User:Jankoj2/sandbox

Self Replicating Concrete

Synthesis and Fabrication

Self-replicating concrete is composed of a hydrogel and sand scaffold. Within the scaffold are synechococcus bacteria. The sand and hydrogel scaffold is used because it is less harsh on the bacteria when compared to a normal concrete environment, and allows for more viability. This scaffold lacks the high pH, ionic strength, and temperatures upon hardening associated with typical concrete paste. The synechococcus bacteria are able to biomineralize calcium carbonate, which increases the overall strength and durability of the scaffold, allowing the scaffold to be used as concrete or mortar.

This image shows the fracture energy of a living building material in comparison to two controls,one with no cyanobacteria and one with no cyanobacteria and a high pH.

Properties

The bacteria in this material react to humidity changes. The bacteria are most active and reproduce the best in conditions with 100% humidity. As humidity decreases, cell replication and mineralization activity decrease. However, these cells have the ability to create new generations by introducing them to a new sand and hydrogel scaffold and new cellular media. With the beginning of new generations it can be seen that the biomineralization activity of the bacteria increases compared to the prior generation. This allows for faster production and exponential manufacturing growth.

The structural properties of this material are similar to Portland-cement based mortars. Self replicating concrete has a modulus of 293.9 MPa and can undergo a yield stress of 3.6 MPa. It also has a fracture energy of 170 N. This is much less than most standard concrete, which can reach up to a few kN. While the fracture energy of self-replicating concrete is not similar to that of standard concrete, its maximum stress reaches the minimum required value for Portland-cement based concrete, which is approximately 3.5 MPa.

Uses

This self-replicating concrete can be used in various applications. While cell growth, reproduction, and biomineralization activity are highest at a humidity of 100%, a drop to 50% does not have a large impact on the cellular activity, meaning that this material can be used in most environments. One major factor is how increasing and decreasing the humidity affect the mechanical properties. The cells grow more efficiently in high humidity, but the material is stronger under conditions with low humidity. This means that the application of this material must be tailored to its environment.

This material can be used in more humid environments as a crack filler on roads, walls and sidewalks. The high humidity will allow the cells to grow, creating more calcium carbonate, strengthening the material, and naturally filling in the crack. In drier environments, the self-replicating concrete can be used more structurally, because of the increased strength due to lack of humidity.

Another large upside to this material pertains to the manufacturing. As long as new sand hydrogel scaffolds are introduced, multiple generations can be made from one sample of this material. This means that the self-replicating concrete can be mass produced on an exponential scale, assuming each generation is able to be cared for and properly maintained. Furthermore, the bacteria used to make this concrete absorbs carbon instead of emitting carbon like most cements, which account for 8% of the world's carbon footprint. This self-replicating concrete material is not meant to replace standard concrete, but to open up a new class of materials, with a mixture of strength, ecological benefits, and biological functionality.