[0001] The invention refers to a self-healing bitumen which comprises microcapsules breakable at will by irradiation, said microcapsules comprising: a polymer shell obtainable by means of a multi-step polymerization method; and a core comprising a bitumen rejuvenator and a radiation absorber.
1. A microcapsule comprising: a polymer shell; and a core comprising a bitumen rejuvenator and a radiation absorber; said microcapsule being obtainable by a process comprising: i) preparing an emulsion comprising droplets of an organic phase which comprise the core materials; and ii) encapsulating said core materials by polymerizing in situ at least one prepolymer at the periphery of said droplets, wherein the polymerization is carried out in two or more steps by mixing a first portion of prepolymer with the emulsion so that a first polymerization step takes place, performing a second polymerization step with a second portion of prepolymer, and optionally performing further polymerization steps with further portions of prepolymer. 2. The microcapsule according to claim 1, wherein the polymer shell is selected from the group consisting of aldehyde condensation polymers, alginates, polyethylenes, polyamides, polystyrenes, polyisoprenes, polycarbonates, polyesters, polyacrylates, polyureas, polyurethanes, polyolefins, polysaccharides, epoxy resins, vinyl polymers, and mixtures thereof. 3. The microcapsule according to claim 2, wherein the polymer shell is selected from the group consisting of aminoplast, phenoplast and amino-phenoplast resins. 4. The microcapsule according to claim 3, wherein the polymer shell is selected from the group consisting of melamine-formaldehyde (MF), urea-formaldehyde (UF), melamine-urea-formaldehyde (MUF), phenol-formaldehyde (PF), urea-phenol-formaldehyde, and their derivatives. 5. The microcapsule according to any one of claims 1 to 4, wherein the bitumen rejuvenator is a bio-based or mineral oil. 6. The microcapsule according to any one of claims 1 to 5, wherein the radiation absorber is a microwave absorber that absorbs radiation in the wavelength range from about >1 mm to about 1 m. 7. The microcapsule according to claim 6, wherein the radiation absorber is selected from the group consisting of metals, metal salts, metal oxides, metal carbonates, metal sulfides, carbon, carbon black, nanoparticulate carbon or nanotubes, silicon carbides, silicon, alkali metal salts and alkaline earth metal salts and polymers. 8. The microcapsule according to claim 7, wherein the radiation absorber is selected from the group consisting of carbon nanotubes, carbon black, Fe<3>O<4>, and graphite. 9. The microcapsule according to any one of claims 1 to 8, wherein: the polymer shell is selected from the group consisting of aminoplast, phenoplast and amino-phenoplast resins; the rejuvenator is selected from the group consisting of paraffinic oils, aromatic extracts, naphtenic oils, triglycerides & fatty acids-based products and tall oils or any mixture thereof; and the radiation absorber is a microwave absorber that absorbs radiation in the wavelength range from about >1 mm to about 1 m. 10. A process for preparing microcapsules according to any one of claims 1 to 9, said process comprising: i) preparing an emulsion comprising droplets of an organic phase which comprise the core materials; and ii) encapsulating said core materials by polymerizing in situ at least one prepolymer at the periphery of said droplets, wherein the polymerization is carried out in two or more steps by mixing a first portion of prepolymer with the emulsion so that a first polymerization step takes place, performing a second polymerization step with a second portion of prepolymer, and optionally performing further polymerization steps with further portions of prepolymer. 11. A self-healing bitumen comprising the microcapsules according to any one of claims 1 to 9. 12. An asphalt mixture or an infrastructure comprising the self-healing bitumen according to claim 11. 13. Use of microcapsules according to any one of claims 1 to 9 in the preparation of a self-healing bitumen. 14. A method for repairing an infrastructure which comprises the self-healing bitumen according to claim 11, said method comprising irradiating the infrastructure in the wavelength range of the absorption of the radiation absorber.