Concrete is one of the most used building materials nowadays, it is, however, one of the CO2 contributors which lead to environmental pollution. A lot of costs are being incurred to maintain concrete after the construction of the buildings. The cracks that form in the concrete sometimes are sealed manually hence shortening the life of a particular structure. Additionally, self-healing concrete is a revolutionary building material that helps to solve the issue of cracks soon. There are two types of self-healing, natural and artificial. However, in the review, we focus on the artificial self-healing to project how it impacts architectural designs.

Self-healing is that method when a particular material can repair itself back to the original state. From the various research done, it has been noted that the concept of self-healing is autogenic, it happens over a specified period time. The researchers have also examined that, sometimes, a building can stand up for an extended period time with minimal maintenance. This naturally occurs when the non-hydrated cement clinker mixes with moisture repairing the cracks. But, in the constructions being done today, non-hydrated cement has been reduced, and this reduces the natural healing effect. People, therefore, have to shift to an artificial self-healing method.

The first artificial method of self-healing was invented in 1994, the first approach and method use a healing adhesive which is encapsulated inside a microcapsule. Here, the formation of a crack causes breakage of the microcapsule hence releasing the healing agent. This at the end heals the break. In this case, the adhesives can be stored in the longer tubules or the short fibers. There are, however, two main types of artificial self-healing of concrete that were introduced. The two main types are;

Bacterial-based healing process; this method is also called bio-concrete. In this case, the concrete uses just a simple process to heal the crack. To achieve this mechanism, the concrete is designed to have the following things. (a) Precursor-Like calcium lactate (Ca(C3H5O2)2) and (b) microcapsules where the bacteria is planted. This can also be added to the mixture; it has to be put in place that it can germinate once the water reaches the crack. According to the researchers, once germination of bacteria takes place, limestone(CaCo3) is produced by the multiplying bacteria (Seifan, 2016). Planting of bacteria in this case also add a double shield which prevents steel corrosion. In this case, the bacteria used is alkali resistant and spore-forming. This is the essential bacteria to use since it can live up to 200 years.

The following diagram shows an illustration of bacteria based self-healing.

Bacteria-based self-healing concrete

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Shape memory polymers; this is the 2^ndartificial method that can be used in self-healing of concrete. This is a method that helps construction to return to their original state by just applying a stimulus. The principles involved in this method are both automatic and autogenic. Here, there is an artificial system created to increase natural autogenic healing and seal concrete cracks.  The polymers here are semi-crystalline polymers, and they have a predefined shape that is memorized in their structure. This later helps the polymers to return to their original state. In case a crack occurs, a system will be triggered, activating heating of the shape memory polymer within the crack. After the activation takes place, shrinkage of the shape memory occurs generating a tensile force as a result of tendon restrained nature (Li, 2010). This causes the crack to close itself. Finally, autogenously healing occurs. The following diagram shows an illustration of shape memory polymers self-healing.

Shape- memory polymers

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Among the two artificial self-healing methods, the most common is bacteria basedself-healing. A lot of people believes that this method will change how architects think and designs, we also feel that the synthetic method will also change concrete from eco-harming to eco-friendly.

References

Seifan, M., Samani, A.K., and Berenjian, A., 2016. Bioconcrete: next generation of self-healing   concrete. Applied microbiology and biotechnology, 100(6), pp.2591-2602.

Li, G. and Uppu, N., 2010. Shape memory polymer based self-healing syntactic foam: 3-D           confined thermomechanical characterization. Composites Science and Technology, 70(9),     pp.1419-1427.

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