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More durable concrete structures by autonomous repair of damage

This paper was not found in any repository; the policy of its publisher is unknown or unclear.
This paper was not found in any repository; the policy of its publisher is unknown or unclear.

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Abstract

Like broken bones are able to heal themselves, it would be desirable that damaged concrete may be repaired autonomously as high costs are related to the repair. Actually, concrete already has some self-healing properties ; when cracks appear, water enters and reacts with unhydrated cement grains which results in crack healing. However, only small cracks can be healed in this way. Therefore we want to improve the self-healing efficiency by adapting the concrete matrix. By introducing high amounts of fibres several small cracks appear instead of one large crack. Combination with superabsorbent polymers provides immediate crack sealing and also regain in strength in non-saturated environment. Another methodology is to embed encapsulated polymeric agents in the matrix. When crack appear, the capsules break and the agent is released. Upon contact of both compounts, they react and the crack is healed. This technique is also combined with CaCO3 precipitation of bacteria. In that case, non only polymers but also bacteria and nutrients are encapsulated and released upon cracking. First the polymer reacts, later the bacteria start to convert the nutrients into CaCO3 crystals which make the polymer structure more dense and thus seal the cracks completely. As crack healing by means of bacteria uses a repair material which is more compatible with concrete we also try to seal cracks by only using bacterial CaCO3. Therefore, bacteria are embedded inside aggregates. Upon cracking, bacteria are exposed to the air and when water enters the crack bacteria become active and fill the crack with CaCO3. From the first results it was noticed that due to autonomous crack healing, water permeability is reduced and regain in mechanical properties is obtained. This means that more durable concrete structures may be obtained by using the proposed self-healing techniques.