Earthquakes are, unfortunately, a constant threat for some. All engineering and architectural planning has to consider the possible effects of earthquakes and how to diminish the blow. In 2017 alone, the world was hit with approximately 1566 earthquakes ranging from a magnitude of 5 to 8+. So, the question at hand is: how do we fight the inevitable?
Chief among earthquake-related concerns is the stability and security of an infrastructure. It’s so important because infrastructure failure is responsible for the majority of earthquake related deaths. Other terrible outcomes include the skyrocketing number of people who could become homeless, the collapse of cities, the destruction of landmarks and cultural icons, and the mental state of those affected. However, with well-thought designs and appropriate materials in place, it is possible to build infrastructures more resistant to earthquakes.
The defense plan
The following three words can potentially revolutionize the earthquake engineering world: crumb rubber concrete (CRC). This concept is making waves in various industries and disciplines. It sparks interest in civil engineers, working to find the next architectural breakthrough, as well as environmentalists, always curious to find if an eco-friendly alternative exists. Recent research has shown that with this new mix of concrete, buildings are able to better withstand the shock of an earthquake.
What is crumb rubber concrete?
You may already know that concrete’s make-up is part paste and part aggregates. The paste ingredient is cement; whereas the aggregate is typically a mix of sand and gravel. Now, substitute a portion of the aggregate solution with rubber from used tires instead - now you have crumb rubber concrete. Some say it's even the future of infrastructure.
The presence of rubber is believed to make infrastructures better equipped to endure seismic waves. With this possibility in mind, experimental research was conducted to further explore its benefits.
Three concrete columns were built. Two used the conventional concrete formula, while the third was constructed using crumb rubber concrete. These columns were then tested under axial compression, meaning that pressure was evenly applied to the top surface of the column. Researchers then gradually increased the reversed cyclic load placed on the columns, putting them through the same kind of stress they would endure during an actual earthquake. Researchers were interested in ductility, the ability of the material to stretch; the damping ratio, or how vibrations reduce aftershock; and dissipation of energy.
After enduring the seismic load, the crumb rubber concrete column had a higher hysteretic damping ratio and greater energy dissipation, while sustaining the same lateral load as the conventional columns. This was especially impressive as it proved to exhibit higher ductility and less cracking of the cement. This combination of qualities resulted in the rubberized column sustaining far less damage than the conventional columns.
This research opened the door to further questions as well. Researchers found that when using rubber crumb sizes of 1.18 - 2.36mm, they saw almost no effect on key factors such as the damping ratio. However, upon increasing crumb size to 6mm, they achieved a 62% increase in concrete damping. With such minor details causing major differences, additional research needs to be conducted to find the most effective mix.
Used tires are literally piling up in landfills around the world. Each year, one billion tires are discarded and considered to be at the end of their useful life. With this ever-growing issue, finding yet another creative way to recycle used tires is in everyone’s best interest. With the need of concrete in civil development, crumb rubber concrete offers an environmentally-friendly alternative that will give these end-of-life tires a new beginning.
So, perhaps the main takeaway is that the solution to infrastructure failure due to earthquakes in the future could be right under our nose, or sitting in a landfill.