Smart Additives for Self-Sealing and Self-Healing Concrete
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Smart Additives for Self-Sealing and Self-Healing Concrete Nele De Belie1, Kim Van Tittelboom1, Didier Snoeck1 and Jianyun Wang1,2 1
Magnel Laboratory for Concrete Research, Ghent University, Belgium
2
Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Belgium
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 fibers several small cracks appear instead of one large crack. Combination with superabsorbent polymers, also called hydrogels, provides immediate crack sealing. Another methodology is to embed encapsulated polymeric agents in the matrix. When cracks appear, the capsules break and the agent is released. Upon contact of both components, they react and the crack is healed. This technique is also combined with CaCO3 precipitation of bacteria. In that case, not 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 denser 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.
INTRODUCTION Concrete is the one of the most popular construction materials. However, it is quite vulnerable to cracking because of its inherent heterogeneity, low tensile strength and the nonideal service environments. Although reinforced concrete is designed to crack (with limited crack widths) and the cracks do not pose structural problems, these cracks provide an easy path for water and other aggressive substances to penetrate inside the concrete matrix and may impair the long term durability. If cracks grow too large, there is a need for repair. Repair agents are then applied from the outside and penetrate into the cracks. This technology may be suitable for repairing large cracks. For small and deep cracks, it will be difficult for healing agents to reach the inner part. Therefore, an alternative repair method by means of a self-healing process is envisaged. Healing agents are incorporated into the concrete matri
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