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Written by Morgan Kaenzig de Denu
Traditional concrete is brittle and has good load-bearing capacity, but it often fails under tensile load or cracks due to temperature changes or vibrations. However, bendable concrete is strong, resilient, and flexible.
Each year 30 billion tons of concrete are used globally, making concrete the second-most-consumed material on Earth. In 2021, the U.S. alone consumed 109 million metric tons of concrete and shipped out 393 million cubic yards of ready-mixed concrete. However, traditional concrete is brittle, inflexible, and vulnerable to natural and man-made forces, from earthquakes to bomb blasts. Plus, the extreme conditions caused by climate change have placed additional pressure on our concrete structures, resulting in more frequent and costly maintenance.
Enter bendable concrete.
Traditional concrete typically has a low tensile strength, can be severely compromised by cracks, and is composed of water, aggregates, air, and Portland cement. In contrast, bendable concrete, also known as engineered cementitious composite (ECC), is a little different. Developed by Victor C. Li and his colleagues in the University of Michigan’s Department of Civil and Environmental Engineering in the 1990s, bendable concrete is lighter, more flexible, and
less likely to develop large cracks than traditional concrete because it doesn’t contain coarse aggregate. Instead, it includes small fibers, such as silica, polypropylene, asbestos, glass, carbon fiber, polyvinyl alcohol, steel, jute, and sisal.
These fibers are organized into a microstructure, reinforcing the concrete and increasing its flexibility. They are covered with an anti-friction coating which allows them to slip over one another, enabling the concrete to become more flexible and preventing the formation of cracks.
Sand, silica fume, fly ash, and blast furnace slag can increase bendable concrete’s strength and flexibility, while superplasticizers can increase its workability. Commonly used superplasticizers include sulphonate, lignin, lignosulfonates, polycarboxylate ether, melamine formaldehyde, and naphthalene. It’s also possible to improve flexibility by adding latex to the concrete mixture.
Bendable concrete outshines its traditional counterpart in many ways. In addition to being stronger, more durable, and less brittle than conventional concrete, bendable concrete:
While traditional concrete can’t bend or give without breaking, bendable concrete has a much higher tensile strength. Bendable concrete’s strain capacity can be as high as 7% (compared to traditional concrete’s strain capacity of approximately 0.01%), making it hundreds of times more flexible and able to withstand a lot of tension without fracturing. This also makes bendable concrete ideal for use in vibration-prone environments, such as areas along fault lines that frequently experience earthquakes.
While traditional concrete often experiences large cracks that lead to immediate structural failure and other major problems, bendable concrete typically experiences microcracks and smaller deformations thanks to its fibrous structure. As a result, bendable concrete breaks apart more slowly and safely than traditional concrete, making it ideal for use in buildings and infrastructure.
Bendable concrete is also naturally 20%-40% lighter than traditional concrete. Plus, the fibers used in bendable concrete offer reinforcement and tensile strength, reducing or eliminating the need for heavy steel bar reinforcement.
While structures made from traditional concrete typically require around 28 days to cure, those made of bendable concrete generally take just 7 days.
It’s also worth noting that bendable concrete is self-healing. The extra dry cement, CO2, and water will react and form calcium carbonate to fill microcracks. Researchers found that 1-5 wet-dry cycles were able to heal cracks up to 60 micrometers wide.
This is a stark contrast to how water exploits hairline fractures in traditional concrete structures without waterproof sealants, undergoes freeze-thaw cycles, and expands small fractures into large cracks.
Since flexible requirement requires less steel reinforcement, architects and engineers have far more freedom when it comes to the form and shape of their project. This can be particularly beneficial when building skyscrapers.
Bendable concrete also emits fewer harmful gases into the atmosphere than conventional concrete. Plus, embedding nano-titanium particles into the composite can help the concrete neutralize pollutants, resulting in cleaner air in urban environments.
Since bendable concrete is more resistant to cracking and is self-healing, it has a longer lifespan and requires fewer repairs (and all the time, energy, and carbon output associated with them) over the years. This can offset the bendable concrete’s higher initial costs, resulting in a lower overall project cost.
Bendable concrete has a lot to offer, but it isn’t perfect. For one, installing bendable concrete requires skilled labor. It’s also important to note that:
● Bendable concrete has a much higher upfront cost. (It can cost up to three times as much as traditional concrete.)
● It can be difficult to obtain materials used in bendable concrete.
● Bendable concrete may have weaker compressive strength than conventional concrete.
● The conditions under which bendable concrete is made and the quality and proportion of materials used affect the concrete’s flexibility and quality.
Since bendable concrete has a much higher tensile strain capacity than regular concrete, it is less likely to break down due to shaking and vibrations, making it ideal for use in buildings in areas that frequently experience earthquakes. For example, Kitahama, the tallest residential tower in Osaka, Japan, uses bendable concrete.
Roads and Bridges There are 612,677 bridges in the U.S., and 54,259 are structurally deficient. Luckily, bendable concrete helps bridges and roads resist cracking and forming potholes. Since bendable concrete is flexible and self-healing, it also eliminates the need for expansion and contraction joints and can cut maintenance costs. For example, using bendable concrete instead of regular concrete in Michigan’s Grove Street Bridge deck in Ypsilanti cut costs by 37% and reduced carbon emissions by 39%.
Concrete canvas is often used in protective umbrellas and shelters for military equipment, though it can also help control erosion. It needs to be durable and strong, making bendable concrete an ideal material choice.
Due to supply chain concerns and technical factors, bendable concrete has not yet experienced widespread adoption in the construction industry. However, as more companies experiment with cost-effective materials and more people learn about bendable concrete’s advantages, the material will likely gain popularity.
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