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Abstract

Encapsulated healing agents may delay the growth of reflective cracking in asphalt mixtures and contribute to delay the maintenance of asphalt surfaces. When crack damage appears in the asphalt, the capsules membrane ruptures, and the healing agents are released in the vicinity of the cracks. This experimental research shows the rate at which the oil is released from the capsules when the asphalt is exposed to cyclic loading and its capacity to improve the natural crack self-healing capacities of the asphalt. Using a combination of mechanical and chemical testing, it was found that most of the capsules resist asphalt mixing and compaction. It was found that in porous asphalt, the oil is released gradually during the lifetime of the asphalt, while in dense asphalt, the oil is released at the time when cracks start appearing. This is an indication that the gradation of asphalt is a critical parameter to design the strength of capsules for asphalt self-healing. Furthermore, the self-healing efficiency of capsules is higher in porous and stone mastic asphalt than in dense asphalt mixture. Finally, it has been found that there is a moment in the lifetime of an asphalt road when the capsules are most effective to self-heal the existing crack damage.

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... Zhang et al. (2019) call attention to the nonrealistic aspect of using static loading to induce the rejuvenators release into the asphalt and simulate the actual stress condition occurring in the asphalt pavement. More recent publications (Menozzi et al. 2015;Salih et al. 2018;García et al. 2020b, a) have used fatigue tests in the 3-point bending (3PB) over elastic foundation configuration to quantify self healing as an extension of fatigue life of asphalt samples subject to reflective cracking, at different levels of damage. In this manner, García et al. (2020b) investigated the level of damage, in terms of reflectivecracks development, that asphalt mixtures should undergo to promote the initiation of cracks and the breakage of capsules so that self healing reaches its maximum. ...
... More recent publications (Menozzi et al. 2015;Salih et al. 2018;García et al. 2020b, a) have used fatigue tests in the 3-point bending (3PB) over elastic foundation configuration to quantify self healing as an extension of fatigue life of asphalt samples subject to reflective cracking, at different levels of damage. In this manner, García et al. (2020b) investigated the level of damage, in terms of reflectivecracks development, that asphalt mixtures should undergo to promote the initiation of cracks and the breakage of capsules so that self healing reaches its maximum. Independent of the loading level or type of mixture, the most significant fatigue-life recovery was achieved after subjecting the samples to 35% of their fatigue life and then applying a resting period. ...
... This paper aims to evaluate the self healing of a dense-graded asphalt mixture via the repair of reflective cracking using the 3PB over elastic foundation fatigue test. By considering the findings of García et al. (2020b), the asphalt samples were healed at the optimum healing moment and the effect of different healing periods was investigated. The calcium-alginate capsules are composed of soybean oil and waste cooking oil (WCO), which have not been used before for this healing system. ...
Article
Embedded encapsulated rejuvenators have been proven to enhance the crack-healing ability of asphalt. This healing mechanism is autonomous as it is triggered by the energy resulting from the axles' passages on the road: an advantage over other engineered healing methods. However, compared to the advances on crack healing by externally triggered methods, the understanding of the healing mechanism by the action of encapsulated rejuvenating agents is still evolving. Based on the findings of García et al. (2020b) on the optimum damage level to heal reflective cracking in asphalt mixtures with calcium-alginate capsules, this study further investigates the effect of different healing times (24, 48, and 72 h) on healing levels of fatigue-damaged asphalt mixtures. In parallel, the performance of encapsulated new soybean oil and waste cooking oil (WCO) is compared via their characterization and effects on the mechanical properties of asphalt. The embedded capsules decreased the resistance to moisture damage, stiffness, and durability of the base asphalt. Nevertheless, considerably greater self-healing indexes were observed, which were even more pronounced for longer healing times. In the field, these mixtures' full healing capability would not be achieved at once as long periods of traffic closure are not feasible. Also, the asphalt deformation results in higher self-healing indexes due to the embedded capsules. Encapsulated WCO promoted the highest healing values, possibly because these capsules were more easily damaged and the oil better diffused into the asphalt.
... Furthermore, in previous researches, asphalt has been engineered to improve its self-healing properties and close reflective cracks more effectively. For example, in references [26][27][28], electromagnetic induction or microwaves [29][30][31] was proposed to reduce the viscosity of bitumen which, in the laboratory, closed reflective cracks in asphalt beams by up to 120 s, rather than in hours or days [32] as it happens in asphalt that is not treated with electromagnetic induction. ...
... This triggers the release of the healing agent which, from the experimental results, contributes to close cracks in the asphalt [40,41]. In reference [26], it was found that the sunflower oil released by the cap-sules when a load is applied over the asphalt caused a decrease in the bitumen viscosity. Due to the bitumen viscosity reduction and the load applied, the asphalt materials were compacted making the bitumen flow into the air voids and cracks. ...
... We used sunflower oil because it is readily available in the UK. As it was reported in [26,35,40], the shell of the capsules, which contained the oil was made of low viscosity sodium alginate, 95% purity, (C 6 H 7 O 6 Na in powder) and calcium chloride (CaCl 2 in granular pellets) provided by Sigma-Aldrich, UK. The encapsulation procedure was extensively described in [4,40,42]. ...
Article
It has been proven that the addition of encapsulated bitumen rejuvenators into the asphalt mixtures can improve their natural self-healing properties, prolonging their lifespan. However, in order to use Ca-alginate capsules as an additive for self-healing roads, they must not reduce the performance properties of the pavement. This paper presents the results of a multivariable experimental study that aims to select the capsule size and strength that optimise the asphalts self-healing properties for mitigating reflective cracking, skid resistance, fatigue durability, deformation under loading (rutting) and the amount of oil released in the bitumen. The capability of the encapsulated bitumen rejuvenators to mitigate the reflective cracking effect was assessed by reproducing the traffic-induced reflective cracks in stone mastic asphalt mixtures. Cyclical loading tests were carried out using a laboratory wheel tracker to analyse the fatigue durability, self-healing properties and rutting effect. Furthermore, computerised tomography scanning technology was used to analyse the changes in the internal structure of the capsules inside the asphalt. Finally, Fourier-transform infrared spectrometry was applied to measure the amount of oil released by the capsules. It was concluded that (i) the oil released does not influence the skid resistance, (ii) capsules delay reflective cracking of asphalt and (iii) rutting increases proportionally to the oil released.
... Also, the researchers found that crack healing with the encapsulation technique can delay the occurrence of reflective cracks in the pavement, but it marginally reduces the skid resistance of asphalt pavement(Norambuena-Contreras et al., 2019b;Ruiz-Riancho et al., 2021). The effectiveness of the encapsulation technique was found to be greater in an open-grade asphalt mixture like porous asphalt or stone mastic asphalt; this was due to the amount of mastic in the asphalt mixture, which influences how the asphalt gets deformed under cyclic loading and the flow of mastic(Garcia-Hernández et al., 2020;Xu et al., 2019a). ...
Article
Bio-based and nature-inspired solutions have been investigated recently to develop sustainable, resilient, and durable construction including but not limited to roadway infrastructures. This paper reviews state-of-the-art studies on self-healing, self-cleaning and self-rejuvenating asphalt, and concrete construction. This review draws three conclusions. (1) Self-healing construction materials have the potential to significantly extend the service life of construction elements. Urban and industrial wastes such as food waste, biomass, metals have been used to create self-healing construction materials that are more environmentally friendly. (2) Self-cleaning construction materials not only remove pollution by repelling water on their superhydrophobic surface, but also cut building and infrastructure maintenance costs, while improving cities’ air quality by degrading pollutants such as NOx. Pavement engineers have exploited self-cleaning characteristic to facilitate the de-icing of pavements and lengthening the service life of pavements. (3) Self-rejuvenating materials including bio-oils can revitalize materials and delay aging; bio-oils can also be used to make bio-binders, thereby reducing the need for petroleum-based binders. The optimum concentration of bio-oil for asphalt modification depends on the chemical structure of oils. Still, regardless of dosage, self-rejuvenating binders improve asphalt workability and performance at low temperatures and increase the resistance of the asphalt mix to fatigue and cracking. This review also identified critical research gaps, including (1) the lack of a reliable, unified, and standard method to accurately measure construction materials’ self-healing, self-cleaning and self-rejuvenating properties; (2) the lack of long-term field performance data to conduct comprehensive life cycle assessment and life cycle analysis; (3) the lack of accurate technoeconomic analysis to facilitate market entry of abovementioned solutions. Addressing these gaps and determining contribution of nature-inspired and bio-based technologies to a carbon neutral economy along with issuing carbon certificates can facilitate the widespread application of these technologies while promoting resource conservation and sustainability.
... Consequently, this can have a knock-on effect on their route to market and practical implementation for asphalt self-healing. More recently, researches led by Garcia-Hernández et al. (2020), Micaelo et al. (2016);and Norambuena-Contreras, Liu, et al. (2019a, 2019b, 2022 have prepared free-of-surfactants O/W emulsions incorporating low-cost rejuvenators for the synthesis of different size capsules based on the ionic gelation principle. These emulsions are stabilised due to the weighting effect of the biopolymeric encapsulating agent (typically alginate), increasing the viscosity of the continuous phase, thus reducing the movement of the droplets, and preventing them from coalescing. ...
... As a wide variety of building materials are included in the self-healing concept, asphalt mixtures have also been included in this method and many studies have been carried out [14][15][16]. In their study, Garcia-Hernandez and his team aimed to improve the reflection cracks by adding microcapsules to the asphalt mixture [17]. Gomez-Meijide and his team added metal particles to the mixture in order to improve the asphalt mixture by induction heating method and obtained successful results [18]. ...
... Asphalt binder acting as adhesive bonding aggregates in asphalt pavement is exposed to the continuous traffic loads and environmental changes during service, resulting in the potential formation of cracks [1]. The consequence of the accumulated cracks is serious damage to the mechanical properties and a significant decrease in the service life of asphalt pavement [2]. ...
Article
Asphalt with self-healing property prevents the formation and propagation of cracks in asphalt pavements, while rejuvenation encapsulation and induction heating suffer from unsustainable nature and energy consumption. Herein, dynamic covalent chemistry was used to endow asphalt binder with self-healing property via modifying the asphalt with diselenide-crosslinked polyurethane elastomer. Fourier-transform infrared spectrometer and thermal-gravimetry results indicate that diselenide-bonds were stably introduced into the asphalt binder. The results from healing tests illustrated that diselenide bonds enhance the self-healing capability of polyurethane elastomer and asphalt binder, especially at the early stage after a fracture. This study opens up novel perspectives for preparing asphalt with self-healing property attributed to dynamic covalent chemistry.
... The assisted heating for self-healing can achieve the repair of microcracks in the asphalt pavement. Beyond traditional techniques, the maintenance could be based on novel technics, from rejuvenator capsules in the composition of the asphalt mixture [13,14] to induction [15] and microwave heating [8,16] of the asphalt mixture. In heating pavements by microwaves, the oscillation, rotation, or vibration of molecules, generate heat from inside, known as volumetric heating [1,17]. ...
Article
The present research studies the properties that predict the susceptibility of aggregates for bituminous mixtures to microwave heating. In particular, the relationship between the dielectric properties of the rock and its susceptibility to microwave radiation. Several laboratory tests on 26 aggregates from different sources (igneous, metamorphic, and sedimentary) have been carried out. The targets were to determine the susceptibility to microwaves as measured by the direct heating parameter T70 (the time needed by the aggregate to reach the temperature of 70 °C in standard conditions) and to measure the dielectric constant, the loss factor, and the loss tangent of the rocks by the cavity perturbation method. As a result, a model for the relationship between the T70 parameter and the loss tangent has been proposed. The model contributes to a more in-depth knowledge of the complex phenomenon of aggregate heating with microwaves, which is crucial for developing self-healing asphalt pavements based on the heating treatment with microwaves.
... Further, Mansoori et al. [81] found that the healing in asphalt with and without self-healing agents is very similar at temperatures above 40 • C. The study recommended not to incorporate capsules in high temperature conditions. Garcia et al. [82] carried out a comprehensive investigation on the healing abilities of different types of asphalt mixtures such as dense asphalt, stone matrix asphalt (SMA), and porous asphalt (PA). The study inferred that if the mix is denser, the healing agents are released faster, the release is gradual in case of porous asphalt. ...
Article
Maintenance and rehabilitation at appropriate time is essential for the asphalt pavements to serve the traffic till the end of their design lives. However, frequent production and application of asphalt mixes for maintenance is not only uneconomical, but also generates lot of greenhouse gases. Therefore, different technologies have been evolved for internal rectification of the defects before they are observed through naked eyes, which are popularly known as self-healing technologies. Self-healing in pavements can be achieved through incorporation of healing agents, induction heating, microwave heating, and other healing technologies, which use different nanomaterials, and polymers as self-healing additives in asphalt. Different hybrid technologies have also been studied for self-healing of asphalt. This paper provides a general outlook on the healing mechanisms, design, and implementation of different self-healing technologies in asphalt pavements. The paper also identifies scope for further research in this area, which will serve as a foundation for further advancement in self-healing technologies, as most of them are still in their early stages of research.
... Asphalt concrete, as an excellent road paving material, is widely used in highway, airport runway and other infrastructure fields [1][2][3][4][5]. The service performance of asphalt pavement is affected by a variety of external factors such as cyclic traffic loading, seasonal variation of temperature and moisture. ...
Article
Traditional methods to characterize material deterioration of asphalt mixture are typically destructive to the local integrity of the inspected structure, which is therefore not suitable for the large-scale assessment in an efficient fashion. In this paper, an ultrasonic nondestructive evaluation (NDE) method based on the principle of second harmonic generation (SHG) of Rayleigh surface waves is proposed to apply for the quantitation of cracking variation of asphalt specimens subjected to the fracture-healing cycles. The nonlinear parameter which is the relative amplitude of second harmonic is used to caliber the crack growing in the loading tests and crack healing under the elevated temperature. The feasibility of SHG technique in the crack characterization is justified by the excellent correlation of nonlinear parameter with the crack development corresponding to the fracture force and the crack shrinkage corresponding to the rising temperature. The sensitivity of SHG technique to the crack variation is further demonstrated through a comparison with width measurements from the crack detector. The SHG measurements present an alteration of orders of magnitude with respect to the alternative change of crack. Particularly the SHG measurement demonstrates an excellent capability to distinguish the tiny cracks after the first three healing cycles, compared to the zero reading of crack detector. The findings in this work indicate that the SHG technique is a potentially viable and robust method to characterize microstructural variation of asphalt mixture.
Article
Shape memory epoxy resin (SMER) is a new type of intelligent polymer material, that can sense the stimulus of temperature change and return to an initial state by adjusting its mechanical parameters. To improve the deformation recovery performance of the asphalt mixture based on the high solar energy absorption of asphalt pavement, SMER is proposed for application in asphalt mixtures. A novel test was put forward to measure the deformation recovery performance of the asphalt mixture with and without SMER. The influences of the SMER dosage, loading rate and deformation recovery temperature on the deformation recovery performance of the asphalt mixture were investigated. In addition, the infrared thermal imaging test was used to explore the improvement mechanism of SMER on the deformation recovery performance of the asphalt mixture. The final deformation recovery rate of the asphalt mixture increased with increasing SMER dosage, loading rate and temperature. When the SMER dosage, loading rate and deformation recovery temperature are 3%, 18 mm/min and 70 ℃, respectively, the final deformation recovery rate reaches 97%, which indicates that the deformation of the asphalt mixture under the above conditions almost completely recovers. According to the results of the infrared thermal imaging test, the deformation recovery mechanism of SMER in asphalt mixtures is that the shape memory function of SMER is motivated by the pavement temperature and initiated by solar energy, and then the surrounding materials around the SMER are restored under the restoring force generated by the SMER. The deformation of the asphalt mixture can be recovered in the above process and the appearance of rutting in asphalt pavement can be slowed.
Article
Asphalt mixture is a self-healing material, which implies that its cracks can close autonomously. The limitation is that the self-healing occurs very slowly, and cracks tend to open faster than they close. To improve the self-healing rate, encapsulated oil has been added to the asphalt mixture. When the capsules rupture, the oil is released, which promotes the filling of the cracks by bitumen. Properties such as the internal structure, composition and size of the capsules, may influence their rupture. This paper focuses on sunflower oil encapsulated in a porous calcium-alginate structure; the influence of capsules’ (i) strength and (ii) size in their compressive strength and, the influence of the capsules’ (i) thermal expansion, (ii) thermal resistance and, (iii) internal structure, in the release of the oil have been analysed. The results showed that the strength of the capsules was influenced by the pore size of the calcium-alginate structure, that the capsules could resist the temperature that is reached during asphalt mixing and compaction and, that approximately 50% of the oil may not be released during self-healing.
Article
Fatigue damage is one of the main distresses responsible for the deterioration of asphalt roads. Self-healing, occurring during rest periods, has been shown to increase the total number of loading cycles. The increase is assumed to depend on the time at which healing is induced and the healing duration. In the first damage stage, in which damage is caused by thixotropy, self-heating and permanent deformation, the recovery is equal to the reversible phenomena thixotropy and self-heating. In the second and third damage stages, the closure of cracks starts to dominantly contribute to the gain of additional loading cycles. The healable crack volume depends on the healing method and healing duration, and includes aspects of the crack type. If the healable volume is insufficient to completely close cracks, the healing efficiency decreases due to exponential crack growth. Other occurring phenomena related to the healing process, like thermal degradation, could lead to a further increase in loading cycles at the expense of other asphalt performance aspects. The heterogeneity of asphalt introduces uncertainty into measurements. Hence, the optimal healing time to induce healing for a maximum extension of loading cycles can be determined only in a range.
Article
Asphalt aging is a major cause of distresses in asphalt pavement, seriously decreasing the in-service performance and shortening the lifetime of pavement. Traditional asphalt rejuvenating methods usually consume a great deal of worker and energy resources. This study encapsulated rejuvenator to automatically realize in-situ rejuvenation of aged asphalt in pavement. Soybean oil was selected as the asphalt rejuvenator, and its effectiveness in rejuvenating the aged asphalt was identified. Then it was encapsulated into three kinds of calcium alginate capsules by the orifice coagulation bath method. Next, the micromorphology, internal structure, density, mechanical strength, and thermal stability of the capsules were characterized using digital microscopy, stereomicroscope, graduated cylinder test, uniaxial compressive test, and thermogravimetric analysis, respectively. The effects of the capsules on the pavement performance of asphalt mixture were analyzed. Test results showed that the soybean oil effectively recovered the properties of the short-term aged asphalt binder at an optimum content of 2% by binder mass, and it was encapsulated successfully in capsules with diameters of about 2 mm. There were many slight bumps and indentations on the capsule surface, and many pores filled with soybean oil inside the capsule. The density of the capsules was close to that of the asphalt binder, providing a favorable condition for their uniform distribution in the asphalt mixture. It was proved that the capsules can resist the mechanical and thermal conditions during road construction. The pavement performance of asphalt mixture containing capsules still met the requirement of the specification in China. The findings of this paper are helpful to prolong the service life of asphalt pavement and reduce the maintenance costs in the long run, ultimately contributing to the development of smart and sustainable pavement.
Article
Calcium alginate capsules encapsulating rejuvenator are a promising self-healing technology for asphalt pavement, but the high cost and low preparation efficiency of the capsules cannot meet the requirements of application. This research proposed an efficient method for preparing low-cost calcium alginate capsules using industrial calcium sodium and self-developed reaction kettle. To enhance the strength and assure the survival of the capsules in asphalt mixture, attapulgite was incorporated in different proportions to form composite shell capsules, and their microstructure, thermal stability, mechanical strength, and release behavior of the rejuvenator were investigated. It was found that the composite shell capsules prepared with 2.0 wt% industrial sodium alginate solution and industrial sodium alginate to attapulgite ratio 1:1 had clear multi-cavity structure, high thermal stability, and sufficient mechanical strength for their use in asphalt mixture. The multi-cavity composite shell capsules within asphalt mixture can gradually release the rejuvenator inside in wheel tracking test. The test result showed that the capsules can release 82.67% of the rejuvenator and significantly soften the binder when they suffered 115,200 cycles of compression loading (equivalent to 7 years traffic loading on capsules within a medium traffic grade pavement), indicating that the rapid prepared composite capsules can release rejuvenator to soften asphalt binder and enhance the crack-healing property of asphalt pavement during the service life.
Article
The inherent self-healing ability of asphalt is insufficient and fails to timely repair the cracks due to the combined effect of temperature variation, air oxidation, ultraviolet exposure and traffic loading. Rejuvenator encapsulation based on self-healing asphalt is a green sustainable preventive maintenance technology for asphalt pavement. During the last decade, rejuvenator encapsulation for asphalt self-healing has been a research hotspot and calcium alginate hydrogels encapsulating rejuvenator is a promising self-healing technology. Hence, this review sheds light on the recent advances of calcium alginate hydrogels encapsulating asphalt rejuvenator including self-healing capsules and fibers. The synthesis methods of calcium alginate capsules and fibers containing rejuvenator were elaborately introduced, and their surface morphology, interior structure, mechanical strength, thermal stability, rejuvenator content, distribution and survival in asphalt materials were systematically analyzed. Besides, the effect of capsules and fiber on the mechanical property and pavement performance of asphalt concrete were explored. Additionally, a comprehensive review about the effect of calcium alginate capsules and fibers on self-healing ability of asphalt materials were presented, and the rejuvenator release mechanism and release ratio of them in asphalt mixtures were expounded. In a nutshell, this review aims at highlighting the current research achievements on alginate capsules and fibers containing rejuvenator in asphalt materials, and inspiring enhanced self-healing methods for smart and sustainable maintenance of asphalt pavement.
Experiment Findings
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Experiment Findings
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Article
This paper aims to quantify stone loss mitigation due to the action of architected cellular particles that can absorb impact energy. The architected cellular particles presented in this paper are additives for asphalt that have been designed to absorb impact energy through an internal porous structure filled with a bitumen-compatible liquid that controls their strength. The experimental programme is divided into four phases: Cellular particle manufacturing and morphological analysis; optimisation of asphalt mixture performance by selecting the cellular particle content based on mass loss, rutting and skid resistance testing; study of mass loss with varying compaction energy and asphalt gradation and microstructural and energy absorption analysis. It was concluded that (i) the asphalt’s mass loss linearly decreased as the cellular particle content was increased, (ii) up to 1% of architected cellular particle content by total weight of the mixture reduced mass loss without producing adverse effects in the asphalt, (iii) architected cellular particles deformed during testing, absorbing the impact load energy.
Article
Calcium alginate capsule can gradually release the encapsulated rejuvenator after compressive loading, thus realize self-repairment of micro cracks and in-situ regeneration of aged asphalt in pavement. Nevertheless, plain calcium alginate capsules show weak mechanical strength and over-quick oil release speed and thus long-term self-healing effect cannot be achieved. Calcium alginate/diatomite composite capsules with varying manufacturing parameters were synthesized through using orifice-coagulation method, which aims to improve mechanical strength and retard the rejuvenator release of the capsules. A series of performance tests were carried out in order to characterize the interior structure, thermal property, compression strength, relative rejuvenator content and rejuvenator incorporation rate of the prepared capsules. Meanwhile, the spatial location and premature rejuvenator release of capsules within asphalt concrete after manufacturing process were investigated. The rejuvenator release ratios of capsules in asphalt mixture beams after compressive loading were explored. Furthermore, the healing levels of test beams after the compressive loading and healing period were also evaluated. The calcium alginate/diatomite capsules had obvious multi-cavity structure and the diatomite with multi-pore structure offered extra rejuvenator storage units for the capsules. Meanwhile, the incorporation of diatomite could improve the thermal resistance and compressive strength and made the rejuvenator release speed of calcium alginate capsules decelerate obviously. The test beams containing diatomite modified capsules obtained acceptable healing level after long-term compression loading, which indicated that the addition of modified capsules into asphalt mixtures realize the long-term healing of the pavement.
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Several capsules were prepared using two different waste oils (vegetable oils and mineral oils), five different oil/water ratios, and four different amounts of sodium alginate as a polymer matrix. Capsules with waste oils were characterized by physical, thermal, and mechanical properties to define the more effective capsule for asphalt self-healing purposes. The capsules were added in ratios of 0.25%, 0.50%, 0.75%, and 1.0% by total weight of mastic. The crack-healing efficiency of the optimum capsules was evaluated at two different curing temperatures (25 °C and 40 °C) on asphalt mastic samples using three-point bending tests. The main results proved that capsules could survive the mixing and compacting processes and releasing the encapsulated waste oils inside them by the action of mechanical loads. 100 ml water, 500 ml waste oil, and 17.5 gr sodium alginate were found to be the optimum capsule content for both types of oils. An increased rate of water/oil resulted in decreased free compressive strength. It was further detected that the self-healing levels of asphalt mastic samples with capsules demonstrated 80% higher healing levels compared to samples without capsules and the level of self-healing depended on the ratio of capsules added into the mixtures and the curing temperature applied.
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This paper presents an experimental study to evaluate the mechanical and crack-healing properties of stone mastic asphalt (SMA) mixtures with encapsulated rejuvenators. With this goal, calcium alginate capsules with encapsulated sunflower oil as the rejuvenating agent have been manufactured and added into the SMA mixtures. Physical and mechanical properties of SMA with and without capsules have been evaluated following the British standard tests. Healing properties of SMA by the action of capsules have been assessed using three-point bending (3PB) tests applied on test beams conditioned at different healing times, from 5 to 216 h. The spatial distribution of the capsules in the SMA mixtures was evaluated by using X-ray computed microtomography. Results showed that the capsules can resist the manufacturing process without significantly reducing their properties. Additionally, testing of the mechanical properties of SMA mixtures with and without encapsulated rejuvenators presented similar results. Moreover, capsules showed a good spatial distribution inside the SMA samples. It was found that capsules with encapsulated oil increase the crack-healing properties of SMA when compared to mixtures without encapsulated rejuvenators. Overall, the results proved that the capsules with asphalt crack-healing purposes can be safely used in asphalt pavement construction without affecting its properties.
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This study investigated the effect of seven healing agents on crack healing ability of long-term aged asphalt and its mortar. Different healing agents including sunflower oil, aromatic oil, bitumen emulsion, and maltene-based emulsions were used. The crack healing of asphalt made use of two asphalt disk samples and healing was evaluated using direct tensile tests. For asphalt mortar, notched semi-circular samples were used. Test results indicated that the crack healing of asphalt and its mortar depended strongly on the type of healing agent. In general, asphalt healed faster than its mortar. Asphalt healing could be well improved by using oil agents, while asphalt mortar could be well healed with maltene-based emulsions. The crack healing of asphalt mortar developed rapidly followed by a steady state of increase. Initial crack healing using healing agents could be contributed by the diffusion and softening effects, which resulted in low strength recovery. Long term healing could lead to the bonding reconstitution in the cracks, which were decisive for the final strength gain. The promising healing agent should be able to achieve maximum strength recovery to resist cracking as well as a sufficient re-healing ability to deal with crack opening and closing.
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This paper presents the self-healing results of asphalt mixtures by the action of capsules containing sunflower oil as encapsulated rejuvenator. Three different capsule contents, 0.10, 0.25 and 0.50% by total weight of the mixture, were added to the samples. The mechanical and thermal properties of capsules have been evaluated. In addition, the effect of the capsule addition and the healing temperature on the self-healing properties of asphalt mixtures have been evaluated through three-point bending tests on the cracked asphalt beams with, and without, capsules. The test was implemented by comparing the strength recovery of the broken beams after healing to their original flexural strength. It was proven that the capsules can resist the mixing and compaction processes and break inside the asphalt mixture as a result of applying external mechanical loads, releasing the encapsulated oil. The capsules content in asphalt mixture has a significant influence on the healing level, where a higher capsule content led to obtaining higher healing levels. Likewise, asphalt with, and without, capsules presents an increase of the healing level when the temperature increases. Finally, it was proved that healing temperature has higher influence on the healing levels of the asphalt below 40ºC.
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With a wide range of requirements throughout the world, high-quality road management is subject to increasing demand from a perspective of customer-oriented levels of service. In recent years, road administrators are requested to create a visual map of a road network to monitor conditions. To fulfill these requirements, this study conducted as follows. Firstly, this paper introduces a new compact road profiler to collect the profile data at ease. Using the international roughness index (IRI) to assess public roads in local cities of Japan?s Hokkaido prefecture, this study also provides real-time monitoring of pavement roughness conditions. Moreover, this study deals with an effective method for visualizing collected IRI data as an attribute in a geographic information system (GIS) and the database of Japan digital road map (DRM). Secondly, the authors present the measurement results of IRI at two different cities during different seasons by using GIS to compare the road conditions. According to the results clarified on different statistical characteristics of road profiles, this study recommends that it is necessary to establish pavement management system (PMS) in consideration of road class, network of local city, and evaluation and management of road conditions in winter quantitatively. Finally, the authors measure and evaluate ride quality by assessing differences between the inner wheel path (IWP) and outer wheel path (OWP) of the vehicle into account, using the previously mentioned profilers and the driving simulator, which is called KITDS. Results show that information from both wheel paths contributes to improve current monitoring process regarding pavement surface, and expects to construct a high level of PMS for road administration in the future.
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The self-healing of cracks in asphalt mixture is mainly due to the drain of the bitumen contained in the space between the aggregates, into the cracks. Until now, it was believed that the physical principles affecting the flow of bitumen are influenced by gravity and surface energy of bitumen and the aggregates. In this study, we show that the thermal expansion of bitumen plays an important role in the self-healing of asphalt mixture. To demonstrate this, asphalt mortar beams were manufactured and broken in two pieces by means of three-point bending tests. Self-healing was induced in asphalt mixture by increasing its temperature using a convection oven, at temperatures that ranged from 40 °C to 120 °C. The self-healing ratio was calculated by comparing the force required to break the test specimens before and after heating. Furthermore, a test was designed that consisted of bitumen raising through a capillary tube from a bitumen container. To account for the effect of thermal expansion, the bitumen container was fully enclosed except for the capillary tube. To account for the effect of surface energy on the bitumen’s capillary flow, the capillary tube was placed in a container that was open to the atmosphere. The rise of bitumen was monitored at temperatures that ranged from 40 °C to 120 °C. Finally, activation energies were derived from the rise of bitumen in the capillaries, viscosity changes and the self-healing progression. It was found that the activation energy of asphalt self-healing is similar to that of bitumen rising due to thermal expansion, which confirms the contribution of thermal expansion on asphalt self-healing by the effect of increasing temperature.
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In recent decades, researchers have revealed the great healing potential of asphalt and proposed various novel methods to inspire and improve the self‐healing capacity of asphalt aimed to prolong the service life of asphalt pavement. In this review, up to date research progresses in induction healing and embedded rejuvenator encapsulation are presented, respectively. Meanwhile, the trial section applications of induction healing and capsule healing are highlighted, which show promising results. Finally, some recommendations for the future development of self‐healing asphalt are proposed. Incorporating self‐healing technologies in asphalt pavement has huge potential to prolong the service life of asphalt pavement. To this aim, induction healing and capsule healing technologies have been tested in laboratory and applied in the trial sections. This review paper states the development of these technologies and illustrates how they revolutionize asphalt pavement design.
Article
Asphaltic materials have self-healing properties due to the capacity of bitumen, a viscoelastic liquid with a temperature- and time-dependent viscosity, to flow and/or drain into cracks. Different types of bitumen have different adhesive and rheological properties depending on the refining process, chemical composition, and origin of the bitumen. In addition, other factors that affect the self-healing capacity are the resting period between traffic loads, filler content and ambient temperatures. To further investigate the influencing factors for asphalt self-healing for macro cracks, the authors have selected five types of bitumen, which are commonly used in road constructions, from different sources. The self-healing was assessed by manufacturing asphalt mastic beams and breaking these beams. Healing was induced by either convection or induction heating. The rheological and compositional properties of bitumen were correlated to the healing characteristics of the beams tested. Interestingly, the physical, rheological and chemical properties of bitumen did not influence healing properties, as the thermal expansion coefficient, surface energy and density of the bitumen used were similar. Hence, healing became similar as the influence of viscosity became minor compared to other driving forces.
Article
This paper presents the self-healing results of asphalt mastic by the action of calcium-alginate capsules containing sunflower oil. The morphological, physical, thermal and mechanical properties of the capsules have been evaluated. Additionally, the effect of the capsule oil content and the healing temperature on the self-healing properties of asphalt mastic have been evaluated. It was proven that the capsules can resist the mixing and compaction processes and break inside the asphalt mastic due to mechanical loads, releasing the oil. Healing levels in the asphalt mastic samples with capsules were greater than samples without capsules. The healing level depended on the oil content of the capsules and temperature.
Article
In this research calcium-alginate capsules containing vegetable oil that can release their content due to a mechanical trigger have been made and mixed in asphalt mixture to improve its natural self-healing properties. The physical, mechanical and self-healing properties of asphalt mixture containing these capsules have been evaluated for the first time. Three different capsule contents were used, with oil-to-bitumen ratio 1.1, 2.8 and 5.5, respectively. Capsules were strongly bonded to the asphalt mixture and results showed similar mechanical performance to that of asphalt with and without capsules in the water sensitivity, particle loss and permanent deformation tests. This shows that capsules for asphalt self-healing can be safely used in the road, without affecting its quality. Asphalt containing capsules had slightly lower stiffness, which can be easily solved by reducing the size of the capsules in the future. Furthermore, a new method for testing asphalt containing capsules was designed and tested. It was found that cracked asphalt mixture with capsules recovered 52.9% of initial strength at 20 °C versus 14.0% of asphalt mixture without capsules.
Conference Paper
This paper investigated the self-healing performance of asphalt concrete using semi-circular bending test. The healing index is defined as the ratio of healed strength and initial strength of asphalt concrete specimen and used to evaluate the self-healing potential of asphalt concrete after macroscopic fracture. The test results show that the self-healing ability of asphalt concrete depends on heating temperature, healing time and confining pressure. Temperature has a decisive effect on self-healing ability of asphalt concrete. The self-healing index shows an exponential relationship with temperature. The healing time is also an important factor to influence the self-healing ability of asphalt concrete. The relationship between self-healing index and the time of self-healing was found being linear. On the other hand, applying confining pressure on the cracked surface can accelerate the crack healing and improve the self-healing ability. When the temperature is lower than 60ºC, the effect of confining pressure on self-healing ability is more significant. This indicates that the pavement crack at deeper depth may have the greater self-healing potential as compared to the crack at pavement surface.
Article
The paper studied the impacts of different air void parameters on the fatigue life of asphalt mixture based on discrete element method (DEM). By using discrete element software PFC3D (Particle Flow Code in Three Dimensions), virtual three-dimensional fatigue test was built according to the laboratory four-point bending beam fatigue test with stress-controlled loading mode. And the feasibility of virtual fatigue test was confirmed by laboratory testing data. Based on virtual fatigue test, the influences by content, distribution, size and orientation of air voids on the fatigue life of asphalt mixture were evaluated. It is found that, higher air void content leads to lower fatigue life of asphalt mixture especially when the air void content exceeds the designed air void content of asphalt mixture, interconnected air voids with bigger size is more harmful to the fatigue life of asphalt mixture than the independent air voids with smaller size especially when the orientation of air voids is parallel to the fatigue loading direction, and the non-distribution of air voids within asphalt mixture specimen also has important influences on the fatigue life of asphalt mixture especially for the variation of the air void distribution within the central-bottom section of asphalt mixture specimen. Thus, to guarantee the fatigue durability of asphalt mixture, it is important to improve the content, distribution and microstructure of air voids within asphalt mixture.
Article
The natural self-healing ability of asphalt mixtures can be enhanced with encapsulated rejuvenators: when crack damage appears the capsules release healing agents, which dissolve bitumen and drain into the cracks. In this study, the effect of a new type of capsules in the mechanical properties and the self healing ability of asphalt mixtures is investigated. Sunflower oil was encapsulated in calcium-alginate, and protected with a hard shell made of epoxy-cement composite. Results show that the hard shell was not required for these capsules to resist mixing and compaction procedures. Capsules deformed and broke with loading, releasing oil that diffused in the bitumen in less than 24 h. Healing of cracks in asphalt mixture led to an increase of stiffness. However, asphalt specimens with capsules had lower deformation resistance. Computer tomography scanning of specimens showed large reductions in cracks around the capsules, after resting 4 days at 20 �oC.
Article
Self-healing microencapsulation in asphalt concrete is an emerging technology that would allow this particular material to resist cracking damage caused by vehicular and environmental loading. The objectives of this study were to evaluate the effects of asphalt rejuvenators on asphalt binder, to select a suitable healing agent for asphaltic materials, and to develop a synthesis procedure for the production of microencapsulation of asphalt rejuvenators. Produced microcapsules were characterized using scanning electron microscopy (SEM) to assess the effects of preparation parameters on the size and morphology of the microcapsules. Based on the results of the experimental program, it was concluded that the use of sunflower oil as a rejuvenator was effective in reversing the aging of asphalt binder and to positively affect both the high-temperature and low-temperature grades of the binder. In contrast, the use of PennzSuppress as a rejuvenator was not effective in reversing the aging of asphalt binder and only marginally influenced the grades of the aged and extracted binders at both low and high temperatures. Based on these results, microencapsulation of sunflower oil was selected given its effectiveness in reversing the aging of asphalt binder. A synthesis procedure was developed for the preparation of microencapsulation of sunflower oil and to characterize microcapsule properties such as diameter and morphology.
The Shell Bitumen Handbook
  • J Read
  • D Whiteoak
J. Read, D. Whiteoak, The Shell Bitumen Handbook, Thomas Telford, 2003.
A State-of-the-Art Review of Different Conditions Influencing the Behavioral Aspects of Flexible Pavement. International Congress and Exhibition
  • P Chandak
  • A B Tapase
  • S S Sayyed
  • A C Attar
P. Chandak A.B. Tapase S.S. Sayyed A.C. Attar, A State-of-the-Art Review of Different Conditions Influencing the Behavioral Aspects of Flexible Pavement. International Congress and Exhibition ''Sustainable Civil Infrastructures: Innovative Infrastructure Geotechnology", DOI: 10.1007/978-3-319-61908-8_2; 2018.