Team:SZU-China/Description
Project Description
Concrete Problem
As we all know, reinforced concrete is the most widely used construction material in the world. Concrete is more resistant to being squashed and rebar can hold high tensile strength. Together they can make a perfect match for construction building.
However, as time goes by, there will be small cracks happening inside of the concrete which are on millimeter level. And we call them micro-cracks. These micro-cracks all have the potential to broaden larger and deeper while usually escaping the detection of human eyes. Then when the cracks turn into bigger ones, the water vapor in the air will penetrate through and rust the steel bars inside. The rusted steel bars are usually 3-4 times larger than its original volume, leading the wall to swell and the cracks to further broaden. Then more water vapor and other corrosive characteristics will enter to erode the rebar, making things worse.
This kind of vicious circle will weaken the steel bars greatly, resulting in safety problem for the construction and the people live inside. What's worse, it will substantially reduce the working life of almost all the public constructions like tunnels and bridges. According to surveys, European Union spends 60 hundred million on repairing tunnels and bridges per year.
Apparently this is a problem needed to be fixed. Nowadays people use high pressure to pump the Inorganic cement or other kind of adhesive into the cracks and wait for it to become solid so the cracks can be blocked. But it won’t be a onetime thing, instead people might have to do over constantly. It takes up a lot of manual labor thus very expensive.
Our Solutions
In order to offer this crack problem a better solution, in an easier synbiologic way, this year we try to design a "self-healing" system for the concrete. That is, when there is a micro-crack appearing, our system can be switched on and concrete can start to repiar itself. And we choose the calcium carbonate to be the "medicine" for those cracks.
The idea is, we constructed a kind of bacteria producing calcium carbonate and then embedded it into the concrete as micro-capsule. Once the concrete starts cracking, the capsule gets split out to activate the bacteria inside. In this way, they can begin to produce the CaCO3, thus filling the crack.
There are 3 main gene factors essential in the construction of our system, which are presented below.
GERMINATION
GerA gene serves as a biosenor to start the spore germination when liquid L-alanine is available for GerA receptor inductioin.
Carbonic anhydrase
Carbonic anhydrase gene serves as CO32- production module, which then binds with free Ca2+ to form CaCO3 as crack-filling material.
ALKALINE-RESISTANT
nhaC gene serves as a Na+-H+ antiporter, thus improving the alkali resistance.
Through the methods of synthetic biology, we increase the alkali tolerance, germination rate and mineralization capacity of Bacillus subtilis significantly. Then, we use a kind of special material MCC to warp the spore of Bacillus subtilis into microcapsules, while adding the necessary nutrients for germination together. This microcapsule is embedded into concrete in a certain proportion. When the micro-cracks inside the building appear, the microcapsules are torn by the tension of the wall breaking and the water will permeate to dissolve the nutrient, which stimulates the spore into the germination status and finally returns to normal metabolism. Carbonic anhydrase of Bacillus subtilis promotes CO2 hydration to produce HCO32-, which binds to free Ca2+ and OH- in the environment to form calcium carbonate deposits, thereby enabling microcracks to self-repair and isolate the external environment from further corrosion of the internal reinforcement.
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