Concrete has become an imperative element of the architectural structure of buildings, roads, tunnels, and bridges globally. It’s value as a construction material is evident in its frequent use. It’s global usage is double that of steel, aluminum, wood, and plastics combined. Despite its popularity, like any construction material, it can be subject to decay and damage. Recent research and development in the construction industry saw the creation of a new form of self healing concrete.
This innovative technology uses bacteria to create chemical reactions in cracking concrete, which causes the cracks to heal themselves. This innovation has potential to save a huge amount of money on reconstruction, particularly in areas prone to earthquakes.
The Use Of Concrete In Modern Construction
Concrete, a composite material using cement and aggregate, is present in most of society’s structures. It’s popularity is due to its value, safety, and durability as a material. It is cheap and sustainable to produce, and is unreactive, making it a safe housing material option. It is also built to last, experiencing much lower levels of erosion than other construction materials. In fact, when concrete does crack, it can heal itself to some degree, if the crack is under 0.2mm in size.
However, cracks do not always stay minimal, and in areas with varying temperatures, these small cracks can become detrimental to structural stability. When water seeps into small cracks, and then freezes, this can widen the crack, posing a bigger threat to concrete health. In addition, if cracks reach the steel reinforcements often found in concrete structures, erosion can take place, which poses a danger for the overall structure of a building.
In these cracking situations, external reconstruction is the typical solution. Builder teams will refill cracks with liquid concrete, to stop the gradual widening of the crack.
Yet, reconstruction teams require time and money. In some cases, fixing cracks poses logistical issues, if they’re underground or high up on buildings.
Self Healing Concrete
The creation, therefore, of self-healing concrete is a huge innovation in construction maintenance.
Bacteria are added to the concrete mix, and serve to mend micro cracks in the structure before they are able to expand. The bacteria react with the water and oxygen that gets into concrete cracks, causing them to work at filling the crack with limestone.
This self healing concrete has also been termed bio-concrete and bacterial concrete.
The discovery was made by Dr Henk Jonkers and his team of microbiology researchers back in 2011. Jonkers’ focus was on creating innovative, durable, and bio-based construction materials.
The Science
Jonkers placed a range of bacteria into the concrete, as well as calcium lactate. When cracks formed in the concrete, the bacteria acted as a catalyst to convert the unhydrated calcium lactate into calcium hydroxide. The latter chemical then reacted with the carbon dioxide in the crack to produce limestone. It is this limestone that seals the crack.
Without cracks forming, the bacteria lays dormant, and can continue to do so for 200 years. It is only when they are exposed to oxygen and water that they begin to germinate.
You can either add the bacteria and calcium lactate to the concrete, or you place the bacteria into clay pellets, which are then placed in the concrete. The bacteria will then germinate when the crack penetrates the clay capsule wall. The former method is currently viewed as the preferred, due to the latter requiring specialised laboratory equipment and high costs.
What Does This Mean?
This is highly innovative for the construction industry. It will require significantly less maintenance on a huge range of structures, including buildings, roads, bridges, and tunnels.
Particularly for areas that experience high levels of earthquakes, this could save a great deal of time and money. While bacteria cannot fix crumbled buildings, their impact could be hugely influential in areas that experience frequent, low intensity earthquakes which cause minimal damage.
While the initial cost of this innovative self healing concrete is higher than traditional concrete costs. The long term expenditure demonstrates a reduction in cost, as there will be less need for reconstruction.
The use of bio-technology has excelled the construction industry to new levels of innovation and development. Self Healing concrete poses a sustainable and durable solution to current disadvantages of concrete, particularly in earthquake prone areas.
