Cracks can develop in concrete immediately after curing or after a long period of time. Minor cracks do not impact structural stability. However, larger and deeper cracks expose the concrete as well as the reinforcement steel to atmospheric elements. Over a period of time, it can lead to deterioration of the structure to an extent that major repairs would be needed. The challenge is higher in structural members that are constantly exposed to harsh conditions such as basement of buildings, tunnels, bridges, and structures near the sea.
Scientists took inspiration from self-healing of biological ‘structural’ components like bones to research if similar systems can be developed. For self-healing to happen, the concrete needs to ‘know’ when cracks develop and then ‘heal’ itself. One such research program, with an aim to develop self-healing concrete commercially, is HEALCON (http://www.healcon.eu/). This collaborative project is funded by the European Union’s Seventh Framework Programme for research, technological development and demonstration. The HEALCON project aims to develop self-healing concrete for both early stage and long-term cracks.
In one method, self-healing is achieved by incorporation of suitable bacteria (Like Bacillus pseudofirmus), along with nutrients (Like Calcium Lactate), during concrete mixing. When a crack occurs, the bacteria near the crack get activated by atmospheric elements, feed on the nutrient and release calcium carbonate CaCO3, which fills the cracks. Simple as it sounds, there are many aspects to be researched for this process to occur with acceptable performance. The bacteria should remain active for the full life of the structure, activate as soon as a crack occurs and produce enough CaCO3 to fill the crack fully. To understand better, you can watch a video at https://www.youtube.com/watch?v=laqACVY1U_k.
For challenging applications, where loads are dynamic (bridges), the material used for self-healing needs to be suitably flexible. Researchers have developed technology to use elastic polymeric healing agents.
Self-healing concrete has the potential to save billions of dollars in maintenance of buildings and other infrastructure. Further, by extending the life of concrete structures, the ecological footprint can be reduced.
At the current stage, the cost of self-healing concrete works out to over double that of regular concrete. For self-healing concrete to be commercially viable, the cost would need to be brought down to a marginal premium over regular concrete. Work in this direction is already being done. Post development, the product would need to be commercialized and sold widely across the world.
Concrete is a widely used material, the very basic component in housing and infrastructure. Given the potential benefits of self-healing concrete, we hope that this technology develops quickly.