|Transmission electron microscope image shows cellulose nanocrystals, tiny structures derived from renewable sources that might be used to create a new class of biomaterials whose applications include concrete admixtures imparting improved cement hydration and strength development.|
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.
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, he observes: Not all cement particles are hydrated after being mixed, leaving pores and defects that hamper strength and durability. Cellulose nanocrystals increase cement hydration, allowing more of the concrete matrix to cure and yielding a stronger finished structure.
Zavattieri conducted an investigation with Jason Weiss, Purdue’s Jack and Kay Hockema Professor of Civil Engineering and Pankow Materials Laboratory director; Associate Professor of Materials Engineering Jeffrey Youngblood; doctoral student Yizheng Cao; and, U.S. Forest Service Forest Products Laboratory researcher Robert Moon. Their findings appear in the journal, Cement and Concrete Composites. The National Science Foundation-backed research dovetails the work of P3Nano, a public-private partnership supporting development and use of wood-based nanomaterial for a wide-range of commercial products.