Illinois Flexibility Index Test Research Articles

Impact of Nonrecyclable Plastics on Asphalt Binders and Mixtures

Low-density polyethylene (LDPE) and polystyrene (PS) were evaluated for incorporation as binder additives to enhance the potential performance of asphalt concrete (AC) mixtures, as well as addressing global rising concerns over nonrecyclable plastics accumulation. Incorporation of LDPE and PS in asphalt binder resulted in an increase in its complex moduli over a range of temperatures and frequencies, as determined using frequency sweep (FS) and linear amplitude sweep (LAS) tests. AC performance tests were conducted, including the Hamburg wheel-tracking test (HWTT) to assess potential rutting, the Illinois flexibility index test (I-FIT) to determine cracking potential, the indirect tensile strength test (ITS) to assess moisture susceptibility, and the dynamic modulus for structural capacity. Two control AC mixes were designed, utilizing aggregates from different sources. For each AC mix, the aggregate blend and binder content were kept constant, with only the binder type changed. LDPE and PS were added through a wet process in one mix. Dry and wet processes were used in the other mix. Waste plastics–modified AC mixes, in both wet and dry processes, exhibited reduced rutting potential. However, the cracking potential and moisture damage susceptibility varied, depending on the modified AC mix. The addition of waste plastics had no impact on AC dynamic modulus. The results for waste plastics–modified AC mixes were compared with those for styrene-butadiene-styrene (SBS)–modified AC mixes. While waste plastics modification provided improvement over the control mixes, the performance fell short of that of the double-pump SBS-modified mix.

Prediction of asphalt concrete flexibility index and rut depth utilising deep learning and Monte Carlo Dropout simulation

ABSTRACT Asphalt concrete (AC) balanced mix design (BMD) relies on laboratory testing to meet both the Illinois Flexibility Index Test (I-FIT) and the Hamburg Wheel Tracking Test (HWTT) by varying aggregate gradations and asphalt cement contents. AC mix designers would benefit from estimating the impact of constituent materials’ properties on I-FIT and HWTT before conducting a BMD trial. This study focused on the development of two deep learning models to predict I-FIT flexibility index (FI) and HWTT rut depth. The models were created based on a I-FIT database of 19,138 datasets and a HWTT database of 7602 datasets (after data preprocessing was conducted). Two deep neural networks (DNNs) were then trained to predict FI and rut depth. Monte Carlo Dropout simulations were then used in the DNN models to compute a distribution of predicted FI and rut depth. The distribution of predicted FI and rut depth provides a best estimate and range of FI and rut depth. The developed models provide a distribution of predictions with a coefficient of variation (CoV) lower than 30% for both the I-FIT and HWTT models, respectively.

Comparative fracture resistance assessment of rubber-modified asphalt mortar based on meso-and macro-mechanical analysis

ABSTRACT This study investigates the effects of ground tire rubber (GTR) on the cracking resistance of asphalt mortar from different analysis scales. Furthermore, the effectiveness of different fracture test methods was compared for GTR-modified asphalt mortar, including the indirect tensile cracking test (IDEAL-CT), disk-shaped compact tension test (DCT) and Illinois flexibility index test (I-FIT). To achieve this, a mesoscopic fracture test based on the SEM-Servo Plus device was proposed firstly to obtain the micro-parameters of constitutive models in discrete-element modelling (DEM). A unified fracture modelling procedure that can avoid any interference factors was carried out for comparative fracture analysis. Results from the tests and simulations show that rubber filler plays a positive role in enhancing the fracture properties of the asphalt mortar. The fracture energy measured by IDEAL-CT is almost 5–6 times of the DC(T) test and 1.5–2 times of the I-FIT test. It is not an inherent attribute of material and can only be regarded as a relative index for fracture resistance evaluation. The FI and CTindex obtained from the I-FIT and IDEAL-CT test show a weak correlation of fracture resistance, especially when comparatively evaluating the GTR-modified asphalt mortar with minor difference in filler content.

Cracking performance evaluation and modelling of RAP mixtures containing different recycled materials using deep neural network model

This study evaluates the cracking resistance of recycled asphalt pavement (RAP) mixtures including waste engine oil (WEO), crumb rubber (CR), and steel slag aggregates using the Illinois flexibility index test (I-FIT). Performance indices, derived from both this study and another, were predicted by comparing deep neural network (DNN), linear, and polynomial regression models via a k-fold cross-validation process. I-FIT test results demonstrated that WEO, steel slag aggregates, and specific CR proportions enhance cracking resistance while RAP utilisation decreased it. In terms of modelling, it was found that the most appropriate prediction model for the dataset structure of this study is the deep neural network model. The DNN model sensitivity analysis identified WEO as key for high and intermediate temperature (I-FIT) performance. Meanwhile, CR significantly impacted intermediate temperatures (IDEAL-CT), while RAP influenced moisture susceptibility. This model proves reliable and efficient, suggesting its potential for predicting the performance of recycled mixtures.

Asphalt Concrete Mix Design Optimization Using Autoencoder Deep Neural Networks

Asphalt concrete (AC) balanced mix design (BMD) is based on the selection of aggregate gradation, component volumetrics, and binder content to control pavement cracking and rutting potential. The Illinois Flexibility Index Test (I-FIT) and the Hamburg Wheel Tracking Test (HWTT) results, used to predict cracking and rutting potential, respectively, are used in the BMD approach. However, BMD generally relies on a trial-and-error process to identify the aggregate gradation and binder content needed to meet volumetrics and optimize I-FIT and HWTT results. Minimizing or eliminating the trial-and-error process would increase productivity and accuracy. Therefore, this study proposes an autoencoder deep neural network (ADNN) to develop optimized AC mix design alternatives that can meet a prescribed flexibility index (FI) and rut depth (RD). Autoencoders are a type of neural network designed for representation learning composed of an encoder and a decoder. The encoder detects a structured pattern in the original input data to create a compressed representation of the AC mix design. The decoder reconstructs the compressed representation. The proposed autoencoder is composed of an encoder of five hidden layers, a latent space of one node, and a five-hidden-layer decoder. Models were created from a database of 5,357 data sets that include mix properties, I-FIT FI, and HWTT RD (after data preprocessing was conducted). An autoencoder was then trained to predict the total binder content, and aggregate gradation based on a target mix type, FI, and RD.

Balanced Mix Design Benchmarking of Asphalt Mixtures Produced in Vermont

Performance testing is an important tool to complement volumetric properties for improving asphalt pavement performance. Vermont Agency of Transportation (VTrans) began evaluating the Hamburg wheel-tracking test (HWTT) in 2015, the Illinois flexibility index test (I-FIT) in 2018, and the indirect tensile cracking test (IDEAL-CT) as another index-based test to investigate along with the I-FIT, as a step toward balanced mix design (BMD) implementation. An increase in the use of recycled materials in asphalt mixtures produced in Vermont was anticipated in their Standard Specifications for Construction. This study is an attempt in this direction. The tests were conducted on reheated plant mixtures sampled from paving projects in Vermont and the results were analyzed to (1) develop baseline rutting and cracking performance; (2) evaluate the effects of mixture properties on performance test results; (3) compare IDEAL-CT results and I-FIT results; and (4) compare performance test results with specification criteria proposed by VTrans for evaluating the rutting and cracking resistance of asphalt mixtures. Several mixture properties, viz., nominal maximum aggregate size (NMAS), binder grade, binder content, and recycled content, were found to have significant effects on mixture rutting and cracking resistance. The test results showed a direct correlation between FI and CTindex for the dataset of VTrans mixtures. The information from this research will help VTrans to achieve its goal to move beyond the use of volumetric properties for asphalt mixture design and acceptance and serve as an example for other agencies in exploring the implementation of BMD for improving asphalt pavement performance.

Laboratory Investigation into the Partial Replacement of Aggregates with Recycled High-Density Polyethylene in a Dense Graded Asphalt Mix

Plastic waste is a growing concern today, as landfills fill up and pollution leads to global climatic problems. Some research has been conducted on using plastics in asphalt, but the effect that high-density polyethylene (HDPE) can have in the performance of the asphalt is not understood. This research examines the impact on the moisture damage, rutting, and cracking resistance of recycled HDPE plastics as a portion of aggregates in a dense graded asphalt mix. Two types of recycled HDPE were used—flakes and pellets. Mixes with 5% by volume of recycled HDPE were designed and compared with a control mix. The results indicate that the use of recycled HDPE allowed for a reduction of 0.5% binder requirement. Tensile strength ratio testing showed that, with no anti-stripping agent, the HDPE-modified mixes had acceptable moisture resistance. Both types of HDPE-modified mixes showcased superior rutting resistance based on the flow number parameter. However, the use of HDPE decreased the cracking resistance of the mixes measured with the Illinois Flexibility Index Test at intermediate temperatures. The dynamic modulus test indicated a decrease in the stiffness of the mixes at low temperatures and confirmed the increase of the stiffness at high operating temperatures. Overall, the results indicate that the use of HDPE as partial replacement of aggregates is feasible and future research could explore balancing the performance of the HDPE-modified mix.

Optimization of CLS Content of Asphalt Mixtures Based on Balanced Mix Design Approach

Over the years, there have been many studies on the performance improvement of asphalt mixtures using different materials and additives, especially those of the recycled variety, because of the environmental benefits they bring to the design. This study investigated the properties of asphalt mixtures made with different amounts of calcium lignosulfonate (CLS), which is a waste product, and used the Balanced Mix Design (BMD) approach to determine the appropriate mix design for CLS-containing mixtures. In this process, the results of the dynamic creep test were used as a measure of rutting resistance, the results of the indirect tensile test were used as a measure of moisture susceptibility, and the results of the Illinois Flexibility Index Test (IFIT) and Indirect Tensile Cracking Test (IDEAL-CT) were used independently as a measure of cracking resistance. On the other hand, since previous studies have suggested that CLS has antiaging properties, the specimens were made and tested in two groups: those with long-term aging and without long-term aging. So the objective was to determine the amount of CLS that should ideally be used as a bitumen additive in aged and unaged asphalt mixtures. The results showed that using 15% or 20% CLS will always yield acceptable outcomes in terms of BMD criteria for both aged and unaged conditions. However, a CLS content of 10% may also be acceptable for both aged and unaged conditions if IDEAL-CT results are used as the measure of cracking resistance.

Balanced Mix Design Production Analysis of Asphalt Mixtures in Vermont

Performance testing has been recognized by state highway agencies and the asphalt paving industry as an important tool to complement volumetric properties for improving asphalt pavement performance. Thus, the Vermont Agency of Transportation (VTrans) began evaluating the Hamburg wheel-tracking test in 2015, Illinois flexibility index test in 2018, and indirect tensile cracking test in 2020 as steps toward balanced mix design (BMD) implementation. These tests were conducted on reheated common plant-produced asphalt mixtures for multiple shadow projects, and the results were analyzed to determine the typical production variability observed in the performance testing results. Production variability is important to assess potential specifications in field production, especially for statistical quality acceptance procedures, such as percent within limits. Based on the percent within limit analysis, most of the modified Type IVS (i.e., 9.5 mm) mixtures would be acceptable based on the proposed performance requirements, while those found not acceptable were close to meeting the performance requirements and would need minimal adjustments. The lot data was further examined to generate typical lot production variability values for potential use in specification development. The information from this research effort will help VTrans achieve its goal to move beyond solely volumetric properties for asphalt mixture design and acceptance and serve as an example for other agencies exploring the implementation of BMD for improving asphalt pavement performance.

Investigation of the Effect of Oxidative Aging and Temperature Sensitivity on the Illinois Flexibility Index and Disc-Shaped Compact Tension Tests

This study investigated the sensitivity of the Illinois flexibility index test (I-FIT) and the disc-shaped compact tension [DC(T)] test with respect to oxidative aging and testing temperature. For this purpose, five plant-produced surface course asphalt mixtures covering a wide range of performance-graded asphalt cement (PGAC) were utilized. As for oxidative aging sensitivity, two methods of forced-draft oven aging, at 85°C for 120 h and at 95°C for 72 h, were utilized. Furthermore, to measure the temperature sensitivity, the I-FIT test was conducted at 23°C, 24°C, 25°C and PGAC intermediate temperatures, while the DC(T) test was conducted at −18°C, −24°C, and −30°C. In this study, the analysis of the I-FIT test results from oxidative aging showed that both methods of aging caused a reduction in flexibility index values of asphalt mixtures, and the flexibility index values after two methods of aging were statistically comparable. Moreover, even though oxidative aging caused a reduction in DC(T) fracture energies of asphalt mixtures containing hard PGAC, the fracture energies before and after the two methods of aging were statistically similar for asphalt mixtures. The analysis of the I-FIT test results from testing temperature sensitivity showed that the flexibility index values of asphalt mixtures containing hard PGAC at 23°C were statistically dissimilar to those at 25°C when the testing temperature dropped from 25°C to 23°C. Consequently, regarding the I-FIT test, the comparable flexibility index values from the two methods of oxidative aging suggested utilization of forced-draft oven aging at 95°C for 72 h as a less time-consuming method compared to forced-draft oven aging at 85°C for 120 h to evaluate the effect of oxidative aging. In addition, the variability in flexibility index values due to the drop in testing temperature suggested exercising caution when conducting the test on asphalt mixtures containing hard PGAC.

Development of a Laboratory Operations-Friendly Long-Term Loose Mix Aging Protocol for New Asphalt Pavements

New asphalt pavements are often designed to last 15 to 20 years without a major rehabilitation. However, an asphalt mix gets stiffer and more brittle with pavement service life because of aging. As cracking resistance decreases at higher aging levels, pavement structural design and performance verification need to consider the long-term aging characteristics of asphalt mixes. The research presented in this paper developed long-term loose mix aging protocols that are more friendly to routine laboratory operations. Based on a theoretical aging model and the IDEAL cracking test, two aging protocols are equivalent to the 3- and 6-day loose mix aging durations at 95°C provided by NCHRP 9-54, which are 20 h at 110°C and 20 h at 120°C, respectively. These new long-term aging protocols were then confirmed by the Texas Overlay Test and the Illinois Flexibility Index Test. The integration of these protocols into a comprehensive framework for mix design, pavement performance verification, and production testing is discussed. In brief, these new long-term aging protocols would be employed for evaluating cracking resistance only in the pavement performance verification stage, whereas the short-term aging protocol, namely, 2 h at the compaction temperature, would be applied to Superpave volumetric evaluation, balanced mix design (BMD), and production testing. These two new aging protocols combined with BMD rapid performance tests and performance prediction tests make this comprehensive framework very practical and efficient.

Influence of ageing and moisture damage on the Illinois flexibility index value of polymer modified asphalt mixture

Asphalt pavements undergo ageing and moisture damage over the service life. The ageing and moisture process resulted in more cracking susceptibility and lowered pavement serviceability. Recently, the semi-circular bending (SCB) test has been widely utilised to characterise the fracture resistance of asphalt mixtures. In this study, the Illinois Flexibility Index Test (I-FIT) were utilised to investigate the impact of long-term ageing and moisture damage on the cracking resistance of asphalt mixtures modified by crumb rubber and plastic waste. This test is currently being adopted as a routine test in Illinois and has shown good correlations with the field cracking performance of asphalt mixture. For the Semi-Circular Bending (SCB) test, a sample width of 50 mm and a notch length of 15 mm was used for conducting the fracture test using a constant loading rate of 50 mm/min and a test temperature of 25 °C. The fracture energy-based crack mouth opening displacement of the control and modified mixtures was also evaluated using Digital Image Correlation (DIC). The results showed that the flexibility index (FI) values from the I-FIT are sensitive to the modifier type (elastomers or plastomers) and long-term ageing while underestimating the impact of moisture conditioning on the fracture performance of asphalt. Fracture energy results were higher for the rubberised mixture compared to the control and plastic waste modified asphalt mixture. Ageing condition has noticeably decreased the flexibility index (FI) of the rubberised mixture and consequently reduced the fracture performance.

Application of Balanced Mix Design Strategies to Missouri Dense-Graded Asphalt Mixtures

This study focused on the improvement or redesign of dense-graded mixtures in Missouri by applying various strategies typified by a balanced mix design (BMD) approach. Briefly, the BMD approach involves designing mixtures using appropriate thresholds of mixture performance tests to control major distresses. In this study, two existing dense-graded mixtures from Missouri were adopted with 33% binder replacement by recycled asphalt pavement (RAP). Appropriate thresholds from three commonly used cracking tests, namely the disk-shaped compact tension test, or DC(T), the Illinois Flexibility Index Test (I-FIT), and the indirect tensile asphalt cracking test (IDEAL-CT), were paired with the Hamburg wheel track test (HWTT) toward the improvement or rebalancing of mixes designed before the availability or specified use of these tests. Preliminary test results showed that the existing mix designs did not satisfy the cracking thresholds adopted in this study, and thus the following modifications were made to the mixtures: (a) replacing the base binder with a softer grade binder, (b) adding a rejuvenator, and (c) adding ground tire rubber (either 10% or 20% by weight of base binder). According to the results, modification with rubber and softer binder was the most efficient strategy for improving and balancing DC(T) fracture energy and HWTT performance. On the other hand, the use of a softer binder or rejuvenator led to the best success in meeting semicircular bend (SCB) (I-FIT) and IDEAL-CT test requirements in balance with HWTT requirements.

A Sensitivity Study to Evaluate Intermediate Temperature Cracking Tests for Vermont Asphalt Mixes

The State of Vermont began implementing balanced mix design (BMD) in late 2019. Since 2020, both Hamburg wheel tracking test (HWTT) and Illinois flexibility index test (I-FIT) results were required to be included in the mix design submittal along with the traditional Superpave volumetric design. This paper presents a part of the ongoing benchmarking efforts in Vermont, among many other states around the country, and compares the sensitivity of the two popular intermediate temperature cracking tests [I-FIT and indirect tensile cracking test (IDEAL-CT)] to the design factors of mixes produced in Vermont. Both laboratory-produced and plant-produced mix data are evaluated, and the factors analyzed include mix type, design gyrations, production facility, binder grade, and binder supplier. We found that IDEAL-CT shows much higher sensitivity to the design factors than I-FIT according to the data presented in this study. Therefore, it is recommended that Vermont Agency of Transportation (VTrans) adopt IDEAL-CT as the intermediate temperature cracking test for BMD implementation rather than I-FIT, due to the higher sensitivity and simplicity of IDEAL-CT. Regression models are further developed for IDEAL-CT using selected mix properties to guide the mix design adjustment. Similar studies are highly recommended for other state agencies that are interested in implementing BMD.

Application of percent within limits concepts on a balanced mix design of asphalt mixtures

ABSTRACT Many agencies have incorporated rutting, and more recently cracking laboratory tests in the design process of asphalt mixtures with the objective to produce a balance between the stability and durability of the final product. Although this performance-engineered mixture design (PEMD), called here balanced mix design (BMD), offers compelling benefits, it raises a number of questions regarding its compatibility with construction practices. The objective of this work is to relate a BMD method with realistic binder content construction tolerances by applying concepts of a percent-within-limits (PWL) approach to field QC/QA, accounting for the variability of both the laboratory performance tests and construction. Four Arkansas mixes were evaluated using the Illinois flexibility index test (I-FIT) and the asphalt pavement analyzer (APA), for which binder content (Pb) and compaction level (%Gmm) were varied in the laboratory. Monte Carlo simulations were employed to generate binder content variability distributions based on BMD diagrams. New approaches for setting PWL lower and upper specification limits (LSL and USL respectively), as well as a criterion for defining the constructability of a BMD are proposed.

Cracking performance predictions using index-volumetrics relationships with direct tension cyclic fatigue test and Illinois Flexibility Index Test (I-FIT)

This paper introduces a methodology to predict fatigue cracking indices from asphalt mixture volumetric conditions using the index-volumetrics relationship (IVR). Two different tests, the Illinois Flexibility Index Test (I-FIT) and the direct tension cyclic fatigue test, were conducted using two North Carolina plant-mixed lab-compacted (PMLC) mixtures, RS9.5C and RI19.0C, obtained from field projects. Several mixture samples were collected from different truck loads for each mixture. The research team determined three sets of fatigue index values from the I-FIT, i.e., flexibility index (FI), cracking resistance index (CRI), and balanced cracking index (BCI) values, and determined another set of fatigue index values, Sapp index values, from the direct tension cyclic fatigue tests. IVRs for the individual mixtures and test indices were developed and then used to predict the fatigue index values at the volumetric properties that were not used in the IVR development. A good agreement was found between the predicted and measured index values. Except for the BCI values of the RS9.5C mixture, most of the I-FIT cracking test results showed counterintuitive trends with regard to air void content; however, the Sapp index showed more intuitive trends in both mixtures. The effect of binder content on the index values was not included in this study due to an inherent limitation of PMLC mixtures, which is the narrow range of binder content for the collected mixture samples compared to air void content.

“Simplified” Cracking Tests: Evaluation of the IDEAL-CT Performed Using a Marshall Testing Platform

Abstract In considering the implementation of a cracking test for asphalt mixes, attention should be given to both the accuracy and the practical implications of equipment cost and ease of use. This study evaluated the applicability of the indirect tensile asphalt cracking test (IDEAL-CT) performed using a Marshall frame with an in-house-assembled data acquisition instrumentation, compared with the Illinois flexibility index test (I-FIT) protocol using a modern asphalt materials performance test (AMPT). Both flexibility index (FI) and cracking resistance index (CRI) values were obtained from the I-FIT tests. Mixes representing five in-service pavements exhibiting different levels of cracking performance are included. Despite an unstable (and out of specification) loading rate on the Marshall testing frame, IDEAL-CT test results compared favorably with those of the I-FIT performed on the AMPT. The CTIndex exhibited less variability than the FI but more variability than the CRI. The CTIndex appears to discriminate cracking-related behavior in a manner consistent with the FI and CRI. This study indicates the potential for using the IDEAL-CT on a Marshall frame—offering laboratories potentially significant savings in both equipment and specimen preparation costs.

Factors Contributing to Fatigue Cracking in Flexible Pavements in Oklahoma: A Case Study Using Laboratory and Field Investigation and AASHTOWare Simulation

Fatigue cracking is one of the major structural distresses in flexible pavements. In this study, probable causes of fatigue cracking were investigated using field and laboratory testing and In this study, probable causes of fatigue cracking were investigated using field ang laboratory testing and AASHTOWare Pavement ME Design (PMED) simulations. Field tests including Ground Penetrating Radar (GPR), Falling Weight Deflectometer (FWD), and Dynamic Cone Penetration (DCP) were performed on a flexible pavement section of US 412 located in Noble County, Oklahoma. Also, asphalt cores and soil samples were collected for laboratory testing. The GPR test results revealed significant delamination in the asphalt layer. Also, the GPR images indicated that the disturbance zone was confined within the asphalt layer and cracks were generated from surface as well as from existing pavement layers below. The DCP and FWD test results indicated that the pavement section was not structurally adequate to support traffic and needed rehabilitation in the near future. The moduli of the asphalt layers were found to be quite low, indicating improper compaction during construction. Also, the densities of the top-lifts of the asphalt cores were found to be low. Moreover, the cracking resistance of the extracted asphalt cores was poor based on the Illinois flexibility index test results. Superpave Performance Grade of the extracted binder indicated excessive aging of the binder because of long exposure to the environment. The brittleness of mix resulting from aging was considered a potential contributor to fatigue cracking of the pavement at this site. A parametric study was conducted to understand the variation of fatigue cracking with the changes in input properties in PMED, namely pavement structural components and material properties. Pavement thickness, roadway densities, and layer moduli of existing underlying pavement were found as the most influential factors. The findings of the parametric study supported the findings of the field and laboratory investigation.

Evaluation of Asphalt Mixture Performance Using Cracking and Durability Tests at a Full-Scale Pavement Facility

In the asphalt materials community, the most critical research need is centered around a paradigm shift in mixture design from the volumetric process of the previous 20-plus years to an optimization procedure based on laboratory-measured mechanical properties that should lead to an increase in long-term pavement performance. This study is focused on advancing the state of understanding with respect to the value of intermediate temperature cracking tests, which may be included in a balanced mix design. The materials included are plant-mixed, laboratory-compacted specimens reheated from the 2013 Federal Highway Administration’s (FHWA’s) Accelerated Loading Facility (ALF) study on reclaimed asphalt pavement/reclaimed asphalt shingle (RAP/RAS) materials. Six commonly discussed intermediate temperature (cracking and durability) performance testing (i.e., Asphalt Mixture Performance Tester [AMPT] Cyclic Fatigue, Cantabro, Illinois Flexibility Index Test [I-FIT], Indirect Tensile Cracking [ITC, also known as IDEAL-CT], Indirect Tensile Nflex, and Texas Overlay Test) were selected for use in this study based on input from stakeholders. Test results were analyzed to compare differences between the cracking tests. In addition, statistical analyses were conducted to assess the separation among materials (lanes) for each performance test. Cyclic fatigue and IDEAL-CT tests showed the most promising results. The ranking from these two tests’ index parameters matched closely with ALF field performance. Furthermore, both showed reasonable variability of test data and they were successful in differentiating between different materials.

Relationship between Rheological Indices and Cracking Performance of Virgin, Recycled, and Rejuvenated Asphalt Binders and Mixtures

Long-term cracking performance of asphalt mixtures is heavily influenced by asphalt binder rheology, and changes in binder stiffness, ductility, and aging condition significantly affect the cracking resistance of the corresponding asphalt mixture. This study evaluated the effectiveness of several common and recently developed binder rheological indices in capturing the effects of binder performance grade (PG) and source, recycled binder content, recycling agent (rejuvenator) dose, and long-term aging. These binder rheological indices included the Superpave intermediate-temperature PG (PGI), the Glover-Rowe (G-R) parameter, the crossover temperature (Tδ = 45°), the rheological index (R-value), and ΔTc. This study also directly compared the binder rheological indices with the cracking performance of corresponding asphalt mixtures to explore possible correlations and their robustness. Asphalt mixture cracking performance was evaluated using the Illinois Flexibility Index Test (I-FIT) for intermediate-temperature cracking, and the disk-shaped compact tension (DCT) test and the uniaxial thermal stress and strain test (UTSST) for low-temperature cracking. Results indicated that all the binder rheological indices (except PGI) consistently captured the effects of binder blend composition and proportions and aging condition, with a few exceptions. Results also showed that the G-R parameter, the crossover temperature (Tδ = 45°), and ΔTc had the best correlation to asphalt mixture and field core cracking performance as compared with other rheological indices (PGI and R-value), with ΔTc demonstrating the overall best correlation to mixture cracking performance.