Characterization of Alaskan Hot-Mix Asphalt containing Reclaimed Asphalt Pavement Material

In order to properly characterize Alaskan HMA materials containing RAP, this study evaluated properties of 3 asphalt binders typically used in Alaska, PG 52-28, PG 52-40, and PG 58-34, and 11 HMA mixtures containing up to 35% RAP that were either produced in the lab or collected from existing paving projects in Alaska. Various binder and mixture engineering properties were determined, including true high binder grades, complex modulus (|G*|), and phase angle (δ) at high performance temperatures, MSCR recovery rate and compliance, BBR stiffness and m-value, DTT failure stress and strain for binders, and dynamic modulus, flow number, IDT creep stiffness and strength for mixtures. Binder cracking temperatures were determined through Thermal Stress Analysis Routine (TSAR) software along with BBR and DTT data. Mixture cracking temperatures were determined with IDT creep stiffness and strength data. It was found that rutting may not be a concern with Alaskan RAP mix, while low-temperature cracking concerns may still exist in RAP mix in Alaska. A savings of $13.3/ton was estimated for a 25% RAP mix, with consideration of Alaskan situations. Many recommendations for future RAP practice and research are recommended based on testing results and cost analysis.Alaska Department of Transportation Statewide Research Offic

Laboratory and Field Evaluation of Modified Asphalt Binders and Mixes for Alaskan Pavements

In order to properly characterize modified asphalt binders and mixes for Alaskan pavements, this study evaluated properties of 13 asphalt binders typically used in Alaska from three different suppliers, and 10 hot mix asphalt (HMA) mixtures which were either produced in the lab or collected from existing paving projects in Alaska. Various binder and mixture engineering properties were determined, including true high binder grades, complex modulus (G*), and phase angle (δ) at high performance temperatures, multiple stress creep recovery rate and compliance, bending beam rheometer stiffness and m-value, Glover-Rowe parameter, ΔT, rheological index, and crossover frequency for binders, and rut depth, critical strain energy release rate (Jc), Indirect tensile (IDT) creep stiffness and strength for mixtures. Binder cracking temperatures were determined using asphalt binder cracking device. Mixture cracking temperatures were determined with IDT creep compliance and strength data. It was found that rutting and cracking resistances of the mixtures with highly modified binders were better than the mixture with unmodified asphalt binder (PG 52-28). Future recommendations for highly modified asphalt binders applications and research were provided based on laboratory testing results and field survey evaluation

Cracking in asphalt materials

This chapter provides a comprehensive review of both laboratory characterization and modelling of bulk material fracture in asphalt mixtures. For the purpose of organization, this chapter is divided into a section on laboratory tests and a section on models. The laboratory characterization section is further subdivided on the basis of predominant loading conditions (monotonic vs. cyclic). The section on constitutive models is subdivided into two sections, the first one containing fracture mechanics based models for crack initiation and propagation that do not include material degradation due to cyclic loading conditions. The second section discusses phenomenological models that have been developed for crack growth through the use of dissipated energy and damage accumulation concepts. These latter models have the capability to simulate degradation of material capacity upon exceeding a threshold number of loading cycles.Peer ReviewedPostprint (author's final draft

Evaluation of Low Temperature Properties of HMA Mixtures

The deterioration of flexible pavements due to low temperature cracking is a significant and costly problem in the State of Nevada. The Nevada Department of Transportation initiated several research efforts aimed at exploring Nevada's problem with this distress. The research evaluated several newly developed low temperature performance tests under Nevada's conditions. The goal of the research was to determine the applicability of the tests for characterizing the low temperature response of Nevada's asphalt binders and HMA mixtures. This paper summarizes Nevada's experience with the SHRP low temperature tests and specifications; highlighting the effectiveness of the Superpave PG binder grading system and Thermal Stress Restrained Specimen Test. The contribution of asphalt aging to Nevada's cracking problem is also included in the paper. An investigation of the Superpave Performance Graded Binder tests has determined that the bending beam rheometer and the direct tension test correlate very well and it may not be necessary to run both tests as they are set up in the current Superpave specifications. The TSRST appears to provide the greatest value for evaluating low temperature properties of HMA mixtures. Findings from the research indicate that there are some significant correlations between the low temperature properties of asphalt binders and HMA mixtures if the mixtures are aged appropriately. This emphasizes the need to implement the appropriate conditioning procedure when low temperature cracking is used as part of the mix design and evaluation process. On the other hand, the research showed that when using polymer-modified asphalt binders, the low temperature grade of the asphalt binder maybe conservative enough where testing ofthe HMA mix may not be necessary

DEVELOPMENT OF INDIRECT RING TENSION TEST FOR FRACTURE CHARACTERIZATION OF ASPHALT MIXTURES

Low temperature cracking is a major distress in asphalt pavements. Several test configurations have been introduced to characterize the fracture properties of hot mix (HMA); however, most are considered to be research tools due to the complexity of the test methods or equipment. This dissertation describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be deployed at the Department of Transportation level. The primary advantages of this innovative and yet practical test include: relatively large fracture surface test zone, simplicity of the specimen geometry, widespread availability of the required test equipment, and ability to test laboratory compacted specimens as well as field cores. Numerical modeling was utilized to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. To develop the test procedure, a laboratory study was conducted to determine the optimal test parameters for HMA material. An experimental plan was then developed to evaluate the capability of the test in capturing the variations in the mix properties, asphalt pavement density, asphalt material aging, and test temperature. Five plant-produced HMA mixtures were used in this extensive study, and the results revealed that the IRT fracture test is highly repeatable, and capable of capturing the variations in the fracture properties of HMA. Furthermore, an analytical model was developed based on the viscoelastic properties of HMA to estimate the maximum allowable crack size for the pavements in the experimental study. This analysis indicated that the low-temperature cracking potential of the asphalt mixtures is highly sensitive to the fracture toughness and brittleness of the HMA material. Additionally, the IRT fracture test data seemed to correlate well with the data from the distress survey which was conducted on the pavements after five years of service. The maximum allowable crack size analysis revealed that a significant improvement could be realized in terms of the pavements performance if the HMA were to be compacted to a higher density. Finally, the IRT fracture test data were compared to the results of the disk-shaped compact [DC(t)] test. The results of the two tests showed a strong correlation; however, the IRT test seemed to be more repeatable

Evaluation of Warm Mix Asphalt for Alaska Conditions

INE/AUTC 11.0

Evaluation of Structural Contribution of Asphalt Mixtures Through Improved Performance Indices

A variety of approaches are available to design the pavement structures. These approaches are generally divided into two main categories as empirical and mechanistic-empirical (M-E) methods. The most widely used empirical method is the AASHTO 1993 design approach which uses material specific coefficients (layer coefficients) to quantify the structural capacity provided by each pavement layer. These coefficients are experimentally developed values from the AASHO road test which was conducted in the early 1960s and are based on statistical regressions. Almost no fundamental or engineering mixture properties or explicit failure criterion were used in their original development. On the other hand, the M-E approaches use fundamental mixture properties such as complex modulus (E* and phase angle) to determine the pavement’s structural response. However, M-E approaches require extensive data for local calibration and as a results, many state agencies are still using the empirical approach. One of the major modifications in the AASHTO 1993 design approach has been to update the layer coefficients (a-value) of the asphalt mixtures using different mechanistic and performance-based measures. The layer coefficients have significant influence in determining the layer thickness which translates into the structural contribution of the layers as well as the long term performance of the pavement and consequently the construction and maintenance costs. Therefore, it is critical to determine reliable a-values that are most relevant to the regional conditions and locally used materials. A set of 18 commonly used mixtures in New Hampshire were selected for performance testing and evaluation of structural contribution in terms of layer coefficients. In order to develop the layer coefficients, comprehensive research was performed on the performance and properties of the mixtures through different mechanistic-based laboratory testing methods. In addition, mixtures from all over the New England region were used to develop and validate three novel performance index parameters for rutting, fatigue and transverse cracking. The developed parameters were incorporated with the field distress data such as International Roughness Index (IRI) in order to develop mechanistically informed layer coefficients for New Hampshire flexible pavement design approach

Quantification and Characterization of Fracture Resistance in Asphalt Concrete Based on R-Curve Method

The application of fracture energy is widely applied in the evaluation of cracking in the laboratory for asphalt concrete. However, this single number does not provide information on the characterization of the initiation and propagation of cracks. The Resistance Curve method, or R-Curve, is widely applied in characterizing various materials including, but not limited to, metal, polymer, rock, and composite. This research R-Curve method introduces asphalt concrete through a stepwise approach. First, in chapter one, there is a literature review of the history of fracture mechanics, fracture research in asphalt concrete, and an examination of the role of R-Curve application in various materials. Second, the current widely applied fracture energy analysis techniques are studied comprehensively for three types of asphalt concrete, three levels of aging, and two levels of moisture condition. The main limitation of fracture energy found in this chapter is that fracture energy alone is not always able to differentiate the fracture resistance of the three different materials examined. Third, the R-Curve method is applied to analyze and evaluate the same materials examined in chapter two. It is found that R-Curve can characterize and quantify the crack initiation and propagation, and the effects of aging and moisture damage on crack propagation are captured. Finally, a further investigation of R-Curve is performed to establish the envelope R-Curve considering the internal factors of aggregate size and binder grade, and the external factors of testing temperature and loading rate. The effects of aggregate size, binder grade, temperature, and loading rate on crack initiation and propagation are found by the parameters of cohesive energy and energy rate that are extracted from R-Curve. In conclusion, it is found that the R-Curve method can characterize and quantify the crack initiation and propagation for asphalt concrete

Understanding Oxidative Aging of Asphalt Binder and it\u27s Effects on Cracking Susceptibility of Asphalt Mix

Every year around 400 million tons of asphalt mix is being laid in the United States and a significant portion of it is required for pavement rehabilitation. Cracking is one of the most common pavement distresses that is still not fully understood by the researchers. Very few states mandate tests for cracking resistance during the mix design phase; in addition, the test methods vary a lot from state to state. In the presence of oxygen, the asphalt binder over time undergoes chemical changes and becomes stiff which is known as oxidative aging that makes asphalt pavement more susceptible to cracking. Therefore, proper characterization of asphalt aging is a prerequisite to study the cracking mechanism of asphalt mix. In this dissertation, efforts are given for characterization of oxidative aging, investigation of the effect of aged binder on cracking susceptibility, and development of an antioxidant to reduce the aging-induced cracking. In this study, rheological characterization of laboratory aged binder and extracted binder from asphalt mix was performed using dynamic shear modulus of the binder to understand oxidative aging. Then the correlation between laboratory binder aging and binder aging in asphalt mix was established and a Rolling Thin Film Oven (RTFO) aging test protocol for warm mix asphalt (WMA) was developed. Another factor for cracking susceptibility of asphalt pavement is the excessive content of reclaimed asphalt pavement (RAP). RAP is added to the hot mix asphalt (HMA) for economic and environmental interest but the highly aged binder in RAP makes the mix stiffer and escalates the cracking. Because it is quick and simple, the viability of using a handheld Fourier Transformed Infrared (FT-IR) spectrometer was investigated to detect and quantify the aging of binder by measuring the absorbance intensity of carbonyl groups. An in-situ test method was developed to determine the reclaimed asphalt pavement (RAP) content in the plant mix using a handheld FT-IRS. The use of rejuvenators is the most suitable strategy to accommodate a higher amount of RAP in HMA and bio-based rejuvenators are of high interest. In this study, four types of cracking tests were performed on asphalt mix made with two different categories of rejuvenators: petroleum-based and bio-based oil. It was concluded that petroleum-based aromatic oil performed better to restore the cracking potential of the mix with high RAP content. Sound understanding of the cracking mechanism is necessary to find the right cracking susceptibility test for asphalt mix and design a cracking resistant mix. A finite element model of semi-circular bend (SCB) test of asphalt mix incorporating the cohesive zone material (CZM) model was performed using ANSYS to simulate and predict the fracture potential of asphalt mix as conducted in the laboratory according to ASTM D 8044 test method. The CZM properties of fine aggregate mastic (FAM) needed for ANSYS model of SCB test was determined by a laboratory double cantilever beam test and corresponding finite element model of double cantilever beam test., It was concluded that critical energy release rate (Jc) of asphalt mixture predicted from ANSYS model of SCB test was precise when compared with the laboratory SCB test of asphalt mix. Finally, locally sourced Lignin was used as an asphalt performance enhancer as well as an antioxidant. It was observed that lignin could improve the high-temperature performance grade of the binder and reduce the aging index. Mix made of lignin modified binder showed better cracking resistance by improving the flexibility index. Through this study, understanding oxidative aging helped with developing a revised short-term aging protocol for warm mix asphalt. One of the immediately implementable outcomes of this research is the in-situ application of handheld FT-IR spectrometer for quality control during the mix production at the plant through determining the reclaimed asphalt pavement content. This research will contribute to choosing suitable rejuvenators by understanding the cracking mechanism of asphalt mix through different tests. The finite element cohesive zone material model developed in this study can precisely predict fracture resistance of the mix in semicircular bending test by performing a double cantilever beam test of fine aggregate mastic. Viability of using bio based rejuvenator for RAP mixes and also the suitability of utilizing locally sourced lignin as an oxidant in asphalt binder were addressed in this research and the findings will help implement these environmentally friendly alternatives in resolving cracking related problems in asphalt pavements

EFFECTS OF AGGREGATES ON PROPERTIES AND PERFORMANCE OF MASTICS AND SUPERPAVE HOT MIX ASPHALT MIXTURES

Superpave, a set of advancements in testing devices and specifications for asphalt binders and mixtures, was limited to address the effects of aggregates. Because aggregates represent around 95% in mass of the asphalt mixtures, it is important to understand how these materials affect properties and performance of such mixtures. This research focus on how different types and contents of aggregates affect properties of mastics and asphalt mixtures, and their performance considering the viscoelastic nature of the asphalt material. Five different types of aggregates and hydrated lime were used for sample fabrication together with two different binders. Several different tests were performed to the aggregates separately. Viscoelastic properties for both mastics and hot mix asphalt mixtures were characterized. In addition, the mixtures produced with those aggregates were also evaluated for rutting and fatigue performances using the APA and UTM-25kN machines. Among the studies conducted in this research work are: restricted zone, a controversial concept and its redundancy; rutting potential of mixtures with different coarse and fine angularities; the stiffening potential of binders provided by different fillers; the stiffening provided by different contents of hydrated lime to asphalt concrete mixtures and fatigue and rutting potential of mixtures with different contents of hydrated lime. The results indicate that the restricted zone should not be a criterion for the selection of mixture gradations, that angularity somewhat affects the rutting potential of asphalt concrete mixtures, that fillers of different materials provide different gain in stiffness for binders and that this improvement is binder dependent. Also, hydrated lime was found to have higher stiffening potential than general mineral fillers used in this study. Hydrated lime was also proven to improve the stiffness of asphalt concrete mixtures. Even though stiffening the mixtures, hydrated lime was shown to improve the fatigue performance of the mixtures. Finally, this filler also improved the rutting resistance of mixtures