Hot-mix Asphalt Overlays Research Articles

Characterizing the cracking and fracture properties of geosynthetic interlayer reinforced HMA samples using the Overlay Tester (OT)

Reflective cracking is one of the undesirable distresses occurring in hot-mix asphalt (HMA) overlays; costing highway agencies millions of tax payer dollars in maintenance and rehabilitation activities. To mitigate this distress, crack-impeding interlayer materials such as geosynthetic interlayers are specified to protect the HMA overlays as part of maintenance and rehabilitation strategies. Currently however, there is no universally standardized laboratory crack test method to aid in the selection of the most appropriate geosynthetic interlayer material for maximum crack resistance and performance. This study was undertaken to evaluate the laboratory cracking-resistance and fracture performance of different geosynthetic interlayer materials embedded in HMA samples. As a means to investigate its applicability for testing interlayer materials, the Overlay Tester (OT), in a monotonic tensile loading mode (3.375mm/min) at 0°C, was explored as the study test method. Eight different geosynthetic interlayer products with different properties were compared to a ‘control specimen’ using a dense-graded HMA mix. Although field validation is still warranted, the study results indicated a substantial improvement (over 20%) in the laboratory crack and fracture performance of the geosynthetic interlayer reinforced samples over the Control samples; suggesting that use of these interlayer materials may be beneficial in mitigating reflective cracking in HMA overlays. For the test conditions considered, the OT test in monotonic tensile-loading mode also exhibited promising potential as a rapid crack test method for testing geosynthetic interlayer materials. The sample crack failure mode, test repeatability, and statistical variability in the test data were generally within reasonable expectations.

Simulation-Based Methodology for Developing Performance-Related Specifications for Pavement Preservation Treatments

AbstractCurrent materials and construction specifications for pavement preservation treatments are predominantly prescriptive and rarely correlate the initial quality of the treatment to its future performance. As a result, it is difficult for highway agencies to account for the performance lost or gained due to differences between the as-designed treatment and as-constructed treatment. Also, these specifications may not incentivize contractors to focus on factors that affect the treatment’s long-term performance. To account for these limitations, this paper provides a simulation-based performance-related specification (PRS) methodology for pavement preservation treatments, with application to thin hot-mix asphalt (HMA) overlays. Through performance prediction models and lifecycle cost analysis, this methodology determines pay factors based on the probability distributions of the total lifecycle costs of the as-designed and as-constructed treatments and the unit bid price. The developed PRS methodology wa...

Comparison of Fuzzy AHP and Fuzzy TOPSIS for Road Pavement Maintenance Prioritization: Methodological Exposition and Case Study

For road pavement maintenance and repairs prioritization, a multiattribute approach that compares fuzzy Analytical Hierarchy Process (AHP) and fuzzy Technique for Order Preference by Ideal Situation (TOPSIS) is evaluated. The pavement distress data was collected through empirical condition surveys and rating by pavement experts. In comparison to the crisp AHP, the fuzzy AHP and fuzzy TOPSIS pairwise comparison techniques are considered to be more suitable for the subjective analysis of the pavement conditions for automated maintenance prioritization. From the case study results, four pavement maintenance objectives were determined as road safety, pavement surface preservation, road operational status and standards, and road aesthetics, with corresponding depreciating significance weights ofW=0.37,0.31,0.22,0.10T. The top three maintenance functions were identified as Thin Hot Mix Asphalt (HMA) overlays, resurfacing and slurry seals, which were a result of pavement cracking, potholes, raveling, and patching, while the bottom three were cape seal, micro surfacing, and fog seal. The two methods gave nearly the same prioritization ranking. In general, the fuzzy AHP approach tended to overestimate the maintenance prioritization ranking as compared to the fuzzy TOPSIS.

A stochastic optimization approach for the selection of reflective cracking mitigation techniques

PurposeIn Hot Mix Asphalt (HMA) overlays, the existing cracks in the underlying pavements can propagate upward to the new added overlay and may cause Reflective Cracks (RC). These cracks allow water infiltration to the underlying layers and causes further moisture damage as well as weakening the unbound layers. Over the years, several methods have been developed for mitigating the RCs. This study aims to investigate the current reflective cracking mitigation methods and develop a methodology for the selection of appropriate mitigation technique. The developed model is then applied to a case study in the state of Florida. MethodTo accomplish this goal, a nationwide literature review was conducted to better understand the current in practice methods in the United States. Moreover, a life cycle cost analysis (LCCA) in five different road types was performed to find the annuity of roadway rehabilitation for each of the mitigation methods. The uncertainty in the LCCA results is represented using Exploratory Modeling and Analysis (EMA) method. Then through a Multi Criteria Decision Making (MCDM) model, a stochastic optimization model was developed to find the appropriate reflective cracking mitigation solution under Florida’s climate and road conditions, based on different cost and performance weights. ResultsBased on the available data for the state of Florida, the LCCA results indicate that the annuity of maintaining the roadway with Fabrics and ISAC are lower compared to other methods. However, the results of stochastic optimization model reveal that while looking at the performance and cost at the same time, different methods would be more feasible. For instance, while the cost of the used method does not matter at all and only performance matters, STRATA® is more probable to be the appropriate mitigation technique. The findings of this research are critical for decision makers to better understand the most cost-effective mitigation technique in different conditions.

Bayesian Model for Predicting the Performance of Pavements Treated with Thin Hot-Mix Asphalt Overlays

Recent studies suggest that thin hot-mix asphalt (HMA) overlay is one of the most frequently used preservation techniques for HMA pavements. This preservation treatment is often applied to address functional problems, such as roughness, raveling and weathering, and friction loss. A novel probabilistic model is provided for predicting the international roughness index (IRI) values of asphalt pavements treated with thin HMA overlay. The model consists of two tightly coupled components. The first component is a set of artificial neural networks responsible for predicting the IRI value of the existing pavement if no treatment is applied, and the second one is a set of Bayesian regression models responsible for predicting the reduction in IRI value owing to applying the thin HMA overlay. The model considers key design and material characteristics of both the existing pavement and the thin overlay, and site factors. The developed Bayesian models have less than 5% outliers (i.e., data points falling within either 2.5% tail area of model predictions), indicating high goodness of fit for these models. It is hoped that this IRI prediction model will enable pavement engineers to estimate the performance, service life, and life-cycle costs of thin HMA overlays.

Research of Rigid Pavement on Structure Combination of HMA Overlays

To study the influence of structure combination on performance of rigid pavement hot-mix asphalt (HMA) overlays, four Hot-mix asphalt overlays are prepared for the research at the base of long-term performance of experimental roads. The results indicate that the SMA +AC+SMA sandwich structure can effectively restrain reflective cracking and rut. In addition, the structure can reduce the thickness and cost of pavement.

Modeling flexible pavement overlay performance for use with quality-related specifications

Recent advancements have been made relating the constructed properties of bituminous materials to the flexible pavement performance over time. The research in this study explores one of the newly-developed prediction tools to assess its potential for designing longer-lasting asphalt mixtures in the state of Rhode Island. A parametric study was first conducted to establish performance-related specification (PRS) relationships for hot mix asphalt (HMA) overlays, which make up the majority of pavement projects in Rhode Island, using the Quality-Related Specification Software (QRSS). A framework was developed for use in setting post-construction targets for rutting performance in asphalt pavement overlays, in order to achieve the pay factors selected by the Rhode Island Department of Transportation and to encourage better quality construction. Because the majority of pavement construction done in Rhode Island involves flexible overlays, assumptions involving mixture densification due to traffic, distress severity levels, and aging rates were made to enable the proposed modeling of an overlay as two newly constructed layers in order to overcome the limitations in the QRSS software. Regression equations showed a significant percentage of predictive model predicted life differences (PLD) can be captured by utilizing a relationship between PLD and the difference between as-built and job mix formula (JMF) effective dynamic modulus (|E*|) values. The analysis showed that structural thickness and binder viscosity are critical to predicting PLD. Results showed that the PLD in terms of overlay rutting performance does not vary significantly with realistic adjustments to the as-built targets. Judging by the level of importance associated with stiffness values throughout the program, a procedure seeking to relate stiffness directly to service life with a small number of variables appears to be an optimal choice for future endeavors. By relating stiffness, major input categories (structural design, traffic, etc.), and service life, software users can predict a service life parameter, without embarking on a full mixture design process or |E*| testing sweep. It is recommended that a model be developed for alligator cracking and top-down cracking in HMA overlays using structural thickness, binder viscosity, and the |E*| of the constructed asphalt mixture.

Effects of an Asphalt Rubber Membrane Interlayer on Pavement Reflective Cracking Performance

AbstractWhen hot mix asphalt (HMA) overlays are placed on distressed flexible or rigid pavement, it is only a matter of time before cracks in existing pavement reflect to the new overlay surface. Asphalt rubber membrane interlayer (ARMI) is one type of interlayer system that has been suggested to mitigate reflective cracking in HMA overlay. However, in terms of reflective cracking performance, mixed results were reported. Also, the ARMI layer has the potential to contribute to instability rutting. In this study, composite specimen interface cracking (CSIC) tests were performed on composite specimens constructed with and without the ARMI layer to evaluate its effects on HMA overlay reflective cracking performance. HMA fracture mechanics was employed to characterize the mechanism of ARMI layer effects on HMA overlay reflective cracking resistance. Results indicate that ARMI not only cannot delay reflective cracking, but it also reduces reflective cracking resistance to some extent.

Strain response of hot-mix asphalt overlays in jointed plain concrete pavements due to reflective cracking

Reflective cracks appear in asphalt overlays placed on top of a concrete pavement above the locations of joints and cracks in the concrete slab. This paper presents the results of a finite element study on the response at the bottom of the HMA overlay. The effects of subgrade and subbase strengths, vehicle speed, overlay thickness, and pavement temperature are investigated in order to identify the parameters involved in the deterioration of the overlay. An extrapolation of the strain history curve for various pavement design parameters is presented to estimate the number of load repetitions that lead to bottom–up crack initiation.

Impact of Three State Practices on Effectiveness of Hot-Mix Asphalt Overlay

The effectiveness of pavement treatments is a function of several factors, including material quality, design, distribution of pavement condition states (conditions and rates of deterioration) before treatment, and construction quality. Because of these factors, state highway agencies have established estimates of treatment service lives with significantly wide ranges. These wide ranges make the calculation of treatment benefits or effectiveness a difficult task unless the role of each factor that affects service life is well understood. This study analyzed the impacts of the state of the practice of Colorado, Louisiana, and Washington on the effectiveness of thin (< 2.5 in.) hot-mix asphalt (HMA) overlay treatment. This paper reports that analysis of time-series pavement condition and distress data of previously treated pavement sections can be tabulated in a matrix format to demonstrate a snapshot examination of past practice. Such matrices are called treatment transition matrices (T2Ms). The data in the matrices express the probability that a pavement treatment will have certain effectiveness. T2Ms for pavement projects subjected to thin HMA overlays by three state highway agencies are discussed. Differences in treatment effectiveness were related to differences in the state of the practice in the three states. Selection of treatment timing and project boundaries significantly affected treatment effectiveness, and similar states of the practice yielded similar treatment effectiveness.

An analysis of the cost-effectiveness of rigid pavement rehabilitation treatments

This paper analyses the costs, effectiveness, and cost-effectiveness of three standard rehabilitation treatments of rigid pavements using historical data from the state of Indiana. Treatments investigated are Hot Mix Asphalt (HMA) Overlay, Patching, and Portland Cement Concrete (PCC) Overlay. Performance criteria used are the sudden decrease in surface roughness after treatment, treatment service life, and increase in average pavement condition over the service life. Cost-effectiveness is the ratio of treatment effectiveness to treatment cost. Results suggest that Patching and PCC Overlay treatments are the most effective on the basis of short term and long term effectiveness, respectively. The results also show that at relatively small levels of traffic loading, a change in climatic severity has greater influence on treatment effectiveness than that at higher levels of traffic loading. On the basis of cost-effectiveness, the results suggest that PCC Patching appears to be the best treatment.

Field Evaluation and Cost-Effectiveness of Saw and Seal Method to Control Reflection Cracking in Composite Pavements

The Louisiana Department of Transportation and Development has tested various techniques and treatments to control reflection cracking in composite pavements since the 1970s. However, the performance and cost-effectiveness of these methods have not been consistently evaluated. The objective of this study was to evaluate the performance of hot-mix asphalt (HMA) overlays of portland cement concrete pavement sections built with the saw and seal method across the state and to assess the cost-effectiveness of this treatment method. To achieve this objective, projects with sufficient years in service and with available untreated segments were selected for detailed performance and economic evaluation. The performance of 15 different pavement sections constructed with the saw and seal method was monitored for 6 to 14 years. From the results of the analysis, it was concluded that the majority of the sites showed a positive improvement with use of the saw and seal method: 40% of the sections showed an improvement in service life from 1 to 3 years and 47% of the evaluated sections showed an improvement ranging from 4 to 12 years. The average level of improvement to the pavement service life was 4 years. The vast majority of sections (80%) indicated that the saw and seal method was cost-effective as compared with regular HMA overlays. This treatment method appeared to be more cost-effective for low to medium traffic volumes. Finite element results validated that joints constructed in the HMA overlay allowed it to move with the underlying layer and to dissipate energy generated from expansion and contraction in the concrete layer and from wheel loading without cracking.

Analysis of Rutting Performance Impacting Factors in HMA Overlay Mixture Design

It is reasonable to assume that hot-mix asphalt (HMA) overlay rutting occurs only in HMA overlay(s) because of rutting from the existing pavement, if any, most of which had already occurred before the HMA overlay(s) was placed. So, this paper focuses only on the HMA overlay itself. Many factors—such as the asphalt binder grade, the aggregate gradation, the types of aggregates, the volumetric parameters of the mixtures, etc.—potentially influence the HMA rutting performance when designing an HMA overlay mix. In this paper, a Hamburg Wheel Tracking Test (HWTT) device is employed in order to evaluate the rutting performance of HMA overlay mixes in terms of the rut depth at specified wheel passes. An experimental design is developed to cover the different combinations of aggregates, gradations, and asphalt binder types. Through extensive laboratory tests and statistical analyses, the most significant impacting factors were identified. The corresponding HWTT rut depth prediction models were developed with high R2 values (>0.80). With these models and established rut depth criteria, the maximum allowable asphalt content that can be used without causing rutting problems was estimated for different overlay mixes. Furthermore, the models and estimated maximum allowable asphalt content were preliminarily verified by performance data of the National Center for Asphalt Technology test track sections and WesTrack test sections.

Sand Mix Interlayer to Control Reflective Cracking in Hot-Mix Asphalt Overlay

This study examines the behavior of traffic-induced reflective cracking in hot-mix asphalt (HMA) overlays with and without a sand mix interlayer and evaluates the interlayer's performance to control reflective cracking. A three-dimensional finite element (FE) model was built for a typical HMA overlay constructed over a jointed concrete pavement. A linear viscoelastic model and a bilinear cohesive zone model were incorporated into the FE model to characterize continuum and fracture behavior of the HMA overlay and the sand mix interlayer. One pass of an overload was applied to force reflective cracking development. Then the reflective cracking resistance capacity of the HMA overlay was quantified with a limit-state load that resulted in macrolevel reflective cracking in the entire cross-sectional area of the HMA overlay. This study found that the sand mix interlayer enhanced the reflective cracking resistance capacity of the HMA overlay by a factor of 1.17 to 2.45 because of the sand mix's higher fracture toughness. The performance benefit was more dominant at an early service life of the HMA overlay. As the elastic modulus of a base layer decreased, the reflective cracking potential was found to increase, but the sand mix interlayer was still effective in retarding reflective cracking.

Neural Networks Modeling of Stress Growth in Asphalt Overlays due to Load and Thermal Effects during Reflection Cracking

Although several techniques have been introduced to reduce reflective cracking, one of the primary forms of distress in hot-mix asphalt (HMA) overlays of flexible and rigid pavements, the underlying mechanism and causes of reflective cracking are not yet well under- stood. Fracture mechanics is used to understand the stable and progressive crack growth that often occurs in engineering components under varying applied stress. The stress intensity factor (SIF) is its basis and describes the stress state at the crack tip. This can be used with the appropriate material properties to calculate the rate at which the crack will propagate in a linear elastic manner. Unfortunately, the SIF is difficult to compute or measure, particularly if the crack is situated in a complex three-dimensional (3D) geometry or subjected to a non- simple stress state. In this study, the neural networks (NN) methodology is successfully used to model the SIF as cracks grow upward through a HMA overlay as a result of both load and thermal effects with and without reinforcing interlayers. Nearly 100,000 runs of a finite-element program were conducted to calculate the SIFs at the tip of the reflection crack for a wide variety of crack lengths and pavement structures. The coefficient of determination (R 2 ) of all the developed NN models except one was above 0.99. Owing to the rapid prediction of SIFs using developed NN models, the overall computer run time for a 20-year reflection cracking prediction of a typical overlay was significantly reduced. DOI: 10.1061/(ASCE)MT.1943-5533.0000153. © 2011 American Society of Civil Engineers. CE Database subject headings: Cracking; Neural networks; Predictions; Models; Finite element method; Thermal factors. Author keywords: Reflective cracking; HMA overlay; Neural networks; Prediction model; Fracture mechanics; Finite element.

Development, Calibration, and Validation of a New M-E Rutting Model for HMA Overlay Design and Analysis

The purpose of this paper is to present a new mechanistic-empirical (M-E) rutting model developed for hot-mix asphalt (HMA) overlay thickness design and analysis. After reviewing existing rutting models in the literature, it was found that the well-known VESYS layer rutting model still is a rational choice and was adopted with minor modification to model HMA overlay rutting development. The main feature of the proposed M-E HMA overlay rutting model is to characterize layer specific permanent deformation properties rather than global rutting parameters used in the Mechanistic-Empirical Pavement Design Guide. For each specific layer, the proposed model requires rutting parameters α and μ; and these rutting parameters, which are two of the fundamental input parameters required in the proposed M-E rutting model, can be directly determined from the repeated load test following the test protocol discussed in the paper. Additionally, the proposed M-E HMA overlay rutting model was calibrated using 8 test sections of the National Center for Asphalt Technology (NCAT) Test Track 2006, and the calibrated model was further validated using two sets of independent rutting data: three test sections of the NCAT Test Track 2000 and four test sections of Special Pavement Study 5 on US175, Texas. Thus far, satisfactory results have been obtained. However, more field performance data are needed for further model improvement.

Development, Calibration, and Verification of a New Mechanistic-Empirical Reflective Cracking Model for HMA Overlay Thickness Design and Analysis

The purpose of this paper is to present a new mechanistic-empirical (ME) reflective cracking model developed for hot-mix asphalt (HMA) overlay thickness design and analysis. After reviewing existing models, the reflective cracking model based on Paris’ law of fracture mechanics was considered as the state of the practice and was selected as the basis for the ME model development in this study. The model consists of stress intensity factor and fracture properties (A and n) as the fundamental input parameters for modeling reflective crack propagation caused by both traffic loadings (bending and shearing) and thermal effects (temperature variations). For practical application, 32 SIF regression equations were developed for HMA overlays with three levels of load transfer efficiencies (10, 50, and 90%) at joints/cracks under various traffic loading spectrums (bending and shearing) based on more than 1.6 million finite element simulations and computations. For the thermal induced reflective cracking, a “hybrid” approach, similar to the Strategic Highway Research Program low temperature cracking model, was proposed. In this hybrid approach, the viscoelastic properties of the HMA mixes were considered through the thermal stress at the “far field” (σVE-far), which then ties with the stress intensity factor (Kthermal) determined through regression equations. Also, the required fracture properties (A and n) can easily be determined in the laboratory using the overlay tester that has unique features with respect to specimen size, specimen preparation, and relatively short testing time (about 15 min). Additionally, the proposed reflective cracking model was preliminarily calibrated using three HMA overlay field-case studies, and then verified using California’s heavy vehicle simulator test results. Currently, more calibration is underway, but more field performance data are definitely needed for further model calibration and verification.

Costs and Benefits of Thin Surface Treatments on Bituminous Pavements in Kansas

This study investigated the benefits and costs of commonly used thin surface treatments for maintenance of bituminous pavements in Kansas. Cost and performance data were collected from the Kansas Pavement Management Information System for all treatments applied from 1992 to 2006. Results show that seal coats have a short average service life on Interstate highways. The average life on non-Interstate highways is about 4 years. This life is slightly lower than that for other thin surface treatments, including hot-mix asphalt (HMA) overlays. Seal coats also have a significantly lower equivalent uniform annual cost than do all other thin surface treatments in Kansas. A comparison of pavement benefit values before and after application showed that seal coat could not mitigate distresses better than other methods, especially thin HMA overlays. However, its performance is quite similar to that of the modified slurry seal.

Prediction of Reflection Cracking in Hot-Mix Asphalt Overlays

Reflection cracking is one of the main distresses in hot-mix asphalt (HMA) overlays. It has been a serious concern since the early 20th century. Until now, only limited research has been performed to predict reflection cracking. Mechanistic-based models were calibrated to field data to produce a design process for predicting reflection cracks. Three cracking mechanisms (bending, shearing traffic stresses, and thermal stress) were taken into account to evaluate the rate of growth of the three increasing levels of distress severity (low, medium, and high). The cumulative damage done by all three cracking mechanisms is used to predict the number of days for the reflection crack to reach the surface of the overlay. The result of this calculation is calibrated to the observed field data (severity and extent), which has been fitted with an S-shaped curve. In the mechanistic computations, material properties and fracture-related stress intensity factors are generated using efficient artificial neural network algorithms. The axle load spectra were used to represent traffic stresses, and a new model of predicting pavement temperature was incorporated into the thermal stress model. The HMA overlay was over either asphalt pavement or jointed concrete pavement in all four major climatic zones. The results of this calculated mechanistic approach showed HMA's ability to efficiently reproduce field observations of the growth extent and severity of reflection cracking. The computer running time for a 20-year prediction of a typical overlay was between 1 and 4 min.

Performance of Recycled Hot-Mix Asphalt Overlays in Rehabilitation of Flexible Pavements

The most frequent application of recycling materials in pavements is the reuse of reclaimed asphalt pavement (RAP) to produce recycled hot-mix asphalt (HMA). When designed properly, RAP mixes have demonstrated quality comparable to virgin HMAs in laboratory tests. Despite all the information available about the quality of RAP mixes, obstacles still promote their more frequent use in pavement engineering. Short- and long-term field performance of RAP mixes was investigated compared with virgin HMA overlays used in flexible pavements. Data from the 18 Specific Pavement Studies-5 (SPS-5) sites from the Long-Term Pavement Performance program located across the United States and Canada were used. Performance data were collected during periods ranging from 8 to 17 years. Repeated measures analysis of variance was the statistical analysis tool chosen, pairing distress measurements with survey dates to compare performance and response. The results suggest that in the majority of scenarios RAP mixes have performance statistically equivalent to virgin HMA mixes. The statistical equivalency of deflections suggests that RAP overlays can provide structural improvement equivalent to virgin HMA overlays.