Aravind Krishna Swamy

Validating the Fatigue Endurance Limit for Hot Mix Asphalt

This report presents the findings of research performed to investigate the existence of a fatigue endurance limit for hot mix asphalt (HMA) mixtures, the effect of HMA mixture characteristics on the endurance limit, and the potential for the limits incorporation in structural design methods for flexible pavements. The report describes the research performed and includes proposed standard practices using various experimental and analytical procedures for determining the endurance limit of HMA mixtures. Thus, the report will be of immediate interest to materials and structural design engineers in state highway agencies and engineers in the HMA construction industry.

Application of Elastic-Viscoelastic Correspondence Principle to Determine Fatigue Endurance Limit of Hot-Mix Asphalt

The fatigue endurance limit is one of the properties of hot-mix asphalt (HMA) that govern fatigue behavior of flexible pavements. Some approaches for determining the endurance limit of HMA are empirical in nature, such as the phenomenological approach. This often requires a series of tests at different strain levels and subsequent determination of the relationship between strain and number of repetitions for failure. The mechanics-based dissipated energy approach is more fundamental. However, it fails to take viscoelastic effects into account. Both approaches require considerable amounts of time and resources. This paper presents an alternative approach for determining the fatigue endurance limit of asphalt concrete by means of the elastic–viscoelastic correspondence principle, by separating the effect of viscoelasticity from that of damage development. Three different asphalt concrete mixes, replicates of the National Center for Asphalt Technology (NCAT) test track mixes, were tested for validation of the proposed methodology. Initially the cut and cored samples were tested for dynamic modulus to construct the master curves. With the data, viscoelastic properties were determined by interconversion techniques. In the next stage, fatigue tests were conducted under different strain amplitudes, starting from low to high. Then the strain data were converted to pseudostrain via the elastic–viscoelastic correspondence principle. The endurance limit was determined by identifying the strain level at which a loop between stress and pseudostrain began to develop. Endurance limit values thus determined are comparable to those obtained by flexural tests performed at NCAT. The proposed methodology can contribute to considerable savings in time and resource requirements.

Effect of Mode of Loading on Viscoelastic and Damage Properties of Asphalt Concrete

The objective of this research was to study the effect of the mode of loading on viscoelastic properties and damage characteristics of asphalt concrete. Four 12.5-mm nominal maximum aggregate size mixtures were designed according to Superpave® specifications. The specimens prepared with these mixtures were tested under uniaxial, biaxial, and flexure modes to obtain viscoelastic and damage properties. Viscoelastic and damage properties depended on loading mode and testing frequency. Statistically significant differences were found between mean values of measured modulus under different modes of loading. Also, regions of overlap in phase angle measurements were observed. A systematic variation in viscoelastic properties was found between different loading modes. The specimen underwent damage at a faster rate under the uniaxial mode than under the flexure loading mode. At a given value of normalized pseudostiffness, the damage parameter ratio, computed with parameters obtained under different modes of loading, remained approximately the same and was a function of material properties.

Impact of RAP on the Volumetric, Stiffness, Strength, and Low-Temperature Properties of HMA

The increasing cost of virgin asphalt and aggregate has increased the interest in using higher percentages of recycled asphalt pavement (RAP) in hot mix asphalt (HMA) mixtures. The purpose of this research project was to gain a better understanding of how the addition of RAP affects interaction among the aged and virgin binders and the overall properties of HMA. The effects of the addition of RAP were evaluated on a macroscopic scale by comparing the volumetric properties, dynamic modulus, and strength parameters of a series of specimens containing different percentages of RAP from two different sources. Also, the viscoelastic properties of the blended or rejuvenated binder in the recycled mix were back-calculated from the macroscopic properties of the mix using the Hirsch model. Studies have shown that this back-calculation method offers advantages like elimination of the need for extraction of blended binder, the ability to use indirect tension test specimens, and the use of a mechanistic based approach. The back-calculated viscoelastic properties were subsequently used to determine the low-temperature performance grade of the binder in the recycled mix. This research project showed that the percentage of RAP affects the properties of the mixture with respect to mixture volumetrics, dynamic modulus, and strength.

Reclaimed Waste Materials in Sustainable Pavement Construction

This chapter provides an in-depth but brief overview on the possible use of various waste materials for sustainable pavement construction. It compiles a literature review on the research done on such materials and highlights the current issues.

Optimal proportioning for hot recycled mix design under Superpave mix design consideration

While performing recycled (central plant) hot mix design as per Superpave mix design criteria, the quantity of reclaimed asphalt pavement (RAP) is either assumed fixed, or estimated from other fixe...

Properties of asphalt binder and asphalt concrete containing waste polyethylene

ABSTRACT In this study, the effects of addition of waste polyethylene on asphalt binder and asphalt concrete mixture properties were studied. Four asphalt concrete mixtures (each mixture containing different percentages of shredded polyethylene material) were prepared and tested as per Indian specifications. Shredded polyethylene and hot asphalt binder were added to heated aggregate (in same sequence) until all aggregates were coated. The loose mixtures were compacted and tested for its mechanical and volumetric properties. Furthermore, compacted specimens were aged for short- and long-term conditions. The extracted binder from the aged and control mixtures was tested for its rheological properties using a dynamic shear rheometer. Mixtures containing shredded polyethylene showed improvement with respect to the Marshall strength, flow, and volumetric properties. The properties of recovered asphalt binder indicated that the addition of polyethylene improved complex modulus values and decreased phase angle values over range of frequencies.

Significance of RAP Content and Foamed Binder Content on MechanisticCharacteristics of Recycled Foamed Bituminous Mixes

To reduce the energy consumption and CO2 emissions during asphalt production, several environmentally friendly technologies have been developed during the last years. One of these technologies is the cold recycling by using foamed bitumen. Foaming the bitumen reduces the binder viscosity temporarily and increases the volume as well. Homogenous foams are produced by injection of cold water into hot bitumen. The paper presents the results of laboratory testing of the physical and mechanical parameters of the recycled mixes using the foamed bitumen and resistance to the action of water. The aim of the tests was to evaluate the properties of the mixes in terms of the RAP Content and Foam Binder Content. To evaluate the significance of impact of both factors i.e., Foam Binder Content and RAP Content on the distribution of the analyzed parameters, two-way Analysis of Variance (ANOVA) was performed. ANOVA Analysis results suggest that the RAP in cold mixes is not completely acting as black rock implying that some portion of the residual aged binder is possibly rejuvenated or softened by adding new binders.

Prediction of density and viscosity of bitumen

Abstract It is well known fact that temperature and pressure significantly affects density and viscosity of bitumen. The present work utilizes Gene Expression Programming (GEP) approach to develop models to predict density and viscosity of bitumen. To evaluate the accuracy of proposed GEP based models, results reported by various researchers were utilized. This includes test results regarding Athabasca, Cold Lake and Gas free bitumen. The developed GEP based models were compared with the conventional empirical regression equations. The statistical analysis indicates that GEP based models work better than other existing models for density and viscosity of bitumen.

Interrelationship between uncompacted void content of aggregates and asphalt concrete properties

ABSTRACT It is a well known fact that morphological characteristics of aggregates influence the mechanical response of asphalt concrete (AC). Uncompacted void content (UVC) of aggregate is often related to their morphological characteristics. A detailed experimental study was performed to explore relationship between UVC and mechanical response of AC. Initially, aggregates were artificially smoothened using Los Angles abrasion testing machine. UVC was then evaluated using blended aggregates at five levels of smoothness/texture. Increasing aggregate smoothness resulted in decreased UVC values. Higher UVC was obtained with a finer gradation compared to coarse gradation. Three AC mixtures prepared using these smoothened aggregates were tested for their strength and flow properties. A linear, strong positive correlation was found between UVC and Marshall parameters (stability, Marshall quotient). This can be attributed to interparticle resistance developed during mechanical loading. Parabolic relations were found between UVC and retained Marshall parameters. The retained Marshall parameters was found to be a function of UVC. It is concluded that UVC can be effectively used to capture changes in aggregate morphology and AC response.