Inspired by the unique and efficient wound healing processes in biological systems, several approaches to develop synthetic polymers that can repair themselves with complete, or nearly complete, autonomy have recently been developed. This review aims to survey the rapidly expanding field of self-healing polymers by reviewing the major successful autonomic repairing mechanisms developed over the last decade. Additionally, we discuss several issues related to transferring these self-healing technologies from the laboratory to real applications, such as virgin polymer property changes as a result of the added healing functionality, healing in thin films v. bulk polymers, and healing in the presence of structural reinforcements.

Self-healing polymers and composites

A hollow fibre reinforced polymer composite encompassing self-healing and enhanced damage visibility

The world of smart healable materials

Concrete is very sensitive to crack formation. As wide cracks endanger the durability, repair may be required. However, these repair works raise the life-cycle cost of concrete as they are labor intensive and because the structure becomes in disuse during repair. In 1994, C. Dry was the first who proposed the intentional introduction of self-healing properties in concrete. In the following years, several researchers started to investigate this topic. The goal of this review is to provide an in-depth comparison of the different self-healing approaches which are available today. Among these approaches, some are aimed at improving the natural mechanism of autogenous crack healing, while others are aimed at modifying concrete by embedding capsules with suitable healing agents so that cracks heal in a completely autonomous way after they appear. In this review, special attention is paid to the types of healing agents and capsules used. In addition, the various methodologies have been evaluated based on the trigger mechanism used and attention has been paid to the properties regained due to self-healing.

https://biblio.ugent.be/publication/4144354/file/4144368.pdf

Self-Healing in Cementitious Materials—A Review

Use of silica gel or polyurethane immobilized bacteria for self-healing concrete

The goal of this research project is to expand the previous work on a timed adhesive release system for the repair of cracks in concrete. The performance criteria for the adhesive are that it must have a long shell life, be resistant to extreme temperatures, have a high viscosity so it can flow easily into cracks in concrete and it must be strong enough to repair the cracks. The method of encapsulating the adhesive must not degrade over time and it must not be costly. A three-part methylmethacrylate adhesive system was chosen. The adhesive was released from hollow glass tubes coated with a brittle breakable sealer. The experimental results showed the release of the three-part methylmethacrylate adhesive into the matrix created a bond that restored the lost strength due to the cracking and increased flexibility.

https://iopscience.iop.org/article/10.1088/0964-1726/5/3/007/pdf

Three-part methylmethacrylate adhesive system as an internal delivery system for smart responsive concrete

This research is an investigation into the use of liquid core hollow glass capillary fibers for the potential detection of cracking in opaque and semi-opaque brittle materials. The study was originally intended to combine work based on the concept of internal adhesive delivery from hollow fibers for repair with nondestructive analysis of crack location and cracking volume within the same system; however the detection system is the topic of this paper. The liquid filled hollow fibers can carry light. A cracked capillary tube which has released some liquid projects a diffraction pattern from the meniscus at the ends of the adhesive. The size relationship of these meniscuses allows us to predict the location of the fiber crack and the volume of the liquid lost into the matrix. For example, in the case of a standard capillary pipette with one-half of its liquid lost from one end, the two meniscuses projected circles approximately 4 and 2 mm in diameter. If the same amount of liquid is lost not from one end, but from somewhere else along the length of the pipette, the two to one relationship in size will remain, but the actual size will vary with distance of the meniscuses from the projection screen. The clarity of these relationships should allow later prediction of matrix crack location and volume.

https://iopscience.iop.org/article/10.1088/0964-1726/6/1/004/pdf

A novel method to detect crack location and volume in opaque and semi-opaque brittle materials

This was an investigation into the feasibility of using liquid core optical fibers for the detection and self repair of cracking in cement or polymer materials generated by dynamic or static loading. These experiments relied on our current research sponsored by the National Science Foundation. That work on the concept of internal adhesive delivery from hollow fibers for repair was here combined with the nondestructive fiber optic analysis of crack location and volume. The combination of the ability to remotely measure crack occurrence in real time and determine the location and volume of crack damage in the matrix is unique in the field of optic sensors. The combination of this with crack repair, rebonding of any detached or broken fibers, and replenishment of liquid core chemicals, when necessary, make this a potentially powerful sensing and repair tool. Work on this research topic was sponsored by the University of Illinois.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

William McMillan

Papers

Three-part methylmethacrylate adhesive system as an internal delivery system for smart responsive concrete

A novel method to detect crack location and volume in opaque and semi-opaque brittle materials

Crack and damage assessment in concrete and polymer matrices using liquids released internally from hollow optical fibers