Haifang Wen

Laboratory Evaluation of Waste Cooking Oil-Based Bioasphalt as an Alternative Binder for Hot Mix Asphalt

Increased environmental regulations and the rising costs of asphalt binder have encouraged researchers to investigate alternative binders that can be used for hot mix asphalt (HMA). This study focused on using bioasphalt as a possible alternative binder to petroleum-based asphalt. To evaluate bioasphalt as a HMA binder, both binder and mixture tests were performed. Bioasphalt was blended with traditional binders at different percentages (0, 10, 30, and 60%) by weight of the base binder. Binder test results, based on constant shear loading tests and multiple stress creep and recovery tests, showed that the addition of bioasphalt decreased the resistance to fatigue and rutting. The HMA mixture performance tests indicated that the addition of bioasphalt to the mix reduced the stiffness of the mix (dynamic modulus) and its resistance to rutting and fatigue cracking, but increased the resistance to thermal cracking. The moisture susceptibility test shows that bioasphalt mixes passed the minimum tensile strength ratio requirement.

Use of fracture work density obtained from indirect tensile testing for the mix design and development of a fatigue model

Bottom-up fatigue cracking, which is a major distress in asphalt pavements, is due to repeated traffic loading that induces tensile stress in the asphalt concrete layers. Fatigue cracks are observed as interconnected cracks in the wheelpath of asphalt pavements. Fatigue cracking can and should be addressed during both the mix design and pavement design. Therefore, a performance indicator is needed during the mix design to select a fatigue-resistant mix. In addition, a fatigue model, which includes the performance indicator, is needed to design the pavement structure. This study is conducted to determine a performance indicator for fatigue and to develop a new fatigue model, based on the Federal Highway Administrations Accelerated Load Facility experiments on fatigue. It is found that the fracture work density (FWD) obtained from indirect tensile testing correlates highly with field fatigue performance, whereas fracture energy fails to correlate with field fatigue performance. A new fatigue model based on FWD is developed herein and is found to be effective in characterising field fatigue performance. Further study is needed to validate the effectiveness of FWD and the new fatigue model.

Characterizing Fatigue of Asphalt Binders with Viscoelastic Continuum Damage Mechanics

Fatigue cracking, either top-down or bottom-up, is one of the major distresses for asphalt pavements. As the binding agent, asphalt binder plays a critical role in the fatigue resistance of hot-mix asphalt (HMA). Accurate characterization and proper selection of fatigue-resistant asphalt binders could prolong the fatigue life of asphalt pavement. The fatigue indicator currently used in the Superpave® binder specification is based on the fatigue behaviors of asphalt binders within the undamaged, linear viscoelastic range. There have been some controversies on the validity of this parameter. In reality, HMA and asphalt binders develop cracks under repeated traffic loads. Therefore, a more fundamental approach is needed to characterize the fatigue behaviors at a stage of damage to understand the true fatigue mechanism of the asphalt binder. This paper presents the study of the application of viscoelastic continuum damage (VECD) mechanics, which has been successfully applied to HMA, to test results of asphalt binders in the shear mode under various loading conditions. The results indicated that VECD can be effectively applied to asphalt binders, present a good potential for characterizing asphalt binders and predict the contribution to fatigue resistance by means of a fundamental approach that parallels some of the advanced work regarding asphalt mixtures. This potential could allow for a unified model for fatigue of mixtures and binders.

Evaluation of Effects of Recycled Concrete Aggregate on Volumetrics of Hot-Mix Asphalt

Each year around 200 million tons of demolition wastes are produced from aging U.S. infrastructures. Of that amount, 100 million tons are portland cement concrete debris. Disposal of these wastes in landfills has been a traditional solution, but environmental regulations, costs, and a lack of landfill areas have hindered safe disposal. These problems have led to a search for alternate ways of reusing demolition wastes by recycling. Recycling the concrete waste not only reduces the waste disposal problem but also reduces the quarrying of virgin aggregate. The incorporation of recycled concrete as a hot-mix asphalt (HMA) aggregate can be a viable option in terms of costs and environmental considerations. This use of recycled concrete aggregate (RCA) as an HMA aggregate can be beneficial for constructing low-volume roads. RCA differs from virgin aggregates in that there is cement paste on the surface of the recycled concrete. In this study, 5% RCA was evaluated as an HMA aggregate. Mix designs were conducted, and the effect of RCA on the volumetrics of HMA was evaluated. The mix design results indicated that RCA is absorptive, and that as the percentage of recycled concrete increased in the mix, the optimum asphalt content increased linearly. The statistical regression model showed that RCA had significant effects on the volumetrics of the mix.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Modeling the Effects of Temperature and Loading Rate on Fatigue Property of Asphalt Binder

Fatigue cracking is one of three major distresses for asphalt pavement. Asphalt binder is a very important component of asphaltic mixture. The fatigue performance of asphalt binder also greatly affects that of asphaltic mixture. Asphalt binder’s fatigue characteristics are affected by external conditions, such as temperature and loading rate. It is warranted to study the effects of these external conditions on fatigue of asphalt binder and take them into account. New fatigue tests and properties have been proposed to characterize the fatigue behavior of asphalt binders, such as monotonic constant shear-rate tests. This study investigated the effects of temperature and shear rate on fatigue properties of asphalt binder. Two asphalt binders were tested with a range of temperature and shear rates. It was found that time-temperature superposition principle also applies to critical strain energy density and shear strength of asphalt binders. The values of shift factors for building the master curves of critical strain energy and shear strength are comparable.

Long-Term Field Rutting and Moisture Susceptibility Performance of Warm-Mix Asphalt Pavement

Although warm-mix asphalt (WMA) has been used in pavement construction in recent years, the long-term field performance of WMA pavements has not been studied extensively. In response, this study investigated 28 pavement projects in the United States, covering different climate zones, WMA technologies, service years, pavement structures, and traffic volume levels. The long-term field rutting performance between WMA pavements and hot-mix asphalt (HMA) pavements was compared. Field samples were extracted for laboratory experiments. Significant determinants (engineering or material properties) that correlate with rutting performance also were investigated. A simple rutting resistance index obtained from the Hamburg wheel-tracking test was found to be the significant determinant (material property) that correlates best with field rutting performance. The significant mix design parameters that affect the rutting resistance index were analyzed to suggest a better rutting-resistant mix design. In addition, no moisture damage or raveling was observed for the selected projects in the field. Therefore, the moisture susceptibility of the mixes was evaluated in regard to the stripping inflection point of field cores as obtained from the Hamburg wheel-tracking test results. It was found also that most of the mixes that did not include an antistripping agent exhibited a stripping inflection point, suggesting the need for the addition of an antistripping agent in pavement mixtures.

A Laboratory Study to Predict the Rutting and Fatigue Behavior of Asphalt Concrete Using the Indirect Tensile Test

Rutting, fatigue, moisture susceptibility, and thermal cracking are the primary distresses of asphalt pavement. Currently several test methods are used to predict the rutting and fatigue behavior of asphalt concrete. This study uses the indirect tensile (IDT) test to evaluate both the rutting and fatigue behavior of asphalt. Recycled concrete aggregate (RCA) and virgin aggregate are blended at different percentages (0 %, 20 %, 40 %, 60 %, 80 %, and 100 %) to produce mixes with a variety of fatigue and rutting performance. The IDT rutting test was performed by running high temperature IDT flow time and strength tests. In addition, flow number tests were performed using an asphalt mixture performance tester (AMPT). A strong correlation is observed between the high temperature IDT flow time/strength and flow number from AMPT. The test results show that IDT tests can be used to predict the rutting behavior of asphalt concrete at high temperatures. To characterize fatigue, cyclic IDT and monotonic fracture energy tests were performed at intermediate temperatures. At intermediate temperatures, good correlation is found between the fatigue life obtained from cyclic IDT test results and the fracture energy obtained from monotonic fracture test results. Based on the laboratory test results, the IDT test can be used to evaluate both the fatigue and rutting behavior of asphalt concrete. Considering that IDT testing has been used to characterize thermal cracking and moisture susceptibility, the IDT test has the potential to serve as a single performance test for fatigue, rutting, thermal cracking and moisture damage. Validation of the findings with more materials and field performance are recommended.

Development of Phenomenological Top-Down Cracking Initiation Model for Mechanistic–Empirical Pavement Design

The phenomenon of top-down cracking in asphalt pavements has drawn increased attention in recent years, yet the asphalt pavement field still lacks an effective top-down crack initiation model. Many factors contribute to the initiation and propagation of top-down cracking. This study developed a phenomenological top-down crack initiation model for mechanistic–empirical pavement design. Pavements at FHWAs accelerated loading facility were used to develop a top-down crack initiation model based on the failure strain of asphalt mixtures, as obtained from indirect tensile testing. It was found that the current Mechanistic– Empirical Pavement Design Guide top-down cracking model failed to predict top-down cracking in the wheelpath in the field accurately, whereas the proposed failure strain–based top-down cracking model was effective in predicting top-down cracking in the field. In addition, the Level 2 prediction of failure strain is developed here; it is based on binder failure shear strain, air void content, asphalt content, and percentage of aggregate passing U.S. Number 4 and Number 200 sieves. Further studies are needed to validate this new top-down cracking model and to develop an effective crack propagation model.

Toward Development of a New Thermal Cracking Test Using the Dynamic Shear Rheometer

Thermal cracking is one of the primary distresses in asphalt pavements. Asphalt binder, an important component of asphaltic concrete, plays a significant role in the thermal cracking performance of asphalt pavement and should be characterized accurately for proper binder selection. The current Superpave binder specifications for low-temperature cracking, based on creep stiffness and m-values, are not applicable to modified binders. Fracture-based tests are most promising for the prediction of low-temperature cracking of binders, especially modified binders. This study develops a new performance indicator for low-temperature cracking using properties from monotonic testing at a semi-low temperature, 5°C, based on the dynamic shear rheometer (DSR). It is found that the complex shear modulus of binders does not correlate with field thermal cracking performance. Fracture energy shows a moderate correlation with field thermal cracking performance. The correlation is improved when the shear rate is increased. However, failure strain at 5°C correlates very well with field thermal cracking. In addition, failure strain is not sensitive to the shear rate at 5°C. This new test could significantly reduce the costs associated with the purchase of various types of equipment, such as that needed to conduct bending beam rheometer (BBR) or direct tension tests, and could also reduce the amount of testing time. Further study is needed to validate the findings in this study.