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.

In specific:
We transferred gerA gene to be our biosensor. When there is liquid L-alanine. GerA receptor can be induced so the whole chain can be started. We improved the alkali resistance by transfer nhaC because the concrete is high alkaline environment. We put the spores of our Bacillus subtilis into microcapsules, along with nutrients and L-alanine powder. And mix the microcapsule with concrete. When there is a micro crack, the tension of the wall breaking will also break the microcapsule and the water will infiltrate, after the germination that induced by L-alanine. The Carbonic anhydrase gene that we transferred will let CO₂ hydrate to produce CO₃^2-, which then binds with free Ca + in the environment to form calcium carbonate sediment, so the micro cracks are filled. The rebar inside can be protected from rusting. This will highly prolong the working life of the construction.

There are 3 main gene factor 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 CO₃^2- production module, which then binds with free Ca + to form CaCO₃ as crack-filling material.

ALKALINE-RESISTANT

nhaC gene serves as a Na⁺-H⁺ antiporter, thus improving the alkali resistance.