New research demonstrates that cellulose nanocrystals can increase the tensile strength of concrete by 30 percent.
The cellulose nanocrystals (CNCs) could be refined from industrial byproducts generated in the paper, bioenergy, agriculture, and pulp industries. They are extracted from structures called cellulose microfibrils, which help to give plants and trees their high strength, lightweight, and resilience.
“This is an abundant, renewable material that can be harvested from low-quality cellulose feedstocks already being produced in various industrial processes,” says Pablo Zavattieri, an associate professor in the Lyles School of Civil Engineering at Purdue University.
The cellulose nanocrystals might be used to create a new class of biomaterials with wide-ranging applications, such as strengthening construction materials and automotive components.
One factor limiting the strength and durability of today’s concrete is that not all of the cement particles are hydrated after being mixed, leaving pores and defects that hamper strength and durability.
“So, in essence, we are not using 100 percent of the cement,” Zavattieri says.
However, the researchers have discovered that the cellulose nanocrystals increase the hydration of the concrete mixture, allowing more of it to cure and potentially altering the structure of concrete and strengthening it. As a result, less concrete needs to be used.
The cellulose nanocrystals are about 3 to 20 nanometers wide by 50-500 nanometers long—or about 1/1,000th the width of a grain of sand—making them too small to study with light microscopes and difficult to measure with laboratory instruments.
The concrete was studied using several analytical and imaging techniques. Because chemical reactions in concrete hardening are exothermic, some of the tests measured the amount of heat released, indicating an increase in hydration of the concrete.
The researchers also hypothesized the precise location of the nanocrystals in the cement matrix and learned how they interact with cement particles in both fresh and hardened concrete. The nanocrystals were shown to form little inlets for water to better penetrate the concrete.
The findings appear in the journal Cement and Concrete Composites. Researchers from Purdue and the US Forest Service’s Forest Products Laboratory.
The National Science Foundation funded the research.
Source: Purdue University