Nanocrystals extracted from cellulose microfibrils-structures that give plants and trees strength and resilience-can increase concrete tensile strength up to 30 percent by creating tiny water inlets in a matrix and promoting more efficient cement hydration, according to new research from Purdue University, West Lafayette, Ind.
Measuring about 3 to 20 nanometers wide by 50 to 500 nanometers long, or 1/1,000th the width of a grain of sand, cellulose nanocrystals are too small to study with light microscopes and difficult to measure with laboratory instruments.
Purdue University researchers observed their behavior in concrete specimens using a host of analytical and imaging techniques. Because chemical reactions in concrete hardening are exothermic, they found, some tests measured the amount of heat released, indicating increased cement hydration.
Researchers hypothesized nanocrystals’ precise location in a matrix; determined their capacity to form little inlets for improved water penetration; and, learned how they interact with cement particles in both fresh and hardened concrete.
Purdue University associate professor of civil engineering Pablo Zavattieri characterizes the nanocrystals as “an abundant, renewable material that can be harvested from low-quality cellulose feedstocks already being produced in various industrial processes.”
One factor limiting concrete strength and durability is that not all cement particles are hydrated after being mixed, leaving pores and defects that hamper strength and durability, he says.