Krstulovic-Opara, assistant professor of civil engineering at North Carolina State University, has created a high-performance fibre-reinforced concrete (HPFRC), which may save lives, buildings and bridges by changing the way concrete structures fail.
It’s designed in a way that prevents the separation of large pieces of concrete from the structure. When it fails, the pieces remain stuck together, held in place by the stainless steel fibres. The pieces that do separate from the structure are much smaller and less likely to cause injury.
‘We know that concrete structures will eventually fail,’ said Krstulovic-Opara. ‘What we want to do is extend the length of time it takes for the structure to fail and control how it fails.’
One of the problems with conventional concrete is that during extreme structural stress it breaks apart in large chunks and separates from the steel rebars.
Krstulovic-Opara has been developing the HPFRC system using fibre mats injected with a special concrete slurry, a mixture of concrete, aggregate and liquids. The mats are made of recycled stainless steel fibres and come in large rolls that can be cut and shaped to fit the space or use desired. The fibre mats add tensile strength and ductility – energy-absorbing properties – to the concrete.
Krstulovic-Opara has used this advanced concrete composite to strengthen structures against earthquakes in laboratory models. He’s working with a team of colleagues to develop new structural systems that would best employ the advanced features of HPFRCs – high strength, durability, low cost and easy construction – to increase impact resistance to explosive blasts as well.
In addition to its safety features, the HPFRC system may change the way that buildings are built, strengthened or repaired.
Currently, to build a concrete structure workers have to bend steel rebars into frames, build wooden or metal forms around the frames, add concrete and, once the concrete has had time to cure, remove the forms.
Krstulovic’s system eliminates most of these labour costs, because it can be used as both frame and form for structural support of the building. Workers simply shape the fibre mat rolls and inject them with concrete slurry.
For renovations or repairs, they can wrap the fibre mats around existing columns and beams or use the fibre mats as forms and fill them with conventional concrete. The result is a support beam or column that is super strong and more durable than conventional concrete alone.
The HPFRC system is designed to use traditional concrete construction equipment with minimal modifications.
‘This new concrete can reduce the cost of repairing existing concrete structures and give them added strength and durability,’ said Krstulovic-Opara. ‘But, most importantly, because of its design, it can easily be transferred from the laboratory to everyday use.’