Balanced Mix Design Research Articles

Demonstration Project for Ground Tire Rubber and Post-Consumer Recycled Plastic-Modified Asphalt Mixtures

Research has demonstrated that asphalt pavements can be a strategic destination for some of the major streams of waste materials around the globe, such as scrap tires and plastics. Ground tire rubber (GTR) from scrap tires has been used in asphalt pavements since the 1960s but has yet to approach its full potential in relation to market adoption. The heightened restrictions imposed by China in relation to waste stream contamination in 2018 have catalyzed research on incorporating post-consumer recycled (PCR) plastics into asphalt pavements. A field demonstration project was carried out in Columbia, MO to evaluate modern recycled plastic and GTR additives in an asphalt pavement overlay. The demonstration focused on dry-process modification, which requires minimal alterations to an existing asphalt plant and allows a higher amount of recyclates to be utilized. The project was also designed to assist in the Missouri Department of Transportation’s early roll-out of balanced mix design asphalt design and quality assurance specifications. The results of the study indicated the viability of dry-process GTR and PCR plastic additives used with neat (unmodified) asphalt binder as an alternative to binders modified with virgin polymers, chemical treatments, or both, in a wet process. The results of the study also suggest the viability of hybrid wet polymer-modified binder with dry-process PCR plastic as a greener alternative to binders modified with virgin polymers, chemical treatments, or both. Future studies will be needed to examine additional PCR plastic streams, especially mixed polymer streams.

Implementation considerations of Balanced Mix Design in practice: recent experience in Vermont

This paper discusses the implementation considerations of Balanced Mix Design (BMD) in both design and production phases according to the recent experience from the agency and a contractor in Vermont since BMD was implemented by Vermont Agency of Transportation (VTrans) in 2019. In the design, the sensitivity of selected performance tests to mix design factors and the impact of asphalt binder source are two important aspects to consider as both agency and contractor need to understand the implications on the potential change of mix compositions. There are also several critical things to consider if BMD is implemented in production, including but not limited to the impact of production variation, the difference between design and production, and so forth. A case study through a VTrans pilot project constructed in 2020 season is discussed to demonstrate the importance of these considerations.

Development of Balanced Mix Design for Asphalt Mixtures with Very High Reclaimed Asphalt Pavement (Rap)

Development of Balanced Mix Design for Asphalt Mixtures with Very High Reclaimed Asphalt Pavement (Rap)

Effect of Aramid Fibers on Balanced Mix Design of Asphalt Concrete

Fiber-reinforced asphalt concrete (FRAC) was tested using limestone, PG 64-22 binder, and 20% reclaimed asphalt pavement (RAP). After mixing fibers with different lengths and dosages, they were extracted and recovered to evaluate their dispersion in the FRAC. The uniaxial fatigue test, IDEAL CT test, and flow number test were performed on FRAC with different fiber lengths and asphalt contents. The balanced mix design (BMD) approach was then used to analyze the uniaxial and flow number test results in order to evaluate the effect of aramid fibers on fatigue and rutting resistance of the pavement. The dispersion test showed that the 19 mm and 10 mm aramid fibers at a dosage rate of 0.5 g/kg provided the best dispersion. The 19 mm fibers showed better performance test results than the 10 mm and 38 mm fibers. The BMD approach provided ranges of asphalt contents to produce mixes with certain resistances to fatigue and rutting. The BMD approach also demonstrated the effect of fibers with different lengths on increasing the resistance to fatigue and rutting. The study concluded that the 19 mm fibers with a dosage of 0.5 g/kg produce best results. The BMD approach is a good tool that can be used to refine the mix ingredients, including additives such as fibers, in order to optimize pavement resistance to various distresses such as fatigue cracking and rutting.

Precision Estimates and Statements for Performance Indices from the Indirect Tensile Cracking Test at Intermediate Temperature

The Virginia Department of Transportation (DOT) has taken initiatives to implement the Balanced Mix Design (BMD) method to assure the long-term service life of its pavement network from a mixture quality standpoint. As part of this initiative, the cracking tolerance (CT) index obtained from the indirect tensile (IDT) test at intermediate temperature in accordance with ASTM D8225-19 was selected for evaluating the cracking potential of dense-graded surface asphalt mixtures. This prompted the need to generate the precision estimates (repeatability and reproducibility) for the test method for proper implementation during quality measurement practices. Thus, this interlaboratory study was undertaken to determine the precision estimates of the CT index calculated from the IDT test and to develop the associated precision statements. In addition, fracture strain tolerance (FST) and indirect tensile strength were included. Two asphalt mixes with significantly different CT index values were designed for the evaluation. Forty-six pairs of five replicate sets of compacted specimens (one set for each mix) were sent to 41 participating laboratories to be tested at 25°C. The test results were checked for data quality. The effects of loading rate and manufacturers on the indices were also evaluated. The test results indicated that one third of the sets were not tested in full accordance with the ASTM standard, indicating a need for training. The results also indicated that the specified loading rate of 50 ± 2 mm/min in ASTM D8225-19 for the IDT test may need revision. Finally, the precision estimates and associated statements for the three indices were presented.

Balanced Mix Design Benchmarking of Field-Produced Asphalt Mixtures in Maine, U.S.

Performance testing has been recognized by state highway agencies (SHAs) in the U.S. and the asphalt paving industry as an important tool to complement volumetric properties for improving asphalt pavement performance. Thus, Maine Department of Transportation (MaineDOT) initiated a research effort in 2019 to evaluate the cracking and rutting resistance of asphalt mixtures using several performance tests, including the Hamburg wheel-tracking test (HWTT), indirect tensile cracking test (IDEAL-CT), cyclic fatigue test, and stress sweep rutting (SSR) test. These tests were conducted on reheated common plant-produced asphalt mixtures, and results were analyzed to: (1) develop baseline rutting and cracking performance; (2) evaluate the effects of mixture properties on the performance test results; and (3) verify the performance enhancement from the extended use of polymer-modified asphalt binders. Several mixture properties, such as nominal maximum aggregate size (NMAS), binder performance grade (PG), binder content (Pb), and reclaimed asphalt pavement (RAP) %, were found to have statistically significant effects on the mixture rutting and cracking resistance, especially the HWTT and IDEAL-CT results. Based on the proposed criteria for rutting strain index (RSI) and apparent damage capacity (Sapp), the asphalt mixtures tested would provide satisfactory rutting performance under heavy traffic, and satisfactory cracking performance under standard traffic. In addition, based on the IDEAL-CT benchmarking results, mixtures with polymer-modified binder and/or smaller NMAS were found to have higher cracking tolerance index (CTindex) results. The information from the research effort will help MaineDOT to achieve its goal to move beyond sole use of volumetric properties for asphalt mixture design and acceptance with the implementation of balanced mix design (BMD) for improving the field performance of asphalt pavements.

Physicochemical characterization of short and long-term aged asphalt mixtures for low-temperature performance

Current pavement engineering shift towards Balanced Mix Design warrants performance testing of asphalt mixtures at low temperatures. The Bending Beam Rheometer (BBR) is an effective tool to characterize asphalt mixture’s low-temperature properties based on AASHTO TP125. This study utilized the BBR for physical characterization of 32 different asphalt mixtures composed of a PG 64–28 binder, two Job-Mix Formulae (JMF), four different RAP contents, and four different aging methods. Chemically extracted binder from the aged mixtures was then analyzed using the absorbance-based Fourier-Transform Infrared Spectroscopy (FT-IR) to identify the critical functional groups. The FT-IR analysis's semi-quantitative results were validated using the Energy Dispersive X-Ray Analyzer on the Scanning Electron Microscope (SEM-EDX). The reduction of carbon and sulfur concentration due to oxidation was correlated to the loss of cohesion between asphalt mastic and aggregates. Furthermore, microstructural damage was found in the aged specimens at a 200x magnification. Overall, this study provides a comprehensive and feasible method to perform physicochemical characterization of asphalt mixtures.

Validation of Performance-Based Specifications for Surface Asphalt Mixtures in Virginia

The Virginia Department of Transportation (VDOT), like many owner agencies, is interested in ways to facilitate the increased durability of asphalt mixes in an effort to make its roadway network more sustainable, longer lasting, and more economical. The balanced mix design (BMD) method proposes to address this through the incorporation of performance criteria into mix design and acceptance. VDOT has committed to the implementation of the BMD method in an effort to improve asphalt mix performance. The purpose of this study was to continue advancing efforts toward implementation of BMD through the evaluation of 13 asphalt mixes using performance-indicating laboratory tests, validation of the initial performance tests selected for BMD use, and validation of the initial test threshold criteria. Based on the results, the asphalt pavement analyzer (APA) rut test, indirect tensile cracking test (IDT-CT), and Cantabro test were found suitable for continued use in BMD. The current threshold criteria for all three tests were found reasonable based on additional mix testing. The study recommends that APA rut test and IDT-CT results should be compared and correlated to fundamental rutting and cracking tests, respectively, as well as to performance predictions obtained from mechanistic-empirical pavement design simulations, and to field performance for full assurance that test threshold values are appropriate. It was further recommended to evaluate the Cantabro, IDT-CT, and APA rut tests to determine acceptable variability and establish precision statements.

Systematic evaluation of effects of recycled materials and mix design parameters on the rutting and cracking performance of asphalt mixes

Problems associated with the rutting and cracking of asphalt mixes call for the use of balanced mix design and thus have received close attention from researchers and practitioners. The increased use of recycled materials, such as recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS), further complicates the performance of asphalt mixes. Most studies of RAP and RAS have focused on the inclusion of these recycled materials in asphalt mixes designed for research purposes, which could differ from mixes designed by contractors for practical use. Therefore, a systematic review is needed of the effects of recycled materials and mix design parameters on the rutting and cracking performance of mixes designed by contractors. In addition, contractors need guidance in developing asphalt mixes that meet specifications that require rutting and cracking tests instead of simply relying on trial and error. To address these needs, in this study, rutting and cracking tests of forty contractors’ asphalt mix designs were conducted and the most effective design parameters on the performance of asphalt mixes were presented and discussed. These mixes included different percentages of RAP or RAP/RAS, performance grades of binders, design gyration numbers, aggregate gradations, and other volumetric properties. The provided results and discussions can be used as guidance for contractors to improve their mix designs to meet specifications.

High-temperature creep and low-temperature relaxation of recycled asphalt mixtures: Evaluation and balanced mix design

In this study, high-temperature creep and low-temperature relaxation performance of recycled asphalt mixtures, with different contents of reclaimed asphalt pavement (RAP), rejuvenator, and virgin asphalt, were evaluated. The creep index (εp/FN) and relaxation index (ts) were selected as evaluation indices of prepared samples. Based on the comparison of εp/FN and ts of the recycled asphalt mixture and virgin asphalt mixture, a new balance design method was proposed. The results showed that εp/FN increased gradually with the increase of rejuvenator and virgin asphalt when the RAP content was constant, while ts was decreased. It indicated that the high-temperature creep performance of the recycled asphalt mixture was improved, but the low-temperature relaxation performance became poor. The high-temperature creep and low-temperature relaxation evaluation indices could be directly compared, and the accuracy of the comparison results was improved. Therefore, the proposed balanced design was developed based on the comparison of the absolute value by mathematical formulas, which was not only simple or intuitive but also easy to operate. When the RAP content was less than 30 %, the optimum balance point of the high-and low-temperature performance was lmin. When the RAP content was 50 %, the best low-temperature relaxation performance point was the optimum balance point with the prerequisite of a good high-temperature creep performance. It is a new method to analyze the high-and low-temperature performance of recycled asphalt mixtures, which is of great significance to improve the durability of the recycled asphalt pavement.

Local agency transition to balanced mix design

ABSTRACT Construction techniques and mix design methods are subjected to continuous development along with new inventions, technologies, and related implementation strategies. Due to recent materials introduced into asphalt mixtures such as modified asphalt binders, high percentages of Reclaimed Asphalt Pavement (RAP), warm mix technologies, recycling agents, and others, the asphalt industry is rapidly moving toward the Balanced Mix Design (BMD) method. Current asphalt mixture design methods are structured around meeting a range of volumetric requirements and sometimes other properties such as stability and/or moisture sensitivity. Although this allows for volumetric parameters to be monitored and controlled during production, it does not give much engineering insight as to how the mixture will perform under field conditions. The objective of this research was to assist the local agencies in Nevada with the transition from the Marshall method to the BMD, the latest methodology for designing asphalt mixtures, using the Superpave gyratory compactor and performance tests. Based on experimental data, the research team aimed to create an approach for an optimised, and high-performing mix designs with the use of 15% RAP along with an implementation plan that could be adopted by local agencies and serve as an example for other agencies.

Evaluation of the Minnesota Asphalt Mixtures Based on Balanced Mix-Design Approach

AbstractThe State Department of Transportation have started to put into practice performance tests as a part of the volumetric mix design process to evaluate asphalt mixtures performance, including...

Development of a Balanced Mix Design Method in Oregon to Improve Long-Term Pavement Performance

Most state Departments of Transportation (DOTs) and asphalt contractors do not think that commonly used asphalt mixture properties, such as voids in mineral aggregate (VMA), voids filled with asphalt (VFA), and dust-to-binder ratio, reflect the long-term performance of asphalt mixtures. In addition, there are several new additives, polymers, rubbers, and high-quality binder types incorporated into asphalt mixtures today. Volumetric mixture design methods are not capable of capturing the benefits of using all these new technologies on asphalt mixture performance. Furthermore, the interaction of virgin binders with reclaimed asphalt pavement (RAP) mixtures with high binder replacement contents and the level of RAP binder blending into the asphalt mixture are still not well understood. Because of all these complications related to the more complex structure of asphalt mixtures, simple volumetric evaluations to determine the optimum binder content may not result in reliable asphalt mixture designs. Two volumetrically identical mixtures may provide completely different rutting and cracking performance according to laboratory tests. For all these reasons, in this study performance tests for rutting and cracking are incorporated into current asphalt mixture design methods to make it possible to validate or revise the optimum binder content determined by the volumetric mix design method (the only method currently used for asphalt mix design).

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.

Development of a coherent framework for balanced mix design and production quality control and quality acceptance

Asphalt mixtures are becoming increasingly complex, and given ever-changing components of asphalt mixtures, both balanced mix design (BMD) and production quality control and quality acceptance (QC/QA) are critical to have a mixture performing well in the field. This paper established a coherent BMD/QC/QA framework that has four inter-connected components: (1) volumetric mix design and selection of multiple asphalt contents for mixture performance evaluation, (2) mixture performance evaluation at multiple asphalt contents and selection of the balanced asphalt content, (3) mixture performance verification at the balanced asphalt content, and (4) production QC/QA testing. One set of laboratory tests and associated acceptance criteria are recommended for the mixture performance evaluation and the production QC/QA testing and the other set for the mixture performance verification where DOTs can choose their preferred performance verification tests. Furthermore, two practical loose mixture aging protocols are developed, one for short-term aging used in the process of the volumetric mix design, the mixture performance evaluation, and the production QC/QA testing and the other for mid-term aging employed in the mixture performance verification. The recommended short-term aging protocol is to age the loose mixture in a force draft oven for 2 hrs at the mixture compaction temperature, while the mid-term aging protocol consists of three steps: (1) short-term aging, (2) 20 hrs loose mixture aging at 100 °C, and (3) reheating to for compaction. A case study is presented at the end of this paper to demonstrate the whole process of the framework including the actual plant production QC testing.

Application of Balanced Mix Design Methodology to Optimize Surface Mixes with High-RAP Content

The most common use of reclaimed asphalt pavement (RAP) is in the lower layers of a pavement structure, where it has been proven as a valid substitute for virgin materials. The use of RAP in surface mixes is more limited, since a major concern is that the high-RAP mixes may not perform as well as traditional mixes. To reduce risks or compromised performance, the use of RAP has commonly been controlled by specifications that limit the allowed amount of recycled material in the mixes. However, the ability to include greater quantities of RAP in the surface mix while maintaining a satisfying field performance would result in potential cost savings for the agencies and environmental savings for the public. The main purpose of this research was to produce highly recycled surface mixes capable of performing well in the field, verify the performance-based design procedure, and analyze the results. To produce the mixes, a balanced mix design (BMD) methodology was used and a comparison with traditional mixes, prepared in accordance with the requirements of the Virginia Department of Transportation’s volumetric mix design, was performed. Through the BMD procedure, which featured the indirect tensile cracking test for evaluating cracking resistance and the Asphalt Pavement Analyzer (APA) for evaluating rutting resistance, it was possible to obtain a highly recycled mix (45% RAP) capable of achieving a better overall laboratory performance than traditional mixes designed using volumetric constraints while resulting in a reduction in production cost.

Performance Characterization of Recycled-Asphalt Pavement with Stabilized Rubber–Modified Asphalt Using Balanced Mix Design Method

AbstractThe rejuvenator is typically utilized to partially recover the mechanical properties of reclaimed-asphalt pavement (RAP). Although the rejuvenator works effectively in softening the highly ...

Development of a multi-stage semi-circle bending cyclic test to evaluate the cracking resistance of asphalt mixtures

This study aimed to develop, evaluate, and validate a new cyclic cracking assessment test that has advantages over the available monotonic and cyclic cracking assessment tests. Also, it addresses the major concerns related to the implementation of the Balanced Mix Design (BMD) such as long specimen preparation and testing time and the validity of cracking performance assessment tests. The laboratory evaluation findings showed that the proposed test and derived performance indicators were sensitive to the composition of mixes, had variability lower than other cyclic tests, and similar to the one obtained from the monotonic performance indicators. Besides, it correlated well with the observed field cracking performance of sixteen field projects. The derived indicators were able to distinguish between different field cracking performance groups and develop a pass/fail performance cracking assessment threshold.

Development of a performance-related framework for production quality control with ideal cracking and rutting tests

Many state departments of transportation (DOTs) are in the process of developing or implementing performance specifications for asphalt mixes. In addition to balanced mix design (BMD) methods, another critical component of a performance specification is production quality control (QC). Current production QC testing, including asphalt binder content, aggregate gradation, and laboratory compaction density, does not directly relate to mix performance. To ensure what is produced at the plant is similar to what was originally designed in the laboratory, performance tests should be part of the production QC testing. This paper first identifies two simple, practical, performance related tests suited for production QC: Ideal cracking test (IDEAL-CT) and Ideal shear rutting test (IDEAL-RT). Next, the correlations between the IDEAL-CT and -RT with cracking and rutting tests commonly used by DOTs are presented to examine whether these two simple tests still can be used for production QC even if cracking or rutting tests other than the IDEAL-CT and -RT are used for BMD. Furthermore, this paper addresses a practical question: how to rapidly cooling compacted specimens to a testing temperature for QC. This paper also discusses how to establish acceptable QC criteria for the IDEAL-CT and -RT during mixture design. Based on the information presented, this paper recommends a performance-related production QC framework: IDEAL-CT for cracking resistance, IDEAL-RT for rutting resistance, and laboratory compaction density. As demonstrated in a contractor’s QC lab, it is feasible to conduct the new production QC testing on a sublot (say 500 tons of mix production) basis.

Performance of Hot and Cold Recycled Mixtures with High Reclaimed Asphalt Pavement Content

Florida Department of Transportation yearly maintenance and rehabilitation activities include milling and resurfacing of approximately 2,000 lane miles of roadway, with an average resurfacing depth of about 2.1 in. (55 mm). These activities result in the generation and accumulation of roughly 1.8 million tons of reclaimed asphalt pavement (RAP) each year. The use of elevated quantities of RAP in asphalt pavement provides an environmentally responsible solution to the accumulated RAP surplus in some urban areas, while at the same time offering an economical pavement maintenance and rehabilitation option to local agencies facing budget constraints. The objective of this project was to compare the performance of mixtures with 60% RAP content to be used primarily on low volume roads (average daily traffic <750 vehicles) and suggest adequate test methods within the context of a balanced mix design approach. To accomplish this objective, three types of mixtures were considered: hot, cold with emulsion, and cold with foamed binder. Performance testing included intermediate temperature cracking, rutting, moisture susceptibility, and durability. The hot recycled mixtures showed good moisture susceptibility and cracking resistance, especially when rejuvenators were incorporated. The cold recycled mixtures showed poor moisture susceptibility and durability characteristics, which were alleviated when hydrated lime or Portland cement was incorporated in the emulsified and foamed mixtures, respectively. Most hot recycled mixtures, and all the cold recycled mixtures, exhibited poor rutting behavior, likely because of the harsh conditions of the test. A life-cycle cost analysis demonstrated more favorable savings when cold recycled mixtures were used.