Prepared by: Assist. Prof. Dr. Mayada Waheed Falah Head of the Civil Engineering Department – College of Engineering – Al-Mustaqbal University Self-Healing Concrete is an advanced type of concrete designed to automatically seal or repair cracks that develop within it, either naturally or with the assistance of specific triggering mechanisms. This reduces the penetration of water and harmful substances into the concrete, increases its service life, and lowers maintenance costs. How Does Self-Healing Concrete Work? There are several main mechanisms: 1. Autogenous Self-Healing This occurs naturally in concrete, particularly when moisture is continuously available. Continued hydration of unreacted cement particles can help seal small cracks. The precipitation of calcium carbonate within cracks can also contribute to crack closure. This method is limited by crack width and concrete age. 2. Bacterial Self-Healing Certain types of bacteria capable of surviving in the highly alkaline environment of concrete are incorporated into the concrete mixture. When water and oxygen reach a crack, the bacteria become active and produce compounds that lead to the precipitation of calcium carbonate (CaCO₃). The calcium carbonate fills part of the crack, helping to seal it. 3. Self-Healing Using Microcapsules Small capsules containing a healing agent are incorporated into the concrete. When a crack develops, the capsules rupture and release the healing agent, which helps seal the crack. The system can be designed so that the healing reaction is automatically triggered when damage occurs. 4. Self-Healing Using Microvascular Networks or Tubes Small channels or vessels are integrated into the concrete element and filled with repair materials. When damage occurs, the repair material can be released into the cracked area, helping to repair and seal the crack. What Is Its Importance in the Rehabilitation of Concrete Structures? Self-healing concrete is highly important in the field of concrete structure rehabilitation, as it can reduce crack development and water leakage, thereby limiting the penetration of factors that cause corrosion of reinforcing steel. The rehabilitation mechanism can be illustrated as follows: Crack Formation → Ingress of Water and Harmful Agents → Activation of the Healing Mechanism → Precipitation/Reaction of the Healing Material → Crack Sealing → Reduced Permeability → Increased Durability and Service Life Is It Suitable for All Types of Cracks? No. This is a very important point from an engineering perspective. Self-healing concrete does not mean that a structural element can completely repair itself after significant damage has occurred. Its effectiveness is generally more suitable for small to moderate cracks, whereas large cracks or damage that affects structural strength require conventional engineering repair or strengthening techniques.