Development of a self-healing asphalt mixture through the use of encapsulated healing agents

The service lives of asphalt pavements can be extended by using encapsulated rejuvenators in asphalt mixtures, improving the natural self-healing ability of asphalt mixtures. When crack damage occurs, the capsules are broken, releasing the rejuvenator substance into the cracks. In this thesis, a novel type of capsule was manufactured. These capsules included sunflower oil as rejuvenators. The size, morphology, mechanical strength and thermal stability of these capsules were investigated. In addition, the effect of the capsules on the chemical composition of bitumen with time of exposure to broken capsules was evaluated by the FTIR test. In order to determine the properties of the capsules and their effect on the chemical components of the asphalt mixture, the capsules were included in the asphalt mixtures, providing an opportunity to observe the mechanical performance of the asphalt mixtures and their self-healing abilities. Physical, thermal and mechanical properties of the capsules were evaluated. The capsules can resist the mixing and compaction conditions and break inside the mixture releasing the encapsulated oil in small volumes. In addition, it was observed that the addition of capsules did not improve the stiffness modulus of asphalt mixtures compared to mixtures without capsules, and that the mixing order and the aging time did not have a significant influence on the flexural strength of the mixtures. Moreover, the healing levels obtained by the mixtures varied depending on the order of addition of capsules, and mixtures with capsules showed higher healing levels than mixtures without capsules. The levels of healing for the mixtures without aging were greater than those of mixtures after the aging process. The mechanical and self-healing performance of Stone Mastic Asphalt (SMA) mixtures with encapsulated rejuvenators were evaluated. With this purpose, calcium-alginate capsules with encapsulated sunflower oil have been manufactured and added into the SMA mixtures. Physical and mechanical properties of SMA specimens with, and without, calcium-alginate capsules have been evaluated by measuring the stiffness modulus, indirect tensile strength and fatigue tests, and water sensitivity and skid resistance. In addition, self-healing properties of SMA beams with, and without, capsules have been assessed at different healing times, from 5 to 216h. The main results showed that the capsules can resist the mixing and compaction processes without significantly reducing their properties. Additionally, mechanical properties of SMA mixtures with, and without, capsules 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 capsules. The capsules with asphalt self-healing purposes can be safely used in the road construction, without affecting its quality. The self-healing capability of asphalt mixtures containing a new type of capsules with encapsulated sunflower oil as rejuvenating agent. With this purpose, the diffusion capacity of the rejuvenating agent inside of virgin bitumen samples and the healing level of the cracked asphalt mixtures containing of capsules have been evaluated. The main results showed that the rejuvenator concentration inside the bitumen increased with the time and the temperature until the moment where the concentration reached a maximum value that is independent of temperature. In addition, fatigue healing results of asphalt mixture beams with capsules proved that: i) the number of cycles necessary to reach a given percentage of broken capsules reduced when the applied load increased, ii) the results of healing index presented an optimum number of cycles to apply the resting period, at which the obtained life extension was maximum, and iii) the optimum number of cycles to apply the healing treatment decreased when the load increased. CT-Scan results proved that the microstructure of the capsules corresponded to that of a microbead, where the rejuvenating agent can be encapsulated inside of calcium-alginate micropores. The aim of this study was to develop and characterize a self-healing asphalt pavement that can heal itself and rejuvenate at environmental temperatures. This thesis conducted on self-healing provided answers to a lot of questions regarding the subject. However, unsolved problems, such as capsules homogeneous dispersion or capsules service lives, still remain. Further studies could be conducted on these points.