# Bio-Influenced Self-Healing Mechanism in Concrete and Its Testing: A Review
## 3 Results and Discussion
### Type of Test: Destructive and Non-Destructive
At present, there is a lack of large scale production systems and the actual application of bio-concrete in the construction industry. One specific engineering application of bio-concrete is the study conducted by [PERSON] and [PERSON] in 2020 [77]. They carried out a production system for commercial bio-concrete and they applied it to the side wall of the ship lock. From their study, they found that the cracking of concrete was healed completely after 60 days and the leakage within the cracks was blocked effectively. Therefore, concrete with bacteria is one of the possible solutions to produce a more robust and sustainable material in the field of civil engineering. A self-healing concrete became available in the European market in 2017 as the Green-Basilisk BV company commercialized the Basilisk Self-healing concrete with patent number US8460458B2 [78]. It was also worth mentioning that the company claimed that the service life of a concrete structure can be extended by 30% using Basilisk Self-healing concrete. This review paper does not cover in-depth patent search comparison and analysis, since it is more centered on research journals concerning bio-concrete from 2010 to 2020. [PERSON] et al. [79] studied the cost of the utilization of bacteria in concrete, as compared with the conventional concrete. The cost analysis demonstrated that the price of microbial concrete is 2.3- to 3.9-times higher than the price of conventional concrete with a lower quality [80]. This is one of the main reasons for which this concrete with bacteria is not mass produced and not yet widely used in the construction industry. The keywords and document analysis, as shown in Figure 6, revealed that compressive strength, calcium carbonate and cementitious composite are the themes receiving much attention in the research of Bacterial Concrete. It is interesting to note that potential research and development (R&D) would be directed towards filling the research gap about the following topics: (1) Compatibility of bacteria and protective material to concrete; (2) Life Cycle Analysis of bio-concrete; (3) Numerical modeling to optimize the properties and composition of protective material. The majority of the researchers used the Normal Strength Concrete (NSC) as the concrete type for bacteria with 79%, followed by Normal Mortar (NM) with 15% and lastly by Geopolymer Concrete (GPC), Fiber Reinforced Mortar (FRM) and Fiber Reinforced Concrete (FRC) with 2%. There are a lot of researchers working in the domain of concrete as a construction material. Since bacterial concrete is a multidisciplinary topic, it is expected that a lot of researchers outside the domain of civil engineering collaborate with each other. It is expected that the output would be a knowledge-based framework that could serve as a reference in order to improve existing research about bacterial concrete. The outlet direct citation analysis revealed that Construction and Building Materials is considered as the most influential outlet for research on bacterial concrete with 75% technical journals, followed by Cement and Concrete Composites with 15% and lastly by Cement and Concrete Research with 10%. Moreover, the most common source of research came from the following countries: China; United Kingdom; Australia; Belgium. Several gaps and emerging trends are also highlighted, in which microencapsulated technology and acoustic emission could be the emerging methods for evaluating the performance of the bacteria and detecting real time cracks inside the concrete matrix in the future. The nutrient broth is considered as the major contributor to the cost in the bacterial concrete, covering over 60-75% of the cost per cubic meter of concrete [79]. Generally researchers used laboratory grade nutrients, which are quite expensive. The overall cost of bio-concrete can be reduced if there is an alternative and cheap nutrient broth sourced locally that is compatible with a bacteria.