Manual application versus autonomous release of water repellent agent to prevent reinforcement corrosion in cracked concrete

Cracks in reinforced concrete are preferential ingress paths for aggressive substances such as chlorides. As soon as a critical amount of chlorides has reached the steel reinforcement, corrosion will occur. Therefore, crack healing is of utmost importance. However, manual crack repair is very labour intensive. Therefore, the potential of self-healing through the release of a water repellent agent from embedded capsules was compared with the effectiveness of applying this agent on the concrete surface before or after cracking and the effectiveness of injection of the agent into a crack. From the electrochemical corrosion measurements, it was shown that only uncracked samples were able to withstand 135 weekly cycles of exposure to a 33 g/L chloride solution without corrosion initiation of the reinforcement. While samples with manually injected and autonomously healed cracks resisted the exposure conditions for about 50 cycles or more, samples for which the water repellent agent was applied onto the surface after cracking resisted the exposure conditions for 5–42 cycles, while samples for which the agent was applied onto the surface before cracking showed an immediate corrosion initiation similar as was noted for the untreated cracks. From a visualization of the chloride ingress front and determination of the chloride content in the vicinity of the crack, it was noticed that none of the crack treatment techniques performed as well as the uncracked series. Visual inspection of the corroded rebars and determination of the corroded volume of the rebars through computed tomography and macro-cell corrosion current measurements proved again that the uncracked series outperformed the other series. While the corroded volume of the rebars from the uncracked series was almost zero, this value ranged from 15–95 mm³ for the rebars of the other series. However, the latter investigations also showed that release of the agent into the crack, whether this was done in a manual way or autonomously through release from embedded capsules, resulted in a delayed corrosion initiation and lower corrosion propagation rate compared to the application of a water repellent agent onto the surface. This is a beneficial outcome for the further implementation of self-healing approaches, more specifically though the release of encapsulated water repellent agent, in the market.