Asphalt Mixture Performance Tester Research Articles

Mechanical Properties and Performance of Mixtures Containing a High Level of Recycled Materials That Are Designed Using Alternative Approaches

Using recycled asphalt material (RAM) in asphalt mixtures is very common among transportation agencies. With the recent development of balanced mix design methods, it is becoming more important to understand how to optimize mixture performance by offsetting the adverse effects of RAM. In this paper, mixtures from three different sources were adjusted according to the availability adjusted mix design (AAMD) and corrected optimum asphalt content (COAC) methods. Three control mixtures containing RAM, three mixtures containing no RAM, five mixtures designed according to the AAMD method (two of which had 50% reclaimed asphalt pavement content), and two mixtures adjusted using the COAC-based approach were evaluated. Both asphalt mixture performance tester experiments and index tests were used in this study to evaluate material-level indicators of cracking and rutting resistance. Additionally, pavement performance simulations were carried out using AASHTOWare Pavement ME and FlexPAVETM to assess how the observed material-level differences led to differences in structural-level pavement performance. Both the AAMD and COAC methods improved cracking measures. However, the results suggest that the additional virgin binder added through the COAC method without any adjustments to the aggregate structure can have negative consequences for the rutting performance measures. In addition, the mixture and pavement performance results suggest that the AAMD method is a rational approach for including recycled binder availability in mix design procedures to promote improvements in the cracking performance of mixtures by controlling the volumetric properties and the aggregate structure of the mix without having a detrimental effect on rutting resistance.

Effect of Specimen Fabrication Variables on the Measured Mechanical Properties of Asphalt Mixtures Tested in the Asphalt Mixture Performance Tester (AMPT)

Abstract The scope of this research involves the evaluation of the effects of specimen preparation variables—mixing temperature, binder time at mixing temperature, mixer type, mixing time, loose mix conditioning temperature, loose mix conditioning depth, loose mix stirring, mold loading, placement in mold, additional time at compaction temperature before loading in mold, gyratory specimen height, and test specimen air voids—on tests such as the Dynamic Modulus and Flow Number conducted using the Asphalt Mixture Performance Tester (AMPT). The initial testing program to evaluate the precision of the Dynamic Modulus and Flow Number tests (described in National Cooperative Highway Research Program Report 702) indicated that “specimen fabrication is a major component of the between-laboratory variability” for both tests. The expected outcome of this study was that AMPT users—Federal Highway Administration (FHWA), state user agencies, and industry—understand the importance of proper specimen preparation and the effect of specimen preparation variables on the results obtained from the AMPT Dynamic Modulus and Flow Number tests. The use of AMPT Dynamic Modulus at 20°C is the most sensitive portion of the modulus-time curve and can provide a general idea of sample preparation impact on other mixture tests. This information comes at critical timing as the United States begins to implement performance-engineered mixture designs, balanced mixture designs, and performance-based pay factors. Based on the findings of the study, recommendations may be made regarding changes to specimen preparation procedures, which are expected to produce more reproducible test results.

Streamlining Asphalt Mixture Dynamic Modulus Testing for Determination of Cyclic Fatigue Index Parameter (Sapp) Based on the Simplified Viscoelastic Continuum Damage Model

As balanced mixture designs move forward, obtaining index properties quickly will become critical to routine application. This paper details a study into streamlining performance tests so that users may make decisions on as-designed and as-built material in a shorter period. This study is unique to asphalt materials research through its use of the Scrum methodology. Scrum is a form of the Agile project management technique often used in software development to manage complex projects. This process can also address the intricacies of applied research, with a focus on delivering high-value products through an iterative procedure. This paper is focused on optimizing temperature–frequency combinations in dynamic modulus (| E*|) tests to generate an equivalent master curve more rapidly. Three different versions of | E*| tests were conducted on four mixtures using combinations of five temperatures and seven frequencies in an asphalt mixture performance tester (AMPT). Cyclic fatigue testing was also conducted, which allowed for computation of the apparent damage capacity ( Sapp). The results for Sapp show that there is no statistical difference between the three versions. Also, analysis showed that the total testing time for | E*| can be reduced by half without significant changes to master curves and values of Sapp generated under the testing sweep prescribed in the test standards. A streamlined testing version is provided based on a predefined evaluation approach to ensure adequate equivalency of critical parameters from the full testing suite.

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.

A Study of Superpave Design Gyrations for High Traffic Surface Mixtures

The methodology of the research that was used to evaluate the comparative results of surface mixes with a nominal maximum aggregate size of 12.5mm is presented in this paper. Also presented are the recommended Ndes values for C-level and D-level mixes, which are designed to handle traffic levels of 3-30 Million and greater than 30 Million ESALs, respectively. In order to determine the amount of asphalt that was present, asphalt concrete mixes were fabricated utilizing the Superpave design process at Ndes levels of 50, 75, 100, and 125 gyrations. Using the Asphalt Mixture Performance Tester instrument, we were able to determine the dynamic modulus (E*) at the design asphalt content for a number of different gyration levels. The E* data and related binder properties were used as input in the AASHTO Darwin-ME software to anticipate the rutting and fatigue performance of the mixtures. This was accomplished by assuming a model pavement section and appropriate traffic levels. In order to determine which Ndes are most appropriate, relative performance indicators for rutting and fatigue have been developed and plotted against asphalt content. The Ndes value of 85 gyrations was found to be ideal for both surface mixes after extensive research.

Ruggedness Evaluation of Dynamic Modulus Test Using Small-Scale Test Specimens for Asphalt Mixture Performance Tester

The small specimen dynamic modulus test (AASHTO TP 132-19) is of paramount importance for the asphalt community since it can be used to characterize and compare asphalt mixtures and the test outcomes can be used as input for pavement performance predictions. Even though the small specimen dynamic modulus test is broadly used, acceptable limits for controlling critical experimental factors still need to be developed. This paper presents the method and outcomes of a ruggedness evaluation of the Asphalt Mixture Performance Tester (AMPT) dynamic modulus test using small-scale test specimens. Three mixtures were evaluated and seven experimental factors were selected: strain peak-to-peak magnitude, specimen perpendicularity, platen-to-specimen diameter difference, specimen height, temperature, compensation springs, and end friction reducers. The analysis identified the statistically significant factors and it was found that the strain peak-to-peak magnitude and temperature were the most statistically significant factors. The specimen height and the type of end friction reducer were not found to be statistically significant factors. Also, higher strain levels and the use of compensation springs resulted in the overestimation of modulus at higher temperatures. Finally, tolerance limits were determined for each ruggedness factor and modifications to the small specimen dynamic modulus test and related standards were proposed.

Investigation of unaged and long-term aged bio-based asphalt mixtures containing lignin according to the VECD theory

In the near future, the world of civil and building engineering will be dominated by the advent of bio-materials. Even the road paving sector is involved in the transition towards more sustainable solutions, promoting at the same time environmental benefits and economic savings. Currently, one of the main goals is to ensure that bio-binders offer good performance, at least comparable with that offered by conventional materials. In the last decades, the exponential increase in traffic volumes has led to various types of asphalt pavement distresses, among which fatigue cracking is one of the most common. Within this context, this study presents the characterization of a bio-based asphalt mixture obtained by replacing 30% of bitumen with lignin, which was compared with a reference asphalt mixture containing a plain bitumen characterised by the same penetration grade. Laboratory produced and compacted specimens were subjected to complex modulus and cyclic fatigue tests with the Asphalt Mixture Performance Tester (AMPT). Both unaged and long-term aging conditions were investigated. The tests and the subsequent analyses were based on the simplified viscoelastic continuum damage (S-VECD) approach. Overall, the results showed that the presence of lignin led to a lower aging susceptibility, but also caused a slight reduction in fatigue life due to an increase in the material stiffness. Furthermore, the obtained results confirmed previous findings deriving from the study of the two binders and from the conventional characterization of the same asphalt mixtures as well.

Repeatability and Reproducibility Analysis for Functional Test Results from Asphalt Mixture Performance Tester Cyclic Fatigue Test

The standards for asphalt mixture performance tester (AMPT) cyclic fatigue testing (AASHTO T 400-22 and AASHTO TP 133-21) enable pavement engineers to predict asphalt mixture performance over a wide range of loading and climate conditions. To enable widespread implementation of AMPT cyclic fatigue testing, precision statements that define the repeatability and reproducibility of the tests are needed. ASTM E691-20 and ASTM C670-15 provide guidance for conducting an interlaboratory study to determine the precision of a test method. However, the standards are written for test methods that yield a single numerical figure as the test result, whereas the cyclic fatigue test yields the damage characteristic curve—a functional relationship—as a primary test result. In this study, a vnorm index was established to quantify variation in the entire damage characteristic curve. Repeatability and reproducibility analysis was conducted using vnorm, six single-point measures of damage characteristic curve variation, and one single-point measure for the fatigue test failure criterion ( D R). The major findings are: (1) the outcomes of repeatability and reproducibility analysis using single-point measures of the damage characteristic curve vary with the chosen point of reference; (2) vnorm demonstrates clear increases in within- and between-laboratory variations with increasing mixture nominal maximum aggregate size (NMAS) values; (3) within-laboratory variation of D R results increases with increasing NMAS for a given specimen geometry while the reproducibility of D R does not depend on the NMAS. Correspondingly, precision limits for both vnorm and D R were recommended and evaluated using a broad set of test results.

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.

Viscoelasticity of Recycled Asphalt Mixtures with High Content Reclaimed SBS Modified Asphalt Pavement

For the concerns of investigating the viscoelastic properties of recycled asphalt mixtures incorporating high content reclaimed styrene-butadiene-styrene (SBS) modified asphalt pavement (RAP-SBS), asphalt mixture performance tester (AMPT) was applied to analyze the dynamic modulus and phase angle of recycled mixtures by the influence of RAP-SBS content, temperature, loading frequency, long-term aging (LOTA), and the incorporation of a rejuvenating agent. Master curves of recycled asphalt mixture regarding dynamic modulus and phase angle are developed, and the viscoelastic properties of recycled mixtures within a wide frequency range are characterized with the Christensen–Anderson–Marastean (CAM) model. Eventually, the one-way analysis of variance (ANOVA) was applied to investigate the role of factors on the viscoelasticity of recycled mixtures. The research indicates that (1) the elastic component of recycled mixtures elevates with the increasing of RAP-SBS content and loading frequency; as a result, the high-temperature stability of it enhances, while it is prone to cracking at low temperatures; (2) RAP-SBS content should be selected according to specific characteristics of pavement. For most cases, a content of 50% is recommended; (3) the recycled mixtures incorporating high-content RAP-SBS mixed with a rejuvenating agent has outstanding aging resistance performance; (4) RAP-SBS content is observed to have a significant influence on the viscoelasticity of recycled mixtures.

Experimental Investigation of Cracking and Impact Resistance of Polymer- and Fiber-Enhanced Concrete for Ultra-Thin Whitetopping.

In order to investigate the effectiveness of polymer modification and fiber reinforcement on the cracking and impact resistance of concrete materials prepared for ultra-thin whitetopping (UTW), carboxyl butyl benzene latex and polyformaldehyde fibers were added to the conventional cement concrete mix. In addition, test methods that used an asphalt mixture performance tester (AMPT) and mechanical rammer were developed to evaluate concrete cracking and impact resistance, respectively. Results from the AMPT test revealed that the cracking resistance can be enhanced with polymer and fiber, especially the initial tensile load peak, which can be improved by more than 40% when fiber and polymer compound modification is applied. Meanwhile, the impact loading test revealed that the inclusion of both fiber and polymer results in a two-fold increase in the number of impacts before visible cracking occurs, and the number of blows to failure increased by 21.4%. Moreover, microstructures were investigated by scanning electron microscopy (SEM) to confirm the reinforcing mechanism of both polymer modification and fiber reinforcement.

Evaluating the Sensitivity of Intermediate Temperature Performance Tests to Multiple Loose Mixture Aging Conditions Using the FHWA Accelerated Loading Facility’s RAP/RAS Experiment

With the advancement of Balanced Mixture Design (BMD), laboratory performance tests for asphalt materials are being assessed for their relation to cracking performance in the field. However, most BMD applications do not account for long-term aging. This gap limits the appropriateness of thresholds and the potential of BMD to improve pavement performance as more amounts of the additives and reclaimed materials available can behave in drastically different fashions between early, intermediate, and late stages of service. In this study, five mixtures with documented field performance from the Federal Highway Administration’s Accelerated Loading Facility were subjected to long-term oven aging (LTOA) protocols. In addition to reheating loose mixtures containing reclaimed asphalt pavement and shingles, the two LTOA methods were 8 h at 135°C and 3 d at 95°C. The objective of this paper is to compare aging approaches, particularly whether equivalence between long-term aged procedures exists, and to highlight the sensitivity (or lack thereof) of common laboratory mixture performance tests. The Indirect Tensile Cracking (IDEAL-CT), Illinois Flexibility Index, Asphalt Mixture Performance Tester cyclic fatigue, and dynamic modulus tests were employed. The results show a collapse in mixture cracking indices when LTOA is incorporated, raising concerns over BMD implementation using criteria established exclusively with short-term oven aging. Use of [Formula: see text] presented a universal and logic shift in response from the reheated to LTOA state, affirming utility as an aging index. Blending insights can possibly be gleaned from the data, although 95 and 135°C LTOA procedures yield mostly equivalent linear viscoelastic and cracking indices.

Effects of Ground-Granulated Blast-Furnace Slag Used as Filler in Dense Graded Asphalt

Industrial waste materials are increasingly being used in asphalt to improve pavement quality and reduce environmental impacts. The aim of this research was to test the pavement distress-related effects of using ground-granulated blast-furnace slag (GGBFS) as a filler in hot mix asphalt. There is potential for GGBFS to be integrated into Western Australian (WA) asphalt pavements. GGBFS was used as a replacement for the conventional hydrated lime (HL) filler used in mix designs of the Main Roads WA specifications. A control mixture (1.5% HL) was compared with three prototype mixtures containing 1.5%, 3% or 5% GGBFS instead of HL. To investigate their characteristics, we conducted wheel tracking tests, four-point bending tests, and assessments with an asphalt mixture performance tester (AMPT). The findings support the use of GGBFS in asphalt pavements. The mixture with 3% GGBFS had the best fatigue life, rutting resistance and AMPT results.

Temperature dependence of dynamic and static modulus of elasticity of lightweight expanded clay aggregate concrete

The paper presents experimental research the static and dynamic modulus of elasticity of lightweight expanded clay aggregate concrete with averaged density of 1000 kg/m3. The static and dynamic modulus are obtained depending on the influence of temperature in the range from 5 to 50 °C with a step of 15 °C. The dynamic modulus was determined without pre-compression with a testing machine Asphalt Mixture Performance Tester. Besides the modulus of elasticity of lightweight concrete, the temperature dependence of unconfined compressive strength was also determined. Analysis of experimental data showed that with an increase in temperature, strength and modulus of elasticity slightly decrease, which is typical for concretes. For all cases, the temperature dependence can be characterized according to the linear law. Comparison of the static and dynamic modulus of elasticity showed that the dynamic modulus is 60-74% greater than the static modulus over the entire range of the studied temperatures.

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.

Performance evaluation of temperature effect on hot in-place recycling asphalt mixtures

Hot in-place recycling (HIR) is a novel technique to rehabilitate the surface layer of the pavements, in which recycling agents are commonly utilized to restore the binder rheological properties of reclaimed asphalt pavements (RAP). Considering the energy consumption and smoke issue, the heating temperatures for HIR containing 100% RAP mix are usually controlled around 110 °C, which is significantly lower than that for the traditional hot mix asphalt (HMA). . To evaluate the effect of temperature on the performance of 100% recycled asphalt mixtures after the HIR process, the materials obtained from an HIR project were remixed and compacted at different temperatures (110 °C, 120 °C, and 130 °C). The asphalt mixture performance tester, asphalt pavement analyzer test, Superpave indirect tension tests, and moisture susceptibility tests were conducted to evaluate the performances of the HIR mix. The staged extraction tests were used to identify the mobilized RAP binders under different temperatures. It was revealed that mixtures heated with a higher temperature exhibit better cracking and moisture resistance performances. It was also found that a larger proportion of the RAP binders can be activated to coat the aggregates at a higher mixing temperature, which may increase the rutting potential.

Comparison of varied specimen geometry for simplified VECD test with pulse-rest period

The viscoelastic continuum damage (VECD) model has become one of the promising methods for interpretation of asphalt mixture’s fatigue and damage behavior based on real physical responses, while asphalt mixture performance tester (AMPT) is the current standardized facility used for VECD characterization test. Since there is a trend to reduce the specimen size used in AMPT tests while maintaining the accuracy of test results, this paper investigated AMPT specimens’ geometry effect on VECD tests and the resultant damage characteristic curves when rest period is inserted after each load cycle (pulse-rest). A series of specifically designed dynamic modulus tests and simplified VECD (S-VECD) tests are conducted on three different sample geometries. The results have agreed with existing findings of that, in comparison to standard sizes, small specimen can produce reasonably accurate dynamic modulus master curves at low to medium temperatures, with the variation at higher temperature found to be caused by fluctuation of loading measurement. Remarkably, at both temperatures (12 and 20°C), a reduced size specimen is able to produce reasonably accurate damage characteristic curves either with 0.3s pulse-rest period or without rest period. Else, the small size specimen demonstrates high likelihood of controlled failure location within the measuring range. The results increase confidence of using reduced specimen size for VECD and rest period healing research by AMPT, with benefit of saving significant experimental time and material consumption.

A dissipated pseudo strain energy-based failure criterion for thermal cracking and its verification using thermal stress restrained specimen tests

Low-temperature cracking is one of the most prevalent types of distress in asphalt concrete pavements in regions where the air temperature undergoes a significant daily drop. This paper proposes a failure criterion that correlates the dissipated pseudo strain energy (DPSE) at the time of failure with the reduced strain rate. Uniaxial direct tension monotonic tests, axial compression dynamic modulus tests, and direct tension cyclic fatigue tests were performed using the Asphalt Mixture Performance Tester (AMPT) for a wide range of asphalt mixtures with different reclaimed asphalt pavement (RAP) contents, binder contents, virgin binder performance grades, and aging levels. The results show that the simplified viscoelastic continuum damage (S-VECD) model, which is characterized by the dynamic modulus and cyclic fatigue test results, can predict the stress-strain behavior of a given mixture subjected to monotonic tests at different temperatures and loading rates. This finding allows the prediction of DPSE in monotonic tension tests using the S-VECD model. The thermal stress restrained specimen test (TSRST) was then used to verify the DPSE-based failure criterion and the ability of the S-VECD model to predict thermal fracture behavior. The study results show that the predicted fracture temperatures match the measured ones for the study mixtures with reasonable accuracy. The study also used data from mixtures whose RAP contents, binder contents, virgin binder grades, and aging levels were systematically altered to verify the reasonableness of the proposed procedure to evaluate the differences in thermal fracture performance that are due to changes in these factors. The ability to predict the fracture stress and fracture temperature measured via the TSRST using the S-VECD model and the suggested DPSE failure criterion is of substantial practical and technical importance because it allows the prediction of both fatigue cracking and thermal cracking using a single set of tests, i.e., AMPT dynamic modulus and cyclic fatigue tests.

Strain-Level Determination Procedure for Small-Specimen Cyclic Fatigue Testing in the Asphalt Mixture Performance Tester

With an increase in small-specimen cyclic fatigue testing using the Asphalt Mixture Performance Tester (AMPT), researchers have observed that the strain-selection guidelines in AASHTO TP 107-14 that are intended for large AMPT cyclic fatigue tests are inadequate for testing small specimens. The machine compliance factor is significantly different for testing small specimens compared with large specimens because of different required load levels, resulting in a significant offset in the relationship between the input strain and the number of cycles to failure. To this end, this paper presents the development and verification of a phenomenological model that relates strain levels to dynamic modulus and number of cycles to failure for small-specimen AMPT cyclic fatigue tests, as well as the development of a corresponding stepped strain-level determination procedure that takes into account cases when the initially selected strain-level results in an unexpected number of cycles to failure. The final procedure includes a table with input strain levels and step strain increments for a wide range of dynamic modulus values as well as a flow chart to guide the use of the step strain adjustment procedure.

Rutting and Fatigue Properties of Cellulose Fiber-Added Stone Mastic Asphalt Concrete Mixtures

This paper investigates dynamic response, rutting resistance, and fatigue behavior of three stone mastic asphalt (SMA) concrete mixtures selected on basis of nominal maximum aggregate size (NMAS): 25 mm, 19 mm, and 12.5 mm using cellulose fiber added as 0.3% of the total weight of aggregate. Superpave gyratory specimens were fabricated and subjected to the dynamic modulus (E∗) and flow tests (flow number and flow time) using an asphalt mixture performance tester. The E∗ test results were employed to develop stress-dependent master curves for each mixture, indicating that the mixture with the NMAS of 25 mm is relatively stiffer than other tested mixtures; this mixture also exhibits excellent strength against rutting failure. In addition, fatigue parameter, which is derived from dynamic response and phase angle, is determined, and results reveal that 12.5 mm NMAS mix has relatively better resistance to fatigue than other selected mixtures. Furthermore, nonlinear regression model specifications were utilized to predict accumulated strains as a function of loading cycles. Also, a flow number model is developed that predicts the rutting behavior of mixtures, and results suggest that model predicted and observed outputs of 25 mm SMA mix are found to be very close. The results of this study help in understanding the performance and behavior of cellulose fiber-added stone mastic asphalt concrete mixtures under varying simulated temperature and stress levels, which can be used in areas where the premature failure of flexible pavements is often observed. The testing protocol employed in this study will also help in evaluating pavement performance using Mechanistic-Empirical Pavement Design Guide.