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The aim of this study is to develop a constitutive model capable of describing the effects of confinement pressure on the mechanical behaviour of asphalt mixtures. The model is developed within the context of a Gibbs-potential based thermodynamic framework. Functional forms are assumed for the Gibbs potential and the rate of dissipation, which is maximised to obtain the constitutive model. The Gibbs potential and the rate of dissipation are formulated to have separate components corresponding to the spherical and deviatoric parts of the stress tensor. Additionally, one of the model viscosity parameters is formulated to be pressure-dependent. The efficacy of the model is demonstrated with the aid of experimental measurements conducted at four different confinement pressures ($0\comma\; 70\comma\; 140\comma\; 380\, {\rm kPa}$ 0 , 70 , 140 , 380 kPa ) and two different temperatures (40 and $55^{\circ }{\rm C}$ 55 ∘ C ) (Rahmani et al. 2013, Effect of confinement pressure on the nonlinear-viscoelastic response of asphalt concrete at high temperatures, Construction and Building Materials, 47, 779–788; 2017, Constitutive modeling of coupled aging-viscoelastic response of asphalt concrete, Construction and Building Materials, 131, 1–15; Bazzaz et al. 2018, A straightforward procedure to characterize nonlinear viscoelastic response of asphalt concrete at high temperatures, Transportation Research Record, 2672 (28), 481–492). Some of the test results are used to calibrate the model, while the remaining data are used for model validation. It is found that the model reasonably predicts the mixture responses in the axial and radial directions at different confining pressures and temperatures. [ABSTRACT FROM AUTHOR]

This study addresses the utility of polyelectrolytes, i.e., cationic poly(diallyldimethylammonium chloride) (PDADMAC) and anionic polystyrene sulfonate (PSS), as additives to improve properties of the polymer-stabilized soil. This paper specifically focuses on the resistance of polymer-stabilized soils to degradation and/or damage during and following multiple wetting–drying cycles (zero, one, two, three, five, and seven cycles). Each cycle consisted of 24 h of moisture conditioning using capillary rise followed by 24 h of drying. Then, these specimens were evaluated for their unconfined compressive strength (UCS). The microstructure and composition of the soils were investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray fluorescence analysis (XRF). Based on the results, the soils used in this study for polymer treatment were primarily composed of carbonates and silicates with a small amount of clay minerals. The polyelectrolyte stabilizers (PDADMAC and PSS) and polyelectrolyte complexes (PECs) were added to the soils at dosages ranging from 0.2% to 1.6% by weight of dry polymer to dry soil. Treated soils demonstrated increased UCS compared with untreated counterparts. The untreated soils exhibited rapid degradation of UCS and mechanical collapse within three to four wetting–drying cycles. On the other hand, the polymer-treated soils exhibited a strength reduction of between 10% and 50% following the first cycle and then maintained the UCS of about 3–6 MPa after completion of all wetting–drying cycles. Furthermore, the stabilized soil demonstrated significant improvement in toughness compared with their untreated and cement-treated counterparts. The ability of the polymer-stabilized soils to stand up to wetting–drying cycles is a key finding and contribution of this study. [ABSTRACT FROM AUTHOR]

The process of reclaimed asphalt pavement (RAP) recycling may occur multiple times during the life of the pavement. This study investigates the effect of multiple recycling on binder properties by employing a virgin 3045 PEN grade binder that was aged in the laboratory intended to simulate aging of binders in RAP. The aged binder was rejuvenated using two bio-oils and one softer binder. The doses of the bio-oils and softer binder were determined by matching the continuous high-temperature performance grade (PGH) of the rejuvenated RAP binder to that of the virgin binder. This aging and rejuvenation cycle was repeated three times. Finally, fatigue and rutting performance of the binder was evaluated for the three reuse levels. Results indicate that the material can be reused up to three cycles keeping good performance on fatigue or rutting. However, care should be taken regarding the cumulative effect of bio-oils causing an over-softening effect on the of the RAP. [ABSTRACT FROM AUTHOR]

There has been growing interest in the use of polyethylene (PE) in the asphalt industry as one way to mitigate the adverse environmental impact of waste plastics. The main goal of this study was to evaluate the potential use of low-density polyethylene (LDPE) as a modifier for use in asphalt mixtures. In addition, this study also explored the potential synergistic impact of using elastomeric polymers typically used with asphalt binders as a co-modifier along with LDPE. This study was based on a comprehensive evaluation of the rheological and performance-related properties of asphalt binder from two very different sources as well as asphalt mixtures produced using a subset of these binders. Typical methods that are standard practice in the industry and methods that are being developed to evaluate the performance metrics of asphalt binders and mixtures were used. The two chemically diverse base binders and redundancy in the evaluation process were introduced to ensure a more robust evaluation of the expected properties. Overall, results demonstrate that although the impact of LDPE on the expected performance of the binder may vary with the source of binder, LDPE can be successfully used to enhance the properties of the asphalt binder in most respects, particularly with the synergistic use of a conventional elastomeric modifier. [ABSTRACT FROM AUTHOR]