In recent years, although the research on intelligent bionic concrete has been carried out at home and abroad, some valuable achievements have been made. Such as cement-based conductive composites, cement-based magnetic composites, cement-based composites that shield magnetic fields and electromagnetic waves, cement-based composites that self-diagnose damage, and cement-based composites that automatically adjust environmental temperature and humidity. However, how to timely, effectively and quickly repair and heal the cracks and damage of concrete structures has not yet formed a relatively perfect theory and mature technology. At present, only a few countries such as the United States and Japan are in the stage of laboratory exploration, and no substantial progress has been made.
The research on self-protection of concrete cracks can be traced back to 1925. Abram found that after the tensile strength test of concrete specimen cracked, it was put outdoors for 8 years, and the crack actually healed and the strength doubled. Later, Norwegian scholar Stefan Jacobson's research also showed that the compressive strength of concrete recovered by 4-5% after freezing and thawing damage and placed in water for 2-3 months. On the self-protection of concrete cracks, researchers at home and abroad put forward various methods. Inspired by the biological world, the researchers imitated the animal's bone tissue structure and the mechanism of regeneration and recovery after trauma, and adopted the method of combining adhesive materials with base materials to make the materials have the function of self-repair and regeneration after injury. Composite special components in traditional components of concrete or form intelligent bionic self-healing network system in concrete. When cracks appear in concrete materials, part of the adhesive flows out and goes deep into the cracks, so that the concrete cracks heal again.
J.- S.Ryu, a Japanese scholar at the University of California, Berkeley, and Nobuaki Otsuki, a professor at tokyo institute of technology, have done some research on electrochemical technology to repair reinforced concrete cracks, and obtained some experimental results. First, they prefabricated cracks on a concrete specimen with a size of100×100× 200mm, which may be surface cracks or through cracks. Then, the pre-cracked sample is immersed in 0. 1mol/L MgC 12 or Mg(NO3)2 solution, and the current density is 0.5 ~ 65432. Because of the high current density near the crack tip, electrodeposition is first formed at the crack tip, and the radius of curvature of the crack tip gradually increases, and finally it can be completely passivated. Then cover the concrete surface with electrodeposition of about 0.5~2mm. The fracture closed the fastest two weeks before electrification, and almost completely closed after 4 ~ 8 weeks, and the permeability decreased. Some scholars add special active inorganic cementing materials and organic compounds to concrete, and rely on their own further hydration reaction and slow hardening of organic substances under alkaline conditions to achieve the purpose of self-repair and self-passivation of concrete cracks.
In the early 1990s, Professor Hirozo Mitsuhashi, a scholar from Tohoku University, Japan, mixed hollow capsules or glass fibers with adhesives, and injected them with water glass, diluted water glass and epoxy resin as repair agents respectively. Once the concrete cracks under the action of external force, some capsules or hollow fibers break, and the adhesive flows out into the cracks, so that the cracks in the concrete can be healed again. Their test method is to test the strength recovery rate of concrete specimens after repairing cracks with different repairing agents by making concrete specimens of 7 days and 28 days old.
Japanese scholar Tamiya Numa also studied the influence of different fiber content, size and water-cement ratio in self-repairing concrete on the self-repairing of concrete. Glass fiber with a diameter of 3 mm ~ 5 mm and a content of 3% ~ 5% has little effect on the compressive strength of concrete. However, too much glass fiber will reduce the strength of concrete. Different water-cement ratios also have great influence on the compressive strength of repaired concrete. The greater the water-cement ratio, the lower the compressive strength of concrete.
From 65438 to 0994, Professor Carolyn Dry of the University of Illinois injected acetal polymer solution as adhesive into hollow glass fiber or hollow glass short tube and buried it in concrete, thus forming an intelligent bionic self-healing neural network system. When the concrete structure is damaged and cracked in use, the repairing agent contained in the pipeline or short pipe flows out and penetrates into the crack, and the repairing glue is consolidated due to chemical action, thus inhibiting the crack and repairing the crack. After three-point bending test, it is found that the strength of the repaired concrete specimen has been greatly improved compared with the original one, and the ductility of the material has also been greatly improved.
1995, in cooperation with the University of Illinois, the National Science Foundation of the United States put forward a sensing device filled with repair glue, which can sense the possibility of cracking of concrete components and make them heal, so as to realize self-diagnosis and self-repair of concrete.
During the period of 1996, the ATRE laboratory of the University of Illinois in the United States pre-installed repair pipes containing low modulus repair glue on the concrete bridge deck. When the concrete shrinks laterally, the pipeline breaks due to the lateral shrinkage strain, and the repair glue is left outside the pipeline to fill the cracks on the bridge deck. Experiments show that this method is feasible to repair cracks caused by lateral contraction of bridge deck. Because of the low elastic modulus of the repair adhesive, the fracture healing zone has greater deformation resistance than before cracking.
On this basis, Professor Carolyn Dry also tried to prepare bionic concrete materials according to the structure and formation mechanism of animal bones. The basic principle is that calcium phosphate cement (including monomer) is used as matrix material and porous woven fiber mesh is added. In the process of cement hydration and hardening, porous fiber releases polymerization initiator, which polymerizes with monomer to form polymer, and the water left by polymerization reaction participates in cement hydration. As a result, a large number of organic and inorganic substances are formed on the surface of the fiber web, which are interspersed and combined with each other. The final composite material is an inorganic-organic composite material with similar animal skeleton structure, and its performance has excellent strength and ductility. In addition, in the course of material use, if cracks or damages occur, porous organic fibers will release polymers and heal the cracks or damages. Japanese scholar H.Hilalshi and British scholar S.M.Bleay studied the self-protection effect of cracks on coagulation by similar methods in 1998 and 200 1 respectively. At present, the research on smart material structure in China generally focuses on its self-diagnosis and adaptive function, and the research on self-repair is still in its infancy.
Nanjing University of Aeronautics and Astronautics Key Laboratory of Intelligent Materials and Structures Aviation Science and Technology is in a leading position in the research field of intelligent composite materials in China. In 1997, they used shape memory alloy (SMA wire) and liquid-core optical fiber to study the self-diagnosis and self-repair methods of damage in composite structures. The overall scheme is analyzed, and preliminary tests are made with epoxy resin E44 and E5 1. Shape memory alloy and liquid-core optical fiber are embedded in concrete, and the outgoing light of optical fiber is received by photosensitive tube. When the damage occurs, the self-diagnosis and self-repair network composed of liquid-core optical fiber makes the glue flow into the damaged part, and at the same time, the SMA short fiber at the damaged part is locally excited to generate local compressive stress, so that the liquid-core optical fiber at the damaged part is broken and bonded. The damaged part is self-healing. When the adhesive contained in the liquid-core optical fiber flows to the damaged part, the heat generated by SMA excitation will greatly improve the curing quality and make the self-healing better.
200 1, Yang Hong of Nanjing university of aeronautics and astronautics proposed to realize self-diagnosis and self-repair of intelligent structures with hollow fibers. In this paper, the research method of hollow fiber for intelligent structure is pioneered and its application is studied. In addition, a composite diagnosis and repair system embedded in hollow optical fiber is designed to detect the damage degree and location of composite materials and self-repair the damaged parts. Shape memory alloy (SMA) wires are also embedded in the composites to improve the strength, safety and reliability of the composites. The research object is paper honeycomb and resin matrix composites, and the self-repair of composites is studied by injecting glue into hollow optical fibers. The experimental results show that the repaired paper honeycomb composite completely reaches the normal properties of the material, and the tensile and compressive properties of the repaired resin matrix composite are greatly restored under the condition of complete damage.
The bionic self-diagnosis and self-healing intelligent concrete studied by the State Key Laboratory of Concrete Materials Research of Tongji University imitates the biological perception of trauma and the function of biological tissue to heal wound parts. The so-called sixth component, such as bionic sensor and liquid-core fiber with adhesive, is combined with the traditional components of concrete to form an intelligent bionic self-diagnosis and self-healing network system in concrete. Bionic sensors can diagnose and warn in time when concrete materials are damaged. When micro-cracks appear in concrete materials, some liquid-core fibers break, and the adhesive flows out into the cracks, so that the concrete cracks heal again and the performance of concrete materials can be restored and improved. The research of this intelligent composite material can realize the active diagnosis, real-time monitoring and timely repair of concrete materials, ensure the safety of concrete structures with advanced consciousness and prolong the service life of concrete structures.