While many of us might think that concrete structures such as bridges simply stand unaided for decades at a time, the fact is that they require maintenance as often as once every five years. An experimental new type of rebar, however, could drastically change that.
The problem with existing concrete structures lies in the steel rebar rods that are embedded within them for support. As these rust over time, the rust occupies more space than the original non-corroded rebar. The rusted steel thus pushes out against the surrounding concrete, leading to spalling, a process in which concrete cracks and falls away from the main structure.
According to Dr. Mahbube Subhani, who is a Lecturer in Civil Engineering at Australia's Deakin University, reinforced concrete structures typically require some maintenance every five years or so, along with major rehabilitation every 20 years. This state of affairs prompted Subhani and Dr. Kazem Ghabraie to produce a new non-rusting rebar, made of a carbon and glass fiber-reinforced polymer.
The material is reportedly stronger than rebar made of regular steel, and is one-fifth the weight of reinforced-steel rebar. Additionally, it requires only a quarter as much energy to produce.
It is now about to be used in the construction of a pedestrian bridge in the Australian city of Geelong. The researchers believe that once the bridge is constructed, it should require no maintenance for the rest of its planned 100-year lifespan.
Additionally, instead of cement, the concrete used for the bridge will incorporate fly ash obtained from coal combustion – cement production is one of the major sources of manmade carbon dioxide emissions. Deakin researchers have previously developed eco-friendly concrete in which waste glass was used as aggregate.
"We have replaced the steel reinforcing bar normally used in steel reinforced concrete with more durable carbon and glass fiber reinforced polymer," says Subhani. "This bridge should not require any maintenance for the whole of its design life."
Source: Deakin University
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