When many of us think about carbon fibre uses, what often springs to mind is the automotive sector. Carbon fibre components have become part and parcel of a range of vehicles, particularly high-performance sports cars and motorcycles, thanks to their combination of strength and light weight.
Ferrari car dealer Continental Autosports (CA) says carbon fibre is five times lighter than steel, yet is less dense than aluminium, one of the lightest metals available. CA says: “In a contest between two otherwise identical cars, the vehicle with carbon fibre parts is likely to outperform the model with parts made from traditional materials, because shedding weight allows it to make the most of its powertrain.”
While this has enormous potential for car manufacturers and owners, other industries—including construction—are cottoning on to what carbon fibre and its properties can offer them.
Where does carbon fibre come from?
But what exactly is carbon fibre and where did it come from?
According to materials manufacturer Zoltek, a carbon fibre is a long, thin strand of material about 0.005mm to 0.010mm in diameter and composed mostly of carbon atoms. Adds Zoltek: “The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fibre. The crystal alignment makes the fibre incredibly strong for its size.”
Zoltek says the vast majority of carbon fibres (90%) are made from a hard synthetic resin called polyacrylonitrile, while the rest are produced from rayon or petroleum pitch. Effectively “cooking” the threads in an industrial oven renders them incredibly strong, thanks to their high carbon content, which are then treated and wound into coils, ready for use.
Carbon fibre has been around for more than 150 years. It was invented in 1860 by English scientist and physicist Sir Joseph Wilson Swan, who used the material in his version of a light bulb. It was later taken up by US inventor and engineer Thomas Edison for his own lighting system. A move to using tungsten in these light bulbs soon rendered carbon fibres unnecessary, and its properties went unnoticed for decades.
Then, from the 1950s through to the 1970s, a number of discoveries pushed carbon fibre technology into new areas, notably for the US military, and it was given a significant boost when used in aircraft engines developed by Rolls-Royce.
Today, carbon fibre is used in an array of applications, from the aforementioned automotive sector to aircraft interiors, wind turbine blades, safety apparel and construction.
Carbon fibre uses in construction
Carbon fibre properties, which include tensile strength, stiffness, high temperature tolerance, chemical resistance and fatigue resistance, have inevitably proved attractive to architects, designers and developers.
According to the Civil Engineering Portal (CEP), applications include strengthening structures made with concrete, steel, timber, masonry and cast iron. Retrofitting is also undertaken to increase the load capacity of old structures like bridges, while it is used to enhance shear strength and for flexure in reinforced concrete structures.
Other carbon fibre uses include replacement for steel, pre-stressing materials and strengthening cast-iron beams, the CEP says.
Since it is a non-corroding material, using carbon fibre enables concrete layers to be much thinner, as there is no steel core to protect from corrosion, says Teijin Carbon, which has been manufacturing synthetic and carbon fibres since the 1930s.
“Carbon concrete leads to a reduction in the amount of concrete used in buildings, with side benefits like lower logistic costs and shorter construction and drying times … [while] its conductivity makes it an integral material for smart buildings, conducting heat and energy, transmitting information about a building’s parameters and shielding electromagnetic interference,” the company adds.
Challenges of building with carbon fibre
Like any material, while the advantages of carbon fibre are evident—strength, minimal impact on its integrity due to corrosion and greatly reduced weight—it also has its downsides.
The material is labour-intensive and relatively expensive to produce, and making it requires a lot of energy. And while it is a great conductor of heat and electricity, this could be problematic in a building where such conductivity could be an issue.
And although carbon fibre performs very well under laboratory conditions, conditions in the field can be extreme and these, say experts, should be taken into account. According to Horse Construction, “the design tensile strength of carbon fibre should be considerably reduced from the laboratory data.”
There is also the question of carbon fibre’s sustainability credentials. According to the Union Cycliste International, carbon fibre material “is difficult to recycle and not biodegradable. Carbon fibre cannot be re-melted and recycled like aluminium, and until recently, no sustainable end-of-life solution has been available for carbon fibre.”
Composites Construction UK (CCUK), which provides a range of construction services, acknowledges that like any material that requires a lot of energy to produce carbon fibre has the potential to have an adverse impact on the environment, but it also says certain types of carbon fibre are greener than others.
“One type of carbon fibre that is considered `green` is lignin-based carbon fibre—a natural resource with 50%-71% carbon content—which can be used on general applications with low thermal conductivity, high-temperature resistance and projects that require minimal mechanical work.”
“While carbon fibre as a product is not biodegradable, some aspects of carbon fibre—like the resin from carbon fibre-reinforced plastic—can be recycled relatively easily. This is done using a recycling process called pyrolysis, where high heat is used to burn the resin off wherever the carbon fibre-reinforced plastic has been used.”
CCUK stresses it is important to know that carbon fibre can be damaged during certain recycling processes, and the matrix resin materials “may not survive.”
The future of carbon fibre technology
What then does the future hold for carbon fibre, and carbon fibre use in construction in particular? Estimates suggest the compound annual growth rate of the global carbon fibre market between now and 2028 will be anywhere between around 10% and 12.5%, with demand dominated by aerospace and defence industries.
The main area in construction where carbon fibre can make an impact is in concrete formulations. Carbon fibre properties can improve the tensile strength of concrete through a series of mesh-like mats placed in layers throughout the material.
Experts suggest as well as being distributed in this way, carbon fibre can also be distributed throughout concrete using a nozzle process in a targeted manner.
Buildings made predominantly out of carbon fibre may be wishful thinking, but construction is nevertheless waking up to the potential for using the material’s qualities of strength and lightness.