A Concrete Discovery

Imagine a road full of cracks, and then a gentle rain comes down and the road automatically repairs itself, or imagine, a bridge full of fractures caused by an earthquake, and in minutes the bridge automatically seals the fractures. Welcome to the world of self healing materials.bent-ecc

This is not a dream of far, far away future. We are actually making very significant progress in creating self healing materials right now. In fact, recently researchers in University of Michigan have discovered a new self healing concrete that has the potential to revolutionize the building industry.

Before we talk about this discovery it is important to know that self healing material is not a new field of study or a new concept. In fact, 20 centuries ago Romans had created self healing material (without knowing it).

That’s when Romans used mortar to hold stones and bricks together. Unbeknown to them, the mortar they created healed itself by spontaneous chemical reactions. These reactions were the result of mortar getting in contact with moister, so when a small crack would appear a chemical reaction would start and will seal the crack.

Furthermore, according to  Zwaag (editor of Self Healing Materials) the first patent  polymer  with intentional self healing characteristics appeared in 1966.

In summary, self healing material has been around for a while, but there hasn’t been many that meet our needs today.  The discovery of new self healing concrete by University of  Michigan researchers perhaps will change that, and soon we will be able to use this material in everyday projects today.

Details of the Discovery

This material is created by professor Victor Li and his team. They have created an ECC (Engineered Cementitious Composites) that has self healing ability.

Self healing process is accomplished through various natural phenomena which includes the following:

  1. Further hydration of un-reacted cement
  2. Expansion of the concrete in cracks
  3. Solid water impurities
  4. Crystallization of calcium carbonate Source

According to Li’s previous paper (available here), however, crystallization of calcium carbonate is the main mechanism for self healing.

Since above phenomena occurs naturally, researcher didn’t have to invent a new one. However, self healing doesn’t work for cracks that pass certain threshold in width. The threshold is 150 micrometers. Therefore, if we want self healing concrete we need to control width of the cracks.

The main accomplishment of Victor team is the creation of ECC that has precise control over cracks. The ECC they created has the crack width under 60 micrometers which means, of course, that the material can self heal through the phenomena described above.

The result is that we have very durable concrete, and according to UMICH’s website experiments showed that after the concrete repair itself, it recovered almost all of its strength-  even after putting tensile strain of  about 3 percent.

Indeed this new material seems to be very promising. It could help us build durable and sustainable structures that can withstand earthquakes and storms. Now let’s take advantage of it. Let’s build the Bering Strait Bridge .

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