Reader Response Draft 1 (Self-Healing Concrete)

In the article, “The Self-Healing Concrete That Can Fix Its Own Cracks,” Spinks (2015) stated that Hendrik Jonkers created self-healing concrete innovation to “decrease the amount of new concrete produced, lower maintenance and repair costs for city officials, building owners and homeowners” by inlaying self-activating limestone-producing bacteria into the concrete. The self-healing concrete has a longevity of up to 200 years and helps to reduce carbon emitters. However, the concrete can only repair up to 0.8mm wide of cracks and cost €30 per metre cube more than normal concrete. According to Alker, who is director of policy at the UK Green Building Council believes that it will be hard to convince the industry to adopt the new innovation. It will take unconventional consumers and developers who are willing to test their building with the new concrete to demonstrate positive results before others will support. Jonker has also been experimenting across the world where he claims that the people realized the profit because they can save from maintenance cost.

The article discussed about the possibility of the self-healing concrete winning over the construction industry. However, it did not provide sufficient information to convince the industry to adopt the innovation.

Concrete structures serve under various conditions. As presented in Table 2, some concrete structures serve under water. As shown in Table 1, one of the most necessary conditions for autogenous self-healing and self-healing based on bacteria or mineral admixtures is that water is present in cracks. Therefore, for concrete structures under water autogenous self-healing and self-healing based on bacteria or mineral admixtures can be designed. However, selfhealing based on adhesive agents is not suitable for concrete structures under water because presence of water in cracks prevents from the release of adhesive agents into cracks and the hardening of adhesive agents.

 For concrete structures underground, in water-rich regions water can penetrate into cracks immediately after cracking. This case is similar to that concrete structures are under water. Autogenous self-healing and self-healing based on bacteria or mineral admixtures, but not adhesive agents, are recommended. In some regions where water is not extremely rich, it takes some time for water to fill the cracks. For this case self-healing based on adhesive agents is a possible mechanism to be applied. Moreover, wet-dry cycles usually take place in cracks of concrete structures underground. Wet-dry cycles facilitate penetration of CO2 into cracks. As shown in Table 1, dissolved CO2 facilitate the precipitation of calcite during autogenous healing and the healing based on bacteria. In most of the serving time of concrete structures in the open air, water is absent in cracks. This condition makes autogenous self-healing and self-healing based on bacteria or mineral admixtures very difficult. As presented in Table 1, dry condition of cracks is good for selfhealing based on adhesive agents. Therefore, self-healing based on adhesive agents can be applied in these structures. If autogenous self-healing and self-healing based on bacteria or mineral admixtures are designed for these structures, additional water should be supplied to cracks in purpose. Additional water can be supplied to cracks by using a vascular system described in Section 3 or by spraying water to concrete surfaces.

For indoor concrete structures elements, it is difficult to supply additional water to cracks. In this case, autogenous self-healing and self-healing based on bacteria or mineral admixtures are hardly applied.

In this paper, different mechanisms of self-healing, i.e. self-healing based on adhesive agents, self-healing based on bacteria, self-healing based on autogenous self-healing were described. Their required conditions were summarized. The previous investigations showed that all mechanisms of self-healing are effective to some extend under particular conditions. However, there is still a lack of information about the efficiency of different self-healing in field application. Actually, concrete structures serve under particular conditions that can limit the choice of self-healing mechanisms. In this paper, concrete structures were categorized according to serving conditions. Potential self-healing mechanisms are pointed out according to the required conditions of each self-healing mechanism. However, no detailed information is available about the application of self-healing in concrete structures under particular serving conditions. More investigations of self-healing in concrete structures in field are necessary.

Spinks, R. (2015, June 20). The self-healing concrete that can fix its own cracks. The Guardian. https://www.theguardian.com/sustainable-business/2015/jun/29/the-self-healing-concrete-that-can-fix-its-own-cracks

Huang HL (2014,nd). A review on self-healing in reinforced concrete structure in view of serving conditions. 

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.847.6335&rep=rep1&type=pdf