presented.

Permanent deformation behaviour of reinforced flexible pavements built on soft soil subgrade

This study focuses on evaluating the effectiveness of using various geogrid products to improve permanent deformation resistance in soft subgrade soils commonly encountered during roadway construction in Pennsylvania. Permanent deformation behaviours of the soft soils both with and without the inclusion of geogrids were investigated. Cyclic moving wheel loads were applied through a reduced-scale accelerated pavement testing (APT) device, a one-third-scale model mobile load simulator (MMLS3). Tests were conducted on two soil types, each modified with three different biaxial geogrids placed at the base–subgrade interface. The total permanent deformation/surface rutting of the pavement and the permanent deformation of the subgrade were measured at selected intervals of the wheel loading applications. The pavement sections were trenched upon completion of the accelerated testing to measure the deformed profiles of the cross sections from which the permanent deformations in the asphalt layer and the base layer were determined. Sections modified with geogrids were found to have similar performance with the control section in terms of the total permanent deformation. While the geogrids did not show significant effects on the asphalt layer permanent deformation, sections with geogrids consistently showed a significantly higher base layer permanent deformation as compared to the control sections. Measurements of the subgrade permanent deformation showed that two of the geogrids consistently reduced the permanent deformation of subgrade built with the two types of soft soil. The relative layer contribution to the total permanent deformation suggested a base layer failure in both sets of the accelerated tests, most likely due to the inadequate compaction of the base layer during construction. Sections modified with geogrids exhibited a significantly higher base layer contribution, along with a significantly lower subgrade contribution, to the total permanent deformation, whereas the control section showed the opposite of the layer contributions.

Fully Coupled Three-Dimensional Train-Track-Soil Model for High-Speed Rail

With the increase of train speed, track modeling has faced great challenges as traditional static or quasi-static analyses become insufficient. Many track models have not had a train model and defined the wheel–rail interaction force as a stationary, independent, and empirical loading profile. In fact, the wheel–rail contact force is a function of train–track interaction and is difficult to predetermine. Another limitation of two-dimensional track models is the lack of sophisticated three-dimensional soil parts; this deficiency becomes critical when train speed is high enough to cause significant wave motion in the subgrade soil. A fully coupled three-dimensional train-track-soil model is developed and verified by a benchmark finite element program. Case studies are then described to demonstrate the capability of this track model.

Use of creep compliance interconverted from complex modulus for thermal cracking prediction using the M–E pavement design guide

The objective of this study is to evaluate the creep compliance (D(t)) of asphalt concrete (AC) mixtures for thermal cracking prediction of flexible pavements. Various AC overlay design factors influencing the thermal cracking resistance of flexible pavements, such as mixture properties and pavement structure, were included in the evaluation. Two sources of D(t) data were considered: (1) measurement from indirect tensile test and (2) numerical interconversion of complex modulus E*. Design input levels in the mechanistic–empirical design guide software do significantly impact the predicted thermal cracking distresses. For AC maintenance overlay design purposes, level 1 and 2 analyses yield very similar thermal cracking predictions, whereas level 3 analysis significantly underpredicts the extent of cracking when compared with to level 1 analysis. Some discrepancy exists in the thermal cracking predicted from measured and interconverted D(t) due to the inherent approximation nature of numerical interconversion methods. However, level 1 and 2 analyses using interconverted D(t) values provide results closer to the predictions from measured D(t) values than does level 3. Three mixtures are used in this study. The various analyses indicate that using a more ductile AC mixture for the surface layer significantly reduces the amount of thermal cracking at failure.

Evaluation of Rigid Pavement Joint Seal Movement

The subject of sealing concrete pavement joints has been studied for many years, and a wealth of technology exists for successfully installing pavement joint seals. However, in practice, a great deal of inadequate performance has been observed by highway agencies in the United States in recent years. A primary reason for the observed problems is inadequate control of construction processes. Another very significant factor affecting the performance of joint seals is climatic conditions. Examined are the effects of climate on the movement of rigid pavement joints. Temperature, joint movement, and other data collected as a part of the Long-Term Pavement Performance (LTPP) program data collection for seasonal sites have been used to assess actual joint movements in various climatic conditions throughout the United States and Canada. These measured data are compared with theoretically calculated joint movements. In most cases the actual movements appear to be greater than those theoretically predicted. On the basis of measured joint openings from LTPP seasonal sections, the conclusion is made that the measured joint opening values are greater than joint opening values calculated using the AASHTO equation described below. The data also provide evidence that irregular joint openings are present at all the sites evaluated.

Field Instrumentation and Testing Data from Pennsylvania’s Superpave In-Situ Stress/Strain Investigation

The Pennsylvania Department of Transportation (PENNDOT) is sponsoring the Superpave In-Situ Stress/Strain Investigation (SISSI), which will complete its firth year in May, 2006. The purpose of the SISSI project is to provide data essential to the validation and regional calibration of Superpave and the Mechanistic-Empirical Pavement Design Guide (MEPDG). SISSI is a unique, state-of-the-art instrumentation and analysis project that encompasses eight different Superpave pavement sections across Pennsylvania, including both new pavements and overlays. The uniqueness of the SISSI project is that the selected pavement sections were instrumented as-designed and as-constructed on full-scale public highways, to represent actual practices and materials, without modification for this research, and with minimal interruption to the construction process. The sections are exposed to normal traffic, but evaluated seasonally and yearly using a loaded test vehicle. The project also takes advantage of the latest developments and equipment in the field of instrumentation technology for the full-scale investigation of pavement performance. The project includes detailed monitoring of the construction process, intensive materials characterization, detailed load-response information, traffic and environmental data, and performance measures. This paper briefly reviews the instrumentation and data collection at the eight sites. Examples are provided of the data acquired from the instrumentation, and the interpretation of that data. Data examples are included from the dynamic gauge response under the controlled truck loading and corresponding WIM (weigh-in-motion) analysis, and from the subsurface environmental gauges