Encapsulation of polymeric healing agents in self-healing concrete: capsule design - CAPDESIGN

Project summary

We consider that € 40–120 million of the maintenance costs for concrete bridges, tunnels and retaining walls in the European Union could be saved by application of self-healing concrete. For self-healing concrete with polymeric healing agents (e.g. PUR, PMMA), the bottleneck for valorization is however the encapsulation technique since the capsules have to possess multifunctional properties. The capsules with embedded healing agent (i) have to protect the healing agent for a long time, (ii) have to release the healing agent when cracking occurs and (iii) should not influence the fresh concrete workability and the early and long term mechanical properties. More important, we are looking for capsules which can easily be mixed in concrete and/or can survive the placement technique (e.g. projection). In that way, the concrete production / application process is not too much affected and the processing costs will not rise. The contradictory requirements make it however difficult to find a suitable encapsulation material: on the one hand, we want no breakage during concrete preparation / application, but on the other hand, we strive for immediate breakage of the capsules when a crack appears. Since no commercial products seem to be appropriate, the challenging objective of CAPDESIGN will be to develop, optimize and test new capsules for applications in self-healing concrete. In addition, an innovative and specific placement technique by projection / injection of the capsules in association with concrete will be developed. Its main objective is to provide a greater durability of the capsules during the concrete placement. The benefit of capsules which can survive mixing / application is that (i) the cost of self-healing concrete can be reduced, (ii) companies can be more easily persuaded to produce self-healing concrete, (iii) self-healing concrete can be valorized. Of course, as self-healing concrete does require much less repair, the application of self-healing concrete will lead to a lot of economic, environmental and social benefits, for example a reduction of traffic jams, an increased safety level, etc.