Performance-related Specifications Research Articles

Principles for Incorporating Recycled Materials into Airport Pavement Construction for More Sustainable Airport Pavements

Current international waste policy promotes the reduction and re-use of waste materials, and in some cases, specifically calls for the use of recycled materials in pavements. Consequently, there is a need to understand the performance of recycled materials in airport pavements, as well as the overall sustainability benefit. This paper reviews several recycled materials and their applications to asphalt concrete, cement concrete, and bound and unbound granular materials in the context of airport pavements. Additionally, it reviews sustainability quantification methods, as well as implementation challenges for using recycled materials in airport pavements. For comparing pavements with and without recycled materials, a triple bottom line approach is appropriate. The triple bottom line approach should use life cycle cost assessment and life cycle assessment for the financial and environmental impacts, respectively, as best-practice, with frameworks and guidelines already established. For social impacts, it is recommended to quantify the reduction in virgin material use which relates to intergenerational equity by ensuring access to materials by future generations. Because there are still implementation challenges for the airport pavement industry, principles are developed that aim to promote uptake of recycled materials. These principles include sorting and processing, minimising haulage distances, and ensuring performance of pavement layers through performance testing and performance-related specifications.

Experimental and Computational Fluid Dynamic Study of Water Flow and Submerged Depth Effects on a Tidal Turbine Performance

This study involves an experimental and numerical analysis of the Hunter turbine, a vertical axis turbine utilized for tidal energy. A laboratory model of the Hunter turbine, featuring an aspect ratio of 1.2, was designed and tested. Numerical equations, including the Reynolds-averaged Navier–Stokes (RANS) constant, were analyzed through computational fluid dynamics (CFD) software using the k-ω turbulence model to forecast turbine performance and other related flow specifications, such as pressure lines, stream velocity, and pressure. This simulation was conducted on the surface of the turbine blade, and the results were obtained accordingly. The experimental data were utilized to verify the numerical results, and the difference between the two was reasonably acceptable. The turbine was studied in six different flow coefficients and four different vertical positions. The results indicated that the power coefficient increased as the submerged depth from a water-free surface increased, and after a specific depth, the output power remained constant. It was also observed that the minimum depth from a water-free surface for maximum power coefficient was three times the diameter of the turbine drum (3D).

Case Studies of Asphalt Pavement Quality Assurance Specifications, Performance-Related Specifications, and Performance-Based Specifications

Quality assurance (QA) specifications for asphalt pavement construction measure quality characteristics to adjust payments. The measured quality characteristics are assumed to empirically relate to performance. The validity of this assumption, however, has been questioned in recent years; thus, there has been increased interest in finding ways to more directly evaluate the performance of the as-constructed materials. One proposed method to meet this need involves using the Asphalt Mixture Performance Tester (AMPT) and its associated test methods, which measure fundamental material properties that are then used to calculate the fatigue cracking performance index, Sapp, and a rutting strain index (RSI). These indices can be used in performance-related specification (PRS) or performance-based specification (PBS) frameworks to determine the pay adjustments during the construction of asphalt pavement. While PBS requires measured indices, PRS uses index-volumetrics relationships (IVRs) to predict Sapp and RSI based on conventional acceptance quality. Payment can then be based on a percent within limits (PWL) approach. This paper demonstrates how pay adjustments can be made for a paving project in Indiana following three different QA specification frameworks: the current QA specifications framework in the Indiana Department of Transportation, a PRS framework using IVRs, and a PBS framework that employs measured Sapp and RSI. For each framework, the main elements of the specification were identified and determined. The specification limits for Sapp and RSI and weight factors in composite pay factor equations were determined such that the resulting pay factors are comparable to pay factors obtained from the current QA practices.

Developing Performance-Based Mix Design Framework Using Asphalt Mixture Performance Tester and Mechanistic Models

This paper proposes a performance-based mix design (PBMD) framework to support performance-related specifications (PRS) needed to establish relationships between acceptable quality characteristics (AQCs) and predicted performance, as well as to develop fatigue-preferred, rutting-preferred, and performance-balanced mix designs. The framework includes defining performance tests and threshold values, developing asphalt mix designs, identifying available performance levels, conducting sensitivity analysis, establishing the relationships between AQCs and predicted performance, and determining performance targets and AQC values for the three PBMDs using predicted performance criteria. Additionally, the framework recommends selecting the PBMD category for each asphalt layer to minimize pavement distresses. In this study, the proposed PBMD protocol was applied to FHWA accelerated loading facility (ALF) materials using asphalt mixture performance tester (AMPT) equipment coupled with mechanistic models. The study developed nine mix designs with varying design VMAs and air voids using the Bailey method. The cracking and rutting performance of the mix designs were determined by direct tension cyclic (DTC) fatigue testing, triaxial stress sweep (TSS) testing, and viscoelastic continuum damage (S-VECD) and viscoplastic shift models for temperature and stress effects. The study found that adjusting the design VMA was the primary way to achieve required performance targets. For fatigue-preferred mix design, the recommended targets were a cracking area of 0 to 1.9%, a rut depth of 10 mm, and a design VMA of 14.6 to 17.6%. For rutting-preferred mix design, the recommended targets were a cracking area of 18%, a rut depth of 0 to 3.8 mm, and a design VMA of 10.1 to 13.1%. For performance-balanced mix design, the recommended targets were a cracking area of 8.1 to 10.7%, a rut depth of 4.6 to 6.4 mm, and a design VMA of 12.6 to 14.3%. Finally, pavement simulation results verified that the proposed PBMD pavement design with fatigue-preferred mix in the bottom layer, performance-balanced mix in the intermediate layer, and rutting-preferred mix in the surface mix could minimize bottom-up cracking propagation without exceeding the proposed rutting performance criterion for long-life.

Integrating Quality Assurance in Balance Mix Designs for Durable Asphalt Mixtures: State-of-the-Art Literature Review

Delivering durable asphalt concrete within a reasonable cost is one of the great ambitions of pavement material engineers. This state-of-the-art review article documents the efforts spent in the past two decades to ensure the durability and performance of asphalt mixtures in mix design and production. A perspective with the attempt to integrate laboratory mix design, plant production quality assurance, and field place acceptance is applied in the review. The development of the performance specification and performance mix design is summarized. The paper categorizes performance specification into index-based performance specification and predictive performance specification that include performance-related specification and performance-based specification. The approaches to developing index-based performance mix design/balanced mix design and predictive performance mix design are also compared in the review. The challenges and solutions in incorporating performance tests in asphalt productions are documented and discussed. The challenges include selecting performance testing methods, determining index threshold limits, estimating and incorporating testing variability and uncertainty, determining sampling position and testing frequency, and so forth. The paper also provides suggested areas of future research and implementation activities.

Advanced fatigue and rutting characterisation of Polish asphalt mixtures based on the VECD model and viscoplastic shift model

The advanced asphalt mixture performance-related specifications (AM-PRS) recently developed in USA can allow an optimisation of the design process of asphalt pavements thanks to the possibility to fully take into account the intrinsic material properties. In this study, four typical Polish mixtures, i.e. a Stone Mastic Asphalt (SMA) for wearing course, two mixtures for binder course with neat bitumen or Polymer modified Bitumen (PmB), and a mixture for asphalt base course with neat bitumen, were investigated by applying such advanced framework. The fatigue performance was studied through the simplified viscoelastic continuum damage (S-VECD) approach, whereas the rutting properties were assessed through the viscoplastic theory of the shift model. The findings were consistent with the composition of the studied mixtures, demonstrating the reliability and applicability of the AM-PRS even for typical Polish mixtures. Specifically, the high amount of soft PmB made the SMA mixture tough against fatigue cracking, but also more prone to rutting. The two binder mixtures exhibited good performance against both fatigue and rutting, and the polymer modification improved the toughness and increased the stiffness at high temperatures. The base mixture is expected to suffer fatigue cracking more than rutting, likely due to the low amount of bitumen and coarser aggregate gradation. These results can be used in the future for pavement performance predictions with FlexPAVETM software programme to ultimately optimise the design of Polish pavements.

Evaluation of the significance of different mix design variables on asphalt mixtures’ cracking performance measured by laboratory performance tests

Cracking is one of the primary distresses for asphalt pavements. This study is motivated to investigate the significance of the various mix design variables in determining the cracking performance of asphalt mixtures including both intermediate and thermal cracking performance, contributing to a better understanding of the mix design to improve the mixture cracking performance and promoting the development and implementation of the performance related specification and performance based specification. Total 20 mixtures were tested and evaluated in this study. The most current state of the practice mixture performance tests, including the Complex Modulus (E*) test, Semi Circular Bending (SCB) test, Disk Shaped Compact Tension (DCT) test and Direct Tension Cyclic Fatigue (DTCF) test were conducted on these mixtures for characterization of their cracking performance. The advanced statistical analysis methods were employed on the generated data base to investigate the significance of the mix design variables on determining the cracking performance parameters measured from the laboratory tests. The correlations between the various cracking performance parameters measured from the tests were also evaluated in this study. The results show that the binder related mix variables play the significant role for determining both the low temperature and durability cracking performance of asphalt mixture. For evaluation of the mixture fatigue cracking performance, several aggregate related variables in addition to binder variables are identified as the significant factors. Correlation analysis shows that mixture rheological based cracking parameter G-Rm does not show the strong correlations with neither the facture indices measured from the DCT and SCB tests nor the fatigue parameters measured from the DTCF test. This study also develops a simplified linear regression model as a predesign tool for evaluation and prediction of mixture cracking performance in general.

Development of a Performance-Related Framework for Asphalt Mixture Design for the Illinois Tollway

Various agencies have begun to research and introduce performance-related specifications (PRS) for the design of modern asphalt paving mixtures. The focus of most recent studies has been directed toward simplified cracking test development and evaluation. In some cases, development and validation of PRS has been performed, building on these new tests, often by comparison of test values to accelerated pavement test studies and/or to limited field data. This study describes the findings of a comprehensive research project conducted at Illinois Tollway, leading to a PRS for the design of mainline and shoulder asphalt mixtures. A novel approach was developed, involving the systematic establishment of specification requirements based on: 1) selection of baseline values based on minimally acceptable field performance thresholds; 2) elevation of thresholds to account for differences between short-term lab aging and expected long-term field aging; 3) further elevation of thresholds to account for variability in lab testing, plus variability in the testing of field cores; and 4) final adjustment and rounding of thresholds based on a consensus process. After a thorough evaluation of different candidate cracking tests in the course of the project, the Disk-shaped Compact Tension—DC(T)—test was chosen to be retained in the Illinois Tollway PRS and to be presented in this study for the design of crack-resistant mixtures. The DC(T) test was selected because of its high degree of correlation with field results and its excellent repeatability. Tailored Hamburg rut depth and stripping inflection point thresholds were also established for mainline and shoulder mixes.

Development of preliminary transfer functions for performance predictions in FlexPAVE™

Mechanistic-empirical design and performance-related specifications are state-of-the-art tools for designing pavements and determining incentives/disincentives for paving contracts. These methods require the reliable prediction of pavement performance throughout the pavement’s design life. One such prediction program is FlexPAVE™, which applies three-dimensional viscoelastic finite element analysis with moving loads to calculate the pavement’s mechanical responses under traffic loading and given climate data. The simplified viscoelastic continuum damage model and shift model are used to calculate the fatigue damage in the pavement’s cross-section and the rut depths, respectively. With regard to fatigue damage, a fatigue transfer function is needed to convert the computed cross-sectional damaged area (i.e., the damage level) to the cracked area on the pavement surface. With regard to rut depth, a rutting transfer function is needed to calibrate the predicted rut depths. In this study, preliminary transfer functions for the predicted fatigue damage and rut depths were developed using four sets of field measurement data obtained from test sections in the United States, Canada, and South Korea that include interstate highways and an accelerated testing facility. Good agreement between the predicted performance and field observations was found after calibration of FlexPAVE™.

Pavement performance predictions using performance-volumetric relationship and evaluation of construction variability: Example of MaineDOT shadow project for the development of performance-related specifications

This paper describes the process chain for a shadow project of the Federal Highway Administration’s Asphalt Mixture Performance-Related Specifications (PRS) by the MaineDOT. Eleven mixture samples were acquired from a field project selected by MaineDOT and were performance-tested for calibration (a ‘four corners’ procedure) and verification to develop the performance-volumetric relationship (PVR) for the selected mixture. The PVR function for the selected mixture worked reasonably well to predict pavement performance at the volumetric conditions that were not included in the PVR development and reflected reasonable trends with regard to various field densities.

Framework for Hybrid Performance-Based Quality Assurance for Flexible Airfield Pavements

AbstractIt is common practice to adopt prescription specifications and performance-related specifications in airfield pavement construction. Limited studies have been reported in the literature on ...

Construction quality acceptance performance-related specifications for chip seals

The research described herein details the establishment of a framework for construction quality acceptance performance-related specifications (PRS) for chip seal surface treatments. This paper establishes acceptance quality characteristics (AQCs) and relationships between the AQCs and related chip seal performance measures. This work is a critical step in developing PRS for constructed chip seal treatments and establishing suitable guidelines for the PRS. The main objective of this paper is to determine appropriate test methods to evaluate each defined AQC. The relationships that are established between the AQCs and chip seal performance are used to define performance ranges and threshold values for a particular performance measure. These performance ranges and threshold values then can be used to define pay factors for the constructed chip seal section. The threshold values and pay factors for each AQC described herein are preliminary recommendations and require further validation prior to implementation. However, this research demonstrates how these PRS would be utilized to ensure acceptable chip seal construction quality in the field. The developed construction quality acceptance PRS framework uses the percent within limits (PWL) concept to determine whether a chip seal lot passes the PRS threshold values and whether the contractor receives full pay, is subject to a pay penalty, or fails the construction PRS and must correct the chip seal within the first year in service, which constitutes the typical warranty period for contracted chip seal work. Finally, recommendations are made as to the next steps in the development and validation of these construction quality acceptance PRS that are needed for implementation by contractors and state roadway maintenance agencies. • A framework is developed for the performance-related specification of chip seal surface treatments. • Relationships are identified between acceptance quality characteristics (AQCs) and critical chip seal performance measures. • Practical test methods are identified to measure the AQCs. • Recommendations are made for the establishment and future implementation of pay factors for chip seal construction.

Development dynamic monitoring technologies used in the Puguang high-sulfur gas field

There is lack of performance monitoring technologies and related standards and specifications in the Puguang gas field, which is ultra-deep with high sulfur content. In this paper, five key technologies of dynamic monitoring were developed and the related standards and specifications were formulated by investigating high-sulfur gas fields at home and abroad, combined with equipment development, laboratory experiments, theoretical research and field tests. The five key technologies include gas production profile logging, downhole sampling and fluid phase analysis, dynamic water invasion prediction and water producing horizon identification, gas well productivity testing and evaluation, and development monitoring and safety control of high-sulfur ultra-deep wells. Then, these key technologies were applied for verification in the Puguang gas field. And the following research results were obtained. First, the sulfur-resistant gas production profile logging tool has a temperature resistance of 175 °C and pressure resistance of 105 MPa. Forty-three well times gas production profile logging is carried out with a success ratio of 100%. Second, the high-sulfur downhole pressure sampler has a temperature resistance of 150 °C and pressure resistance of 70 MPa. Seven well times downhole pressure sampling is carried out with a success ratio of 100%. Third, elemental sulfur is precipitated in the formation when the formation pressure drops to 29.5 MPa. And no sulfur is deposited in the wellbore when the production rate of gas well is higher than 20 × 104 m3/d. Fourth, water producing horizons can be identified accurately and water breakthrough time of gas wells can be predicted by using water producing horizon identification technology and dynamic water invasion prediction model. Water influx rates can be controlled and water-free gas production period of gas wells can be extended by optimizing and adjusting the working systems of gas wells. And fifth, full coverage of gas well productivity testing is realized by using the testing technology of "downhole implanted gauge & cable delivery & wellhead flow-variable rate", pressure calculation model and well testing interpretation model, and the productivity evaluation results of gas wells are accurate. Sixth, the dynamic gas tight pressure of the cable multi-stage leakage control system of super-high pressure and gas tightness is 50 MPa, and the processing technology for waste gas of blowout hookup is applied to 143 well times testing operation with zero leakage and zero pollution. In conclusion, these performance monitoring technologies have been playing an important role in scientifically formulating the production and reserves increase measures and ensuring long-term stable production of the Puguang gas field.

Development of a Performance-Volumetric Relationship for Asphalt Mixtures

This paper aims to establish the relationship between the volumetric performance of asphalt mixtures and their performance in relation to pavement fatigue cracking and rutting. A good performance-volumetric relationship (PVR) can dramatically improve the working efficiency of mixtures and can be used in future performance-engineered mixture design and performance-related specifications. For this study, three asphalt mixtures were first designed to incorporate systematic changes in volumetric conditions, then fatigue cracking and rutting performance tests were conducted at each condition. Statistical analyses of the results suggest that a first-order (linear) model and power model would be an appropriate form of the PVR function. The number of volumetric conditions required to calibrate the PVR function is also investigated. Finally, a rule of thumb for selecting the volumetric conditions for the model calibrations is provided. The verification results show that the proposed PVR function is able to capture the response of mixture performance to changes in volumetric conditions.

Development of performance related specifications for chip seal treatments

ABSTRACT Road agencies are increasingly incorporating performance-related specifications (PRS) in construction contracts to specify quality in terms of parameters related to desired long-term performance. PRS provides a means to account for the value lost or gained by the variances of the designed performance parameters from the specified target values. The use of PRS for pavement preservation treatments (e.g. chip seals) has been generally non-existent. The objective of this paper is to establish a step-by-step procedure for formulating chip seals PRS guidelines. The percent embedment (PE) of aggregates into emulsified asphalt was selected as the acceptance quality characteristic (AQC). Chip seal specimens with varying percent embedment levels were prepared using aggregate and emulsion types in Michigan. Aggregate loss and bleeding were selected as performance indicators. Laboratory tests were conducted to compute PE, aggregate loss and bleeding for the chip seal specimens. Relationships were developed between quality measures, service life, and pay factors. The expected pay curves were developed based on quality measures and were used to establish acceptable and unacceptable quality levels. The pay factors were evaluated to ensure fair payments for the quality of work produced. The work presented will provide the general guidelines for developing PRS for chip seal projects.

Development and Demonstration of Hot Mix Asphalt Design Guidance for Mix Performance-Related Specifications

As they adopt mechanistic-empirical (ME) methods for flexible pavement design, road agencies are starting to incorporate performance-related specifications (PRS) for hot mix asphalt materials to assure that the as-built materials meet the performance requirements assumed in the pavement structural design. PRS pose new challenges for materials producers and contractors who have never had to relate volumetric mix design parameters to performance requirements such as fatigue life and rutting resistance. The objective of this paper is to describe the development of guidance for materials producers and contractors to support their decision making with regard to changes to mix designs to meet PRS requirements. The guidance was first developed based on known experience. To validate the guidance and demonstrate its usage, a production mix meeting Superpave volumetric requirements for California state highways was selected as the starting point for a set of adjustments applied to the mix. The effects of each adjustment were evaluated by conducting laboratory tests to determine mechanistic performance parameters used in structural design. The mechanistic performance parameters evaluated in this study include stiffness, fatigue resistance, and rutting resistance. The initial experience-based mix design guidance was found to be generally consistent with the laboratory test results for the example mix, albeit with some minor exceptions. The mix design guidance was then revised based on findings from this study. It is recommended that the revised guidance be used as non-mandatory advisory information for projects with PRS and that it be further improved with more results.

Performance-related specification and payment modifiers in highway construction projects

PurposeThe ability to measure and assess “quality” is essential in building and maintaining a safe and effective transportation system. Attaining acceptable quality outcomes in transportation projects has been a reoccurring problem at both the federal and state levels, at least partially, as a result of poorly developed, inefficient or nonexistent quality assurance/quality control (QA/QC) processes. The purpose of this paper is to develop and implement a new QA/QC process that focuses on a novel double-bounded performance-related specification (PRS) and corresponding pay factor policy that includes both lower and upper quality acceptance and payment reward boundaries for bridge concrete.Design/methodology/approachThe authors use historical data to design different payment scenarios illustrating likely industry responses to the new PRS, and select the single scenario that best balances risk between the agency and industry. The authors then convert that payment scenario to a pay factor schedule using a search heuristic and determine statistical compliance with the PRS using percent-within-limits (PWL).FindingsThe methodology offers an innovative approach for developing an initial set of pay factors when lifecycle cost data are lacking and the PRS are new or modified. An important finding is that, with a double-bounded PRS, it is not possible to represent pay factors using the simplified table PWL currently employed in practice because each PWL value occupies two separate positions in the payment structure – one above the design target and one below it. Therefore, a more detailed set of pay factors must be employed which explicitly specify the mean sample value and the design target. The approach is demonstrated in practice for the Agency of Transportation in state of Vermont.Research limitations/implicationsThe authors demonstrate a novel approach for developing a double-bounded PRS and introduce a payment incentive/disincentive policy with the goal of improving total product quality. The new pay factor policy includes both a payment penalty below the contracted price for failing to meet a specified performance criterion as well as a payment premium above the contracted price that increases as the sample product specification approaches an “ideal” design value. The PRS includes both an upper and lower acceptance boundary for the finished product as opposed to only a lower tail acceptance boundary, which is the traditional approach.Practical implicationsThe authors illustrate a research collaboration between academia and a state agency that highlights the role academic research can play in advancing quality management practices. The study involves the use of actual product performance data and is operational as opposed to conceptual in nature. Finally, the authors offer important practical insights and guidance by demonstrating how a new PRS and pay factor policy can be developed without the use of site-specific historical lifecycle cost (LCC) data that include detailed manufacturing, producing and placement cost data, as data related to product performance over time. This is an important contribution, as the development and implementation of pay factor policies typically involve the use of historical LCC data. However, in many cases, these data are not available or may be incomplete.Social implicationsWith the new PRS and pay factor schedule, the Agency expects shrinkage and cracking on bridge decks to decrease along with overall maintenance and rehabilitation costs. A major focus the new PRS is to actively involve industry partners in quality improvement efforts.Originality/valueThe authors focus on a major modification to an existing QA/QC process that involves the development of a new PRS and an associated pay factor policy undertaken by the Vermont Agency of Transportation. The authors use empirical data to develop a novel double bounded PRS and payment schedule for concrete and offer unique operational/practical insight and guidance by demonstrating how a new PRS and pay factor policy can be developed without the use of site-specific historical LCC. Typically, PRS for in-place concrete have only a lower tail acceptance boundary.

Indirect Tensile Test (IDT) to Determine Asphalt Mixture Performance Indicators during Quality Control Testing in New Jersey

In recent years, there has been a growing interest in incorporating performance testing during the mixture design and quality control testing of asphalt mixtures. The move toward utilizing performance related specifications (PRS) and balanced mixture design concepts have pushed the need for asphalt mixture performance testing to the forefront. Numerous researchers have proposed a variety of laboratory tests that have showed promise at predicting asphalt mixture performance, yet most of these test methods are never adopted due to a number of issues often cited by the asphalt industry: (1) equipment cost; (2) equipment/test method complexity; and (3) time/labor effort required. The research presented here summarizes the effort to evaluate the indirect tensile test (IDT) as a potential performance indicator for hot-mix asphalt that can be easily utilized during quality control testing at an asphalt plant. Utilizing the same test equipment and basic procedure, both high-temperature rutting and intermediate-temperature fatigue cracking can be evaluated in a timely manner. Comparison testing to more standardized and accepted rutting and fatigue cracking test methods have shown excellent agreement, indicating that the suite of IDT tests have potential for adoption within a quality control testing program. Examples of criteria are given utilizing the New Jersey Department of Transportation’s (NJDOT) PRS.

Toward the development of performance-related specification for bio-rejuvenators

The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) has many benefits. However, premature cracking has become a serious concern for mixes containing RAP/RAS. Recently, a variety of bio-rejuvenators have been developed to address the premature cracking issue. However, there is no purchasing specification available for bio-rejuvenators. This paper presents the efforts made toward the development of performance-related specification for bio-rejuvenators. A total of eight bio-rejuvenators including seven commercial bio-rejuvenators and one recycled vegetable oil, were evaluated in this study. Their chemical and rheological properties and aging characteristics were measured. In addition, the effectiveness of the eight bio-rejuvenators in improving low temperature property of (recycled) asphalt binders was investigated. Although rheological dynamic viscosity has a fair correlation with the stiffness based low temperature performance grade (PG), the chemical property, total fatty acid content is the preferred performance indicator, because (1) the low temperature PG of recycled asphalt binders is controlled primarily by relaxation property (or m value); and (2) the total fatty acid content has much better correlation with the m-based low temperature PG than the dynamic viscosity. The total fatty acid content was verified by mixing pure fatty acid compounds (palmitic acid, oleic acid, and linoleic acid) with a virgin PG64-22 binder. The identified performance indicator was further confirmed by testing blends of recycled binder/virgin binder/three bio-rejuvenators. Additionally, two field test sections with 30% recycled RAP and bio-rejuvenators were constructed for validation. Laboratory test results of the plant mixes collected from the field clearly validated the effectiveness of total fatty acid content as the performance indicator for bio-rejuvenators. At the end of this paper, a framework of performance-related specification for bio-rejuvenators is proposed. A total of seven aspects of bio-rejuvenators are included: (1) total fatty acid content for bio-rejuvenator classification, (2) saturated fatty acid content for avoiding potential negative effect of wax, (3) flashing point for safety, (4) dynamic viscosity for pumping bio-rejuvenators to the mixing drum, (5) dynamic viscosity ratio of RTFO residue to original rejuvenator for screening out the bio-rejuvenators susceptible to short term aging, (6) RTFO (or TFO) mass loss for avoiding massive loss of volatiles, and (7) specific gravity.

Fatigue Performance Prediction of Asphalt Pavements with FlexPAVETM, the S-VECD Model, and DR Failure Criterion

Reliable predictions of asphalt materials and pavement performance are important elements in mixture design, mechanistic-empirical pavement design, and performance-related specifications. This paper presents FlexPAVE™, a pavement performance prediction program. FlexPAVE™ is a three-dimensional finite element program that is capable of moving load analysis under realistic climatic conditions. It utilizes the simplified viscoelastic continuum damage (S-VECD) model to predict asphalt pavement fatigue life. This S-VECD model currently incorporates the so-called GR failure criterion to define the failure of asphalt mixtures. In this study, a new failure criterion for the S-VECD model, designated as the DR criterion, has been developed to remedy some of the shortcomings of the GR failure criterion. This DR criterion has been implemented successfully in FlexPAVETM. In this paper, FlexPAVETM is used to simulate the fatigue performance of field test sections. These test sections include various pavement structures, such as perpetual pavements and accelerated load facility test pavements in the United States, South Korea, and China, as well as various materials, such as warm-mix asphalt, reclaimed asphalt pavement, and mixtures with modified binders. The DR-based FlexPAVETM predictions have yielded good agreement with the field measurements and show more reasonable trends compared to predictions obtained using the GR failure criterion.