Potential of genetically engineered strains to enhance concrete strength: A Review

The gradual development of microcracks reduces concrete's durability. Their appearance reduces performance properties, including water resistance, frost resistance, and strength. One promising approach to lowering microcrack development is the use of spore-forming bacteria that can precipitate calcium carbonate in the environment. When water enters concrete cracks, bacterial spores germinate and initiate mineralization, facilitating partial restoration of the material's structure. The first experiments on producing bioconcrete were conducted in the mid-2000s and demonstrated that bacteria can form calcite particles up to 100 µm in size and seal microcracks. Concrete has a limited capacity for self-healing through atmospheric carbonation, in which CO₂ reacts with calcium hydroxide to form calcite; however, this process is slow and unpredictable. In most biotechnological systems, CaCO₃ precipitation is enhanced by the enzymatic hydrolysis of urea, catalyzed by the enzyme urease. In addition to the urease pathway, alternative mechanisms for urea degradation to form carbonates are also known. For example, the amidolyase pathway, in which allophanate is formed from urea, and in a subsequent reaction, allophanate hydrolase decomposes it to ammonia and bicarbonate. Furthermore, in microcracks with elevated CO₂ content, bicarbonate can be produced by carbonic anhydrase. However, in the surface layers of concrete exposed to the atmosphere, this approach is apparently impossible due to the reverse reaction, as the dehydration of bicarbonate to CO₂, which will escape into the atmosphere. This publication hypothesizes that combining urease and carbonic anhydrase may yield better results in concrete stabilization. Both enzymatic reactions produce hydrocarbonates, but CO₂, the product of the first reaction, becomes the substrate for the second. The creation of new genetically engineered strains with genes encoding enzymatic systems based on the described pathways can increase the efficiency of mineralization and improve the performance properties of bioconcrete.