Crack formation is a commonly observed phenomenon in concrete structures. Although micro crack formation hardly affects structural properties of constructions, increased permeability due to micro crack networking may substantially reduce the durability of concrete structures due to risk of ingress of aggressive substances particularly in moist environments. In order to increase the often observed autogenous crack-healing potential of concrete, specific healing agents can be incorporated in the concrete matrix. The aim of this study was to quantify the crack-healing potential of a specific and novel two-component bio-chemical self-healing agent embedded in porous expanded clay particles, which act as reservoir particles and replace part of regular concrete aggregates. Upon crack formation the two-component bio-chemical agent consisting of bacterial spores and calcium lactate are released from the particle by crack ingress water. Subsequent bacterially mediated calcium carbonate formation results in physical closure of micro cracks. Experimental results showed crack-healing of up to 0.46 mm-wide cracks in bacterial concrete but only up to 0.18 mm-wide cracks in control specimens after 100 days submersion in water. That the observed doubling of crack-healing potential was indeed due to metabolic activity of bacteria was supported by oxygen profile measurements which revealed O2 consumption by bacteria-based but not by control specimens. We therefore conclude that this novel bio-chemical self-healing agent shows potential for particularly increasing durability aspects of concrete constructions in wet environments.

Quantification of crack-healing in novel bacteria-based self-healing concrete

Self-healing concrete by use of microencapsulated bacterial spores

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

A review : Self-healing in cementitious materials and engineered cementitious composite as a self-healing material

Use of bacteria to repair cracks in concrete

Concrete cracks due to its low tensile strength. The presence of cracks endangers the durability as they generate a pathway for harmful particles dissolved in fluids and gases. Without a proper treatment, maintenance costs will increase. Self-healing can prevail in small cracks due to precipitation of calcium carbonate and further hydration. Therefore, the use of microfibres is proposed to control the crack width and thus to promote the self-healing efficiency. In the current research, crack sealing is also enhanced by the application of superabsorbent polymers. When cracking occurs, superabsorbent polymers are exposed to the humid environment and swell. This swelling reaction seals the crack from intruding potentially harmful substances. Mortar mixtures with microfibres and with and without superabsorbent polymers were investigated on their crack sealing and healing efficiency. Regain in mechanical properties upon crack healing was investigated by the performance of four-point-bending tests, and the seal...

/pdf/self-healing-cementitious-materials-by-the-combination-of-3a9w3jdrtc.pdf

Self-healing cementitious materials by the combination of microfibres and superabsorbent polymers

It has been estimated that, in Europe, 50% of the annual construction budget is spent on rehabilitation and repair of the existing structures [1] . Therefore, autonomous crack healing of concrete, a construction material that is highly susceptible to cracking, would be desirable. In this research, an encapsulated healing agent was embedded in the mortar matrix to obtain self-healing properties. Upon crack appearance, the capsules break and the healing agent is released, causing crack repair. By means of Computed Tomography and visual observation of the crack faces, filling of the cracks with healing agent was observed. It was seen that more than 50% of the original strength and stiffness could be regained after self-healing. It was also found that the water permeability could be reduced by a factor 102 to 104 due to autonomous crack healing. As a consequence, the proposed technique may be used for partial restoration of concrete properties after cracking.

Kim Van Tittelboom

Papers

Use of bacteria to repair cracks in concrete

Self-Healing in Cementitious Materials—A Review

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

Self-healing cementitious materials by the combination of microfibres and superabsorbent polymers

Self-healing efficiency of cementitious materials containing tubular capsules filled with healing agent