ABSTRACT
After several years of research in the Magnel Laboratory (Belgium) to obtain concrete with self-healing properties, the most promising self-healing approaches were tested on a larger scale (150 mm × 250 mm × 3000 mm beams). The first self-healing approach, consisted of the incorporation of encapsulated healing agent (SHC-PU). A one-component polyurethane was encapsulated by tubular glass capsules, which were embedded inside the concrete matrix. In total 350 capsules, filled with polyurethane, were prepared and positioned within the mould by means of a network of wires attached through the walls of the mould 10 mm below the top. As soon as cracks appear in the hardened concrete matrix, the brittle glass capsules, which are crossed by one of these cracks, will break. Due to capillary action, the healing agent will be released from the capsules and will be drawn into the crack. There, the agent will contact moisture inside the pores of the cementitious matrix causing a foaming reaction and hardening of the agent, finally leading to autonomous crack repair. The second self-healing approach which was ready to be tested on a larger scale, consisted of the use of hydrogels or superabsorbent polymers (SAPs, SHC-SAP). These were added to the concrete upon mixing. This self-healing mechanism is not immediately activated at the moment cracks appear but requires water ingress into the cracks to become active When water enters into the cracks, contact with the SAP particles near the crack surface will result in immediate swelling of the particles and thus blockage of the crack. However, over time the particles will release their water content again so the crack blocking effect will be gone but on the other hand the slowly released water will become available to the cementitious matrix and will result in permanent crack closure by further hydration of unhydrated cement particles and calcium carbonate precipitation of leached calcium hydroxide if also carbon dioxide is available within the crack. To evaluate the autonomous crack healing efficiency, a comparison was made with a reference beam (REF), containing no embedded self-healing approach.
