Bacterial Healing Research Articles

Encapsulating immobilized ureolytic bacteria yields self-healing concrete apropos sustainable transportation materials: A review

Transportation networks must be resilient to withstand the effects of climate change and natural calamities. Concrete infrastructure must endure extreme weather, flooding, and seismic catastrophes better than many other types of construction to guarantee the sustainability of transportation services. Self-healing concrete is unquestionably the material of the future that could address these issues. Researchers have discovered a self-healing process in automatic repairing the concrete cracks up to 1.8 mm width. This is made possible by ureolytic and non-ureolytic microorganisms from Bacillus family that cause bacterial precipitation and production of calcite that seal cracks, which could extend the serviceability of concrete. Concrete structures can be restored, and damage prevented through different self-healing mechanisms, such as microvascular healing, bacterial healing, capsule-based healing, and autogenous repair. Research reveals that concrete's capacity to repair itself is greatly enhanced by a mixture of self-healing mechanisms. Moreover, the encapsulation of immobilized bacteria with expanded clay, calcium alginate beads, or other porous materials that can hold onto nutrients and bacteria for an extended period resulted in a considerable improvement in the healing ratio. The main objective of this study is to enumerate all the potential challenges and limitations of the recent studies in self-healing concrete to draw a viable conclusion which is necessary for establishing rules and testing procedures for up-scale implementation.

Use of Bacteria Externally for Repairing Cracks and Improving Properties of Concrete Exposed to High Temperatures

The current paper presents the results of an experimental study on the application of calcium carbonate precipitation bacteria as a new approach to repairing damaged concrete when exposed to high temperatures. To do so, cylindrical and cubic concrete specimens were initially exposed to heat in a furnace for 1 h, after reaching two different temperatures of 600 and 800 °C. A heat rate of 5.5 °C per minute was used to achieve the target temperatures. Then, two types of bacteria, namely Sporosarcina pasteurii and Bacillus sphaericus, with cell concentration of 107 cells/mL, were utilized externally, to repair the thermal cracks, enhancing the mechanical properties and durability of the damaged concrete. The efficiency of the bacterial remediation technique was then evaluated through compressive strength, ultrasonic pulse velocity (UPV), and electrical conductivity tests on the control specimens (unexposed to heat), and those exposed to high temperature with or without bacterial healing. The experimental results demonstrate that the compressive strength of the test specimens exposed to temperatures of 600 and 800 °C decreased by about 31–44% compared with the control ones. However, compared to those damaged at 600 and 800 °C, the compressive strength of specimens repaired by the S. pasteurii and the B. sphaericus showed increases of 31–93%. This increase is associated with the precipitation of calcium carbonate in the deep and superficial cracks and pores of the damaged specimens. Furthermore, the ultrasonic pulse velocity of the specimens subjected to bacterial remediation had a significant increase of about 1.65–3.47 times compared with the damaged ones. In addition, the electrical conductivity of repaired specimens decreased by 22–36% compared with the damaged specimens.