Mechanical Response Of Asphalt Mixture Research Articles

Fracture resistance of polymeric wastes modified asphalt using R-curve and digital image correlation

Characterising the fracture properties of asphalt mixtures is a critical step toward a better pavement design. This study aims to investigate the mechanical response of asphalt mixtures modified with crumb rubber and plastic waste. These modified mixtures have been introduced in road construction based on the basic understanding of their mechanical properties. The R-curve based cumulative fracture energy and digital image correlation (DIC) technique were used to assess the fracture behaviour of the modified asphalt. The asphalt mixtures were examined under a monotonic semi-circular bending test for unconditioned, aged- and moisture-conditioned samples. The digital image analysis technique was used to construct the resistance curve based on the cumulative fracture energy. The DIC technique was used to capture the sample’s strain field for the control and modified mixtures. Results showed that the rubberised asphalt promoted crack propagation, whilst plastic waste resisted cracking by prolonging the crack initiation phase compared to the conventional asphalt. Strain fields derived by DIC demonstrated different mechanical contributions for both modifiers under the fracture test.

Investigation on internal mechanical response of asphalt mixture during creep test utilizing the Smart Aggregate

• Internal mechanical response of asphalt mixture to the creep behavior was investigated using Smart Aggregate. • Effects of particle location, stress level and temperature on the internal mechanical response were analyzed. • Relationship between internal mechanical response and creep behavior was discussed for asphalt mixture. The micro-mechanical behaviors of asphalt pavement play the essential role in its macro-mechanical properties and damage evolution. However, the efforts to research the micro-mechanical mechanism of asphalt mixture are still not enough, especially from a particle level in the laboratory. This study aims to investigate the internal mechanical response of asphalt mixture to the creep behavior with the assistance of built-in Smart Aggregate. After calibrating the force measurement for the Smart Aggregate, it was embedded in the asphalt mixture to monitor the inter-particle forces during the uniaxial static creep tests. Meanwhile, various test conditions, including particle location, stress level and temperature, were concerned to analysis their influences on the mechanical response of the Smart Aggregate. In addition, the relationships between internal mechanical responses and creep behavior were discussed. Results indicate that the applied force has a nonlinear relation to measured voltage of the Smart Aggregate, and can be obtained according to the regression model after calibration. During creep test, the Smart Aggregate performs well in acquiring the internal mechanical response of asphalt mixture. The inter-particle forces show uneven along the direction of loading stress during the creep test in asphalt mixture. The measured force increases monotonously whilst the strain increasing during creep evolution. Regarding the same temperature, there are significantly linear relations between instantaneous elastic modulus and measured force at the beginning and between eventual stiffness modulus and measured force at the end in dual logarithmic scales. Meanwhile, the slope k f of force curve in the steady shows strongly linear relation to the slope k s in equi-velocity creep stage on the Cartesian coordinates.

Effects of composite geometric characteristics of coarse particles on interface interactions of aggregate-asphalt system

The complex geometric morphologies and contact status of aggregate particles and the interface interactions between aggregate and asphalt significantly affect the compaction properties and mechanical response of asphalt mixtures. The spreading-combination method was proposed to build the calculation model of composite geometric indexes to quantitatively characterize the composite geometric characteristics of the particle system. The effects of composite geometric characteristics on the interface interactions of the aggregate-asphalt system were analyzed adopting the contact-slip tester. The results indicate that the measures of shape, texture, and angularity respectively denote perimeter, surface area, and volume. The composite shape index is primarily affected by the number of particles. Smaller-sized coarse aggregates and fine aggregates exercise a greater impact on the composite texture index, while the composite angularity index is more sensitive to large-sized coarse aggregates. The fine particles attach to the surface of coarse aggregates, diminishing the contributions of the composite texture characteristics of coarse aggregates to the particle contact strength of the particle system. The larger the composite angularity index, the more significant the lubricating effect of asphalt on particle contact. However, asphalt can transform a part of the interference effect of the fine aggregates into the bonding effect of the skeleton. The composite angularity index is positively correlated with the skeleton bonding index, which can be used to evaluate and predict the interface interactions of the aggregate-asphalt system.

Effect of the Solvents Content on the Mechanical Response and Compactability of Asphalt Mixtures Fabricated Using Castilla’s Paving-Heavy Crude Oils

The paving-heavy crude oils (PHCO) are natural cut-back asphalts composed by a high content of asphalt cement and a portion of solvents. These materials have been used in Colombia since the 90’s to improve low volume traffic roads. The existence of solvents in the PHCO allows mixing it with the aggregates in cold conditions. Then, before compaction, these asphalt mixtures require a curing process (i.e., process of partial loss of solvents from the PHCO) to ensure its proper performance. However, at present there is no consensus on the loss of solvents to specify for the curing process of mixtures fabricated with PHCO. Given this situation, this study assesses the effect of the partial content of solvents on both the mechanical response and compactability of asphalt mixtures produced using PHCO from the Castilla’s oil field (CA); a material extensively used in the East region of Colombia. The study included conducting and analyzing conventional characterization tests of the mixture constituent materials, surface free energy testing on both mastics and the aggregate, mix design, and characterization of both mechanical response and compactability of the mixtures fabricated using the CA and a control asphalt. Corresponding results led to identify and quantify a progressive improvement in both the adhesion quality of the mastic-aggregate interfaces and the mechanical response of the asphalt mixture as a function of the reduction of the solvents. These results suggest the convenience of compacting the asphalt mixtures fabricated using the CA after allowing a loss of 50% of the solvents obtained from the CA via atmospheric distillation at 360°C.

Master Curve Establishment and Complex Modulus Evaluation of SBS-Modified Asphalt Mixture Reinforced with Basalt Fiber Based on Generalized Sigmoidal Model.

Basalt fiber has been proved to be a good modified material for asphalt mixture. The performance of basalt fiber modified asphalt mixture has been widely investigated by extensive researches. However, most studies focused on ordinary static load tests, and less attention was paid to the dynamic mechanical response of asphalt mixture incorporating with basalt fiber. This paper aims to establish the master curve of complex modulus of asphalt mixture incorporating of styrene-butadiene-styrene (SBS) polymer and basalt fiber using the generalized Sigmoidal model. Both loading frequency and temperature were investigated for dynamic mechanical response of asphalt mixture with basalt fiber. In addition, based on the time-temperature superposition principle, the master curves of complex modulus were constructed to reflect the dynamic mechanical response at an extended reduced frequency range at an arbitrary temperature. Results indicated that the generalized Sigmoidal model in this paper could better reflect the dynamic mechanical response accurately with correlation coefficients above 0.97, which is utilized to predict the dynamic mechanical performances accurately. Simultaneously, the modulus values exhibit an increasing trend with loading frequency and decrease versus temperature. However, the phase angle values showed different trends with frequency and temperature.

A new dynamic modulus predictive model for asphalt mixtures based on the law of mixtures

The dynamic modulus (|Em*|) of asphalt mixtures is one of most fundamental mechanical parameters used in flexible pavement design, which has been extensively estimated through various predictive models. However, most of existing dynamic modulus predictive models does not fit well for the purpose of the Level 3 (the lowest input level) flexible pavement design in the current AASHTOWare Pavement ME Design due to the following major deficiencies: (1) lacking physical significance; (2) providing poor prediction accuracy; and (3) requiring laboratory testing to obtain key model parameters. To address these deficiencies, this paper is aimed to develop a new model on the basis of the law of mixtures. First, a large database is collected and revised for the new model development. Two exiting law of mixture models are then evaluated in terms of the mode prediction accuracy, and neither of them provided satisfactory prediction results. A new model is subsequently developed, which involves using a parallel form to represent the contribution of each of three phases (asphalt, aggregate and air void) to the |Em*| as well as utilizing a standard sigmoid function to characterize the mechanical response of asphalt mixture. Statistical analysis shows that the new model has comparable prediction performance with traditional Witczak models, but with significantly lower number of input variables and relatively higher model quality. Supplemental data collected from laboratory tests and independent literature sources finally validate that the new model has the capability to provide an accurate prediction of |Em*| with an R2 value up to 0.90. In these regards, the new model is believed to be a good candidate for the |Em*| prediction of asphalt mixtures for a reliable Level-3 flexible pavement design.

Optimization of the Calcium Alginate Capsules for Self-Healing Asphalt

It has been demonstrated that calcium alginate capsules can be used as an asphalt healing system by pre-placing rejuvenator (healing agent) into the asphalt mix and releasing the rejuvenator on demand (upon cracking). This healing mechanism relies on the properties of capsules which are determined by the capsule preparation process. In this study, to optimize the calcium alginate capsules, capsules are prepared using varying Alginate/Rejuvenator (A/R) ratios. Light microscope microscopy and Environmental Scanning Electron Microscope (ESEM) are employed to characterize the morphology and microstructure of these capsules. Thermal stability and mechanical property are investigated by thermogravimetric analysis (TGA) and compressive tests. The testing results indicate that higher alginate content results in smaller diameter and lower thermal resistance, but higher compressive strength. The optimum A/R ratio of calcium alginate capsules is found to be 30/70. To prove the effectiveness of the optimized capsules, the capsules are embedded in asphalt mortar beams and a bending and healing program is carried out. The effect of capsule shell material on the mechanical response of asphalt mixture is evaluated through three-point bending on the mortar beams embedded with blank capsules (without the healing agent). Aged mortar beams containing alginate capsules encapsulating rejuvenator demonstrate a higher strength recovery after bending tests, which indicates effective healing due to the release of the rejuvenators from the capsules.

Mechanical response of asphalt mixtures under partial saturation conditions

Quantifying the impact of environmental conditions on the mechanical properties and performance of hot mix asphalt (HMA) materials is a necessary task to achieve high-quality pavement structures. Although the influence of temperature in the behaviour of these viscoelastic materials has been well determined, there is still a lack of information regarding the impact of moisture on the mechanical response of HMA. Studies in this direction should consider that under actual field conditions, these mixtures are usually in a partial saturation state. Within this context, this work evaluates the mechanical response of an HMA through the quantification of the axial tension, axial compression and shear moduli of the mixture, after subjecting it to different relative humidity environments. The experimental plan was conducted using the recently developed Hollow-Cylinder Tester for Asphalt Mixtures equipment, and the results demonstrate that partial saturation strongly influences the rheological properties of these mixtures.

Development of an image-based multi-scale finite-element approach to predict mechanical response of asphalt mixtures

Image-based simulation of complex materials is a very important tool for understanding their mechanical behaviour and an effective tool for successful design of composite materials. Asphalt concrete (AC) as one of these multi-phase complex materials is a composite of asphalt binder, air voids, and mineral aggregate particles. Simulation of AC with numerical methods is not a new topic but is faced with many challenges. In addition to requiring tremendous computational cost, it is not clear yet how to effectively model the aggregate-to-aggregate contact behaviour during loading and deformation. In this paper, an image-based multi-scale modelling is introduced to reduce the computational cost significantly by reducing the amount of elements in the numerical model. In this approach, the “up-scaling” and homogenisation of each scale to the next is critically designed to improve accuracy. In addition to this multi-scale efficiency, this study introduces an approach for consideration of particle contacts at each of the scales in which mineral particles exist. The finite-element (FE) analysis is performed in the study at four scales, namely asphalt binder, mastic, mortar, and asphalt mixture scales. The well-known FE software ABAQUS is used to conduct FE simulations at all scales. The inputs are based on the experimentally derived measurements for the binder viscoelastic properties from which the binder constitutive model is implemented into the software via the user material subroutine. For the scales of mastic and mortar, the two-dimensional (2D) images of mastic and mortar scales were generated artificially and used to characterise the properties of those scales. Finally, the 2D scanned images of asphalt mixtures after elimination of fine aggregate particles are used to study the asphalt mixture behaviour under uniaxial creep and recovery loading. Comparison between experimental results and the results from the model shows that the model developed in this study is capable of predicting the effect of asphalt binder properties and aggregate micro-structure on mechanical behaviour of AC under repeated creep loading.

A Unified Continuum Damage Mechanics Model for Predicting the Mechanical Response of Asphalt Mixtures and Pavements

Predicting the performance of asphalt pavements is a very challenging task due to the complex behavior of asphalt mixtures and the complex traffic and environmental loading condi- tions to which these pavements are subjected. In this paper, a unified continuum-based mecha- nistic model is presented and its effectiveness in predicting rutting and damage evolution in as- phalt pavements is demonstrated. The model couples the characterization of nonlinear viscoelastic, viscoplastic, and viscodamage behavior of asphalt mixtures. Due to the very high computational cost of predicting the rutting of asphalt pavements through conducting three- dimensional (3D) finite element (FE) simulations under many loading cycles, an effective and simple extrapolation technique is presented for predicting rutting based on conducting 3D FE simulations for a relatively small number of loading cycles and extending the analysis with two- dimensional (2D) FE simulations for very many loading cycles. Further, it is shown that the uni- fied continuum damage mechanics model presented herein can also be used in conducting novel 2D and 3D micromechanical simulations of asphalt mixtures where each constituent (e.g., aggre- gate, mastic) is modeled explicitly. Such micromechanical simulations can be used in guiding the material design of more rutting- and damage-resistant asphalt mixtures and pavements.

Damage-Induced Modeling of Asphalt Mixtures through Computational Micromechanics and Cohesive Zone Fracture

This paper presents a computational micromechanics modeling approach to predict damage-induced mechanical response of asphalt mixtures. Heterogeneous geometric characteristics and inelastic mechanical behavior were taken into account by introducing finite element modeling techniques and a viscoelastic material model. The modeling also includes interface fracture to rep resent crack growth and damage evolution. The interface fracture is modeled by using a micromechanical nonlinear viscoelastic cohesive-zone constitutive relation. Fundamental material properties and fracture characteristics were measured from simple laboratory tests and then incorporated into the model to predict rate-dependent viscoelastic damage behavior of the asphalt mixture. Simulation results demonstrate that each model parameter significantly influences the mechanical behavior of the overall asphalt mixture. Within a theoretical framework of micromechanics, this study is expected to be suitable for evaluating damage-induced performance of asphalt mixtures by measuring only material properties and fracture properties of each mix component and not by recursively performing expensive laboratory tests that are typically required for continuum damage mechanics modeling.