Air content, Compressive strength, Concrete construction, corrosion, Cracking, Moisture content, Reinforcing steel, Tensile strength
Concrete is the most widely used material in construction, offering advantages in terms of moisture and fire resistance, versatility, cost, energy-efficiency, and environmental impact. Concrete provides a relatively high level of compressive strength; its tensile strength, however, is fairly low, and concrete members crack on the tension side under the application of small loads. Hence, most concrete systems generally incorporate reinforcing steel to resist tensile. While reinforcing steel receives a certain level of protection against corrosion from the surrounding concrete, the corrosion of reinforcing steel is still a predominant factor undermining the longevity of the vast concrete-based infrastructure. The presence of both air and water is required for corrosion activity to start, and, after tensile crack formation, it will accelerate. However, corrosion may be slowed down considerably if the diffusion of oxygen and harmful ions, such as chloride ions, through the concrete could be reduced. The new concept of self-healing concrete was introduced over the past decade, and many researchers are still investigating the feasibility of the process at a laboratory scale. There are two objectives for the self-healing concrete: (1) recovery of strength after the formation of cracks and (2) sealing the cracks to prevent further concrete deterioration, such as that resulting from corrosion. Several approaches for concrete self-healing are proposed in the literature, such as bacteria encapsulation, mineral admixture, chemical in glass tubing, etc. Most of the proposed methods focused on the second objective and showed promising results for eliminating or reducing the cracks that form first, when the concrete is still relatively young, under dry or wet conditions. However, very few studies have been done to show the versatility and repeatability of some the most promising approaches, such as bacterial encapsulation.