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Several research groups and laboratories all over the world have taken up the idea of developing an asphalt that has self-healing properties. This technical article presents a general vision about research on self-healing asphalt conducted in The Netherlands and its example of application in Chile through the development of different research projects carried out in collaboration. Source: Revista Estradas N°22, November 2017, Brazil.
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Maintenance and renovation in asphalt pavement become a big problem for the whole world because of its negative effect on resource consumption, environmental pollution and traffic block. This situation is expected to be improved by the emerging self-healing technologies in asphalt. A novel approach for self-healing is to apply embedded encapsulated healing agent in the asphalt binder. When cracks initiate and propagate through the capsules, the healing agent can be released to diffuse into the binder, decrease the stiffness and increase the healing capacity of bitumen. In this paper, healing agent is effectively encapsulated by calcium alginate and the thermal gravimetric analysis (TGA) and compression tests indicate that the prepared capsules can survive from the mixing and compaction of asphalt mixture. When applied to asphalt mastic, the Three point bending tests results indicate that the healing agent do improve the healing efficiency.
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Self-healing technology is a new field within material technology. It represents a revolution in materials engineering and is changing the way that materials behave. Incorporating self-healing technology into the road design process has the potential to transform road construction and maintenance processes by increasing the lifespan of roads and eliminating the need for road maintenance. By decreasing the unnecessary premature ageing of asphalt pavements, self-healing asphalt can reduce the amount of natural resources used to maintain road networks, decrease the traffic disruption caused by road maintenance processes, decrease CO2 emissions during the road maintenance process and increase road safety. In addition to environmental savings, self-healing materials have the potential to deliver significant cost savings for road network maintenance across the EU. There are three main self-healing technologies available for asphalt pavement design: nanoparticles, induction heating and rejuvenation. This chapter reviews all three options and outlines the future development of self-healing asphalt technology.
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Porous asphalt shows excellent performance in both noise reduction and water drainage. Although porous asphalt has these great qualities, its service life is much shorter (sometimes only half) compared to dense graded asphalt roads. Ravelling, which is the loss of aggregate particles from the surface layer, is the main damage mechanism of porous asphalt surface wearing courses. In this research, an induction healing approach (namely, activating the healing process of asphalt concrete through induction heating) was developed to enhance the durability of the porous asphalt roads. Steel fibers are added to a porous asphalt mixture to make it electrically conductive and suitable for induction heating. When micro cracks are expected to occur in the asphalt mastic of the pavement, the temperature of the mastic can be increased locally by induction heating of the steel fibers so that porous asphalt concrete can repair itself and close the cracks through the high temperature healing of the bitumen (diffusion and flow). The closure of micro cracks will prevent the formation of macro cracks. In such a way, ravelling can be avoided or delayed in the end. To make asphalt mastic and porous asphalt concrete electrically conductive and suitable for induction heating, steel (wool) fibers were incorporated into them. The electrical conductivity and induction heating speed of asphalt mastic and porous asphalt concrete were first studied in this research. Asphalt mastic and porous asphalt concrete with steel fibers can be heated with induction energy. There is an optimal volume content of steel fiber in asphalt mastic or porous asphalt concrete to obtain the highest induction heating speed. Adding more steel fiber above this optimal volume content does not increase the induction heating speed anymore. Furthermore, the highest induction heating speed corresponds to the minimum electrical resistivity. However, porous asphalt concrete does not need to be fully conductive for induction heating. Every single steel wool is a heating unit. Nonconductive samples with steel fiber can still be heated with induction heating, but at a low heating speed. The diameter, length and content of steel wool fiber are important for the conductivity and heating speed of asphalt concrete matrix. It is proven that induction heating does not cause extra ageing to bitumen. Addition of steel wool also reduces the binder drainage problem in porous asphalt concrete. The mechanical properties of porous asphalt concrete with steel wool fiber were studied in this research. Adding moderate percentage steel wool to porous asphalt concrete reinforce it by increasing its particle loss resistance, indirect tensile strength and fracture energy, water damage resistance, stiffness and fatigue resistance. The steel wool was optimized to obtain the best particle loss resistance in porous asphalt concrete. 8% steel wool type 00 (volume fraction of bitumen) was considered as the optimal content. The healing potential of porous asphalt concrete with steel wool fiber was also evaluated in this research with both cylinder and beam samples. Damaged porous asphalt concrete with steel wool fiber can greatly restore its stiffness, strength and fatigue life with induction heating, which proves that the healing capacity of porous asphalt concrete with steel wool fiber is enhanced by induction heating. The optimal induction heating temperature is 85 ºC for porous asphalt concrete to obtain the best healing rate. Reheating does not decrease the healing rate of porous asphalt concrete, which means that heating can be repeated when cracks appear again. To apply the induction healing technology in real porous asphalt road, a trial section was constructed on Dutch motorway A58 in December 2010. This trial section survived the past two winters perfectly. Experiments were done on the cores drilled from the trial section and the results coincided with those on the laboratory made samples. The field cores showed good particle loss resistance, high strength, good fatigue resistance and high induction healing capacity. Based on the laboratory experiments and field experiences, induction healing can be a very good approach to enhance the durability of porous asphalt pavement. Finally, some recommendations are given for further research. Steel fiber, mixing technology and induction generator need to be optimized. Modeling work is necessary to fully understand the mechanisms involved in induction healing.
This paper explores the potential use of compartmented alginate fibres as a new method of incorporating rejuvenators into asphalt pavement mixtures. The compartmented fibres are employed to locally distribute the rejuvenator and to overcome the problems associated with spherical capsules and hollow fibres. The work presents proof of concept of the encapsulation process which involved embedding the fibres into the asphalt mastic mixture and the survival rate of fibres in the asphalt mixture. To prove the effectiveness of the alginate as a rejuvenator encapsulating material and to demonstrate its ability survive asphalt production process, the fibres containing the rejuvenator were prepared and subjected to thermogravimetric analysis and uniaxial tensile test. The test results demonstrated that fibres have suitable thermal and mechanical strength to survive the asphalt mixing and compaction process. The CT scan of an asphalt mortar mix containing fibres demonstrated that fibres are present in the mix in their full length, undamaged, providing confirmation that the fibres survived the asphalt production process. In order to investigate the fibres physiological properties and ability to release the rejuvenator into cracks in the asphalt mastic, the environmental scanning electron microscope and optical microscope analysis were employed. To prove its success as an asphalt healing system, compartmented alginate fibres containing rejuvenator were embedded in asphalt mastic mix. The three point bend tests were performed on the asphalt mastic test samples and the degree to which the samples began to self-heal in response was measured and quantified. The research findings indicate that alginate fibres present a promising new approach for the development of self-healing asphalt pavement systems.
This paper aims to evaluate the effect of microwave and induction heating on the self-healing of asphalt mixture test samples. With this purpose, dense asphalt mixtures with four different percentages of steel wool fibres have been prepared to build semi-circular asphalt test samples. Asphalt self-healing has been characterised as the three-point bending strength of test samples before and after healing. This process was repeated ten times in every test sample. Moreover, self-healing was induced in the semi-circular test samples by heating them under microwave and induction. Besides, the chemical degradation of asphalt mixture under microwave and induction heating was monitored by measuring the mass of test samples before and after the heating process. It was found that microwave technology is more effective than induction heating to heal cracks in asphalt roads. Furthermore, the healing level of asphalt mixtures reduced with every healing cycle, until the test specimens could not resist more damage-healing cycles. It could be seen that microwave heating degrades bitumen, and increases the porosity of asphalt mixture. Finally, it was hypothesised that air voids in mixture play an important role in asphalt self-healing by increasing the internal pressure and mobility of bitumen during the heating process.
Microcapsules containing rejuvenator is a promising chemical product applied to prolong the service-lift of asphalt. The aim of this work was to synthesize and characterize the physicochemical properties of novel microcapsules containing rejuvenator by in-situ polymerization of methanol–melamine–formaldehyde (MMF) prepolymer. A two-step coacervation (TSC) was successfully applied to enhance the thermal stability and compactability of shells with the help of styrene maleic anhydride (SMA) as surfactant. The optimum usage of SMA was 1.5–2.0 wt.% of rejuvenator. FT-IR results showed that the rejuvenator had been encapsulated by MMF resin. The parameters of average size, shell thickness, shell density and encapsulation efficiency could be controlled by adjusting the emulsion stirring rate and core/shell ratio. TGA tests indicated that microcapsules had a thermal decomposing temperature higher than the melting temperature of asphalt. Compactability measurements showed that more shell material could encapsulate the core droplets even better. However, surface morphology observation showed that the optimum core/shell weight ratio is 1/3, because excess prepolymer made the microcapsules in an aggregated state. By adjusting the temperature increasing rate of 2 °C min−1, powder microcapsules were easily be fabricated without aggregation.
Rejuvenators are products designed to restore original properties to aged (oxidized) asphalt binders by restoring the original ratio of asphaltenes to maltenes. These products are used to retard the loss of surface fines and to reduce the formation of additional cracks; however, for a rejuvenator to be successful, it must penetrate the pavement surface. Besides, application of a rejuvenator will also reduce the skid resistance of the pavement, which may be significant for runways or other areas where high aircraft speeds are likely to occur. To solve this, in [1], these rejuvenators were encapsulated and mixed in asphalt concrete. The idea is that once the stress in the capsules reaches a certain threshold, the particles break and the rejuvenator is released. This research focuses on the properties of these capsules. Four different types of rejuvenators will be encapsulated and their effect on the properties of the capsules investigated. Besides, the release mechanisms of the capsules will be unravelled. Finally, the capsules will be mixed in a porous asphalt mixture, and their aspect examined under the microscope once the asphalt sample is broken under indirect tensile tests.
Self-healing Technology for Asphalt Pavements, Self-healing Materials, Advances in Polymer Science
  • A Tabaković
  • E Schlangen
A. Tabaković, E. Schlangen, Self-healing Technology for Asphalt Pavements, Self-healing Materials, Advances in Polymer Science, 285-306, 273 (2016).