Posts Tagged ‘Structural’

Researchers at the University of Strathclyde in Glasgow have developed a low-cost paint that, when coupled with electrodes, can detect tiny faults in bridges, mines, wind turbines, and the like before a major structural failure can occur.  David McGahon developed the project for his PhD, alongside Dr. Mohamed Saafi.

 

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“Speaking to Wired.co.uk, Dr Saafi explains that when a wireless sensor network is connected up to the paint, the resultant system is able to detect microscopic faults. “The electrodes connected to the paint act almost like the nerves in the human body,” he says. They will pick up of any changes in the conductivity map — and these changes can be caused by cracks. The electrodes will also pick up on motion, which can indicate structural weakness as well as corrosion.”

Paint designed to detect cracks in bridges

The paint is made using fly ash and carbon nanotubes aligned in a precise manner which are capable of carrying an electrical current.  When a structural deficiency occurs in the structure, the nanotubes will start to bend.  This will cause a change in the conductivity of the current and engineers will be able to pinpoint the location of the structural deficiency.  Due to the contents of the paint, this is also an environmentally friendly product.

Typically, the process of monitoring the structural integrity of these types of structures can be quite costly.  It involves heavy equipment such as lifts and highly trained personnel.  The inspections are also visual, so most cracks and faults are not detected until they can be seen with the naked eye.  At this point, the structure will mostly likely need more money to fix, and the safety of the structure may already be in question.  The new smart paint will help detect areas of concern possibly even before they become a threat to the structural integrity of the structure, and hopefully this will help prevent failures and costly repairs.

A prototype paint has been developed and the team hopes to test this paint on major structures in the coming year.

Graphene is a derivatve of graphite, the lead found in pencils.  Graphite is comprised of loosely bonded layers of carbon atoms and Graphene takes those atoms and tightly binds them into hexagons one layer thick.  The theory of graphene has been around for some time, but in 2004, two Manchester University scientists, Andre Geim and Konstantin Novoselov, along with others, proved that single layers of graphene could be produced.  This achievement won the Nobel Prize for Physics in 2010.

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Research conducted by the University of Columbia tested the strength of graphene.  Through the research, graphene is the strongest material ever tested, approximately 200 times the strength of steel.

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Graphene has many possible uses including replacing silicon in transistors and inert coatings.  IBM and Samsung have been investing in graphene research for the speed capabilities of the transistors.  Currently, IBM has created a 150 GHz transistor, compared to the fastest silicon transistor at 40 GHz.  Graphene is also fairly resistant to many powerful acids and alkalis, and as a transparent material, could be used as a protective coating.

“Researchers at Rice University in Texas have found a way to synthesize graphene using table sugar, giving the material impeccable green credentials.  In the same state, engineers at the University of Texas have even discovered that by replacing the carbon used in ultra-capacitors with graphene, it’s possible to store double the amount of energy. That in itself could revolutionize the renewable energy industry that is currently looking for a new way to store the energy produced by its burgeoning solar and wind farms. If the so-called “smart grid” is to prove successful, a way to store energy for when it’s not sunny or windy is essential.”

– The Telegraph: Graphene: Our Miracle Material

Of course, no product is without a set of issues.  One major one is that graphene does not have a band gap, which means it will never stop conducting electricity.  With silicon, it is possible to switch the material to an “off” position; therefore the replacement of silicon by graphene is not an immediate possibility.

Also, though the material is “stronger than steel” in a mirco sense, it has currently not been tested at a more macro level by producing a larger sample on par with building materials.  This is not to discount the strength of the material, but don’t expect to soon be able to go out and buy graphene beams to replace your steel.

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One other issue with the material is the fact that the properties of the material depend on the fact that it consists of a single layer of carbon atoms.  When more then one layer is present, the attraction forces between the layers causes them to stick together and compromise the material properties.  However, new developments in graphene research have just been published.  Physicists at Linköping University have determined that one solution to this problem is to add an atomic layer of hydrogen between the layers of graphene.  Hydrogen at a given concentration affects the atomic Van der Waals forces.  Van der Waals forces are the attractive or repulsive forces between molecules.  In the case of graphene, the forces attract, but with the hydrogen interrupting, the forces reverse and the layers repulse each other and float a few nanometers apart.  This new development creates the possibility for more uses for the material including:

“Storage of hydrogen as vehicle fuel

Creation of a single graphene sheet by peeling them from a pile that has grown on a substrate of silicon carbide; a method developed at Linköping University

Repulsive forces are ideal for the manufacture of friction-free components on a Nano scale, for example, robots and sensors for medical purposes”

Science Daily: Hydrogen Advances Graphene Use

Concrete is one of the most widely used building materials in the world.  However, concrete is very poor in tension.  That is why steel bars are placed throughout concrete structures to create a composite material that will resist both tensile and compressive forces.  This is a very durable material but it still has a limited lifespan.  This limited lifespan occurs because of one main reason: water.

As already discussed, concrete is poor in tension, therefore, under loads that cause those forces, concrete cracks.  When concrete cracks, water can get introduced into the structure and compromise the integrity of the steel.

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Dr. Henk Jonkers, a faculty member of Civil Engineering and Geosciences at the Delft University of Technology in Delft, the Netherlands decided to approach this problem from a biological angle.  He searched for bacteria use water and calcium lactate to create calcite that is natural cement.  The problem occurred when trying to find bacteria that would survive in a very high pH environment (the typical pH of concrete is 11 or above on a scale from 0-14).  Jonkers and his collegues started looking in the soda lakes of Eygpt and Russia and eventually found a strain of Bacillus that thrived there.

Dr. Jonkers’ bio-concrete has the two key ingredients (the bacteria spores and the calcium lactate) introduced through separate expanded clay pellets. This ensures the ingredients will not come in contact during the mixing process.  Later, cracks will open the pellets and the incoming water will germinate the spores and mix the spore with the calcium lactate, producing calcite and filling in the cracks.

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Though clearly, the main advantage to this bio-concrete is a much longer lifespan of the structure and minimized repair, there are also some disadvantages.  The clay pellets that hold the bacteria and calcium lactate comprise 20% of the volume of the concrete mix.  However, these pellets are weaker than the components of the mix they are replacing, thereby reducing the overall strength of the concrete.  Cost is also a big disadvantage.  Currently, the cost of this self-healing concrete is double that of a standard mix, though Dr. Jonkers and his team are continuing to research better ways to introduce the agents into the mix all for a cheaper cost.

Currently, this product is still being tested.  Full scale testing just started this past year and the team is also trying to address concerns from the industry about lifecycle costs and performance of the product.