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This study focuses on stress–displacement curves and shear fracture energy of asphalt-aggregate systems subjected to direct shear loading for four different experimental conditions. The methodology for measuring shear fracture energy of asphalt-aggregate specimens is presented. Based on comparison of the experimental data, this paper indicates that the single-peak curves (SPCs) tend to envelop the double-peak curves (DPCs) and the values of shear fracture energy of the SPCs are much higher than those of the DPCs for each experimental condition. Using thermodynamic theory and slip theory, energy of interaction between the adhesion and the cohesion within the asphalt-aggregate systems is further analysed. The experimental results clearly show that the reduced fracture energy of the DPCs is related to the shear-dependent slip, including adhesive slip and cohesive slip that occur simultaneously and promote each other in the direct shear testing. This study also illustrates that fracture energy is capable of being a significant parameter in the failure and healing analysis of asphalt pavements. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate linear viscoelastic properties of asphalt mixtures measured under different confining pressures with respect to master curves of complex modulus, relaxation time and modulus of Prony series model. A modified collocation method is utilized to calculate the relaxation modulus of Prony series representation after the relaxation time is selected. The relaxation moduli of two asphalt mixtures under different confining pressures are compared at a wide range of reduced loading times. Finite element simulation is employed to fully investigate the effect of confining pressure on mechanical responses of asphalt pavement. The results show that the construction method of master curves of complex moduli is effective and reliable. The relaxation modulus calculated from the smoothed experimental storage and loss moduli of the same complex moduli are slightly different, and it is impossible to obtain the accurate relaxation time and modulus to well agree with the test data of storage and loss moduli simultaneously at the full range of reduced angular frequencies. As the confining pressure increases, the relaxation modulus does not always increase at the full range of reduced loading time due to the effect of phase angle. As the confining pressure increases, the tensile strains and shear strains in the asphalt layer decrease in the practical speeds of vehicular loading. [ABSTRACT FROM AUTHOR]

In order to investigate rutting behavior in long and steep section of mountainous highway, this paper selected generalized Kelvin model as the constitutive relationship for asphalt mixture, proposed a new method for material parameter identification, provided the tangential stiffness matrix for the generalized Kelvin model, and applied the constant power vehicular loads on the finite model. The results show that the overload, operational speed, and the tangential and vertical forces of the vehicle have a significant impact on the rutting of asphalt pavement. Based on rutting sensibility analysis, this paper also develops a confinement method of the slope grade and length in long and steep section of mountainous highway. [ABSTRACT FROM AUTHOR]

It has been observed that permanent deformation (or rut) in the asphalt pavement at an intersection is much more severe than a deformation away from the intersection due to breaking horizontal forces and longer loading time. This paper presents both experimental and numerical investigations of this phenomenon, and the numerical investigations are validated by three-dimensional fiber-reinforced polymer-optical fiber Bragg grating sensors. First, a field investigation of the rutting at four signalized intersections in Nanjing (Jiangsu, China) leads to the conclusion that under braking traffic and static loads, the values of voids in the mineral aggregate (VMA) and air-void content could be less than the minimum desirable values. Second, the permanent deformations associated with tangential and vertical forces and their loading time assessed with the finite-element method are compared with those measured from instrumentations. This analysis demonstrates that hot-mix asphalt pavement at the intersections should maintain adequate VMA to ensure durability, and a minimum desirable percentage of air voids under slow and standing traffic loads during hot summer days. The permanent deformations at the intersections caused by tangential and vertical forces are both serious and need to be restricted. It is also shown that the permanent deformation is sensitive to both the traffic load and its loading time, but the sensitivity of the load is more pronounced. [ABSTRACT FROM AUTHOR]

Abstract: The development of rutting is one of the most common distresses in asphalt pavement. Especially at road sections with longitudinal slope, the problem is more serious than sections with no slope. This is because the slope decreases the average speed of vehicles running upward, so the total loading time increases dramatically. In China, dynamic stability (DS) in rutting test is used as the main experimental criteria to control the asphalt concrete (AC) materials before construction. It is supposed that the larger the DS index is means the material has better capability of retarding the ruts’ development after constructed. Fixed DS criteria are set for diverse road situations. These differences in situations exhibit in structure and materials, traffic volume, climate condition and the gradient of sloped pavement. This paper aims at establishing a new control approach of AC material for dealing with rutting problem. Finite element method (FEM) is used to simulate two objects: specimen in rutting test and typical actual pavement with slope. In these simulations, the constitutive model of AC is the common basis. Through the model, specimen in rutting test and actual pavement are connected. It provides a possible way to control pavement rutting by computing and providing detailed criteria for specific project with special situations. These criteria change with actual service circumstances of pavement. Compared with fixed criteria, they are more flexible, accurate and feasible for using in rutting control practice. [Copyright &y& Elsevier]

The accumulations of waste plastics and municipal solid wastes from the resident groups and industrial companies have been causing serious environmental issues in the UK, due to difficulties in logistics, sorting, and reuse. In this sense, this paper is stimulated to develop novel approaches to convert some wastes into eco-friendly infrastructural materials, which provides a new way of waste reduction and reuse and extending the service life of asphalt pavement. This study aims to characterise the healing performance of waste-derived bitumen before and after pressure ageing vessel (PAV) ageing based on the crack length. One waste-derived bitumen was fabricated by blending the bio-oil pyrolysed from the organic fraction of municipal solid waste (5 wt%) with a control bitumen (X70) using a high shear mixer at a speed of 150 revolutions per minute (RPM) for 30 min at 150 °C under nitrogen atmosphere. A second waste-derived bitumen was fabricated using the low-density polyethene (LDPE) and mixed with the control bitumen at a concentration of 6 wt% at a speed of 900RPM for 90 min at 180 °C under nitrogen atmosphere. Crack length-based healing index and Ramberg-Osgood model were employed to characterise the healing rate and healing capability of the bitumen, respectively. Material properties (e.g., relaxation modulus and surface energy) of the bitumen used in the healing models were calibrated by linear amplitude sweep test (10 Hz and 20 °C), frequency sweep test (10 Hz, 10–70 °C), and time sweep fatigue-healing test (10 Hz and 20 °C) at a controlled strain level of 5% with different rest durations. Advancing contact angles used in the healing models of the bitumen were measured by a sessile drop tensiometer based on the tilting cradle method. Results show that the bio-oil productively promotes the healing potential and capability of the unaged bitumen, and the LDPE slightly strengthens them. The PAV ageing process evaporates most of the modifier bio-oil; hence, the PAV-aged bio-oil modified bitumen does not show better healing performance than that of the PAV-aged control bitumen. The PAV-aged LDPE modified bitumen has much better healing performance than those of the PAV-aged control bitumen and the PAV-aged bio-oil modified bitumen. The short-term healing rate and healing potential dominate the healing behaviours of the bitumen. The unaged bio-oil modified bitumen heals the fastest (having the highest short-term healing rate) and most (having the highest healing potential), followed by the unaged LDPE modified bitumen, and the unaged control bitumen heals the least and slowest. The PAV-aged LDPE modified bitumen heals the fastest and most, followed by the PAV-aged bio-oil modified bitumen and the PAV-aged control bitumen. The fundamental reason for LDPE's enhancement to bitumen's healing is that the LDPE increased the deformation recovery ability of the bitumen, leading to a higher wetting rate of the cracked surfaces and thus a higher short-term healing rate. However, the LDPE in bitumen cannot accelerate the molecular diffusion to increase the intrinsic healing or the long-term healing rate. • Two waste materials were firstly used to enhance healing ability of bitumen. • Healing properties of bitumen was characterised based on crack length. • Healing rate and potential was modelled using Ramberg-Osgood Equation. • Bio-oil productively promotes healing performance of unaged bitumen. • LDPE strengthens healing performances of unaged and PAV-aged bitumen. [ABSTRACT FROM AUTHOR]

• Constructed and validated Thermo-Hydro-Mechanical model. • Identified the importance of thermal stress and thermoviscoelasticity. • Captured the behaviour of pore water pressure and flow. • Characterised coupled Thermo-Hydro-Mechanical performance. This study aims to characterise the coupled thermo-hydro-mechanical properties of the saturated asphalt pavement under the vehicle load, the thermal deformation and thermoviscoelasticity of the asphalt layer, and the pore water pressure in the voids of the asphalt layer. A thermo-hydro-mechanical model (THMM) was proposed by coupling the governing equations of triple physics of thermal, hydraulic, and mechanical fields. Based on the identification of circular dependence of the above triple physics, weak forms of the coupled governing equations were incorporated into a weak form equation-based finite element software package. The effectiveness and accuracy of the THMM were validated from the perspective of mechanical performance of the asphalt mixture, temperature profile of the asphalt pavement, and hydro-mechanical performance of the asphalt pavement, respectively. Results show that the thermal deformation and thermoviscoelasticity are both vital for performance prediction of the asphalt pavement; the thermal contraction and thermal tensile stress appear in the cool-down asphalt pavement (pavement temperature decreases), and the thermal expansion and thermal compressive stress emerge in the heat-up asphalt pavement (pavement temperature increases). The pore water flows outside of the pavement under the vehicle load and flows back to the pavement when the vehicle load travels far away. Compared with the dry asphalt pavement, the pore water can decrease the effective stress induced by the vehicle load, but it will increase the residual stress when the vehicle load travels away. For the selected undamaged asphalt pavement, the smaller relaxation modulus comes from higher temperature and produces higher hydraulic pressure in the saturated asphalt layer, and vice versa. The maximum differences between the vertical strains under the vehicle load in the saturated and dry asphalt pavements lies in high temperature period of one day, and there are almost no differences when the vehicle loads travels far away. The pore water in the saturated asphalt pavement contributes well to the temperature distribution and generate temperature gradient in the transverse direction of the asphalt pavement. [ABSTRACT FROM AUTHOR]

In order to analyze tire footprints in different conditions and calculate dynamic responses of asphalt pavement with vehicle braking, a tire-pavement coupling simulation system, which can use a viscoelastic constitutive model of asphalt concrete considering temperature dependence, is established. The user subroutine of the material model was programmed by the FORTRAN language, and viscoelastic parameters of the material model were recognized based on dynamic strain data of dynamic impact tests, whose validity was verified by using test data in the literature. The tire-pavement coupling simulation system was established to analyze tire footprints in static and dynamic conditions at different temperatures of asphalt concrete layer, whose calculation accuracy of the numerical simulation was verified. Based on measured temperature data at different depths of an actual pavement structure and the corresponding simulation model, thermal parameters of each layer in the pavement structure were recognized. Field distributions of the viscoelastic parameters in the asphalt concrete layer of the coupling simulation system were obtained by using the heat transfer analysis and the user subroutine. Average braking decelerations of trucks at a chosen intersection were calculated according to the investigation data. Based on the tire-pavement coupling simulation system, peak values of dynamic shear strain in the asphalt concrete layer at the intersection were calculated, which considered the coupling effect between axle loads and temperature fields. [ABSTRACT FROM AUTHOR]