Self-repair that increases durability of concrete structures

Edit Hook

The Natural Process Design, Inc. approach to self-repairing concrete “consists of embedding repair material in hollow fibers in the repair matrix, before it is subjected to damage. Therefore, when cracking occurs, this repair material is released from inside the fibers and enters the matrix, where it penetrates into cracks and rebonds to the mother material of the structure being repaired. The cracking and damage, associated with the low tensile strain capacity, triggers the release of the repair material. This is important because in this way, the material acts in an extensible manner. Further, it does crack and show ductile behavior, but the instant repair of cracks and damage assures that deterioration does not accompany this ‘crack then repair’ behavior. Thus, we repair the problem, where it occurs, and just in time, automatically, without manual intervention. This technique performs better because the adhesive is flexible itself and keeps on releasing with each brittle failure, i.e. crack. The ability to fill in for dimensional gaps has been shown to work with self-repairing adhesives that grow larger in volume. Even with internally released stiff adhesives, self-repaired matrices are less brittle, more ductile, and yet stronger in tension than controls without adhesives.” This technique has been used in bridges. Text is from Summary of Self-repairing Durable Concrete

Key Differentiators

The usual approaches for repair of structural concrete are: polymer injection, prestressing, geomembranes, and polymer wraps. These techniques seek a ductile, less brittle failure. Concrete is a brittle material, and concrete structures are dimensionally unstable because of movement. Consequently, the usual repairs do not hold. All of them are based on addition of a repair material to concrete from the outside in. Natural Process Design, Inc. adds the materials from inside the concrete to repair.Self-healing solves the quality assurance problem and reduces life cycle costs. The extended life reduces the number of replacements, and thus the future costs. This new family of self-repairing materials is less expensive overall because the repair material is built in and available, wherever and whenever it is needed. Therefore, over-designing for damage protection is eliminated. The life cycle cost (which is usually much more than first costs of construction) will yield the most dramatic savings.

Biomimicry Story

Nature often builds with materials that can self-repair–skin, insect exoskeletons, abalone shells, bones, starfish arms. Repair doesn’t occur from outside the organism, but from within. Carolyn Dry from Natural Process Design, Inc. has applied this idea to create self-repairing concrete.

Challenges Solved

Concrete is inexpensive relative to other construction materials, however, damage can greatly reduce its life cycle. Internal damage is common in concrete. Repair of this type of damage is crucial in preventing failures that can progress to ultimate catastrophic failures. However, it is hard to detect micro scale cracks unless they have developed to macroscopic scale flaws. Nondestructive evaluation techniques have limited ability to detect these microcracks. Also, the damage repaired in the field by hand does not restore the original strength of the material.

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