Arash Motamed

Influence of Warm-Mix Additives and Reduced Aging on the Rheology of Asphalt Binders with Different Natural Wax Contents

This paper presents the results of our study to investigate the influence of natural wax in asphalt binders, warm-mix asphalt (WMA) additives, and reduced short-term aging on viscosity, stiffness, susceptibility to permanent deformation, fracture resistance, and thermal cracking resistance of asphalt binders. We used two controls to differentiate between the influence of WMA additive and that of reduced aging on the rheology of asphalt binders. The asphalt binder used in a WMA undergoes reduced short-term aging and consequently has relatively reduced stiffness compared with the binder in a similar hot-mix asphalt (HMA). Results indicate that certain WMA additives compensate, whereas others aggravate the initial reduced stiffness of asphalt binders used in WMA. Short-term aged binders with high natural wax content demonstrated strong interactions with some of the WMA additives and increased susceptibility to permanent deformation. In most cases, pressure aging vessel (PAV) residues of binders with WMA addi...

Influence of Test Geometry, Temperature, Stress Level, and Loading Duration on Binder Properties Measured Using DSR

During the last two decades, several test methods and performance-based test specifications have been developed to select asphalt binders for use under different traffic and environmental conditions. The test equipment and methods are continually being improved to enhance the reliability with which materials can be selected for optimal performance. One of the procedures to assess rutting susceptibility of asphalt binders is the multiple-stress creep recovery (MSCR) test. Although the MSCR is a promising test method, test variables such as stress level, test geometry, and the number of cycles (total time) need to be carefully evaluated. This paper presents findings from a laboratory investigation of some of these variables. The dynamic shear rheometer (DSR) was used to evaluate the mechanical response of the asphalt binder by varying the stress level, test geometry, and temperature. The results were analyzed on the basis of recoverable and permanent strain to estimate the effect of changing geometry and in...

Analytical models to characterise crack growth in asphaltic materials and healing in asphalt binders

Cracking is a prevalent form of distress in flexible pavements. A thorough understanding of the mechanisms that lead to fatigue cracking and self-healing in bituminous materials is the essential and first step towards improving the performance of pavements and the bituminous materials used to construct these pavements. During the last two decades, several researchers have addressed the problem of understanding and modelling fracture and self-healing in bituminous materials at several different length scales. The first part of this paper presents a comprehensive review of the development of an energy-based fracture mechanics model to characterise the crack growth in bituminous materials. A few other approaches to model crack growth in viscoelastic materials that have not been widely used with bituminous materials are also briefly discussed. The second part of this paper presents a comprehensive review of an analytical model that can be used to represent self-healing in asphalt binders. The advantages, limitations and approximations associated with the implementation of the fracture and self-healing models are also discussed.

Quantifying healing based on viscoelastic continuum damage theory in fine aggregate asphalt specimen

The ability of an asphalt mix to heal is an important property that influences the overall fatigue performance of the mix in the field. In this study, an experimental and analytical method based on viscoelastic continuum damage theory was developed to characterize the healing in an asphalt composite (fine aggregate matrix) as a function of the level of damage prior to the rest period and the duration of the rest period. Four different types of fine aggregate matrix (FAM) were tested to quantify overall healing at isothermal conditions. Two different verification tests were conducted to demonstrate that the percentage healing measured using the proposed method are independent of the sequence of loading or rest period. Results from the tests support the hypothesis that the healing characteristics determined using the proposed test method can be treated as a characteristic material property.

Emulsified Asphalt Residue Recovery and Characterization: Combined Use of Moisture Analyzer Balance and Dynamic Shear Rheometer

A new procedure has been developed for residue recovery of emulsified asphalt. The procedure uses a moisture analyzer balance (MAB). The MAB recovery method is quick and simple compared with traditional recovery procedures such as distillation or oven evaporation. Although the MAB procedure has become an ASTM procedure, there have been a limited number of studies on the rheological properties of the emulsion residues recovered by MAB. This research used a dynamic shear rheometer (DSR) to investigate the rheological properties of MAB specimens. The MAB method was used for several types of emulsions, including cationic and anionic emulsions with several modifications. The MAB method developed in this study addresses the issue of breakdown of polymers during recovery of modified emulsions at high temperatures. The study evaluated the effect of recovery temperature on the recovery time and rheological properties of emulsion residues and proposed a new recovery-characterization procedure. The results show that a preliminary performance grade classification of the emulsified asphalt can be made with the combined MAB-DSR procedure. Furthermore, the study quantified the effect of aging that might occur during the recovery and emulsification process on the rheological properties of the emulsion residues. The combined MAB-DSR procedure is proposed to be a cost-effective alternative method to evaluate the performance of emulsified asphalts.

Investigating Nonlinear Response of Asphalt Binders at High Temperature

Computational models at varying length scales are currently being used to improve our understanding of the behavior and performance of asphalt mixtures. The accuracy of these computational models is highly dependent on the use of accurate constitutive relationships and material constants. Typical computational models at the mastic and mortar length scale comprise asphalt binder as the matrix and aggregates as the inclusion. For such models asphalt binder is typically modeled as a linear viscoelastic material with material constants that are typically obtained using a Dynamic Shear Rheometer (DSR). This paper presents a review of the tests methods and models that are used to characterize asphalt binders. This section also includes a review of the nonlinear viscoelastic response of asphalt binders. The second part of this paper investigates in more detail the potential sources for the nonlinear response of asphalt binders and models that can be used to represent this response. A DSR was used to measure the response of asphalt binders subjected to creep-recovery at multiple stress levels and sinusoidal loading at different stress amplitudes, using parallel plate and cone and plate geometries. In addition to the shear stress and strain, the normal stress was also recorded and used in the analysis of the test results. Preliminary results indicate that asphalt binders demonstrate a nonlinear viscoelastic response even at low stress levels due to the biaxial stress state. Test data is presented to demonstrate and verify this form of nonlinear response, which is also referred to as interaction nonlinearity.