Self-healing Asphalt Research Articles

Application of Steel Fibre to Improve the Self-Healing Mechanism of Bituminous Mixtures: A Review

The self-healing mechanism of bituminous mixtures was demonstrated through several studies and was recognised for developing sustainable road pavement. This paper presents a comprehensive summary of various studies related to steel fibre as a self-healing mechanism of bituminous materials. Based on the extensive literature, it was found that steel fibre was likely to be used in the asphalt industry due to several benefits. First, the idea of using steel fibre in pavement engineering materials gives great attention to their utilisation in asphalt. It helps increase the self-healing mechanism and contribute to reducing the problem related to potholes, ravelling, slipping during raining while driving and many more. Second, this study identifies the gap of research for future research in pavement engineering. Finally, some proposals were made for the possible construction of self-healing asphalt.

Smart Self-Healing Capability of Asphalt Material Using Bionic Microvascular Containing Oily Rejuvenator.

It has become one of the research directions of intelligent materials for self-healing asphalt pavements to use a bionic microvascular containing oily rejuvenator. The rejuvenator in a microvascular can carry out the healing of asphalt micro-cracks, thus reducing the damage to and prolonging the life of asphalt pavement. The aim of this work was to investigate the smart self-healing capability of an asphalt/microvascular material through its microstructure and mechanical properties. Microstructure observation indicated no interface separation between the microvasculars and bitumen matrix. Micro-CT images showed that microvasculars dispersed in asphalt samples without accumulation or tangles. The phenomenon of microcracks healing without intervention was observed, which proved that the fractured asphalt sample carried out the self-healing process with the help of rejuvenator diffusing out from the broken microvasculars. The self-healing efficiency of asphalt samples was also evaluated through a tensile test considering the factors of microvasculars content, healing time and healing temperature. It was found that the tensile strength of the asphalt samples was greatly enhanced by the addition of microvasculars under a set test condition. Self-healing efficiency was enhanced with more broken microvasculars in the rupture interface of the asphalt sample. During two self-healing cycles, the self-healing efficiency of the asphalt sample with three microvascular per 1 cm2 of a broken interface were able to reach 80% and 86%. This proves that microvasculars containing rejuvenator play a practical role in the self-healing process of asphalt. With an increase in temperature from 0 to 30 °C, the self-healing capability of the asphalt samples increased dramatically. An increase in time increased the self-healing capability of the bitumen samples. At last, a preliminary mathematical model also deduced that the self-healing efficiency was determined by the individual healing steps, including release, penetration and diffusion of the rejuvenator agent.

Assessment of self-healing asphalt pavement fatigue life using analytical Jc approach and laboratory results

Self-healing asphalt pavements are an alternative and sustainable road infrastructure. Through a literature review and laboratory tests, the authors aimed to develop a methodology to study the efficiency of asphalt pavement self-healing techniques. Results showed that Healing Indexes based on peak loads could be misleading to estimate the effectiveness of self-healing techniques. A novel methodology using the semicircular bending test and the fracture mechanics parameter Jc is proposed to estimate pavement fatigue life extension when self-healing techniques are applied. Following this novel methodology, results show that one cycle of microwave heating of conventional asphalt pavement achieves a 20% fatigue life extension.

Thermal and Mechanical Properties of Calcium Alginate Capsules for Self-Healing Asphalt Concrete

The key physical and mechanical property is the strength of the capsules, which ensure the implementation of the self-healing technology, in which the capsules are not destroyed during the compaction of the asphalt concrete mixture, but are destroyed during the formation of defects in the asphalt concrete. An increase in the content of the reducing agent in the composition of the alginate emulsion leads to a decrease in the breaking load during compression of the capsules, which is explained by an increase in their diameter. But the change in the content of sodium alginate does not have a significant effect on mechanical properties. As a result of exposure to a temperature of 170 °C, a decrease in the strength of the capsules by 22 % after 1 hour of exposure in the burning oven is observed, and with an increase in the time to 4 hours, the strength decreases by 46.9 %. The maximum decrease in the strength index after 4 hours of exposure at a temperature of 160 °C reaches 29.9 %. A decrease in temperature to 150 °C leads to a decrease in the loss of strength. The strength of the capsules decreases by 4 % after 4 hours of exposure at 150 °C. Exposure of capsules to a temperature of 140 °C has no significant effect on strength.

Conductive Compartmented Capsules Encapsulating a Bitumen Rejuvenator

This paper explores the potential use of conductive alginate capsules encapsulating a bitumen rejuvenator as a new extrinsic self-healing asphalt method. The capsules combine two existing self-healing asphalt technologies: (1) rejuvenator encapsulation and (2) induction heating to create a self-healing system that will provide rapid and effective asphalt pavement repair. The work presents a proof of concept for the encapsulation process, which involves embedding the capsules into the bitumen mortar mixture and the survival rate of the capsules in the asphalt mixture. A drip capsule production process was adopted and scaled up to the production of 20l wet capsules at rate of 0.22 l/min. To prove the effectiveness and its ability to survive asphalt production process, the capsules were prepared and subjected to thermogravimetric analysis (TGA) and uniaxial compression Test (UCT). The test results demonstrated that the capsules had suitable thermal characteristics and mechanical strength to survive the asphalt mixing and compaction process. Scanning electron microscopy (SEM) was employed to investigate physiological properties, such as rejuvenator (oil) and iron particle distribution, within the capsules. The electrical resistance tests proved that the capsules were capable of conducting electrical current. The capsules were also tested for their conductive properties in order to determine whether they are capable of conducting and distributing the heat once subjected to induction heating. The results showed that capsules containing higher amounts of iron (alginate/iron powder in a ratio of 20:80 by weight) can efficiently conduct and distribute heat. To prove its success as an asphalt healing system, conductive alginate capsules encapsulating a bitumen rejuvenator were embedded in a bitumen mortar mix. The samples where then subjected to local damaging and healing events, and the degree of healing was quantified. The research findings indicate that conductive alginate capsules encapsulating a bitumen rejuvenator present a promising new approach for the development of an extrinsic self-healing asphalt pavement systems.

Experimental Investigation of the Performance of a Hybrid Self-Healing System in Porous Asphalt under Fatigue Loadings.

Self-healing asphalt, which is designed to achieve autonomic damage repair in asphalt pavement, offers a great life-extension prospect and therefore not only reduces pavement maintenance costs but also saves energy and reduces CO2 emissions. The combined asphalt self-healing system, incorporating both encapsulated rejuvenator and induction heating, can heal cracks with melted binder and aged binder rejuvenation, and the synergistic effect of the two technologies shows significant advantages in healing efficiency over the single self-healing method. This study explores the fatigue life extension prospect of the combined healing system in porous asphalt. To this aim, porous asphalt (PA) test specimens with various healing systems were prepared, including: (i) the capsule healing system, (ii) the induction healing system, (iii) the combined healing system and (iv) a reference system (without extrinsic healing). The fatigue properties of the PA samples were characterized by an indirect tensile fatigue test and a four-point bending fatigue test. Additionally, a 24-h rest period was designed to activate the built-in self-healing system(s) in the PA. Finally, a damaging and healing programme was employed to evaluate the fatigue damage healing efficiency of these systems. The results indicate that all these self-healing systems can extend the fatigue life of porous asphalt, while in the combined healing system, the gradual healing effect of the released rejuvenator from the capsules may contribute to a better induction healing effect in the damaging and healing cycles.

Performance evolution of Fe3O4 used in the production of sustainable self-healing asphalt materials

Studies have shown that the sustainable self-healing ability of asphalt materials under microwave radiation is related to the microwave absorption of the constituent materials. As a typical absorbing material, Fe3O4 and its derivatives have the potential to heal the micro cracks of asphalt materials multiple times by themselves, and enhance the sustainable self-healing properties. However, former researchers have neglected the fact that Fe3O4 will be gradually oxidized at high temperatures, such as 100 °C, resulting in the changes in material properties, microwave absorption and heat-generating capability. Therefore, the effects of different temperatures on the properties of controllable synthesized Fe3O4 were studied at 125 °C (mixing temperature of WMA), 150 °C (mixing temperature of HMA), 175 °C (mixing temperature of HMA with modified binder) and 200 °C (extreme mixing temperature). The phase compositions, chemical structure of synthesized Fe3O4 were characterized firstly. Then, their electromagnetic parameters, reflection loss were studied at a microwave frequency ranging from 1 to 18 GHz. Additionally, heat-generating abilities of them were characterized at usual microwave frequency of 2.45 GHz. Finally, the effects of different content of Fe3O4 on the rheological properties of pure asphalt were studied. The results show that the proportion of γ-Fe2O3 in the samples gradually increase with exposure temperature, and the static magnetic properties gradually deteriorate. The reflection loss of the modified asphalt decreases firstly and then increases. The F-150 modified asphalt has the strongest microwave absorption capacity. Under the 2.45 GHz microwave radiation, the F-150 modified asphalt presents the strongest heat-generating capability and is consistent with the results of reflection loss. It can be seen that the ratio of γ-Fe2O3 and Fe3O4 in F-150 has the best attenuation effect on microwave radiation, and Fe3O4 is more suitable as microwave absorber for self-healing enhancement of HMA.

Dielectric properties versus microwave heating susceptibility of aggregates for self-healing asphalt mixtures

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.

Observation of the microstructure and shape of self-healing microvascular in asphalt

Microvascular containing rejuvenator is a promising smart material for self-healing asphalt of pavement. The objective of this work was to experimentallyobserve the shape and state of self-healing microvascular in asphalt. Polyvinylidene fluoride (PVDF) microvascular containing oily rejuvenator was spun through single-wet-spinning method. Thermogravimetry analysis (TGA) and scan electron microscopy (SEM) morphology results proved that microvascular can endure 300 °C high temperature in asphalt and maintain its own stability. At the same time, the microvascular can withstand drastic temperature changes while still maintaining its integrity. Micro-XCT image indicated no debonding phenomenon was found between the microvascular and bituminous binder. Oily rejuvenator can be safely stored in the microvascular without being affected. At the same time, 3D micro-XCT image showed that the microvascular did not have any entanglement or breakage even under the extrusion of the aggregates. Microvasculars were randomly distributed isotropically in the asphalt. By comparing the shape of long microvascular and short microvascular in asphalt, it is found that short one is more suitable for asphalt. Possible shapes were observed through micro-XCT slides named as C-shape, L-shape, O-shape, S-shape, and V-shape. Microvasculars were squeezed by the aggregate in the asphalt, which deformed and became deflated. However, microvascular remained intact and no breakage occurs. Oily rejuvenator was safely protected in the microvascular. The above intuitive image data are evidence proving that the microvascular containing rejuvenator will be a feasible approach to realize the self-healing and self-rejuvenating process of asphalt.

Pyrolytic oil from waste tyres as a promising encapsulated rejuvenator for the extrinsic self-healing of bituminous materials

Extrinsic self-healing of bituminous materials using encapsulated rejuvenators is a hot topic within road materials. Based on a circular economy vision for more sustainable and resilient asphalt pavements, this study explores for the first time the use of pyrolytic oil from waste tyres as a promising encapsulated rejuvenator to promote the extrinsic self-healing in bituminous materials. Pyrolytic oil-in-water emulsions, and capsules and their components were produced and characterised through gas chromatography-mass spectrometry (GC/MS) and SARA fractions analysis, fluorescence microscopy methods, creaming index, thermogravimetric analysis (TGA-DGT), optical and scanning electron microscopy (SEM), encapsulation efficiency and mechanical properties. Main results showed that the pyrolytic oil capsules presented an adequate morphology for the self-healing asphalt, with a good thermal stability, physical–chemical and mechanical properties. Overall, it was also proven that the pyrolytic oil is a rejuvenator that can diffuse in the aged bitumen reducing its viscosity to promote the self-healing of the microcracks.

Laboratory and Statistical Analysis of the Fatigue Response of Self-Healing Asphalt Mixtures Containing Metal By-Products

Fatigue is one of the main forms of deterioration in asphalt mixtures, endangering their service life due to the progressive appearance and expansion of cracks. A sustainable approach to increase the lifetime of asphalt pavement has been found in self-healing technology, especially if boosted with metal by-products due to their economic and environmental interest. Under these circumstances, this research addressed the fatigue behavior of self-healing asphalt mixtures including industrial sand blasting by-products obtained from sieving and aspiration processes. Hence, a uniaxial fatigue test was carried out to determine whether these experimental mixtures can provide a similar response to that of a reference asphalt concrete (AC-16). This analysis was undertaken with the support of descriptive and inferential statistics, whose application proved the absence of significant differences in the fatigue performance of self-healing experimental mixtures with respect to conventional asphalt concrete. These results suggest that designing self-healing mixtures with metal by-products is a sustainable approach to increase the lifetime of asphalt pavements, while contributing to the circular economy through diverse economic and environmental benefits.

Controllable synthesis of SiC wrapped LDHs to reinforce microwave absorption and exothermic properties of styrene-butadiene-styrene (SBS) polymer modified asphalt

Combination of styrene-butadiene-styrene (SBS) polymer and layered double hydroxides (LDHs) has commonly applied in asphalt to improve anti-ultraviolet aging performance, but it can not afford the reparation of cracks caused by aging of asphalt. Also, few researches focused on the structure and performance changes during synthesis of LDHs. Based on self-healing performance of asphalt, the produced cracks can be repaired by microwave heating. Therefore, the controllable synthesis of traditional microwave absorber SiC to wrap LDHs (SwL) at different temperatures was studied in this paper, and the effects of different SBS/SwL combination on the microwave absorption and exothermic properties of modified asphalt were studied. The SwL was firstly synthesized at 200 °C, 350 °C, 500 °C and 650 °C. Then morphology, phase composition, chemical structure of different SwL were evaluated. Finally, based on different combination of SBS and SwL, the effects of SBS/SwL on the microwave absorption in the frequency band from 1 GHz to 18 GHz and exothermic characteristics at 2.45 GHz of the modified asphalt were analyzed. The results show that SwL can be synthesized successfully, and the processing temperature significantly affects the structure of SwL. The SBS/SwL-200 modified asphalt has the best microwave absorption and exothermic properties. When used in self-healing asphalt, it is more advantageous to choose 200 °C as the synthesis temperature of SwL.

Self-Healing Asphalt: A Systematic Bibliometric Analysis for Identification of Hot Research Topics during the 2003-2018 Period.

The use of self-healing asphalt is a good option to extend the lifetime of roads and to improve the sustainability of pavement management systems. A bibliometric analysis based on the Scopus database was carried out to review the global research related to self-healing asphalt from 2003 to 2018 and to identify relevant quantitative characteristics from the research in this period. The results from this analysis revealed that the number of accumulated publications followed an exponential growth, which confirmed the relevance that this research topic has gained during the last years. The study revealed that China was the most productive country, followed by the Netherlands, where the most prolific institution is located: Delft University of Technology. Some important research features of the two main approaches most frequently used to develop asphalt mixtures with enhanced self-healing abilities (external heating and encapsulated rejuvenating agents) are compiled in this work.

Analysis of the scientific evolution of self-healing asphalt pavements: Toward sustainable road materials

Although researchers have investigated the concept of self-healing asphalt materials for decades, only recently has scientific interest in methods triggering self-healing properties of asphalt increased. Self-healing technologies are expected to increase the service life of materials and reduce their maintenance, decreasing raw materials consumption, greenhouse gas emissions, and negative effects of construction on climate change. Self-healing of asphalt materials has the potential to make important changes in the road construction materials industry, making it more sustainable; however, the literature has not exactly reported a quantitative analysis of the progress or evolution of this scientific topic. Bibliometric and science mapping analyses are methodologies to study through quantitative analysis, the scientific evolution of any knowledge area. Hence, this paper presents a bibliometric and science mapping analysis of the self-healing technology of 292 selected documents found in widely accepted scientific databases, using SciMAT open access software. In addition, the article presents a description of the most important articles based on SciMAT analysis. The results of the study show that the production of documents related to self-healing has been growing since 1994, reaching a peak in 2018 with 60 published articles (21% of the total). In addition, China and the USA have an outstanding performance in the production of documents followed by the Netherlands, UK, Spain, and Chile, although the European continent has the largest number of countries actively developing this research area. The analysis also showed that the most productive authors in the topic of study are Wu, S.P., Little, D.N., Lytton, R.L., and Garcia, A. In addition, analysis showed an increasing development of self-healing pavements topics in new and more specific research areas such as microwave heating, nanocomposites, and microcapsules. Overall, this analysis shows that self-healing asphalt materials technology has been catching the scientific interest of many researchers in recent years; hence, there are many techniques and areas that are being developed and are expanding the branches and different niches in this research area. Therefore, opportunities for researchers to work in this field are developing and are also far from reaching a stage of maturity.

Active polymeric reducing agent for self-healing asphalt concrete

The possibility of using an active polymer component as a reducing agent for the implementation of the self-healing of asphalt concrete technology is considered in the paper. It was found that the thiol-containing urethane AR-polymer is an effective reducing agent capable of replacing traditional reducing agents based on hydrocarbon oils. AR-polymer is a reducing agent that can be encapsulated using alginate technology. The volume of the reducing agent in the capsule is limited to a maximum allowable value of 83±1%, which can be achieved using the alginate technology. It has been proven that the type and properties of the reducing agent does not affect the change in the mechanical properties of the capsules. The strength of the capsules decreases by 2…6% for different ratios of RA/A when the content of sodium alginate decreases from 3.33% to 2.08%. The greatest efficiency of capsules with the maximum content of AR-polymer as a reducing agent and higher strength is achieved when using emulsions containing 2.50% sodium alginate at RA/A = 5.0 ± 0.2.

A Review of Asphaltic Crack Healing Approaches and Its Mechanism

The concept of self‐healing has an excellent potential to extend the life of asphalt pavement. This technology can be considered a sustainable technology due to its ability to reduce the utilization of asphalt mixture production materials used for road maintenance, polluting the environment. It is a complex physicochemical process wherein the molecular diffusion healing mechanisms in asphalt materials are inspired by self‐healing polymeric systems, which describe the self‐recovery behaviors based on polymer chain dynamics. Several methods have been adopted to improve the self‐healing of asphalt, one of which is induction healing. It is the process of heating the asphalt pavement incorporated with an electrically conductive material such as steel fibers, wherein asphalt healing is undertaken via electric field induction. Induction healing via induction heating occurs with eddy current where the electric current flows within the conductive fibers when magnetically susceptible under the magnetic field. Microwave heating is another self‐healing method similar to induction in which magnetic radiation is employed to treat asphalt mixtures instead of the electric field‐induced induction healing processes. The conductive fibers can absorb the electromagnetic (EM) waves to convert them into heat energy through doublet polarization, interface polarization, and electrical conduction dissipation when placed in the microwave field. These two types of heating systems, which are induction heating and microwave heating, are compared and discussed thoroughly in this study. Finally, some recommendations for the future development of self‐healing asphalt are proposed.

Improving microwave healing characteristic of asphalt concrete by using fly ash as a filler

The paper aims to evaluate the usability of fly ash (FA), which is an environmental pollutant, as a filler in asphalt concrete in order to accelerate its microwave heating rate to promote self-healing. In the study, microwave heating rates of asphalt concrete specimens with and without FA were determined via thermographic imaging. Then the three-point bending test was applied to specimens before and after the microwave healing procedure. The crack size of the damaged specimens was also measured via a crack microscope in order to determine the effect of damage levels on microwave healing performance. Test results demonstrated that crack sizes both before and after healing could be interpreted as an indicator of the self-healing performance of the specimen. Microwave heating temperature is the key factor of self-healing, and FA has improved microwave heating rate of asphalt concrete. FA has also improved the healing capability of specimens at some damage levels. It can be concluded that fly ash has great potential as a filler in self-healing asphalt concrete because it can improve self-healing and mechanical characteristics of asphalt concrete, and FA could be reclaimed by using this way.

Survival and activation behavior of microcapsules in self-healing asphalt mixture

Microcapsule technology exhibits great potential in improving the healing efficiency of asphalt mixture and prolonging the service life of the pavement. The capsule should be kept intact in the mixing and compaction process of asphalt mixture, whereas broken to release the healing agents in time when cracks encounter it. This paper aims to investigate the survival and activation behavior of microcapsules in asphalt mixture during construction and service period. By means of the in situ polymerization method, the microcapsules of various sizes were prepared and their particle size distribution, core material content, shell permeability, and other properties were characterized. Based on the quantitative analysis principle of Fourier transform infrared spectrometer (FTIR), the influence of microcapsule size and mixing temperature on the survival rate of microcapsules was analyzed. Meanwhile, the morphology and size distribution of surviving microcapsules was obtained via fluorescence microscope (FM). In addition, the morphologies of microcapsules before and after the bitumen bond strength (BBS) test and dynamic shear rheological (DSR) test were observed by FM to examine the releasing behavior of microcapsules. Finally, the fatigue-rest-fatigue test was performed to investigate the influence of microcapsule size on the healing efficiency of aged asphalt mastic. The results showed that the survival rate could be improved by reducing the construction temperature and the microcapsules size. The loss of microcapsules was more likely to happen in the mixing process rather than in the compaction process. Microcapsules with larger sizes were easier to be activated to remarkably enhance the healing efficiency of the aged asphalt mastic. Notably, the microcapsules with appropriate size are recommended to be added to the mixtures to ensure that the microcapsules survive in the construction process and are activated when cracks appeared.

Thermophysical properties and heating performance of self-healing asphalt mixture with fibres and its application as a solar collector

This paper presents the first analysis on the evaluation of the thermophysical and heating performance of self-healing asphalt mixtures with different contents of steel wool fibres for their potential use as a solar radiation absorbing material in an asphalt solar collector prototype. With this aim, four different dense-graded asphalt mixtures were prepared using the same aggregate gradation and bitumen content, but with different content of steel wool fibres: 0%, 2%, 4%, and 6% by total volume of bitumen. Physical and thermal properties, such as bulk density, air void content, thermal conductivity, specific heat capacity, and thermal diffusivity were evaluated on the asphalt test specimens. Steel wool fibre distribution inside the asphalt mixture samples was also evaluated by X-ray computed microtomography. Moreover, the thermal behaviour of a solar collector prototype, using an asphalt mixture with 4% of steel wool fibres as a solar radiation absorbing material was exposed to solar radiation conditions simulated in laboratory using a novel direct normal irradiance experimental model. This model was developed by the authors to experimentally simulate the maximum and minimum irradiance conditions for the city of Concepcion in Chile. The main results showed that self-healing asphalt mixtures with steel wool fibre addition reduced their thermophysical properties, explained by an increment in their total volume and due to the fibre distribution inside the samples. Additionally, this study proves that asphalt mixtures with 4% of steel wool fibres can be potentially used as a radiation absorbing material, transmitting the infrared radiation from the asphalt pavement surface to the water stored inside it. In short, this study provides the first assessment on the fundamental thermophysical variables of self-healing asphalt mixtures with metallic fibres, with the purpose of exploring their future use for energy harvesting applications.

A novel self-healing system: Towards a sustainable porous asphalt

Self-healing asphalt, aimed to produce a sustainable asphalt pavement using green technology, has been studied in the past two decades. Technologies including encapsulated rejuvenator and induction heating have been proposed, demonstrated in the laboratory, and gradually evaluated in field application. This paper looks into the synergy effect of the above two technologies, where induction heating serves as the asphalt damage repair mechanism, requiring just 2 min heating time and encapsulated rejuvenator will replenish (rejuvenate) aged asphalt binder and reinstate bitumen’s healing ability. Moreover, the increased temperature from induction heating could in turn accelerate the diffusion process of rejuvenator into aged bitumen. In this paper, the healing efficiency of the combined healing system was tested in comparison with autonomous asphalt healing system, induction healing system and capsule healing system. Porous asphalt concrete with various healing systems were prepared and a laboratory ageing procedure was followed to simulate the condition when healing was needed (after years of serving). X-ray computed tomography was employed to visualize the material composition and distribution inside of each healing systems. The properties of binder extracted from the porous asphalt samples were examined by dynamic shear rheometer. Indirect tensile strength and indirect tensile stiffness modulus tests were employed to characterize the mechanical properties of the porous asphalt samples with various healing systems. Finally, the cracking resistance of these healing systems was investigated by semi-circular bending test, and the healing efficiency was evaluated using a bending and healing programme. The results indicated that the combined healing system, with synergistic effects of aged binder rejuvenation and crack healing, shows a longer life extension prospect over the other healing systems.