Self-healing Asphalt Research Articles

Study on Recycling of Steel Slags Used as Coarse and Fine Aggregates in Induction Healing Asphalt Concretes.

Steel slag, a by-product of steelmaking, imposes lots of negative impacts on the environment. For alleviating negative impacts, more and more experiments have been carried out to explore the application possibility of steel slag. The purpose of this study is to explore the feasibility of steel slag being applied in induction healing asphalt concretes to replace coarse and fine aggregate. Surface texture and pore sizes of steel slag were firstly tested, and then steel slag and basalt asphalt mixtures modified with steel fibers were prepared. Moisture susceptibility, dynamic stability, mechanical property, thermal property, induction heating speed, natural cooling speed and healing property of the asphalt mixtures were evaluated. Results showed that steel slags had more obvious holes in the surface while the surface area is much larger than that of basalt. Furthermore, steel fibers and steel slag both have dynamic stability, and steel fibers contribute to increased moisture resistance while steel slag is not. Steel slag asphalt concrete showed better mechanical property and better capacity to store heating. Steel slag asphalt mixtures had a similar heating speed to basalt asphalt mixtures but a significantly slower cooling rate. Finally, the induction healing test and CT scanning test demonstrated that steel slag asphalt mixtures had a similar healing ability to basalt asphalt mixtures. It can be concluded that steel slags have the potential to replace the natural aggregates to be applied in induction heating self-healing asphalt concretes.

An evaluation of the mechanical and self-healing properties of warm mix asphalt containing scrap metal additives

Growing concern over global warming has highlighted the use of warm mix asphalt (WMA) mixtures throughout the asphalt industry. Although WMA offers numerous advantages, it suffers from the problem of low temperature cracking. One solution is the adoption of self-healing asphalt technology. Therefore, this research aims to evaluate the effects of scrap metal additives on the mechanical and self-healing properties of asphalt mixtures through microwave heating. Three types of scrap metal are used in this study, namely steel shavings, recycled tire steel fibers, and copper slag filler. This study evaluates the morphological properties of steel shavings and recycled tire steel fibers using Field Emission Scanning Electron Microscopy (FESEM). In addition, mechanical properties are evaluated by employing moisture susceptibility and deformation strength tests. The thermal properties of samples containing scrap metal and the control sample were monitored using a thermography camera. Finally, the self-healing properties of asphalt samples were assessed by employing microwave heating at three different self-healing times of 20, 30, and 40 s. The results show that when copper slag filler is added, mixtures containing recycled tire steel fibers and metal shavings exhibit a higher degree of resistance to moisture and rutting. In addition, the surface temperature distribution of the samples shows that the use of copper slag filler, recycled steel shavings, or recycled tire steel fibers simultaneously resulted in improved temperature distribution on the sample surface. Moreover, the self-healing results showed that fiber contents higher than 2% can be replaced with copper slag filler.

Самовосстанавливающйся асфальт

Самовосстанавливающйся асфальт

Synthesis of microcapsules with waste oil core and application in self-healing asphalt

In this study, microcapsules containing waste oil as rejuvenator were synthetized and characterized to enhance the self-healing ability of asphalt. Chemical structure, thermal stability, and micro morphology of microcapsules were described by Fourier Transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscope. Self-healing effect of asphalt samples was captured through fatigue-healing test. Results show that microcapsules were fabricated spherical and intact with agglomerated layers, and it has satisfied thermal stability. Addition of microcapsules hardly impacted viscosity of asphalt binder and accelerated the self-healing of asphalt with respect to complex modulus and fatigue life.

Consequences of long-term infrastructure decisions—the case of self-healing roads and their CO2 emissions

What could be the reduction in greenhouse gas emissions if the conventional way of maintaining roads is changed? Emissions of greenhouse gases must be reduced if global warming is to be avoided, and urgent political and technological decisions should be taken. However, there is a lock-in in built infrastructures that is limiting the rate at which emissions can be reduced. Self-healing asphalt is a new type of technology that will reduce the need for fossil fuels over the lifetime of a road pavement, at the same time as prolonging the road lifespan. In this study we have assessed the benefits of using self-healing asphalt as an alternative material for road pavements employing a hybrid input–output-assisted Life-Cycle Assessment, as only by determining the plausible scenarios of future emissions will policy makers identify pathways that might achieve climate change mitigation goals. We have concluded that self-healing roads could prevent a considerable amount of emissions and costs over the global road network: 16% lower emissions and 32% lower costs compared to a conventional road over the lifecycle.

Mechanical experiment evaluation of the microvascular self-healing capability of bitumen using hollow fibers containing oily rejuvenator

Smart microvascular self-healing bituminous composites are considered a promising approach to prolong pavement service life. The objective of this work was to investigate the microvascular self-healing capability of bituminous material by using hollow fibers with oily rejuvenator through a direct-tension mechanical experiment. The hollow fibers with oily rejuvenator were prepared using a wet-spinning approach by applying polyvinylidene fluoride material. The fixed-length hollow fibers with sealed ends were mixed in bitumen to form composite samples. Through a repetitive tensile method, the tension strength data were used to calculate the self-healing efficiency autonomously by considering crack closure and healing at various healing temperatures and times. The scanning-electron-microscope morphology showed that the polyvinylidene fluoride hollow fibers had a tight interfacial structure with bituminous material without debonding. X-ray computed tomography results indicated that the fibers were distributed homogeneously in bitumen. The fiber content and fiber orientation affected the self-healing capability of bituminous samples at 0 °C. To simplify the influence of the above two factors of the fibers, only one fiber was placed in bitumen samples parallel to the tension direction. With an increase in temperature from 0 to 30 °C, the self-healing capability of the bitumen samples increased dramatically. This phenomenon is attributed to the accelerated penetration speed of rejuvenator in the bitumen. An increase in time increased the self-healing capability of the bitumen samples. The rejuvenator may have sufficient time to leak from the hollow fibers and penetrate the bitumen. The results provide a guide to the microstructural design of the vascular fibers and the application of hollow fibers in self-healing asphalt pavement.

Research Progress on Self-Healing and Repairing Technology of Asphalt Mixture Crack

The latest research results at home and abroad have comprehensively analyzed the self-healing and repairing technology of asphalt mixture, and introduced the self-healing mechanism of asphalt and self-healing behavior of asphalt. Active and passive healing methods are mainly discussed. Both methods can effectively enhance the healing properties of asphalt materials and achieve the purpose of repairing cracks and looseness of asphalt concrete pavement. The development of self-healing asphalt concrete technology at home and abroad is expounded, and the application significance and application prospect of the technology are analyzed. The conclusion is that the environmental and social benefits of self-healing asphalt concrete technology are outstanding, and the promotion is of great significance and good development prospects.

Microwave crack healing on conventional and modified asphalt mixtures with different additives: an experimental approach

Self-healing asphalt by increasing bitumen temperature using microwave radiation is an effective technique for crack-healing on asphalt mixtures. Normally, these types of asphalt mixtures contain metal additives that promote microwave heating. However, results from the literature suggest that crack-heling would be possible without additives. If this is possible, existing asphalt pavements could be healed by microwave heating. The objective of this research is to evaluate the crack-healing capabilities of conventional asphalt mixtures without metal additives. With this purpose, the authors studied and compared the crack-healing capabilities of conventional asphalt mixtures without metal additives with modified mixtures containing steel fibre, metal shavings, and Silicon Carbide, the last being a novel ceramic material for the crack-healing of asphalt mixtures by microwaves. The authors conducted three-point bending tests on semi-circular asphalt samples to calculate the flexural strength of asphalt. Results of the research showed that the effect of additives that promote microwave heating on the crack-healing of mixtures was a small reduction of the average healing ratio. Additionally, it was found that the effect of additives that promote microwave heating on the surface temperature of samples was either a small increase or small decrease, similar to the effect observed in the healing of mixtures. X-Ray computed tomography results showed that the virgin aggregates used contained metals, which explains the heating and good crack-healing of the reference mixtures. Overall, results of crack-healing tests indicate that asphalt mixtures with aggregates that naturally heat with microwave radiation could be crack-healed without the addition of additives to promote microwave heating.

Evaluation of sunflower oil’s healing effect in bituminous materials

Recently, sunflower oil has been widely used as encapsulated healing agent for self-healing asphalt. However, few researches have evaluated the healing effect of sunflower oil on aged asphalt binder. As such, this paper investigates the potential healing effect of sunflower oil in bituminous materials. Dynamic shear rheometer (DSR) was employed to evaluate the performance of the asphalt binders. The resultant master curve indicated that by adding 5% sunflower oil, approximately 30% loss of modulus in aged bitumen could be restored. Thus, the test result bear solid testimony that sunflower oil has the potential to fully recover the original rheological properties as well as healing capacity of the asphalt binder.

Preparation of microcapsule and its influence on self-healing property of asphalt

A kind of microcapsule was prepared, and a new type of self-healing asphalt was manufactured by mixing asphalt, microcapsule and curing agent with proper ratio. The ductility(15 °C and 10 °C), softening point and penetration of asphalt were tested both before and after adding microcapsule and curing agent into the asphalt. The results showed that the three indexes were kept in normal ranges after adding microcapsule and curing agent. However, the ductility(10 °C) was lower than the technical standard when the additive amount of microcapsule was 5.0wt%. Whereafter, the influence of additive amount, self-healing temperature and time on the asphalt self-healing property were all investigated by ductility self-healing tests (10 °C). The outcome indicated that the addition of microcapsule into the asphalt promote its self-healing properties obviously. The self-healing rate of blank asphalt in 20 °C and for 3 h was 20%, and when the microcapsule additive amount was 3.0wt%, the rate was improved to 40.0%. The highest self-healing rate was 52.0%. The elevation of temperature and extension of time were both beneficial for the promotion of the self-healing properties of asphalt. However, when healing temperature and healing time were improved to 30 °C and 7 h, the improvement of self-healing rate was not obvious.

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.

Investigation of the Potential Use of Calcium Alginate Capsules for Self-Healing in Porous Asphalt Concrete.

Improving the healing capacity of asphalt is proving to be an effective method to prolong the service life of an asphalt pavement. The calcium alginate capsules encapsulating rejuvenator have been developed and proved to provide successful localized crack healing in asphalt mastic. However, it is not known whether this self-healing asphalt system will improve healing capacity of a full asphalt mix. To this aim, this paper reports on study which investigate effect of the calcium alginate capsules onto self-healing capacity of the porous asphalt mix. X-ray computed tomography (XCT) was used to visualize the distribution of the capsules in porous asphalt. The effect of the capsules on fracture resistance of porous asphalt concrete was studied by semi-circular bending (SCB) tests. A semi-circular bending and healing programme was carried out to evaluate the healing effect of these capsules in porous asphalt concrete. Indirect Tensile Stiffness Modulus (ITSM) tests were employed in order to investigate the influence of the capsules on the stiffness of the porous asphalt concrete. The results indicate that incorporating calcium alginate capsules significantly improve the healing capacity of porous asphalt concrete without compromising its performance.

Indicators of the effectiveness of self-healing asphalt concrete

In the article, indicators reflecting the degree of efficiency of the self-healing technology being developed are proposed the degree of restoration of the operational state of the structure (degree of self-healing); the speed of the process of restoring the operational state of the structure (self-healing rate); durability operational status after self-healing; timeliness of initiation of the self-healing process. Indicators of the effectiveness of self-healing technology are justified by using the Pavement Condition Index (PCI).

Rheological and self-healing properties of asphalt binder containing microcapsules

The objective of this investigation is to prepare the microcapsule and study the rheological and self-healing properties of asphalt containing microcapsules. Urea formaldehyde resin (UF) self-healing microcapsule was prepared by in-situ polymerization method and the monomer properties of microcapsule were characterized. Penetration, softening point, ductility, dynamic shear rheology (DSR), bending beam rheology (BBR) and self-healing tests were conducted to study the rheological property and self-healing ability of asphalt containing microcapsules. The results show that UF microcapsule material has been successfully synthesized, and the microcapsules can withstand the high temperature during the construction of asphalt pavement to a certain extent. Compared with the properties of matrix asphalt, the ductility of self-healing asphalt containing UF microcapsules decreases obviously, the softening point and rutting factor increase slightly, the durability and self-healing ability increase obviously, the low temperature crack resistance decreases slightly.

<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.

Fatigue behavior of microcapsule-induced self-healing asphalt concrete

Abstract Asphalt has an intrinsic self-healing character. However, the rate of damage formation is much higher than the rate of damage healing. To promote the self-healing capability of asphalt materials, micro-encapsulation technique has been regarded as the potential method. To illustrate the benefits of microencapsulation on the pavement engineering, the fatigue behavior of microcapsule-induced self-healing asphalt concrete was investigated. Firstly, the melamine urea formaldehyde (MUF) microcapsules containing rejuvenator were fabricated via an in-situ polymerization method. The surface morphology, the diameter and the shell thickness of the microcapsule were observed by scanning electron microscopy. The thermogravimetric analysis was used to ensure the high temperature stability of the microcapsule. The infrared spectroscopy analysis technology was used to investigate the components of the microcapsule material. Then, a four-point bending fatigue-healing-fatigue test was designed to study the effect of the microcapsule on the fatigue life of asphalt mixture specimen. From the test results, it can be concluded that the addition of 3 wt% microcapsules can double the fatigue life of the AC-10 asphalt mixture.

Self-healing properties of recycled asphalt mixtures containing metal waste: An approach through microwave radiation heating

The concept of self-healing asphalt mixtures by bitumen temperature increase has been used by researchers to create an asphalt mixture with crack-healing properties by microwave or induction heating. Metals, normally steel wool fibers (SWF), are added to asphalt mixtures prepared with virgin materials to absorb and conduct thermal energy. Metal shavings, a waste material from the metal industry, could be used to replace SWF. In addition, reclaimed asphalt pavement (RAP) could be added to these mixtures to make a more sustainable road material. This research aimed to evaluate the effect of adding metal shavings and RAP on the properties of asphalt mixtures with crack-healing capabilities by microwave heating. The research indicates that metal shavings have an irregular shape with widths larger than typical SWF used with asphalt self-healing purposes. The general effect of adding metal shavings was an improvement in the crack-healing of asphalt mixtures, while adding RAP to mixtures with metal shavings reduced the healing. The average surface temperature of the asphalt samples after microwave heating was higher than temperatures obtained by induction heating, indicating that shavings are more efficient when mixtures are heated by microwave radiation. CT scan analysis showed that shavings uniformly distribute in the mixture, and the addition of metal shavings increases the air voids. Overall, it is concluded that asphalt mixtures with RAP and waste metal shavings have the potential of being crack-healed by microwave heating.

Roadway to self-healing highways with integrated wireless electric vehicle charging and sustainable energy harvesting technologies

Development of electric mobility and sustainable energy result in new technologies such as contactless electric vehicle charging and roadway energy harvesting methods, but also self-healing asphalt roads. By combining these technologies a new concept of Future Sustainable Roads for Electric Mobility is created and presented in the paper. This paper bridges the gap created by these unilateral technology developments using a multi-disciplinary approach including placing cautions when necessary and suggesting viable alternatives for optimal utilization of these energy transfer and conversion techniques. Through theoretical analysis, simulations, and tests on lab-scale experimental prototypes, the impact of our proposal is showcased. Thermal and loss models are developed for self-healing asphalt. Also, integration study of solar roads and contactless charging is performed. Applying the insight gained from the results, it is discussed how some challenges also pave a way towards interesting opportunities, for instance, infrastructure sharing for material use optimization and efficient mosaic integration. Finally, an economic viability case study is presented for a future Dutch highway with such newly emerging components.

Snow and ice melting properties of self-healing asphalt mixtures with induction heating and microwave heating

In this paper, the snow and ice melting properties of self-healing asphalt mixtures with induction heating and microwave heating were investigated. The self-healing performance of the mixtures during ice melting process was measured with cyclic three-point bending test as well. The results indicated that the snow and ice melting performance of self-healing asphalt mixtures with appropriate heating techniques was remarkable. The average melting velocity of ice melting was improved from less than 1 g/min (previous researches) to more than 10 g/min, while the average snow melting velocity of steel fiber modified asphalt mixture and steel slag asphalt mixture with microwave heating could reach 53.9 g/min and 48.5 g/min respectively. The water from melted ice/snow played a major role in the melting process of snow with microwave heating. However, the moisture from melted ice/snow on the surfaces of crack prevented the thermal healing of asphalt mixtures. It is recommended that another heating process after the melting process should be applied to promote the healing of cracks as well as to prevent the melted snow and ice water on the pavement from freezing.

The compartmented alginate fibres optimisation for bitumen rejuvenator encapsulation

This article presents development of a novel self-healing technology for asphalt pavements, where asphalt binder rejuvenator is encapsulated within the compartmented alginate fibres. The key objective of the study was to optimise the compartmented alginate fibre design, i.e., maximising amount of rejuvenator encapsulated within the fibre. The results demonstrate that optimum rejuvenator content in the alginate fibre is of 70:30 rejuvenator/alginate ratio. The fibres are of sufficient thermal and mechanical strength to survive harsh asphalt mixing and compaction processes. Furthermore, results illustrate that zeer open asfalt beton (ZOAB) asphalt mix containing 5% of 70:30 rejuvenator/alginate ratio compartmented alginate fibres has higher strength, stiffness and better healing properties in comparison to the control asphalt mix, i.e., mix without fibres, and mix containing fibres with lower rejuvenator content. These results show that compartmented alginate fibres encapsulating bitumen rejuvenator present a promising new approach for the development of self-healing asphalt pavement systems.