Concrete and wood are the literal building blocks of civilization. The latter is a given, but materials similar to concrete date back to before 6500 BC. Ancient Egyptians used it, and then the Romans took the concept a step further and added volcanic ash to make the material stronger and water resistant. Cities have risen and fallen in its rubble, and then been rebuilt with slightly enhanced versions of this staple material—except during the Middle Ages, when the world seemingly lost the recipe for concrete.
Since it reemerged during the 14th century, concrete has evolved but still remains largely a mixture of two components: aggregates and paste. The paste is comprised of cement—once typically lime based but now often polymer based—and water, which binds the aggregates—usually sand and gravel or crushed stone—into a rocklike mass as the paste hardens. It’s a tried and true material, but times do change.
Population growth in the developed world has meant an increase in the use of automobiles, which has led to more roads and other infrastructures. Concrete has proven its abilities, but is it strong enough for the next stage of civilization? Researchers at Purdue University tackled that question but with a modern twist, asking: Could concrete be made stronger by infusing it with microscopic-sized nanocrystals made from wood? According to a recent press release, the answer is yes, and it’s about to be tested on a bridge in California.
“Simply getting out there where people can actually drive on it, I think, is a huge step because you can’t just say it’s a lab curiosity at that point. It has real-world implications,” said Jeffrey Youngblood, a Purdue professor of materials engineering.
Like any chefs working to create a good recipe, the researchers exercised their due diligence before getting this recipe just right. They worked with cellulose nanocrystals—a byproduct generated by the paper, bioenergy, agriculture and pulp industries, and the most common polymer—to develop the best mix for strengthening concrete.
The researchers found that these cellulose nanocrystals create a chemical reaction that increases the hydration of cement particles with less water, which makes the concrete stronger. With other polymers, not all the cement particles are hydrated when the concrete is mixed. This can hamper the material’s strength and durability. The unique properties of cellulose nanocrystals provide an avenue for the water to go where it is needed.
“The good thing about cellulose nanocrystals is it kind of creates a rail for the water to go into a particle,” said Pablo Zavattieri, a professor in the Lyles School of Civil Engineering.
Strength isn’t the only benefit of using cellulose nanocrystals. Less water means less mass, which makes this stronger concrete more efficient and sustainable. Concrete infused with this polymer also sets faster. Down the road, concrete infused with cellulose nanocrystals could be lighter and thinner, which could help decrease carbon dioxide emissions from cement plants.
Wood isn’t the only material that can be used to help improve concrete. Check out Developing Smarter Concrete with Biomaterials to learn more.