Concrete is the most widely used construction material in the world due to its high strength and durability, relatively low cost and readily available constituents. However, over time concrete also becomes susceptible to the elements, leading to structural damage with occasionally catastrophic results. That damage begins with micro-cracks that form in the concrete structures and proceed to propagate. Without costly and time consuming maintenance, water seeping through these cracks may reach the steel reinforcing, thus causing corrosion and major loss of structural integrity.
But what if there is another way?
At Griffith’s School of Engineering, Dr Jeung-Hwan Doh and his team are investigating concrete that is capable of healing itself.
“Self-healing concrete decreases the likelihood of concrete cancer, reduces maintenance costs and increases the lifespan of the concrete structure,” explains Dr Doh.
“We are investigating taking capsules that contain an epoxy and embedding them into the concrete mixture. This epoxy is often used to repair concrete by manually injecting it into cracks. In our scenario, the micro-cracks would fracture the capsule, release the epoxy and ‘heal’ the concrete.”
The research has two principle lines of inquiry: the encapsulation method, which incorporates the optimum viscosity of the liquid in the capsules; and secondly, identifying the type of epoxy that will work best with this method.
“We want the concrete to bleed,” jokes Dr Doh. “We are 3D printing differently shaped capsules that are filled with a viscous red fluid. The capsules are then placed into the concrete during the pouring process. The capsules have to be strong enough to survive the pouring of the concrete, but also brittle enough to break and release this fluid when a crack permeates through the concrete.”
The viscosity of the fluid is important. Too thick and it will not flow out of the capsule; not thick enough and its ‘healing’ effect will be reduced. Among the benefits of the technology, Dr Doh says it could be useful to engineers undertaking visual inspections of concrete infrastructure.
“Any cracks would be readily identifiable through visual inspection as the concrete would be stained around where the capsules had been fractured,” he says. “But our end goal is to perfect the self-healing process in concrete, because not only would this save a lot of money and time, it would also provide engineers with another safeguard against potential failure of structures.”