Asphalt-based Composites Research Articles

Piezoelectric properties and microstructural changes of smart asphalt-based composites containing electroactive polymer and carbon black

The requirements for smart asphalt pavement with piezoelectric properties are becoming necessary as the demand for clean energy and intelligent transportation are increased. To develop asphalt-based composite with electroactive performance for pavement electricity generation and to recycle battery waste, carbon black was first added to polyvinylidene fluoride-hexafluoropropylene to prepare electroactive polymer modifier (EPM) with high content of electroactive crystalline phases. Then carbon black and EPM were added into asphalt to prepare asphalt-based composites containing electroactive polymer (ACEP). The Output voltage, environmental scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and basic performance tests were conducted to study the piezoelectric properties, microstructural changes, electroactivity generation mechanism and basic performance of ACEP. The result shows that 5 % EPM has good dispersion, and stable crystallization rate of about 26 % and considerable electroactive crystalline phase content in asphalt, but more holes and defects inside ACEP appears when EPM is excessive. Also, the addition of EPM can slightly improve low-temperature property and thermal stability of ACEP. This is because the F element in EPM can interact with the polar groups in the gum and asphaltene. The 5 % ACEP sample with a thickness of 5 mm can output a voltage of about 260 mV. The penetration, ductility and softening point of 5 % ACEP were 55.2 dmm, 285 mm and 62.3°C, respectively. It is found that ACEP has a good combination of piezoelectric and basic pavement properties and can be used to build smart asphalt pavement with piezoelectric properties. This also provides a way to recycle battery waste.

Viscoelastic fracture mechanics-based fatigue life model in asphalt-filler composite system

Asphalt-based composites gradually reach the end of their life as the service time increases, which directly leads to fatigue failure of the pavement structure. However, there is currently a lack of a fatigue life model for asphalt-based composites that has a clear physical interpretation. To address this issue, a viscoelastic fracture mechanics-based (VEFM) fatigue life model is proposed to predict the fatigue failure life for asphalt-based composites in this study. The VEFM fatigue life model was established within a viscoelastic fracture mechanics framework and was applied to two types of asphalt-filler composite systems (AFCS). To obtain the model parameters and verify the proposed model, various tests including linear amplitude sweep tests, time sweep tests at low-stress levels and high-stress levels, as well as surface energy tests were conducted on AFCS. The results indicate that the established VEFM fatigue life model can be expressed as a function of the loading level, viscoelastic fracture parameters, initial shear modulus, and surface energy. The initial edge flow of AFCS increases with the temperature and has minimal effect on the fatigue life throughout the fatigue process. A critical fatigue failure point is defined by the curve of damage rate and damage density. The fatigue life of AFCS increases with the temperature while decreasing with the loading level.

Fast nonlinear mechanical features decoupling to identify and predict asphalt-based composites

Nonlinear matrices employed in asphalt-based composites exhibit a prominent nonlinear elastic-viscoplastic-viscodamageable mechanical response. The constitutive model for this type of matrices requires a significant experimental effort to identify the material constants. To alleviate the characterization effort without losing reliability in the mechanical prediction, this paper presents a fast procedure decoupling the elasto-viscoplastic response from the viscodamageable one and facilitating the identification of the material constants via efficient optimization. This procedure relies on a combined experimental–numerical also applicable to other rheologically complex materials like polyurea, thermoplastics or elasto-viscoplastic polycrystals. The experimental part is deliberately designed to only conduct cost- and time-effective monotonic loads at different strain rates in tension and compression. These pure monotonic results are used in the constitutive model to predict more complex loading conditions such as multiple load–unload–reload (LUR) cycles. To do this, an elasto-viscoplastic constitutive model suitable to describe creep-like phenomena and large irreversible deformations is proposed. This model incorporates pressure and strain rate sensitivity, which is essential to capture the compression–tension asymmetry in asphalt-based composites. A rate-dependent damage model is proposed to describe the degradation rate of the elasto-viscoplastic part. The stress and the consistent tangent modulus are derived. The model implementation for user-defined finite element subroutines are given for explicit or implicit solvers. The proposed decoupling facilitates an efficient identification of the constant parameters via an in-house Nelder–Mead-based optimization method. To accelerate the identification, all the stress–strain curves, either in tension or compression, are simultaneously used with applying physically-based constrains. The framework is validated with asphalt matrix at room temperature (24 °C) and verified under LUR conditions at different rates. The identified model predicts correctly the experimental observations, proving its applicability to investigate particle-based composites with highly nonlinear matrices.

Research on Self-Healing Technology of SBS Modified Asphalt Concrete under the Dynamic Loading

Asphalt-based composites have the ability to heal themselves.without the aid of external influences (energy supply or material supplement), the self-healing ability of asphalt mixture is quite limited. In this paper, the efficiency of self-healing of asphalt mixture with Ni-Zn ferrite powders was analyzed based on the concept of microwave heating. We focused on assessing the characteristics of polyurethane (PU), base or styrene-butadiene-styrene (SBS) modified asphalt and its mixtures. The recovery rate of stiffness modulus and the fatigue life extension ratio were adopted to evaluate the self-healing efficiency of asphalt mixture. The analysis results proved that Ni-Zn ferrite powders can promote the self-healing ability of asphalt mixture significantly, the fatigue life extension ratio of 50% damaged ferrite-filled asphalt mixture can reach 1.33.

Effects of selective distribution of alumina micro-particles on rheological, mechanical and thermal conductive properties of asphalt/SBS/alumina composites

Constructing thermal conductive pathways is an effective route to increase the thermal conductivity of thermal interface materials (TIMs). Asphalt/styrene-butadiene-styrene tri-block copolymer (SBS)/alumina composites with alumina micro-particles selectively distributed in SBS (denoted as asphalt/SBS/sd-Al2O3) were fabricated through pre-dispersion of alumina micro-particles in SBS, followed by compounding with asphalt. The effects of alumina distribution on the rheological, mechanical and thermal conductive properties of the asphalt-based composites were systematically studied. Compared with the composites with randomly distributed alumina, i.e., asphalt/SBS/rd-Al2O3, those with selectively and homogeneously distributed alumina micro-particles in SBS formed a continuous thermal conductive SBS/alumina network. Therefore, the asphalt/SBS/sd-Al2O3 composites displayed maximum thermal conductivity enhancement of ~35% at 30 vol% alumina. At 50 vol% alumina, the thermal conductivity of the asphalt/SBS/sd-Al2O3 composites reached ~0.99 W/mK, which is 400% higher than that of the asphalt/SBS blend (0.20 W/mK). Also, the asphalt/SBS/sd-Al2O3 composites possessed higher values of storage modulus, tensile strength and softening point. This work has provided a promising approach to fabricate high-performance and low-cost TIMs.

Digital image correlation-based investigation of self-healing properties of ferrite-filled open-graded friction course asphalt mixture

Asphalt-based composites can self-heal, and this ability can be enhanced with induction heating and microwave heating. However, few methods are available to quantitatively analyze and monitor crack propagation in a composite before and after healing to evaluate the efficiency of self-healing. Digital image correlation (DIC) techniques, which are used herein, are widely applied for this purpose because they can directly measure the displacement field and strain field of an object under load. We conducted a three-point bending fatigue test and a three-point bending fracture test to study the influences of microwave heating time and healing time on the self-healing of asphalt-based composites with 5% ferrite and without ferrite. The influence of ferrite on the strain development process of the specimens was discussed based on the indexes of crack initiation time, crack propagation rate, and horizontal strain. The addition of ferrite can significantly delay secondary cracking and decrease the crack propagation rate of an open-graded friction course (OGFC) asphalt mixture. Based on DIC observations, the optimal microwave heating time for the OGFC asphalt mixture with 5% ferrite is 80 s. Meanwhile, the longer the healing time, the stronger is the healing effect, but the influence of healing time is weaker than that of heating time. Moreover, based on the change in the horizontal strain during crack development, it can be concluded that the addition of ferrite significantly improves the healing effect, in addition to improving the mixture toughness.

Relationship among cohesion, adhesion, and bond strength: From multi-scale investigation of asphalt-based composites subjected to laboratory-simulated aging

Identifying the properties of the bond strength between aggregates and asphalt binders is critical to understand the strength and fracture behavior of asphalt mixture. Some efforts have been made on the effect of aging on the bonding property of the asphalt binder. However, there is no consensus result and the mechanism that drives the change of bonding property remains unclear. The objective of this study is to investigate the influence of aging on the bonding property, and to explain the reason lies behind. To achieve this goal, four neat asphalt binders were treated with short-term aging and long-term aging. The bond strength and the adhesion force were measured by binder bond strength test on a macro scale and atomic force microscope on a micro scale, respectively. Based on the result obtained in this study and previous publications along with the adhesion theories, it is found that a moderate aging contributes to the bond strength while a sever aging does not necessarily improve the bond strength. The change of bond strength under an aging condition can be explained by the cohesion force in asphalt binders and the adhesion force between asphalt binders and aggregates. Based on the results, it can be concluded that the cohesion force increases with aging time as a result of asphaltenes association. The adhesion force increases initially and then decreases, and the wettability is thought to be responsible for the reduction of adhesion force. The adhesion reduction can be observed on the three phases (catana phase, peri phase, para phase) of the asphalt binders, which leads to the adhesion reduction on the whole asphalt binders. These findings help to provide a better understanding of the change of bonding property of asphalt binders during an aging process, which contributes to the improvement of bond strength by enhancing the wettability of each phase in asphalt binders appropriately. The results have practical significance and can help to optimize the materials production process.

<b>Production of self-healing asphalt with steel short fibres and microwave heating: pilot study

This pilot study aims to develop a self-healing asphalt through microwave heating, to reduce processing time, save energy and allow real commercial applications in a near future. Asphalt based composites were produced with different percentages of steel short fibers, obtained from the cutlery industry, to serve as a heat source for microwave radiation. Structural characteristics, morphology, and thermic behavior of the short steel fibers were characterized through X-ray Diffraction, X-ray Fluorescence, Scanning Electron Microscopy and Thermogravimetric Analysis, that was also used to verify the relation between mass variation and temperature of the asphalt-based composite. Temperature was monitored during micro wave heating to determine the heating rate of the composites with different percentage of fibers. Brookfield viscosity, penetration, ductility, softening point and density tests were carried out to characterize physical properties of the most representative asphalt-based composite. Results show the feasibility to use microwave heating in the production of the composite, indicating potential for future application as self-healing asphalt and pavement repair.

Self-healing efficiency of ferrite-filled asphalt mixture after microwave irradiation

Asphalt-based composites have the ability to heal themselves. Under certain conditions, strength and stiffness modulus can be restored so that the fatigue life can be extended. However, without the aid of external influences (energy supply or material supplement), the self-healing ability of asphalt mixture is quite limited. In this paper, the efficiency of self-healing of asphalt mixture with Ni-Zn ferrite powders was analyzed based on the concept of microwave heating. The recovery rate of stiffness modulus and the fatigue life extension ratio were adopted to evaluate the self-healing efficiency of asphalt mixture. Different influence factors, such as heating temperature, healing time and damage level, were analyzed in this study. The analysis results proved that Ni-Zn ferrite powders can promote the self-healing ability of asphalt mixture significantly. It is found that when the asphalt mixture is filled with 80% ferrite powders (volume fraction of mineral powders), under the condition of healing for 3h after heating to 55°C by microwave, the fatigue life extension ratio of 50% damaged ferrite-filled asphalt mixture can reach 1.33.

High-Efficiency Heating Characteristics of Ferrite-Filled Asphalt-Based Composites under Microwave Irradiation

Asphalt concrete is a typical self-healing material, and its self-healing rate is influenced by the temperature. Since microwave irradiation is an efficient way of heating, its use could be a novel approach to heating asphalt pavement. In this study, ferrite particles were mixed into asphalt-based composites to upgrade the microwave absorbing efficiency and then further accelerate the self-healing rate of the composites. The microwave-absorbing capability of three kinds of aggregate and three kinds of filler were studied first. It was found that NiZn ferrite has an excellent microwave-absorbing capability under 2.45 GHz compared to other tested materials. Then the heating rate of asphalt mastic, asphalt matrix, and asphaltic concrete mixture with and without NiZn ferrite fillers were tested. The microwave heating rates of these composites all increase significantly with an increase in NiZn ferrite content. Third, the temperature uniformity of asphalt composites was investigated using an infrared thermal imager and a statistical analysis method. It was found that adding adequate amounts of ferrite fillers could notably improve temperature uniformity. Then, through electromagnetic measurement, it was confirmed that the addition of NiZn ferrite particles to mastic confers an excellent microwave-absorbing capability in a frequency range of 1–2.5 GHz compared to plain asphalt mastic. Finally, a fatigue–rest–fatigue test was used to investigate the effect of microwave heating on the self-healing behavior of ferrite-filled asphaltic concrete mixtures. It can be concluded that the healing capability of asphalt concrete can be significantly increased by ferrite particles’ superior microwave absorption properties, leading to the extension of fatigue life.

Piezoelectric and dielectric behavior of 0-3 asphalt-based composites with carbon black

Asphalt-based piezoelectric composites have great potential to serve as sensors to monitor the health of asphalt pavements due to their compatibility with asphalt pavements and appropriate response behaviors. This paper reports the preparation of asphalt-based piezoelectric composites doped with carbon black to investigate the influence of lead zirconate titanate (PZT) and carbon black contents on the dielectric, piezoelectric, and electromechanical properties of the composites. The addition of carbon black as a conductive phase facilitates the poling process, which improves the poling efficiency. The results indicate that with increasing PZT content, the dielectric constant (εr), piezoelectric strain factor (d33) and planar electromechanical coupling coefficient (Kp) of the composites increase. εr, d33, and Kp of the composites increase with the increase of carbon black content, and the composites with 0.3vol% carbon black present the maximum values of 154.89, 75.74 pC/N and 37.73%, respectively, then decrease with greater carbon black content. However, tanδ shows an opposite trend with the variation of PZT and carbon black contents. With 80vol% PZT and 0.3vol% carbon black, tanδ decreases to the minimum value of 20.80, then increases with further increases in carbon black content. The variation of the mechanical quality factor (Qm) shows little association with the contents of PZT or carbon black.

Thermal Conduction and Insulation Modification in Asphalt-Based Composites

The relationship between thermal conductivity and properties of mixing particles is required for quantitative study of heat transfer processes in asphalt-based materials. In this paper, we measured the effective thermal conductivity of asphalt-based materials with thermal conduction (graphite) and insulation (cenosphere) powders modification. By taking account of the particle shape, volume fraction, the thermal conductivity of filling particles and base asphalt, we present a new differential effective medium formula to predict the thermal conductivity modification in asphalt-based composite. Our theoretical predications are in good agreement with the experiment data. The new model can be applied for predicting the thermal properties of asphalt-based mixture, which is available for most of thermal modification in two-phase composites.

Research on Fatigue Resistance Performance of Nano-Rubber Powder Modified Asphalt

Asphalt pavement has been used in road construction and many other applications for a long time. Because of the heavy loading and busy traffic, pavement distresses such as stripping, raveling, cracking, and moisture damage often occur during its serving life. The possibility of using nano-rubber as a modifier for asphalt was investigated in this research. Fatigue test according to the American Association of State Highway and Transportation Officials (AASHTO) T321-03 standard was conducted. Fatigue resistance performance of the original asphalt concrete and modified asphalt concrete was investigated by means of a four-point bending test with the phenomenological fatigue methodology at two temperatures. The results showed that rubber modified asphalt concretes have good basic physical performance. Also, the flexural stiffness modulus of modified asphalt-based composites had less influence on strain at 5°C, but at 15°C, the effect was obvious. The fatigue performance of nano-rubber modified asphalt-based composite was better than that of base asphalt and Styrene-Butadiene-Styrene (SBS) -modified asphalt. Strain (e) of nano-rubber modified asphalt concrete was smaller, and its fatigue performance was better. Comparing the toughening effect of other ordinary modification powders, a little amount of nano-rubber powder could increase the toughness of modified asphalt concrete greatly and keep them in high tension and heat resistance. Nano-rubber powder modified asphalt has the advantage of aging-resistance, which could improve the service life of the modified asphalt and reduce the maintenance cost of pavement.

Investigation of Static and Dynamic Response of Graphite and Carbon Fiber Modified Conductive Asphalt-Based Composite

The conductive behavior of asphalt concrete can be improved with the addition of conductive materials, thus a multifunctional asphalt-based composite can be obtained. The conductive asphalt-based composite modified by graphite was studied extensively. Conductive materials percentages may have influences on performance of asphalt mixture. The performance of an asphalt pavement is significantly affected by its resistance to permanent deformation and its fatigue performance. The paper presents the results of a project aimed at investigating static and dynamic response as cracking and fatigue behaviors of conductive asphalt-based composite using the ITT. In particular ITT were performed in which the graphite percentages, loading mode was varied. As test results indicate that the addition of graphite shows positive influence on the indirect tensile strength, failure stiffness modulus in static loading test, especially in high loading speed. The number of load cycles to fatigue failure presents a bit decrease with graphite percentages in dynamic loading test. After adding discontinuous carbon fibers, conductive asphalt-based composite shows good fatigue property, which can prevent crack propagation. It can be concluded that the combined modification brings reinforcement effect to asphalt concrete and improves its mechanical and fatigue properties.

Properties evaluation of asphalt-based composites with graphite and mine powders

On account of the high specific surface area, graphite powder could transform more free asphalt to structure asphalt, so the softening temperature of asphalt-based composites (containing mineral powder) was increased from 45 °C to 82 °C upon addition of 9.0 vol.% graphite. Accompanying effects are increase of rutting resistance and decrease of the electrical resistance. Graphite powder and mineral powder together were much more effective than mineral powder alone or graphite powder alone for raising the softening temperature. Furthermore, the increase of electrical conductivity would transform the asphalt-based composites to a kind of smart material, which made strain self-monitoring of asphalt pavement become feasible through the piezoresistivity of electrically conductive asphalt-based composite.

Self-monitoring electrically conductive asphalt-based composite containing carbon fillers

A new novel function materials, structure self-monitoring asphalt-based composite was introduced. The results show that the output resistance of electrically conductive asphalt-based composites would change under cyclic loading and vehicle loading action. The resistance change of conductive asphalt-based composites was aroused by the variation of its interior structure. When the fatigue failure was studied, the larger cracks cut the continuous electrically conductive path and the electron is difficult to overcome the potential barrier of gap. In the early period, the slight deformation and microcrack may be recovered due to the viscoelasticity character of asphalt, which leads to some cracks close again, the output resistance changes a little. But with the shear process performs continuously, the cracks become larger and larger, which would cut the conductive path and block off the transition of electrons, and if the cracks are large enough, the pitch-matrix composites containing carbon fillers will lose electrically conductive function. When the rutting failure was studied, the flowage of conductive substance results in the decrease of substance due to electrically conducting and conductive path decreasing. The decrease of electron volume contribute to electrically conducting and large stone aggregate prevent the electron from transiting. In a word, the variation of output resistance is aroused by the variation of interior structure completely.

Paving Asphalt Production Technologies. Analysis of Effectiveness

The possibilities of using previously approved new process solutions in production of oxidized paving asphalts are examined based on the proceedings of the interindustry conference “Problems in Production and Use of Petroleum Asphalts and Asphalt-based Composites” (Saratov-2000) and recent publications.