Polyurea/polyurethane microcapsules based self healing concrete
In self healing concrete, the propagation of cracks in the material is prevented by embedded microcapsules with an aqueous self healing agent. By adding an encapsulated aqueous solution the effect of autonomous healing of concrete is increased. Microscope studies lead to the conclusion that the capsules do not break upon the mixing process in the mortar production and the solution is released upon cracking. Moreover, reflective microscope tests with colored capsules inside mortars have shown that the capsules release their content when cracks occur. The water reacts with not reacted calcium-hydroxide and silicate particles which are present in concrete and forms a CSH gel which seals the crack. Thus, a large portion of strength can be recovered. The self healing technology has been improved by selective capsule distribution to achieve a recovery of up to 58 %. SEM images gave first insights into how the capsules' appearance is inside a concrete like environment. In terms of corrosion inhibition it was found out that calcium nitrite capsules are working best for corrosion inhibition. Probably by releasing calcium nitrite a protective layer around the reinforcement bars is formed and corrosion is thus minimized. The presented technology is an important contribution to the development of smart, high-performance construction materials and this works has achieved an improvement of the microcapsules based self healing technology and further characterization of the capsules mechanism has been conducted. ^
Svenja Kristin Reinke,
"Polyurea/polyurethane microcapsules based self healing concrete"
Dissertations and Master's Theses (Campus Access).